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Aero Engineering Thermodynamics Unit wise-Question bank Wings of aero UNIT I BASIC THERMODYNAMICS Part-A (2 Marks) 1. What is meant by thermodynamics system? How do you classify it? 2. What is meant by closed system? Give an example. 3. Define an open system Give an example. 4. Distingusih between Open and Closed system 5. Define an isolated system: 6. Define specific heat capacity at constant pressure. 7. Define specific heat capacity at constant volume. 8. What is meant by surroundings? 9. What is boundary? 10. What is meant by thermodynamic property 11. How do you classify the property? 12. Define Intensive and Extensive properties. 13. What do you understand by equilibrium of a system? 14. Differentiate Intensive and Extensive properties 15. State the Kelvin - Planck statement of second law of thermodynamics. 16. State Clausius statement of second law of thermodynamics. 17. Write the third law of thermodynamics. 18. State Carnot's theorem. 19. What are the Corollaries of Carnot theorems? 20. Define - PMM of second kind. 21. What is difference between a heat pump and refrigerator? 22. Define the term COP. 23. Why Carnot cycle cannot be realized in practice? 24. Name two alternative methods by which the efficiency of a Carnot cycle can be increased. 25. Why a heat engine cannot have 100% efficiency 26. When the Carnot cycle efficiency will be maximum? 27. What are the processes involved in Carnot cycle 28. What is mean by heat engine? 29. What do you meant by entropy? 30. Prove Clausius Inequality 31. Write the principle of Increase in entropy
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PART –B (16 marks) 1. one kg of gas expands at CO&11stant pressure from 0.085 m3 to 0.13 Ill).if the initial temperature of the gas is 22.5 °c.find the final. Temperatures, net heat transfer, change in internal energy, pressure of gas. 2. A certain quantity of gas is head at constant pressure from 35 °0 to 185°c. Estimate the amount of heat transferred, ideal work done, change in internal energy,when the initial volume of the gas is 0.6 m^3. 3. Explain and derive Isothermal process 4. Explain and derive Isobaric process. 5. Explain and derive Isochoric process. 6. Explain and derive isentropic process. 7. Explain and derive Polytropic process. 8. Explain the inequivalence of Kelvin Planck’s & Clausius Statement 9. 2kg of gas at a pressure of 1.5 bar. Occupies a volume of 2.5 m^3. If this gas compresses isothermally to 1/3 times the initial volume. Find initial. Final temperature, work done, heat transfer. 10. one kg of air is compressed polytropically (n=1.3) from 1 bar and 27 deg Celsius to 3 bar. Find I. work transfer 2. Heat transfer 3. Change in internal energy. 11. A system receives 42 kJ of heat while expanding with volume change of 0.123 m3 against an atmosphere of 12 N/cm2. A mass of 80 kg in the surroundings is also lifted through a distance of 6 metres. a. Find the change in energy of the system. b. The system is returned to its initial volume by an adiabatic process which requires 100 kJ of work. Find the change in energy of system. c. Determine the total change in energy of the system.
12. A tank contains 2.26 m3 of air at a pressure of 24.12 bar. If air is cooled until its pressure and temperature becomes 13.78 bar and 21.1°C respectively. Determine the decrease of internal energy. 13. Determine work done by fluid in the thermodynamic cycle comprising of following processes a. Unit mass of fluid at 20 atm and 0.04 m3 is expanded by the law PV1.5 = constant, till volume gets doubled. b. Fluid is cooled isobarically to its original volume. c. Heat is added to fluid till its pressure reaches to its original pressure, isochorically. 14. Air at 8 bar, 100°C flows in a duct of 15 cm diameter at rate of 150 kg/min. It is then throttled by a valve upto 4 bar pressure. Determine the velocity of air after throttling and also show that enthalpy remains constant before and after throttling. 15. Determine the power required by a compressor designed to compress atmospheric air (at 1 bar, 20°C) to 10 bar pressure. Air enters compressor through inlet area of 90cm2 with velocity of 50 m/s and leaves with velocity of 120 m/s from exit area of 5 cm2. Consider heat losses to environment to be 10% of power input to compressor.
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16. A frictionless piston is free to move in a closed cylinder. Initially there is 0.035 m3 of oxygen at 4.5 bar, 60°C on one side of the piston and 0.07 m3 of methane at 4.5 bar and – 12°C on the other side. The cylinder walls and piston may be regarded as perfect thermal insulators but the oxygen may be heated electrically. Heating takes place so that the volume of oxygen doubles. Find : a. Final state condition ; (ii) Work done by the piston ; b. Heat transferred to oxygen.
c. Treat both gases as perfect and take : d. For oxygen = 0.88 kJ/kg K, R = 0.24 kJ/kg K e. For methane = 1.92 kJ/kg K, R = 0.496 kJ/kg K. 17. The specific heat at constant pressure of one kg fluid undergoing a non-flow constant pressure process is given by where T is in °C. 18. The pressure during the process is maintained at 2 bar and volume changes from 1 m3 to 1.8 m3 and temperature changes from 50°C to 450°C. a. Determine : i. Heat added (ii) Work done ii. Change in internal energy (iv) Change in enthalpy. 19. A fluid system, contained in a piston and cylinder machine, es through a complete cycle of four processes. The sum of all heat transferred during a cycle is – 340 kJ. The system completes 200 cycles per min. Complete the following table showing the method for each item, and compute the net rate of work output in kW. [8] i. Process Q (kJ/min) W (kJ/min) ΔE (kJ/min) ii. iii. iv. v.
1—2 2—3 3—4 4—1
0 42000 –4200 —
4340 0 — —
— — – 73200 ___
32. Air flows through an adiabatic compressor at 3 kg/s the inlet conditions are 2 bar and 310k and exit conditions are 20 bar and 560 k. compute the net rate of availability transfer and irreversibility. 33. Air in a closed vessel of fixed volume of 0.15 m 3, exerts pressure of 12 bar at 250 °c ,if the vessel is cooled so that the pressure falls to 3.5 bar, determine the final temperature, heat transfer and change of entropy. 34. Explain Carnot engine cycle and its efficiency. 35. Explain the term availability and unavailability. 36. A heat engine operates between a source a 600 °c and a sink at 60 c Determine the least rate of heat rejection per KW net output of the engine.
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37. 0.2 kg of air at 1.5 bar and 27 "c is compressed to a pressure of 15 bar according to the law pv (l.25) =c. determine work done heat flow to or from the air, increase or decrease in entropy 38. Two heat engines operating on carnot cycle are arranged in series. The engine A receives heat at 1000 K and rejects heat at a constant temperature T2. The engine B receives heat rejected by A, and in turn rejects heat to a reservoir at 300 K. Calculate the T2 when a) the efficiency of the two engines are equal b) the work output of the two engines are equal. 39. A carnot engine receives 90kJ from a reservoir at 900 K. It rejects heat to the environment at 300 K. One-fifth of its work output is used to drive a carnot refrigerator. The refrigerator rejects 60 kJ to the environment at 300 K. Find work output and efficiency of the engine, the temperature of the sink for the refrigerator in degree celsius. 40. Three reversible engines of Carnot type are operating in series between the limiting temperatures of 1100 K and 300 K. Determine the intermediate temperatures if the work output from engines is in proportion of 3 : 2 : 1. 41. In a compressor the air enters at 27°C and 1 atm and leaves at 227°C and 1 MPa. Determine the work done per unit mass of air assuming velocities at entry and exit to be negligible. Also determine the additional work required, if velocities are 10 m/s and 50 m/s at inlet and exit respectively. 42. In a gas turbine installation air is heated inside heat exchanger upto 750°C from ambient temperature of 27°C. Hot air then enters into gas turbine with the velocity of 50 m/s and leaves at 600°C. Air leaving turbine enters a nozzle at 60 m/s velocity and leaves nozzle at temperature of 500°C. For unit mass flow rate of air determine the following assuming adiabatic expansion in turbine and nozzle, a. heat transfer to air in heat exchanger b. power output from turbine c. velocity at exit of nozzle. d. Take for air as 1.005 kJ/kg°K. 43. A refrigerator operates on reversed Carnot cycle. Determine the power required to drive refrigerator between temperatures of 42ºC and 4ºC if heat at the rate of 2 kJ/s is extracted from the low temperature region. 44. In a power station, the saturated steam is generated at 200ºC by transferring the heat from hot gases in a steam boiler. Find the increase in total entropy of the combined system of gas and water and increase in unavailable energy due to irreversible heat transfer. The gases are cooled from 1000°C to 500°C and all the heat from gases goes to water. Assume water enters the boiler at saturated condition and leaves as saturated steam
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UNIT II AIR CYCLES Part-A (2 Marks) 1.
What is a thermodynamic cycle?
2.
What is meant by air standard cycle?
3.
Name the various ―gas power cycles‖.
4.
What are the assumptions made for air standard cycle analysis?
5.
Mention the various processes of the Otto cycle.
6.
Mention the various processes of the diesel cycle.
7.
Mention the various processes of the dual cycle.
8.
Mention the various processes of the Brayton cycle.
9.
Define air standard cycle efficiency.
10.
Sketch Otto cycle on p-V diagram and name all the processes.
11.
Plot the Diesel cycle on p-V and T-s diagram (or) Sketch the diesel cycle on p-V and T-s diagrams.
12.
Define mean effective pressure as applied to gas power cycles. How it is related to indicated power of an I.C engine?
13
Sketch the dual cycle on p-V and T-s co-ordinates and name the various processes.
14.
Define the following . (i) Compression ratio (ii) Cut off ratio and (iii) Expansion ratio
15.
Sketch Otto and Diesel cycle for the same compression ratio and heat input and compare the efficiency.
16.
Which cycle is more efficient with respect to the same compression ratio?
17.
For the same compression ratio and heat sup[plied, state the order of decreasing air standard efficiency of Otto, diesel and dual cycle. Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
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18.
Represent the Otto, Diesel and Dual cycle on p-V coordinates for the same compression ratio and same heat input.
19.
What is the range of compression ratio for Otto and Diesel cycle?
20.
Name the factors that affect air standard efficiency of Diesel cycle.
21.
What is the effect of cut-off ratio on the efficiency of diesel cycle when the compression ratio is kept constant?
22.
Define mean effective pressure. What is its physical significance?
23.
Write an expression for mean effective pressure for an Otto cycle in of compression ratio and other parameters.
24.
Write down the expression for mean effective pressure for an Diesel cycle and Dual cycle in of r, p and k.
25.
Write the expression for efficiency of the diesel cycle in of compression ratio and cut-off ratio.
26. 27.
Write any four major differences between Otto and diesel cycle. Draw the p-V and T-s diagram of Brayton cycle (or) Sketch the limited pressure cycle on p-V and T-s diagram and name various processes.
28.
Sketch the schematic arrangement of open cycle gas turbine plant and name the components.
29.
What are all the modifications are caddied out in Brayton cycle? Why?
30.
Is it always useful to have a regenerator in a gas turbine power cycle? Why?
31.
What is the expression for optimum pressure ratio for maximum specific work out-put in Brayton cycle?
32.
Why the gas turbine plants are generally designed for optimum pressure ratio for Maximum specific work output?
33.
When will be the gas turbine cycle efficiency reaches maximum?
34.
In case of regenerative cycle, what are the factors affecting thermal efficiency of the Cycle?
35.
What are the effects of introducing regeneration in the basic gas turbine cycle?
36.
When will the intercooler is provided between two compressors?
37.
What are the effects of providing the intercooler in the gas turbine cycle?
38.
When the reheater is employed in the gas turbine cycle.
39.
What is the condition for maximum work in the case of reheater employed in the gas turbine cycle? Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
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40.
What the effects are of reheat cycle?
1.
Part-B (16Marks) Drive and expression for the air standard efficiency of Otto cycle in of volume ratio.
2.
Drive an expression for the air standard efficiency of Diesel cycle.
3.
Drive an expression for the air standard efficiency of Dual cycle. .
4.
Explain the working of 4 stroke cycle Diesel engine. Draw the theoretical and actual PV diagram.
5.
An engine of 250 mm bore and 375 mm stroke works on Otto cycle. The clearance volume is 0.00263 m³. The initial pressure and temperature are 1bar and 50°C. if the maximum pressure is limited to 25 bar, find the following : a) The air std efficiency of the cycle b) The mean effective pressure for the cycle. Assume the ideal conditions.
6.
A certain quantity of air at a pressure of 1bar and temperature of 70°C is compressed adiabatically until the pressure is 7bar in Otto cycle engine. 465 kJ of heat per kg of air is now added at constant volume. Determine: a) Compression ratio of the engine. b) Temperature at the end of compression. c) Temperature at the end of heat addition. Take for air = 1.0kJ/kg-K, cv = 0.706kJ/kg-K.
7.
In a constant volume Otto cycle the pressure at the end of compression is 15times that at the start, the temperature of air at the beginning of compression is 38°C and maximum temperature attained in the cycle is 1950°C.determine: a) Compression ratio. b) Thermal efficiency of the cycle. c) Work done.
8.
An engine working on Otto cycle has a volume of 0.45m³, pressure 1 bar and temperature 30°C at the beginning of compression stroke. At the end of compression stroke, the pressure is 11 bar. 210kJ of heat is added at constant volume. Determine : a) Pressures, temperature and volumes at salient points in the cycle. b) Percentage clearance. c) Efficiency. d) Net work per cycle. e) Mean effective pressure. f) Ideal power developed by the engine if the number of working cycles per minute is 210. Assume the cycle is reversible. Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
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9.
The stroke and cylinder diameter of a compression ignition engine are 250 mm and 150 mm respectively. If the clearance volume is 0.0004m³ and fuel injection takes place constant pressure for 5% of the stroke determine the efficiency of the engine. Assume the engine working on the diesel cycle.
10.
An engine with 200 mm cylinder dia and 300 mm stroke works on theoretical Diesel cycle. The initial pressure and temperature of air used are 1bar and 27°C. The cut-off is 8% of the stroke. Determine : a) Pressure and temperature at all salient points. b) Theoretical air std efficiency. c) Mean effective pressure. d) Power of engine if the working cycles per minute are 380. Assume that compression ratio is 15 and working fluid is air Consider all conditions to be ideal.
11.
The swept volume of a diesel engine working on dual cycle 0.0053m³ and clearance volume is 0.00035m³. The maximum pressure is 65bar. Fuel injection ends at 5% of the stroke. The temperature and pressure at the start of compression are 80°C and 0.9bar. Determine the air std efficiency of the cycle. Take γ for air = 1.4
12.
The compression ratio for a single cylinder engine operating on dual cycle is 9. The maximum pressure in the cylinder is limited to 60bar. The pressure and temperature of the air at the beginning of the cycle are 1bar and 30°C. Heat is added during constant pressure process upto 4% of the stroke. Assuming the cylinder dia and stroke length as 250 mm and 300 mm respectively, determine : a) The air std efficiency of the cycle. b) The power developed if the numbers of working cycles are 3 per second. Take for air = 1.0 and cv = 0.71
13.
In an engine working on dual cycle, the temperature and pressure at the beginning of the cycle are 90°C and 1 bar respectively. The compression ratio is 9. The maximum pressure is limited to 68 bar and total heat supplied per kg of air is 1750 kJ. Determine a) Pressure and temperature at all salient points. b) Air std efficiency. c) Mean effective pressure.
14.
Air enters the compressor of a gas turbine plant operating on Brayton cycle at 101.325 kpa, 27°C. The pressure ratio in the cycle is 6. Calculate the maximum temperature in the cycle and the cycle efficiency. Assume WT = 2.5WC where WT and Wc are the turbine and the compressor work respectively. Take γ =1.4.
15.
Consider an air std cycle in which the air enters the compressor at 1.0 bar and 20°C. The pressure of air leaving the compressor is 3.5 bar and the temperature at turbine inlet is 600°C. Determine per kg of air: Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
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a) b) c) d) e)
1.
Efficiency of cycle Heat supplied to air Work available at the shaft Heat rejected in the cooler, and Temperature of air leaving the turbine. For air γ = 1.4
The following data in referred for an air standard diesel cycle compression ratio = 15 heat added = 200 KJ/Kg- minimum temperature in the cycle = 25°C Suction pressure = 1 bar Calculate 1. Pressure and temperature at the Salient point. 2. Thermal efficiency 3. Mean effective pressure,
4. Power output of the cycle If flow rate 'of air is 2 Kg/s 2. Air enters the compressor of a gas turbine at 100 KPa and 25 o C. For a pressure ratio of 5 and a maximum temperature of 850°C. Determine the thermal efficiency using the Brayton cycle.
3. An Engine-working on Otto cycle has a volume of 0.45 m3 , pressure 1 bar and temperature 30o,C at the beginning of compression stroke. At the end of compression stroke, the pressure is 11 bar and 210 KJ of heat is added at constant volume. Determine (i) Pressure, temperature and volumes at salient points in the cycle.' (ii) Efficiency.
4. A Dual combustion air standard cycle has a compression ratio of 10. The constant pressure part of combustion takes place at 40 bar. The highest and the lowest temperature of the cycle are 1725 degree C and 27 degree C respectively. The pressure at the beginning of compression is 1 bar.Calculate (I) the pressure and temperature at each key points of the cycle. (ii) The heat supplied at constant volume, (iii) the heat supplied at constant pressure. (Iv) The heat rejected. (v) the work output. (vi) the efficiency and (vii) mep.
5. The compression ratio of an air-standard Otto cycle is 9.5. At the beginning of compression,the air is at 100 kPa, 35°C and 600 cm3.The temperature at the end of isentropic expansion process is 800 K. Determine
a. The highest temperature and pressure in the cycle b. The thermal efficiency c. The mean effective pressure. 6. An air-standard Diesel cycle has a compression ratio of 16 and a cut-off ratio of 2. At the a. beginning of the compression process air is at 95 kPa and 27°C. Determine i. The temperature after the heat addition process ii. The thermal efficiency and iii. The mean effective pressure 7. Show the Otto cycle on P-V and T-S diagrams. Derive expressions for the efficiency and mean effective pressure and plot their variation with compression ratio. Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
8.
In an air standard Diesel cycle, the compression ratio is 16, and at the beginning of isentropic compression, the temperature is 288 K, and the pressure is 0.1 MPa. The maximum temperature in the cycle is 1753 K. Calculate a. The pressure and temperature at all the four important points in the cycle b. The m.e.p. and the cycle efficiency.
UNIT-3 THERMODYNAMICS OF ONE DIMENSIONAL FLUID FLOW Part-A (2 Marks)
1.
What are the various types of nozzles and their functions?
2.
Write down the expression for velocity at exit from steam nozzle.
3.
Derive the expression for the critical pressure ratio in a steam nozzle.
4.
What are the effects of friction on the flow through a steam nozzle?
5.
Write the general energy equation for a steady flow system and from this obtain the energy equation for nozzle.
6.
Define nozzle efficiency and critical pressure ratio.
7.
Explain the phenomenon of super saturated expansion in steam nozzle (or) What is metastable flow?
8.
What are the conditions that produce super saturation of steam in nozzles?
9.
Draw the T-s and h-s plot of super saturated expansion of steam in a nozzle.
10.
What are the effects of super saturation in a steam nozzle?
11.
What are the differences between supersaturated flow and isentropic flow through steam nozzles?
12. 13. 14.
What is meant by steam power cycles? What is meant by work ratio? What is the importance of work ratio in vapour cycles? What are the effects of condenser pressure on the Rankine cycle? Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
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15. Mention the improvements made to increase the ideal efficiency of ranking cycle. 16. Name the different components in steam power plant working on a rankine cycle. 17. What are disadvantages of reheating? 18. List the advantages of reheat cycle. 19. What are the disadvantages of bleeding? 20. Draw the T-s plot of Rankine Cycle 21.
Draw the T-s plot of Reheat rankine cycle
22.
Define Mach Number
23.
Define Stagnation Enthalpy
24.
Define Stagnation Temperature
25. Write the area-velocity relation for an isentropic flow in a variable area duct. What is the effect of Mach number on area-velocity relation? 26. Define Specific impulse 27.
Define thrust
28.
What is jet propulsion?
29.
What are the main components of gas turbine engine used for turbojet aircrafts?
30.
Define propulsive efficiency, Jet thrust, thermal efficiency, Overall efficiency
31.
What is ―after burning‖ in turbojet engines?
32.
Write Continuity, Momentum and Energy equation.
33.
What is the function of tail pipe? PART- B (16Marks)
1.
An impulse turbine having a set of 16 nozzles receives steam at 20 bar, 400° C. The pressure of steam at exist is 12 bar. if the total discharge Is 260 Kg/min and nozzle efficiency is 90% . Find the cross sectional area of each nozzle, if the steam has velocity of 80m/s at entry to the nozzle, find the percentage Increase In discharge.
2.
Dry saturated steam at a pressure of 8 bar enters the convergent divergent nozzle and leaves it at a pressure 1.5 bar. If the flow isentropic and if the corresponding index of expansion is 1.133, find the ratio of 0.3 are at exit and throat for max. discharge.
3.
Steam enters a group of nozzles of a steam turbine at 12 bar and 2200 C and leaves at 1.2 bar. The steam turbine develops 220 Kw with a specific steam consumption of 13.5 Kg/ Kw. Hr. If the diameter of nozzle at throat Is 7mm . Calculate the number of nozzle.
4.
Drive an expression for critical pressure ratio in of the index of expansion Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
5.
In a steam nozzle, the steam expands from 4bar to 1bar. The initial velocity is 60m/s and the initial temp is 200°C. Determine the exit velocity if the nozzle efficiency is 92%.
6.
Dry saturated steam enters a steam nozzle at a pressure of 15bar and is discharged at a pressure of 2.0bar. If the dryness fraction of discharge steam is 0.96, what will be the final velocity of steam, Neglect initial velocity of steam, If 10% of heat drop is lost in friction, find the percentage reduction in the final velocity.
7.
Steam initial dry and saturated is expanded in a nozzle from 15bar at 300°C to 1.0 bar. If the frictional loss in the nozzle is 12% of the total heat drop calculate the mass of steam discharged when exit dia of the nozzle is 15mm.
8.
Dry saturated steam at a pressure of 11bar enters a convergent-divergent nozzle and leaves at a pressure of 2bar. If the flow is adiabatic and frictionless, determine a) The exit velocity of steam b) ratio of cross section at the exit and that at throat. Assume the index of adiabatic expansion to be 1.135.
9.
The nozzles of a De Laval steam turbine are supplied with dry saturated steam at a pressure of 9bar. The pressure at the outlet is 1bar. The turbine has two nozzles with a throat diameter of 2.5mm. Assuming nozzle efficiency as 90% and that of turbine rotor 35%, find the quality of steam used per hour and the power developed.
10. A steam power plant works between 40 bar and 0.05 bar. If the steam supplied is dry saturated and the cycle of operation is Rankine, find : (i) Cycle efficiency (ii) Specific steam consumption. In a regenerative cycle the inlet conditions are 40 bar and 400°C. Steam is bled at 10 bar in Regenerative heating. The exit pressure is 0.8 bar. Neglecting pump work .Determine the efficiency of the cycle. 11. Show the Rankine cycle on h -s and T -s diagrams. Explain the effect of temperature of heat addition and heat rejection on the performance. 12. A simple turbojet unit operates with a maximum turbine inlet temperature of 1200 K, a pressure ratio of 4.25: 1, and a mass flow of 25 kg/s, under ideal conditions. Assume a convergent nozzle is employed. Calculate the total thrust and sfc. Assume that the unit is stationary and at sea-level, where the ambient conditions may be taken as 1 bar and 293 K. Assume air-fuel ratio of 50: 1. Calorific value offuel : 43 MJ/kg. 13. Derive an expression for critical pressure ratio in of the index of expansion 14. Steam enters a group of nozzles of a steam turbine at 12 bar and 2200 C and leaves at 1.2 bar. The steam turbine develops 220 Kw with a specific steam consumption of 13.5 Kg/ Kw. Hr. If the diameter of nozzle at throat Is 7mm . Calculate the number of nozzle 15. Dry saturated steam at a pressure of 8 bar enters the convergent divergent nozzle and leaves it at a pressure 1.5 bar. If the flow isentropic and if the corresponding index of expansion is 1.133, find the ratio of 0.3 are at exit and throat for max. discharge. Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
16. A steam power plant operates on ideal Rankine cycle using reheater and regenerative feed water heaters. It has one open feed heater. Steam is supplied at 150 bar and 600°C.The condenser pressure is 0.1 bar. Some steam is extracted from the turbine at 40 bar for closed feed water heater and remaining steam is reduced at 40 bar to 600°C. Extracted steam is completely condensed in this closed feed water heater and is pumped to 150 bar before mixing with the feed water heater. Steam for the open feed water heater is bled from L.P. turbine at 5 bar. Determine : a. Fraction of steam extracted from the turbines at each bled heater, and b. Thermal efficiency of the system.
17. Draw the line diagram of the components of regenerative Rankine and represent the cycle on T-s diagram. 18. Explain in detail about simple jet propulsion system with neat sketch 19. Explain in detail about ram jet with neat sketch 20. Explain in detail about turbo jet with neat sketch 21. Explain in detail about Turbo prop with neat sketch 22. Explain in detail about Turbo fan with neat sketch 23. Derive the expression of static & stagnation temperature & pressure Ratio 24. A conical diff has entry and exit diameter of 15 cm & 30cm respectively.The pressure, temperature and velocity of air at entry are 0.69 bar, 340 K and 180m/sec respectively. Determine 1. Exit Pressure 2. Exit velocity assume Isentropic flow,γ =1.4 =1.000KJ/Kgk 25. A nozzle in a wind tunnel gives a test section Mach number of 2.0 Air enters the nozzle from large reservoir at 0.69 bar and 310K The cross sectional area of throat is 1000 sq.cm.determine the following quantities for the tunnel for one dimensional isentropic flow: 1. Pressures, Temperatures and velocities at the throat and test sections 2. Area of cross section of the test section 3. Mass flow rate 4. Power required to drive the compressor 26. Air is discharged from a reservoir at P0= 6.91 bar T0=3250C through a nozzle to an exit pressure of 0.98 bar. If the flow rate is 3600 Kg/hr .Determine for the isentropic flow: 1. Throat area , Pressure,and velocity 2. Exit area ,Mach number & 3. Maximum velocity 27. A turbojet engine propels an aircraft at a mach number of 0.8 in level flight at an altitude of 10Km .the datum fir the engine is given below : Stagnation temperature at turbine inlet = 1200 K ,Stagnation temperature rise through the compressor = 175 K ,Calorific value of fuel is 43MJ/Kg,Compressor Efficiency = 0.75 ,Combustion chamber efficiency = 0.975, Turbine Efficiency=0.81 , Mechanical Efficiency of power transmission between turbine and compressor = 0.98, Exhaust Nozzle Efficiency = 0.97, Specific Impulse = 25 sec ,Calculate 1. Fuel air ratio 2. Compresor Pressure ratio 3. Turbine Pressure ratio 4. Exhaust Nozzle Pressure Ratio 5. Mach number of exhaust jet Assume properties of air and combustion gases are same.
UNIT IV REFRIGERATION AND AIR–CONDITIONING Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Part-A (2 Marks) 01.
Define tons of refrigeration and COP.
02.
Define tonne o f refrigeration .Heat is removed from a space at a rate of 42,000kJ/h. Express this heat removal rate in tons.
03.
Show the air- refrigeration cycle on p-V and T-s diagrams.
04.
The door of a refrigerator inside a room was left open. What will happen?
05.
Show the vapour compression refrigeration cycle in T-s diagram and give the COP of a simple cycle.
06.
In a vapour compression refrigeration system, where the lowest temperature will occur?
07.
How does the actual vapour compression cycle differ from that of the ideal cycle?
08.
Name four important properties of a good refrigerant
09.
What is the difference between air conditioning and refrigeration?
10.
What is the function of the throttling valve in vapour compression refrigeration system?
11.
In a vapour compression refrigeration system, where the highest temperature will occur?
12.
The vapour absorption system can use low-grade heat energy in the generator. Is true or false?
13.
Name any four commonly used refrigerants.
14.
Explain unit of refrigeration.
15.
Why throttle valve is used in place of expansion cylinder for vapour compression refrigerant machine.
16.
What are the effect pf superheat and subcooling on the vapour compression cycle?
17.
What are the properties of good refrigerant?
18.
What are the advantages and disadvantages of air refrigeration system?
19.
What are the advantages of vapour compression refrigeration system over air refrigeration system?
20.
What is the objective of under cooling? Sketch the process in T-s diagram?
21.
What is net refrigerating effect of the refrigerant?
22.
Name the refrigerant normally used in simple vapour absorption system.
23.
Name the various components used in simple vapour absorption system. Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
24.
State the condition of the refrigerant at the end of compression in vapour compression system.
25.
Define refrigerant.
26.
What type of condensers are in common uses for vapour absorption refrigeration system?
27.
What is the function of analyzer and rectifier in an absorption system?
28.
State the substances used in the Lithium Bromide system and their functions.
29.
What is psychrometry?
30.
Name some psychrometric processes and represent them on the psychrometric chart.
31.
Define DPT and degree of saturation.
32.
Define Relative Humidity (RH) and Specific humidity.
33.
How are air-conditioning systems classified?
34.
How does humidity affect human comfort?
35.
What are the various sources of heat gain of an air-conditioned space?
36.
What do you mean by the term ―Infiltration‖ in heat load calculations?
37.
Define RSHF, RTH.
38.
On a psychrometric chart, show all the property lines.
39.
Define Apparatus Dew Point (ADP) of cooling coil.
40.
Define by factor (BPF) of a coil.
41.
State the effects of very high and a very low by factor.
42.
Name four important properties of a good refrigerant
1.
Part-B (16 Marks) Draw neat sketch of simple vapor compression refrigeration system and explain.
2.
Explain with sketch the working principle of aqua Ammonia refrigeration system.
3.
Explain with sketch the working principle of water-Lithium bromide refrigeration system.
4.
Briefly explain the cooling load calculation in air conditioning system.
5.
Explain winter, summer, and year round A/c system.
6.
Explain unitary A/c and central A/c system.
7.
Explain any four psychometric processes with sketch.
8.
The atm conditions are 20°C and specific humidity of 0.0095kJ/kg of dry air. Calculate the following: Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
a) Partial pressure of vapour b) Relative humidity c) Dew point temperature. 9.
The air supplied to a room of a building in winter is to be at 17°C and have a relative humidity of 60%. If the barometric pressure is 1.01325bar. find a) The specific humidity b) The dew point under these condition.
10.
0.004kg of water vapour per kg of atmospheric air is removed and temperature of air after removing the water vapour becomes 20°C determine: a) Relative humidity b) Dew point temperature Assuming that condition of atm air is 30°C and 55% R.H and pressure is 1.013bar.
11.
The sling psychrometer in a laboratory test record the following readings: Dry bulb temperature = 35°C Wet bulb temperature = 25°C Calculate the following: a) Specific humidity b) Relative humidity c) Vapour density in air d) Dew point temperature e) Enthalpy of mixture per kg of dry air Take atm pressure = 1.013bar
12.
One kg of air at 35°C DBT and 60% R.H is mixed with 2kg of air at 20°C DBT and 13°C dew-point temperature. Calculate the specific humidity of mixture.
13.
90m³ of air per minute at 20°C and 75% R.H is heated until its temperature becomes 30°C. calculate : a) R.H of the heated air b) Heat added to air per minute.
14.
40 m³ of air at 35°C DBT and 50% R.H is cooled to 25°C DBT maintaining its specific humidity constant. Determine: a) Relative humidity of cooled air b) Heat removed from air
15.
28 tonnes of ice from and at 0°C is produced per day in an ammonia refrigerator. The temperature range in the compressor is from 25°C to -15°C. The vapour is dry and saturated at the end of compression and an expansion valve is used. Assuming a coefficient of performance of 62% of the theoretical, calculate the power required to drive the compressor. Temp °C Enthalpy of liquid Enthalpy of Entropy of Entropy of (kJ/kg) vapour (kJ/kg) liquid vapour (kJ/kgK) (kJ/kgK) 25 100.04 1319.22 0.3473 4.4852 Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
-15 16.
-54.56
1304.99
-2.1338
5.0585
A refrigeration plant works between temp limits -5 and 25°C. The working fluid ammonia has a dryness fraction of 0.62 at entry to compressor. If the machine has a relative efficiency of 55%, calculate the amount of ice formed during a period of 24 hours. The ice is to be formed at 0°C water at 15°C and 6.4kg of ammonia is circulated per minute. Specific heat of water is 4.187kJ/kg and latent heat of ice is 335kJ/kg. Temp Liquid heat kJ/kg Latent heat kJ/kg Entropy of liquid kJ/kgK 25 298.9 1167.1 1.124 -5 158.2 1280.8 0.630
17.
A simple vapour compression plant produces 5tonnes of refrigeration. The enthalpy values at inlet to compressor, at exit from the compressor, and at exit from the condenser are 183.19, 209.41 and 74.59kJ/kg respectively. Estimate a) The refrigerant flow rate b) The power required to drive the compressor c) The COP d) The rate of heat rejection to the condenser. 18. Dry bulb and wet temperatures of 1 atmospheric air stream are 40°0 and 30°c respectively.Determine (a)Humidity (b) Relative humidity (c) Specific humidity. 19. Atmospheric air with barometric pressure of 1.013 bar has 38°c dry bulb temperature and 28°c wet bulb temperature. Determine (a) Humidity ratio (b) Relative humidity (c) dew point temperature. 20. Atmospheric air at 760 mm of Hg has 45°c DBT and 30°c WBT, using psychometric chart calculate R.H, Humidity ratio, DPT, enthalpy, specific volume of air. 21. Atmospheric air at 1 bar pressure has 2.5°0 DBT and 75% RH using psychometric chart, calculate DBT, enthalpy, vapour pressure. 22. Explain sensible heating process, sensible cooling, and humidification process. 23. An air water vapour mixture at 0.1 Mpa, 30°0, 80% RH. Has a volume of 50 m3 Calculate the specific humidity, dew point, wet bulb temperature, mass of dry air and mass of water vapour. 24. The atmospheric conditions are 30ºC and specific humidity of 0.0215 kg/kg of air. Determine : Atmospheric pressure = 756 mm Hg. a. Partial pressure of air b. Relative humidity c. Dew point temperature. 25. 1 kg of air at 24ºC and a relative humidity of 70% is to be mixed adiabatically in a steady state, steady flow device with 1 kg of air at 16ºC and a relative humidity of 10%. Assuming that the mixing is to be carried out at a constant pressure of 1.0 atm, determine the temperature and relative humidity of the stream leaving the device. 26. In a laboratory test, a psychrometer recorded 36ºC DBT and 30ºC WBT. Calculate d. Vapour pressure e. Relative humidity f. Specific humidity g. Degree of saturation Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
h. Dew point temperature i. Enthalpy of the mixture. 27. An air-water vapour mixture enters an adiabatic saturator at 30ºC and leaves at 20ºC, which is the adiabatic saturation temperature. The pressure remains constant at 1 bar. Determine the relative humidity and the humidity ratio of the inlet mixture. 28. The following observation were made during a testing of moist air i. Dry bulb temperature Tdb = 29oC ii. Dew point temperature Tdb = 15oC iii. Total pressure = 1 bar Determine the relative humidity and degree of saturation 29. In a combined heating and humidification process, moist air enters heating coil with the dry bulb temperature 20oC and 30% R.M. After the process the drug bulb temperature and the RH of Air were found to be 40oC and 55% RH. The air es through the heating at the rate of 350 kg/min 30. In an air conditioning plant, fresh air is used to mix up with returned air from conditioned space. The fresh air drawn from atmosphere has the drug bulb temperature 32oC and we bulb temperature 25oC. The fresh air is drawn at the rate of 100m3/min. The returned air from conditioned space has the drug bulb temperature 23oC and relative humidity 50%. The volume flow rate of it 540 m3/min. Determine the (i) dry bulb and web bulb temperature (ii) specific humidity of mixture 31.
A food storage locker requires a refrigeration system of 2400 kJ/min. capacity at an evaporator temperature of 263K and a condenser temperature of 303K. The refrigerant used in Freon -12 and is subcooled by 6°C before entering the expansion valve and vapour is superheated by 7°C before leaving the evaporator coil. The compression of refrigeration is reversible adiabatic. The refrigeration compressor is two cylinder single acting with stroke equal to 1.25 times the bore and operates at 1000r.p.m Temp Absolute Specific Enthalpy Enthalpy Entropy Entropy pressure volume of of liquid of vapour of liquid of vapour bar vapour kJ/kg kJ/kg kJ/kgK kJ/kgK m³/kg 263 2.19 0.0767 26.9 183.2 0.1080 0.7020 303 7.45 0.0235 64.6 199.6 0.2399 0.6854
UNIT V AIR COMPRESSORS Part-A (2 Marks) 1. Classify the various types of air-compressors. Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
2. What is meant by single act ing compressor? 3. What is meant by double acting compressor? 4. what is meant by single stage compressor 5. what is meant by multistage compressor 6. Draw the p-v diagram of a two stage reciprocating air compressor 7. Indicate the applications of reciprocating compressors in industry 8.
What are the advantage s of multi stage compression with inter cooling over single stage compression for the same pressure ratio
9. Define the as applied to air compressors: Volumetric efficiency and isothermal compression efficiency 10. Define the mechanical efficiency and isothermal efficiency of a reciprocating air compressor. 11. Define isentropic efficiency 12. Define mean effective pressure.How is it related to indicated power of an IC engine 13. What is meant by free air delivered? 14. Explain how flow of air is controlled in a reciprocating compressor? 15. What factors limit the delivery Pressure in a reciprocating compressor 16.
Name the methods adopted for increasing isothermal efficiency of reciprocating air compressor.
17. why clearance is necessaty and What is its effect on the performance of reciprocating compressor ? 18. Which type of compression is the best in reciprocating compressor? 19. What is compression ratio? 20. Give the expression for inter cooler pressure 21. what is meant by inter cooler? 22. Give the expression for work done for ba multistage compressor with prefect inter cooling . 23. Give the expression for work done for a two-stage compressor with perfect inter cooling. 24. What are the factors that affect the volumetric efficiency of a reciprocating compressor? 25. Name the compression process in which work done is minimum in a reciprocating air compressor Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
26.
A50-m3/min compressor refers to why?
27.
If C is the clearance ratio for a reciprocating air compressor, what will be the volumetric efficiency?
28.
What is the purpose of using intercooler in multi-stage compression
29.
Discuss the effect of clearance upon the performance of an air compressor.
30.
Give two merits of rotary compressor over reciprocating compressors
31.
Give examples for positive displacement compressor
32.
What is the different between complete (or ) perfect inter cooling and incomplete (or) imperfect inter cooling
33.
How to Increase isothermal efficiency
1.
Part-B (16 Marks) Drive an expression for the work done by single stage single acting reciprocating air compressor.
2.
Drive an expression for the volumetric efficiency of reciprocating air compressors
3.
Explain the construction and working of a root blower .
4.
Explain the construction and working of a centrifugal compressor.
5.
Explain the construction and working of a sliding vane compressor and axial flow compressor
6.
A single stage reciprocating compressor takes 1m³ of air per minute at 1.013 bar and 15°C and delivers it at 7 bar. Assuming that the law of compression is pV1.35 =C, and the clearance is negligible, calculate the indicated power.
7.
If the compressor of prob 1is driven at 300 r.p.m and is a single acting, singlecylinder machine, calculate the cylinder bore required, assuming a stroke to bore ratio 1.5:1 calculate the power of the motor required to drive the compressor if the mechanical efficiency of the compressor is 85% and that of the motor transmission is 90%. 8. Show that in the case of reciprocating compressor, the work input is independent clearance ratio. Explain with the help of p-v diagrams.
9.
Derive an expression for the volumetric efficiency of a two-stage reciprocating compressor in of clearance ratio and Pressure ratio.
10. Steam at 20 bar, 633 K is expanded in a steam turbine to 0.08 bar. It then enters a condenser, where it is condensed to saturated liquid water. The pump feeds back the Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
water into the boiler. Assuming ideal processes, find per kg of steam, the network and cycle efficiency. 11. A simple turbojet is being tested under laboratory conditions at static position. Pressure ratio across the compressor is 5:1; maximum temperature in the cycle is 1200 K. Assume a convergent nozzle is employed. Calculate the total thrust and s.f.c. Ambient conditions are 1 bar and 300 K Air fuel ratio 50:1; C.V. of fuel 40 MJ/kg. 12. With the help of a neat sketch explain the construction and working of a reciprocating air compressor. Derive an expression for the work of compression in of pressure ratio and clearance ratio. 13. With the help of a neat sketch explain the construction and working of a rotary air compressor. 14. Derive an expression for the optimum intermediate pressure of two stage reciprocating compressor with perfect intercooling. 15. A two stage singe acting air compressor compresses 2m3 airs from 1 bar and 20° C to 15 bar. The air from the low pressure compressor is cooled to 25° C in the intercooler. Calculate the minimum power required to run the compressor if the compression follows PV1.25=C and the compressor runs at 400 rpm. 16. A single stage single acting air compressor is used to compress air from 1.013 bar and 25° C to 7 bar according to law PV 1.3 = C.The bore and stroke of a cylinder are 120mm and 150mm respectively. The compressor runs at 250 rpm .If clearance volume of the cylinder is 5% of stroke volume and the mechanical efficiency of the compressor is 85%, determine volumetric efficiency, power, and mass of air delivered per minute. 17. A single stage single acting air compressor is used to compress air from 1 bar and 22° C to 6 bar according to the law PV1 .25 = C. The compressor runs at 125 rpm and the ratio of stroke length to bore of a cylinder is 1.5. If the power required by the compressor is 20 kW, determine the size of the cylinder
18. An air compressor takes in air at 1bar and 20°C and compressor it according to law pV1.2 =C. it is then delivered to a receiver at a constant pressure of 10bar. R=0.287 kJ/kgK determine: a) Temperature at the end of compression b) Workdone and heat transferred during compression per kg of air. 19. A single stage double acting cylinder air compressor is required to deliver 14m³ of air per minute measured at 1.013bar and 15°C. The delivery pressure is 7bar and the speed of 300r.p.m. Take the clearance volume as 5% of the swept volume with the compression and expansion index of n = 1.3. calculate: a) Swept volume of the cylinder b) The delivery temperature c) Indicated power
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Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
20. A single stage double acting cylinder air compressor has a free air delivery (F.A.D) of 14m³ per minute measured at 1.013bar and 15°C. The pressure and temperature in the cylinder during induction are 0.95 bar and 32°C. The delivery pressure is 7 bar and index of compression and expansion, n=1.3. The clearance volume is 5% of the swept volume. Calculate a) Indicated power required b) Volumetric efficiency 21. A single acting two stage compressor with complete intercooling delivered 10.5kg/min of air at 16 bar. Suction occurs at 1 bar and 27 deg c . It follows the Law PV^1.3 Determine 1. Power required to drive the compressor 2.Isothermal Efficiency 3. Free air delivery 4. Heat transferred in the intercooler 5. If clearance ratios of L.P & H.P cylinders are .04&.06 Calculate Swept & Clearance volume for each cylinder
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Aero Engineering Thermodynamics Unit wise-Question bank Wings of aero UNIT I BASIC THERMODYNAMICS Part-A (2 Marks) 1. What is meant by thermodynamics system? How do you classify it? 2. What is meant by closed system? Give an example. 3. Define an open system Give an example. 4. Distingusih between Open and Closed system 5. Define an isolated system: 6. Define specific heat capacity at constant pressure. 7. Define specific heat capacity at constant volume. 8. What is meant by surroundings? 9. What is boundary? 10. What is meant by thermodynamic property 11. How do you classify the property? 12. Define Intensive and Extensive properties. 13. What do you understand by equilibrium of a system? 14. Differentiate Intensive and Extensive properties 15. State the Kelvin - Planck statement of second law of thermodynamics. 16. State Clausius statement of second law of thermodynamics. 17. Write the third law of thermodynamics. 18. State Carnot's theorem. 19. What are the Corollaries of Carnot theorems? 20. Define - PMM of second kind. 21. What is difference between a heat pump and refrigerator? 22. Define the term COP. 23. Why Carnot cycle cannot be realized in practice? 24. Name two alternative methods by which the efficiency of a Carnot cycle can be increased. 25. Why a heat engine cannot have 100% efficiency 26. When the Carnot cycle efficiency will be maximum? 27. What are the processes involved in Carnot cycle 28. What is mean by heat engine? 29. What do you meant by entropy? 30. Prove Clausius Inequality 31. Write the principle of Increase in entropy
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PART –B (16 marks) 1. one kg of gas expands at CO&11stant pressure from 0.085 m3 to 0.13 Ill).if the initial temperature of the gas is 22.5 °c.find the final. Temperatures, net heat transfer, change in internal energy, pressure of gas. 2. A certain quantity of gas is head at constant pressure from 35 °0 to 185°c. Estimate the amount of heat transferred, ideal work done, change in internal energy,when the initial volume of the gas is 0.6 m^3. 3. Explain and derive Isothermal process 4. Explain and derive Isobaric process. 5. Explain and derive Isochoric process. 6. Explain and derive isentropic process. 7. Explain and derive Polytropic process. 8. Explain the inequivalence of Kelvin Planck’s & Clausius Statement 9. 2kg of gas at a pressure of 1.5 bar. Occupies a volume of 2.5 m^3. If this gas compresses isothermally to 1/3 times the initial volume. Find initial. Final temperature, work done, heat transfer. 10. one kg of air is compressed polytropically (n=1.3) from 1 bar and 27 deg Celsius to 3 bar. Find I. work transfer 2. Heat transfer 3. Change in internal energy. 11. A system receives 42 kJ of heat while expanding with volume change of 0.123 m3 against an atmosphere of 12 N/cm2. A mass of 80 kg in the surroundings is also lifted through a distance of 6 metres. a. Find the change in energy of the system. b. The system is returned to its initial volume by an adiabatic process which requires 100 kJ of work. Find the change in energy of system. c. Determine the total change in energy of the system.
12. A tank contains 2.26 m3 of air at a pressure of 24.12 bar. If air is cooled until its pressure and temperature becomes 13.78 bar and 21.1°C respectively. Determine the decrease of internal energy. 13. Determine work done by fluid in the thermodynamic cycle comprising of following processes a. Unit mass of fluid at 20 atm and 0.04 m3 is expanded by the law PV1.5 = constant, till volume gets doubled. b. Fluid is cooled isobarically to its original volume. c. Heat is added to fluid till its pressure reaches to its original pressure, isochorically. 14. Air at 8 bar, 100°C flows in a duct of 15 cm diameter at rate of 150 kg/min. It is then throttled by a valve upto 4 bar pressure. Determine the velocity of air after throttling and also show that enthalpy remains constant before and after throttling. 15. Determine the power required by a compressor designed to compress atmospheric air (at 1 bar, 20°C) to 10 bar pressure. Air enters compressor through inlet area of 90cm2 with velocity of 50 m/s and leaves with velocity of 120 m/s from exit area of 5 cm2. Consider heat losses to environment to be 10% of power input to compressor.
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16. A frictionless piston is free to move in a closed cylinder. Initially there is 0.035 m3 of oxygen at 4.5 bar, 60°C on one side of the piston and 0.07 m3 of methane at 4.5 bar and – 12°C on the other side. The cylinder walls and piston may be regarded as perfect thermal insulators but the oxygen may be heated electrically. Heating takes place so that the volume of oxygen doubles. Find : a. Final state condition ; (ii) Work done by the piston ; b. Heat transferred to oxygen.
c. Treat both gases as perfect and take : d. For oxygen = 0.88 kJ/kg K, R = 0.24 kJ/kg K e. For methane = 1.92 kJ/kg K, R = 0.496 kJ/kg K. 17. The specific heat at constant pressure of one kg fluid undergoing a non-flow constant pressure process is given by where T is in °C. 18. The pressure during the process is maintained at 2 bar and volume changes from 1 m3 to 1.8 m3 and temperature changes from 50°C to 450°C. a. Determine : i. Heat added (ii) Work done ii. Change in internal energy (iv) Change in enthalpy. 19. A fluid system, contained in a piston and cylinder machine, es through a complete cycle of four processes. The sum of all heat transferred during a cycle is – 340 kJ. The system completes 200 cycles per min. Complete the following table showing the method for each item, and compute the net rate of work output in kW. [8] i. Process Q (kJ/min) W (kJ/min) ΔE (kJ/min) ii. iii. iv. v.
1—2 2—3 3—4 4—1
0 42000 –4200 —
4340 0 — —
— — – 73200 ___
32. Air flows through an adiabatic compressor at 3 kg/s the inlet conditions are 2 bar and 310k and exit conditions are 20 bar and 560 k. compute the net rate of availability transfer and irreversibility. 33. Air in a closed vessel of fixed volume of 0.15 m 3, exerts pressure of 12 bar at 250 °c ,if the vessel is cooled so that the pressure falls to 3.5 bar, determine the final temperature, heat transfer and change of entropy. 34. Explain Carnot engine cycle and its efficiency. 35. Explain the term availability and unavailability. 36. A heat engine operates between a source a 600 °c and a sink at 60 c Determine the least rate of heat rejection per KW net output of the engine.
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37. 0.2 kg of air at 1.5 bar and 27 "c is compressed to a pressure of 15 bar according to the law pv (l.25) =c. determine work done heat flow to or from the air, increase or decrease in entropy 38. Two heat engines operating on carnot cycle are arranged in series. The engine A receives heat at 1000 K and rejects heat at a constant temperature T2. The engine B receives heat rejected by A, and in turn rejects heat to a reservoir at 300 K. Calculate the T2 when a) the efficiency of the two engines are equal b) the work output of the two engines are equal. 39. A carnot engine receives 90kJ from a reservoir at 900 K. It rejects heat to the environment at 300 K. One-fifth of its work output is used to drive a carnot refrigerator. The refrigerator rejects 60 kJ to the environment at 300 K. Find work output and efficiency of the engine, the temperature of the sink for the refrigerator in degree celsius. 40. Three reversible engines of Carnot type are operating in series between the limiting temperatures of 1100 K and 300 K. Determine the intermediate temperatures if the work output from engines is in proportion of 3 : 2 : 1. 41. In a compressor the air enters at 27°C and 1 atm and leaves at 227°C and 1 MPa. Determine the work done per unit mass of air assuming velocities at entry and exit to be negligible. Also determine the additional work required, if velocities are 10 m/s and 50 m/s at inlet and exit respectively. 42. In a gas turbine installation air is heated inside heat exchanger upto 750°C from ambient temperature of 27°C. Hot air then enters into gas turbine with the velocity of 50 m/s and leaves at 600°C. Air leaving turbine enters a nozzle at 60 m/s velocity and leaves nozzle at temperature of 500°C. For unit mass flow rate of air determine the following assuming adiabatic expansion in turbine and nozzle, a. heat transfer to air in heat exchanger b. power output from turbine c. velocity at exit of nozzle. d. Take for air as 1.005 kJ/kg°K. 43. A refrigerator operates on reversed Carnot cycle. Determine the power required to drive refrigerator between temperatures of 42ºC and 4ºC if heat at the rate of 2 kJ/s is extracted from the low temperature region. 44. In a power station, the saturated steam is generated at 200ºC by transferring the heat from hot gases in a steam boiler. Find the increase in total entropy of the combined system of gas and water and increase in unavailable energy due to irreversible heat transfer. The gases are cooled from 1000°C to 500°C and all the heat from gases goes to water. Assume water enters the boiler at saturated condition and leaves as saturated steam
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UNIT II AIR CYCLES Part-A (2 Marks) 1.
What is a thermodynamic cycle?
2.
What is meant by air standard cycle?
3.
Name the various ―gas power cycles‖.
4.
What are the assumptions made for air standard cycle analysis?
5.
Mention the various processes of the Otto cycle.
6.
Mention the various processes of the diesel cycle.
7.
Mention the various processes of the dual cycle.
8.
Mention the various processes of the Brayton cycle.
9.
Define air standard cycle efficiency.
10.
Sketch Otto cycle on p-V diagram and name all the processes.
11.
Plot the Diesel cycle on p-V and T-s diagram (or) Sketch the diesel cycle on p-V and T-s diagrams.
12.
Define mean effective pressure as applied to gas power cycles. How it is related to indicated power of an I.C engine?
13
Sketch the dual cycle on p-V and T-s co-ordinates and name the various processes.
14.
Define the following . (i) Compression ratio (ii) Cut off ratio and (iii) Expansion ratio
15.
Sketch Otto and Diesel cycle for the same compression ratio and heat input and compare the efficiency.
16.
Which cycle is more efficient with respect to the same compression ratio?
17.
For the same compression ratio and heat sup[plied, state the order of decreasing air standard efficiency of Otto, diesel and dual cycle. Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
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18.
Represent the Otto, Diesel and Dual cycle on p-V coordinates for the same compression ratio and same heat input.
19.
What is the range of compression ratio for Otto and Diesel cycle?
20.
Name the factors that affect air standard efficiency of Diesel cycle.
21.
What is the effect of cut-off ratio on the efficiency of diesel cycle when the compression ratio is kept constant?
22.
Define mean effective pressure. What is its physical significance?
23.
Write an expression for mean effective pressure for an Otto cycle in of compression ratio and other parameters.
24.
Write down the expression for mean effective pressure for an Diesel cycle and Dual cycle in of r, p and k.
25.
Write the expression for efficiency of the diesel cycle in of compression ratio and cut-off ratio.
26. 27.
Write any four major differences between Otto and diesel cycle. Draw the p-V and T-s diagram of Brayton cycle (or) Sketch the limited pressure cycle on p-V and T-s diagram and name various processes.
28.
Sketch the schematic arrangement of open cycle gas turbine plant and name the components.
29.
What are all the modifications are caddied out in Brayton cycle? Why?
30.
Is it always useful to have a regenerator in a gas turbine power cycle? Why?
31.
What is the expression for optimum pressure ratio for maximum specific work out-put in Brayton cycle?
32.
Why the gas turbine plants are generally designed for optimum pressure ratio for Maximum specific work output?
33.
When will be the gas turbine cycle efficiency reaches maximum?
34.
In case of regenerative cycle, what are the factors affecting thermal efficiency of the Cycle?
35.
What are the effects of introducing regeneration in the basic gas turbine cycle?
36.
When will the intercooler is provided between two compressors?
37.
What are the effects of providing the intercooler in the gas turbine cycle?
38.
When the reheater is employed in the gas turbine cycle.
39.
What is the condition for maximum work in the case of reheater employed in the gas turbine cycle? Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
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40.
What the effects are of reheat cycle?
1.
Part-B (16Marks) Drive and expression for the air standard efficiency of Otto cycle in of volume ratio.
2.
Drive an expression for the air standard efficiency of Diesel cycle.
3.
Drive an expression for the air standard efficiency of Dual cycle. .
4.
Explain the working of 4 stroke cycle Diesel engine. Draw the theoretical and actual PV diagram.
5.
An engine of 250 mm bore and 375 mm stroke works on Otto cycle. The clearance volume is 0.00263 m³. The initial pressure and temperature are 1bar and 50°C. if the maximum pressure is limited to 25 bar, find the following : a) The air std efficiency of the cycle b) The mean effective pressure for the cycle. Assume the ideal conditions.
6.
A certain quantity of air at a pressure of 1bar and temperature of 70°C is compressed adiabatically until the pressure is 7bar in Otto cycle engine. 465 kJ of heat per kg of air is now added at constant volume. Determine: a) Compression ratio of the engine. b) Temperature at the end of compression. c) Temperature at the end of heat addition. Take for air = 1.0kJ/kg-K, cv = 0.706kJ/kg-K.
7.
In a constant volume Otto cycle the pressure at the end of compression is 15times that at the start, the temperature of air at the beginning of compression is 38°C and maximum temperature attained in the cycle is 1950°C.determine: a) Compression ratio. b) Thermal efficiency of the cycle. c) Work done.
8.
An engine working on Otto cycle has a volume of 0.45m³, pressure 1 bar and temperature 30°C at the beginning of compression stroke. At the end of compression stroke, the pressure is 11 bar. 210kJ of heat is added at constant volume. Determine : a) Pressures, temperature and volumes at salient points in the cycle. b) Percentage clearance. c) Efficiency. d) Net work per cycle. e) Mean effective pressure. f) Ideal power developed by the engine if the number of working cycles per minute is 210. Assume the cycle is reversible. Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
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9.
The stroke and cylinder diameter of a compression ignition engine are 250 mm and 150 mm respectively. If the clearance volume is 0.0004m³ and fuel injection takes place constant pressure for 5% of the stroke determine the efficiency of the engine. Assume the engine working on the diesel cycle.
10.
An engine with 200 mm cylinder dia and 300 mm stroke works on theoretical Diesel cycle. The initial pressure and temperature of air used are 1bar and 27°C. The cut-off is 8% of the stroke. Determine : a) Pressure and temperature at all salient points. b) Theoretical air std efficiency. c) Mean effective pressure. d) Power of engine if the working cycles per minute are 380. Assume that compression ratio is 15 and working fluid is air Consider all conditions to be ideal.
11.
The swept volume of a diesel engine working on dual cycle 0.0053m³ and clearance volume is 0.00035m³. The maximum pressure is 65bar. Fuel injection ends at 5% of the stroke. The temperature and pressure at the start of compression are 80°C and 0.9bar. Determine the air std efficiency of the cycle. Take γ for air = 1.4
12.
The compression ratio for a single cylinder engine operating on dual cycle is 9. The maximum pressure in the cylinder is limited to 60bar. The pressure and temperature of the air at the beginning of the cycle are 1bar and 30°C. Heat is added during constant pressure process upto 4% of the stroke. Assuming the cylinder dia and stroke length as 250 mm and 300 mm respectively, determine : a) The air std efficiency of the cycle. b) The power developed if the numbers of working cycles are 3 per second. Take for air = 1.0 and cv = 0.71
13.
In an engine working on dual cycle, the temperature and pressure at the beginning of the cycle are 90°C and 1 bar respectively. The compression ratio is 9. The maximum pressure is limited to 68 bar and total heat supplied per kg of air is 1750 kJ. Determine a) Pressure and temperature at all salient points. b) Air std efficiency. c) Mean effective pressure.
14.
Air enters the compressor of a gas turbine plant operating on Brayton cycle at 101.325 kpa, 27°C. The pressure ratio in the cycle is 6. Calculate the maximum temperature in the cycle and the cycle efficiency. Assume WT = 2.5WC where WT and Wc are the turbine and the compressor work respectively. Take γ =1.4.
15.
Consider an air std cycle in which the air enters the compressor at 1.0 bar and 20°C. The pressure of air leaving the compressor is 3.5 bar and the temperature at turbine inlet is 600°C. Determine per kg of air: Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
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a) b) c) d) e)
1.
Efficiency of cycle Heat supplied to air Work available at the shaft Heat rejected in the cooler, and Temperature of air leaving the turbine. For air γ = 1.4
The following data in referred for an air standard diesel cycle compression ratio = 15 heat added = 200 KJ/Kg- minimum temperature in the cycle = 25°C Suction pressure = 1 bar Calculate 1. Pressure and temperature at the Salient point. 2. Thermal efficiency 3. Mean effective pressure,
4. Power output of the cycle If flow rate 'of air is 2 Kg/s 2. Air enters the compressor of a gas turbine at 100 KPa and 25 o C. For a pressure ratio of 5 and a maximum temperature of 850°C. Determine the thermal efficiency using the Brayton cycle.
3. An Engine-working on Otto cycle has a volume of 0.45 m3 , pressure 1 bar and temperature 30o,C at the beginning of compression stroke. At the end of compression stroke, the pressure is 11 bar and 210 KJ of heat is added at constant volume. Determine (i) Pressure, temperature and volumes at salient points in the cycle.' (ii) Efficiency.
4. A Dual combustion air standard cycle has a compression ratio of 10. The constant pressure part of combustion takes place at 40 bar. The highest and the lowest temperature of the cycle are 1725 degree C and 27 degree C respectively. The pressure at the beginning of compression is 1 bar.Calculate (I) the pressure and temperature at each key points of the cycle. (ii) The heat supplied at constant volume, (iii) the heat supplied at constant pressure. (Iv) The heat rejected. (v) the work output. (vi) the efficiency and (vii) mep.
5. The compression ratio of an air-standard Otto cycle is 9.5. At the beginning of compression,the air is at 100 kPa, 35°C and 600 cm3.The temperature at the end of isentropic expansion process is 800 K. Determine
a. The highest temperature and pressure in the cycle b. The thermal efficiency c. The mean effective pressure. 6. An air-standard Diesel cycle has a compression ratio of 16 and a cut-off ratio of 2. At the a. beginning of the compression process air is at 95 kPa and 27°C. Determine i. The temperature after the heat addition process ii. The thermal efficiency and iii. The mean effective pressure 7. Show the Otto cycle on P-V and T-S diagrams. Derive expressions for the efficiency and mean effective pressure and plot their variation with compression ratio. Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
8.
In an air standard Diesel cycle, the compression ratio is 16, and at the beginning of isentropic compression, the temperature is 288 K, and the pressure is 0.1 MPa. The maximum temperature in the cycle is 1753 K. Calculate a. The pressure and temperature at all the four important points in the cycle b. The m.e.p. and the cycle efficiency.
UNIT-3 THERMODYNAMICS OF ONE DIMENSIONAL FLUID FLOW Part-A (2 Marks)
1.
What are the various types of nozzles and their functions?
2.
Write down the expression for velocity at exit from steam nozzle.
3.
Derive the expression for the critical pressure ratio in a steam nozzle.
4.
What are the effects of friction on the flow through a steam nozzle?
5.
Write the general energy equation for a steady flow system and from this obtain the energy equation for nozzle.
6.
Define nozzle efficiency and critical pressure ratio.
7.
Explain the phenomenon of super saturated expansion in steam nozzle (or) What is metastable flow?
8.
What are the conditions that produce super saturation of steam in nozzles?
9.
Draw the T-s and h-s plot of super saturated expansion of steam in a nozzle.
10.
What are the effects of super saturation in a steam nozzle?
11.
What are the differences between supersaturated flow and isentropic flow through steam nozzles?
12. 13. 14.
What is meant by steam power cycles? What is meant by work ratio? What is the importance of work ratio in vapour cycles? What are the effects of condenser pressure on the Rankine cycle? Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
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15. Mention the improvements made to increase the ideal efficiency of ranking cycle. 16. Name the different components in steam power plant working on a rankine cycle. 17. What are disadvantages of reheating? 18. List the advantages of reheat cycle. 19. What are the disadvantages of bleeding? 20. Draw the T-s plot of Rankine Cycle 21.
Draw the T-s plot of Reheat rankine cycle
22.
Define Mach Number
23.
Define Stagnation Enthalpy
24.
Define Stagnation Temperature
25. Write the area-velocity relation for an isentropic flow in a variable area duct. What is the effect of Mach number on area-velocity relation? 26. Define Specific impulse 27.
Define thrust
28.
What is jet propulsion?
29.
What are the main components of gas turbine engine used for turbojet aircrafts?
30.
Define propulsive efficiency, Jet thrust, thermal efficiency, Overall efficiency
31.
What is ―after burning‖ in turbojet engines?
32.
Write Continuity, Momentum and Energy equation.
33.
What is the function of tail pipe? PART- B (16Marks)
1.
An impulse turbine having a set of 16 nozzles receives steam at 20 bar, 400° C. The pressure of steam at exist is 12 bar. if the total discharge Is 260 Kg/min and nozzle efficiency is 90% . Find the cross sectional area of each nozzle, if the steam has velocity of 80m/s at entry to the nozzle, find the percentage Increase In discharge.
2.
Dry saturated steam at a pressure of 8 bar enters the convergent divergent nozzle and leaves it at a pressure 1.5 bar. If the flow isentropic and if the corresponding index of expansion is 1.133, find the ratio of 0.3 are at exit and throat for max. discharge.
3.
Steam enters a group of nozzles of a steam turbine at 12 bar and 2200 C and leaves at 1.2 bar. The steam turbine develops 220 Kw with a specific steam consumption of 13.5 Kg/ Kw. Hr. If the diameter of nozzle at throat Is 7mm . Calculate the number of nozzle.
4.
Drive an expression for critical pressure ratio in of the index of expansion Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
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5.
In a steam nozzle, the steam expands from 4bar to 1bar. The initial velocity is 60m/s and the initial temp is 200°C. Determine the exit velocity if the nozzle efficiency is 92%.
6.
Dry saturated steam enters a steam nozzle at a pressure of 15bar and is discharged at a pressure of 2.0bar. If the dryness fraction of discharge steam is 0.96, what will be the final velocity of steam, Neglect initial velocity of steam, If 10% of heat drop is lost in friction, find the percentage reduction in the final velocity.
7.
Steam initial dry and saturated is expanded in a nozzle from 15bar at 300°C to 1.0 bar. If the frictional loss in the nozzle is 12% of the total heat drop calculate the mass of steam discharged when exit dia of the nozzle is 15mm.
8.
Dry saturated steam at a pressure of 11bar enters a convergent-divergent nozzle and leaves at a pressure of 2bar. If the flow is adiabatic and frictionless, determine a) The exit velocity of steam b) ratio of cross section at the exit and that at throat. Assume the index of adiabatic expansion to be 1.135.
9.
The nozzles of a De Laval steam turbine are supplied with dry saturated steam at a pressure of 9bar. The pressure at the outlet is 1bar. The turbine has two nozzles with a throat diameter of 2.5mm. Assuming nozzle efficiency as 90% and that of turbine rotor 35%, find the quality of steam used per hour and the power developed.
10. A steam power plant works between 40 bar and 0.05 bar. If the steam supplied is dry saturated and the cycle of operation is Rankine, find : (i) Cycle efficiency (ii) Specific steam consumption. In a regenerative cycle the inlet conditions are 40 bar and 400°C. Steam is bled at 10 bar in Regenerative heating. The exit pressure is 0.8 bar. Neglecting pump work .Determine the efficiency of the cycle. 11. Show the Rankine cycle on h -s and T -s diagrams. Explain the effect of temperature of heat addition and heat rejection on the performance. 12. A simple turbojet unit operates with a maximum turbine inlet temperature of 1200 K, a pressure ratio of 4.25: 1, and a mass flow of 25 kg/s, under ideal conditions. Assume a convergent nozzle is employed. Calculate the total thrust and sfc. Assume that the unit is stationary and at sea-level, where the ambient conditions may be taken as 1 bar and 293 K. Assume air-fuel ratio of 50: 1. Calorific value offuel : 43 MJ/kg. 13. Derive an expression for critical pressure ratio in of the index of expansion 14. Steam enters a group of nozzles of a steam turbine at 12 bar and 2200 C and leaves at 1.2 bar. The steam turbine develops 220 Kw with a specific steam consumption of 13.5 Kg/ Kw. Hr. If the diameter of nozzle at throat Is 7mm . Calculate the number of nozzle 15. Dry saturated steam at a pressure of 8 bar enters the convergent divergent nozzle and leaves it at a pressure 1.5 bar. If the flow isentropic and if the corresponding index of expansion is 1.133, find the ratio of 0.3 are at exit and throat for max. discharge. Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
16. A steam power plant operates on ideal Rankine cycle using reheater and regenerative feed water heaters. It has one open feed heater. Steam is supplied at 150 bar and 600°C.The condenser pressure is 0.1 bar. Some steam is extracted from the turbine at 40 bar for closed feed water heater and remaining steam is reduced at 40 bar to 600°C. Extracted steam is completely condensed in this closed feed water heater and is pumped to 150 bar before mixing with the feed water heater. Steam for the open feed water heater is bled from L.P. turbine at 5 bar. Determine : a. Fraction of steam extracted from the turbines at each bled heater, and b. Thermal efficiency of the system.
17. Draw the line diagram of the components of regenerative Rankine and represent the cycle on T-s diagram. 18. Explain in detail about simple jet propulsion system with neat sketch 19. Explain in detail about ram jet with neat sketch 20. Explain in detail about turbo jet with neat sketch 21. Explain in detail about Turbo prop with neat sketch 22. Explain in detail about Turbo fan with neat sketch 23. Derive the expression of static & stagnation temperature & pressure Ratio 24. A conical diff has entry and exit diameter of 15 cm & 30cm respectively.The pressure, temperature and velocity of air at entry are 0.69 bar, 340 K and 180m/sec respectively. Determine 1. Exit Pressure 2. Exit velocity assume Isentropic flow,γ =1.4 =1.000KJ/Kgk 25. A nozzle in a wind tunnel gives a test section Mach number of 2.0 Air enters the nozzle from large reservoir at 0.69 bar and 310K The cross sectional area of throat is 1000 sq.cm.determine the following quantities for the tunnel for one dimensional isentropic flow: 1. Pressures, Temperatures and velocities at the throat and test sections 2. Area of cross section of the test section 3. Mass flow rate 4. Power required to drive the compressor 26. Air is discharged from a reservoir at P0= 6.91 bar T0=3250C through a nozzle to an exit pressure of 0.98 bar. If the flow rate is 3600 Kg/hr .Determine for the isentropic flow: 1. Throat area , Pressure,and velocity 2. Exit area ,Mach number & 3. Maximum velocity 27. A turbojet engine propels an aircraft at a mach number of 0.8 in level flight at an altitude of 10Km .the datum fir the engine is given below : Stagnation temperature at turbine inlet = 1200 K ,Stagnation temperature rise through the compressor = 175 K ,Calorific value of fuel is 43MJ/Kg,Compressor Efficiency = 0.75 ,Combustion chamber efficiency = 0.975, Turbine Efficiency=0.81 , Mechanical Efficiency of power transmission between turbine and compressor = 0.98, Exhaust Nozzle Efficiency = 0.97, Specific Impulse = 25 sec ,Calculate 1. Fuel air ratio 2. Compresor Pressure ratio 3. Turbine Pressure ratio 4. Exhaust Nozzle Pressure Ratio 5. Mach number of exhaust jet Assume properties of air and combustion gases are same.
UNIT IV REFRIGERATION AND AIR–CONDITIONING Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Part-A (2 Marks) 01.
Define tons of refrigeration and COP.
02.
Define tonne o f refrigeration .Heat is removed from a space at a rate of 42,000kJ/h. Express this heat removal rate in tons.
03.
Show the air- refrigeration cycle on p-V and T-s diagrams.
04.
The door of a refrigerator inside a room was left open. What will happen?
05.
Show the vapour compression refrigeration cycle in T-s diagram and give the COP of a simple cycle.
06.
In a vapour compression refrigeration system, where the lowest temperature will occur?
07.
How does the actual vapour compression cycle differ from that of the ideal cycle?
08.
Name four important properties of a good refrigerant
09.
What is the difference between air conditioning and refrigeration?
10.
What is the function of the throttling valve in vapour compression refrigeration system?
11.
In a vapour compression refrigeration system, where the highest temperature will occur?
12.
The vapour absorption system can use low-grade heat energy in the generator. Is true or false?
13.
Name any four commonly used refrigerants.
14.
Explain unit of refrigeration.
15.
Why throttle valve is used in place of expansion cylinder for vapour compression refrigerant machine.
16.
What are the effect pf superheat and subcooling on the vapour compression cycle?
17.
What are the properties of good refrigerant?
18.
What are the advantages and disadvantages of air refrigeration system?
19.
What are the advantages of vapour compression refrigeration system over air refrigeration system?
20.
What is the objective of under cooling? Sketch the process in T-s diagram?
21.
What is net refrigerating effect of the refrigerant?
22.
Name the refrigerant normally used in simple vapour absorption system.
23.
Name the various components used in simple vapour absorption system. Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
24.
State the condition of the refrigerant at the end of compression in vapour compression system.
25.
Define refrigerant.
26.
What type of condensers are in common uses for vapour absorption refrigeration system?
27.
What is the function of analyzer and rectifier in an absorption system?
28.
State the substances used in the Lithium Bromide system and their functions.
29.
What is psychrometry?
30.
Name some psychrometric processes and represent them on the psychrometric chart.
31.
Define DPT and degree of saturation.
32.
Define Relative Humidity (RH) and Specific humidity.
33.
How are air-conditioning systems classified?
34.
How does humidity affect human comfort?
35.
What are the various sources of heat gain of an air-conditioned space?
36.
What do you mean by the term ―Infiltration‖ in heat load calculations?
37.
Define RSHF, RTH.
38.
On a psychrometric chart, show all the property lines.
39.
Define Apparatus Dew Point (ADP) of cooling coil.
40.
Define by factor (BPF) of a coil.
41.
State the effects of very high and a very low by factor.
42.
Name four important properties of a good refrigerant
1.
Part-B (16 Marks) Draw neat sketch of simple vapor compression refrigeration system and explain.
2.
Explain with sketch the working principle of aqua Ammonia refrigeration system.
3.
Explain with sketch the working principle of water-Lithium bromide refrigeration system.
4.
Briefly explain the cooling load calculation in air conditioning system.
5.
Explain winter, summer, and year round A/c system.
6.
Explain unitary A/c and central A/c system.
7.
Explain any four psychometric processes with sketch.
8.
The atm conditions are 20°C and specific humidity of 0.0095kJ/kg of dry air. Calculate the following: Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
a) Partial pressure of vapour b) Relative humidity c) Dew point temperature. 9.
The air supplied to a room of a building in winter is to be at 17°C and have a relative humidity of 60%. If the barometric pressure is 1.01325bar. find a) The specific humidity b) The dew point under these condition.
10.
0.004kg of water vapour per kg of atmospheric air is removed and temperature of air after removing the water vapour becomes 20°C determine: a) Relative humidity b) Dew point temperature Assuming that condition of atm air is 30°C and 55% R.H and pressure is 1.013bar.
11.
The sling psychrometer in a laboratory test record the following readings: Dry bulb temperature = 35°C Wet bulb temperature = 25°C Calculate the following: a) Specific humidity b) Relative humidity c) Vapour density in air d) Dew point temperature e) Enthalpy of mixture per kg of dry air Take atm pressure = 1.013bar
12.
One kg of air at 35°C DBT and 60% R.H is mixed with 2kg of air at 20°C DBT and 13°C dew-point temperature. Calculate the specific humidity of mixture.
13.
90m³ of air per minute at 20°C and 75% R.H is heated until its temperature becomes 30°C. calculate : a) R.H of the heated air b) Heat added to air per minute.
14.
40 m³ of air at 35°C DBT and 50% R.H is cooled to 25°C DBT maintaining its specific humidity constant. Determine: a) Relative humidity of cooled air b) Heat removed from air
15.
28 tonnes of ice from and at 0°C is produced per day in an ammonia refrigerator. The temperature range in the compressor is from 25°C to -15°C. The vapour is dry and saturated at the end of compression and an expansion valve is used. Assuming a coefficient of performance of 62% of the theoretical, calculate the power required to drive the compressor. Temp °C Enthalpy of liquid Enthalpy of Entropy of Entropy of (kJ/kg) vapour (kJ/kg) liquid vapour (kJ/kgK) (kJ/kgK) 25 100.04 1319.22 0.3473 4.4852 Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
-15 16.
-54.56
1304.99
-2.1338
5.0585
A refrigeration plant works between temp limits -5 and 25°C. The working fluid ammonia has a dryness fraction of 0.62 at entry to compressor. If the machine has a relative efficiency of 55%, calculate the amount of ice formed during a period of 24 hours. The ice is to be formed at 0°C water at 15°C and 6.4kg of ammonia is circulated per minute. Specific heat of water is 4.187kJ/kg and latent heat of ice is 335kJ/kg. Temp Liquid heat kJ/kg Latent heat kJ/kg Entropy of liquid kJ/kgK 25 298.9 1167.1 1.124 -5 158.2 1280.8 0.630
17.
A simple vapour compression plant produces 5tonnes of refrigeration. The enthalpy values at inlet to compressor, at exit from the compressor, and at exit from the condenser are 183.19, 209.41 and 74.59kJ/kg respectively. Estimate a) The refrigerant flow rate b) The power required to drive the compressor c) The COP d) The rate of heat rejection to the condenser. 18. Dry bulb and wet temperatures of 1 atmospheric air stream are 40°0 and 30°c respectively.Determine (a)Humidity (b) Relative humidity (c) Specific humidity. 19. Atmospheric air with barometric pressure of 1.013 bar has 38°c dry bulb temperature and 28°c wet bulb temperature. Determine (a) Humidity ratio (b) Relative humidity (c) dew point temperature. 20. Atmospheric air at 760 mm of Hg has 45°c DBT and 30°c WBT, using psychometric chart calculate R.H, Humidity ratio, DPT, enthalpy, specific volume of air. 21. Atmospheric air at 1 bar pressure has 2.5°0 DBT and 75% RH using psychometric chart, calculate DBT, enthalpy, vapour pressure. 22. Explain sensible heating process, sensible cooling, and humidification process. 23. An air water vapour mixture at 0.1 Mpa, 30°0, 80% RH. Has a volume of 50 m3 Calculate the specific humidity, dew point, wet bulb temperature, mass of dry air and mass of water vapour. 24. The atmospheric conditions are 30ºC and specific humidity of 0.0215 kg/kg of air. Determine : Atmospheric pressure = 756 mm Hg. a. Partial pressure of air b. Relative humidity c. Dew point temperature. 25. 1 kg of air at 24ºC and a relative humidity of 70% is to be mixed adiabatically in a steady state, steady flow device with 1 kg of air at 16ºC and a relative humidity of 10%. Assuming that the mixing is to be carried out at a constant pressure of 1.0 atm, determine the temperature and relative humidity of the stream leaving the device. 26. In a laboratory test, a psychrometer recorded 36ºC DBT and 30ºC WBT. Calculate d. Vapour pressure e. Relative humidity f. Specific humidity g. Degree of saturation Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
h. Dew point temperature i. Enthalpy of the mixture. 27. An air-water vapour mixture enters an adiabatic saturator at 30ºC and leaves at 20ºC, which is the adiabatic saturation temperature. The pressure remains constant at 1 bar. Determine the relative humidity and the humidity ratio of the inlet mixture. 28. The following observation were made during a testing of moist air i. Dry bulb temperature Tdb = 29oC ii. Dew point temperature Tdb = 15oC iii. Total pressure = 1 bar Determine the relative humidity and degree of saturation 29. In a combined heating and humidification process, moist air enters heating coil with the dry bulb temperature 20oC and 30% R.M. After the process the drug bulb temperature and the RH of Air were found to be 40oC and 55% RH. The air es through the heating at the rate of 350 kg/min 30. In an air conditioning plant, fresh air is used to mix up with returned air from conditioned space. The fresh air drawn from atmosphere has the drug bulb temperature 32oC and we bulb temperature 25oC. The fresh air is drawn at the rate of 100m3/min. The returned air from conditioned space has the drug bulb temperature 23oC and relative humidity 50%. The volume flow rate of it 540 m3/min. Determine the (i) dry bulb and web bulb temperature (ii) specific humidity of mixture 31.
A food storage locker requires a refrigeration system of 2400 kJ/min. capacity at an evaporator temperature of 263K and a condenser temperature of 303K. The refrigerant used in Freon -12 and is subcooled by 6°C before entering the expansion valve and vapour is superheated by 7°C before leaving the evaporator coil. The compression of refrigeration is reversible adiabatic. The refrigeration compressor is two cylinder single acting with stroke equal to 1.25 times the bore and operates at 1000r.p.m Temp Absolute Specific Enthalpy Enthalpy Entropy Entropy pressure volume of of liquid of vapour of liquid of vapour bar vapour kJ/kg kJ/kg kJ/kgK kJ/kgK m³/kg 263 2.19 0.0767 26.9 183.2 0.1080 0.7020 303 7.45 0.0235 64.6 199.6 0.2399 0.6854
UNIT V AIR COMPRESSORS Part-A (2 Marks) 1. Classify the various types of air-compressors. Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
2. What is meant by single act ing compressor? 3. What is meant by double acting compressor? 4. what is meant by single stage compressor 5. what is meant by multistage compressor 6. Draw the p-v diagram of a two stage reciprocating air compressor 7. Indicate the applications of reciprocating compressors in industry 8.
What are the advantage s of multi stage compression with inter cooling over single stage compression for the same pressure ratio
9. Define the as applied to air compressors: Volumetric efficiency and isothermal compression efficiency 10. Define the mechanical efficiency and isothermal efficiency of a reciprocating air compressor. 11. Define isentropic efficiency 12. Define mean effective pressure.How is it related to indicated power of an IC engine 13. What is meant by free air delivered? 14. Explain how flow of air is controlled in a reciprocating compressor? 15. What factors limit the delivery Pressure in a reciprocating compressor 16.
Name the methods adopted for increasing isothermal efficiency of reciprocating air compressor.
17. why clearance is necessaty and What is its effect on the performance of reciprocating compressor ? 18. Which type of compression is the best in reciprocating compressor? 19. What is compression ratio? 20. Give the expression for inter cooler pressure 21. what is meant by inter cooler? 22. Give the expression for work done for ba multistage compressor with prefect inter cooling . 23. Give the expression for work done for a two-stage compressor with perfect inter cooling. 24. What are the factors that affect the volumetric efficiency of a reciprocating compressor? 25. Name the compression process in which work done is minimum in a reciprocating air compressor Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
26.
A50-m3/min compressor refers to why?
27.
If C is the clearance ratio for a reciprocating air compressor, what will be the volumetric efficiency?
28.
What is the purpose of using intercooler in multi-stage compression
29.
Discuss the effect of clearance upon the performance of an air compressor.
30.
Give two merits of rotary compressor over reciprocating compressors
31.
Give examples for positive displacement compressor
32.
What is the different between complete (or ) perfect inter cooling and incomplete (or) imperfect inter cooling
33.
How to Increase isothermal efficiency
1.
Part-B (16 Marks) Drive an expression for the work done by single stage single acting reciprocating air compressor.
2.
Drive an expression for the volumetric efficiency of reciprocating air compressors
3.
Explain the construction and working of a root blower .
4.
Explain the construction and working of a centrifugal compressor.
5.
Explain the construction and working of a sliding vane compressor and axial flow compressor
6.
A single stage reciprocating compressor takes 1m³ of air per minute at 1.013 bar and 15°C and delivers it at 7 bar. Assuming that the law of compression is pV1.35 =C, and the clearance is negligible, calculate the indicated power.
7.
If the compressor of prob 1is driven at 300 r.p.m and is a single acting, singlecylinder machine, calculate the cylinder bore required, assuming a stroke to bore ratio 1.5:1 calculate the power of the motor required to drive the compressor if the mechanical efficiency of the compressor is 85% and that of the motor transmission is 90%. 8. Show that in the case of reciprocating compressor, the work input is independent clearance ratio. Explain with the help of p-v diagrams.
9.
Derive an expression for the volumetric efficiency of a two-stage reciprocating compressor in of clearance ratio and Pressure ratio.
10. Steam at 20 bar, 633 K is expanded in a steam turbine to 0.08 bar. It then enters a condenser, where it is condensed to saturated liquid water. The pump feeds back the Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
water into the boiler. Assuming ideal processes, find per kg of steam, the network and cycle efficiency. 11. A simple turbojet is being tested under laboratory conditions at static position. Pressure ratio across the compressor is 5:1; maximum temperature in the cycle is 1200 K. Assume a convergent nozzle is employed. Calculate the total thrust and s.f.c. Ambient conditions are 1 bar and 300 K Air fuel ratio 50:1; C.V. of fuel 40 MJ/kg. 12. With the help of a neat sketch explain the construction and working of a reciprocating air compressor. Derive an expression for the work of compression in of pressure ratio and clearance ratio. 13. With the help of a neat sketch explain the construction and working of a rotary air compressor. 14. Derive an expression for the optimum intermediate pressure of two stage reciprocating compressor with perfect intercooling. 15. A two stage singe acting air compressor compresses 2m3 airs from 1 bar and 20° C to 15 bar. The air from the low pressure compressor is cooled to 25° C in the intercooler. Calculate the minimum power required to run the compressor if the compression follows PV1.25=C and the compressor runs at 400 rpm. 16. A single stage single acting air compressor is used to compress air from 1.013 bar and 25° C to 7 bar according to law PV 1.3 = C.The bore and stroke of a cylinder are 120mm and 150mm respectively. The compressor runs at 250 rpm .If clearance volume of the cylinder is 5% of stroke volume and the mechanical efficiency of the compressor is 85%, determine volumetric efficiency, power, and mass of air delivered per minute. 17. A single stage single acting air compressor is used to compress air from 1 bar and 22° C to 6 bar according to the law PV1 .25 = C. The compressor runs at 125 rpm and the ratio of stroke length to bore of a cylinder is 1.5. If the power required by the compressor is 20 kW, determine the size of the cylinder
18. An air compressor takes in air at 1bar and 20°C and compressor it according to law pV1.2 =C. it is then delivered to a receiver at a constant pressure of 10bar. R=0.287 kJ/kgK determine: a) Temperature at the end of compression b) Workdone and heat transferred during compression per kg of air. 19. A single stage double acting cylinder air compressor is required to deliver 14m³ of air per minute measured at 1.013bar and 15°C. The delivery pressure is 7bar and the speed of 300r.p.m. Take the clearance volume as 5% of the swept volume with the compression and expansion index of n = 1.3. calculate: a) Swept volume of the cylinder b) The delivery temperature c) Indicated power
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
20. A single stage double acting cylinder air compressor has a free air delivery (F.A.D) of 14m³ per minute measured at 1.013bar and 15°C. The pressure and temperature in the cylinder during induction are 0.95 bar and 32°C. The delivery pressure is 7 bar and index of compression and expansion, n=1.3. The clearance volume is 5% of the swept volume. Calculate a) Indicated power required b) Volumetric efficiency 21. A single acting two stage compressor with complete intercooling delivered 10.5kg/min of air at 16 bar. Suction occurs at 1 bar and 27 deg c . It follows the Law PV^1.3 Determine 1. Power required to drive the compressor 2.Isothermal Efficiency 3. Free air delivery 4. Heat transferred in the intercooler 5. If clearance ratios of L.P & H.P cylinders are .04&.06 Calculate Swept & Clearance volume for each cylinder
Official website: www.wingsofaero.in Email: [email protected] Phone: +918870705857/+918220125658 Address: 1/269 KPM puram, Alangulam, Tirunelveli Dt, Tamil Nadu, India - 627853
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