Applied Heat Past Examination Questions

Applied Heat past Examination Questions

1. An Ammonia refrigerator is to produce 2 tonnes of ice per day at -4°C from water at 20°C. if the temperature range in the compressor is between 25°C and -6°C, Calculate the horsepower required to derive the compressor. Latent Heat of ice = 80 kcal/kg, and specific heat of ice= 0. 5

2. A compressor draws 42. 5 m3 of air per minute in the cylinder, at a pressure of 1. 05 kg/cm abs. It is compressed Polytropically pV1. 3=C to a pressure 4. 2 kg/cm2 abs, before being delivered to a receiver. Assuming a mechanical efficiency of 80%

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Calculate:

• a. Indicated horsepower;
• b. Shaft horsepower
• c. Overall isothermal efficiency.

3. A single-stage impulse turbine has a speed of 1000rpm and a mean blade ring diameter of 60 cm. The nozzles are inclined at 22° to the plane of rotation and the specific enthalpy drop is 190 KJ/kg.

Determine:

• a. The relative velocity of the steam at the inlet.
• b. The blade inlet angle.

4. An engine consumes fuel of calorific value 44MJ/Kg at a rate of 45tonne/day. The indicated thermal efficiency is 39% and brake thermal efficiency is 33%.

Calculate:

• a. The indicated power.
• b. The brake power, and. The power lost to friction.

5. The air in a ship’s saloon is maintained at 19°C and is changed twice every hour from the outside atmosphere which is at 7°C. The saloon is 27m by 15m by 3m high. Calculate the kilowatt loading to heat this air taking the saloon to be at atmospheric. Pressure = 1. 013 bar. R for air =0. 287 KJ/kg K.

6. 0. 23kg of air has an initial pressure of 1. 7 MN/m2 and a temperature of 200°C. it is expanded to a pressure of 0. 34 MN/m2 according to the law PV 1. 35 = Constant. Determine the work transferred during the expansion. Take R = 0. 29 KJ/kg K.

7. The equivalent evaporation of a boiler from and at 100°C is 10. 4 kg steam/kg fuel. The calorific value of the fuel is 29800KJ/kg. Determine the efficiency of the boiler. If the boiler produces 15000 kg of steam per hour at 24 bar from feed water of 40°C and the fuel consumption is 1650 kg/h, determine the condition of the steam produced.

8. A single-cylinder, the double-acting steam engine is 250mm bore by 300mm stroke and runs at 3. 5rev/s, steam is supplied at 1035 KN/m2 and the back pressure is 34 KN/m2 and the diagram factor is 0. 81. Determine the indicated power of the engine.

• a. If cut off is at 0. 5 strokes.
• b. If cut off is at 0. 5 stroke.

9. Air enters a nozzle with a pressure of 700 KN/m2 and with a temperature of 180°C. Exit pressure is 100 KN/m2. The law connecting pressure and specific volume during the expansion in the nozzle is pV1. 3=Constant. Determine the velocity at the exit from the nozzle. Take Cp= 1. 006 KJ/kg K and Cv=0. 717 KJ/kg K.

10. A single row, impulse turbine has a mean blade speed of 215 m/s. The nozzle entry angle is at 30° to the plane of rotation of the blades. The steam velocity from the nozzles is 550 m/s. There is a 15% loss of relative velocity due to friction across blades. The absolute velocity at the exit is along the axis of the turbine. The steam flow through the turbine is at the rate of 700 kg/h.

Determine:

• a. The inlet and exit angles of the blades.
• b. The absolute velocity of the steam at the exit.
• c. The power output of the turbine.

11. The high temperature of a Carnot cycle is 400°C and the cycle has a thermal efficiency of 55%. The volume ration of the isothermal processes is 2: 8: 1.

Determine for the cycle:

• a. The low temperature.
• b. The volume ration of the adiabatic processes.
• c. The overall thermal efficiency.

Take r = 1. 4

12. A diesel engine has a compression ratio of 14:1 and an efficiency ratio of 0. 7 when referred to the air standard efficiency. The fuel consumption is 5. 65 kg/h. Take r=1. 4 and the calorific value of the fuel oil is 44500 KJ/kg. Determine the indicated power developed.

13. The analysis of fuel oil is 85. 5% carbon, 11. 9% hydrogen, 1. 6% oxygen, and 1% impurities. Calculate the percentage of carbon dioxide in the flue gasses.

• a. When the quantity of air supplied is the minimum for complete combustion.
• b. When the excess air over the minimum is : (i) 25% (ii) 50% iii) 75%

14. In an air compressor, the air is compressed to the law pVn=constant. The compressor takes in 105 m3/min of air at 1. 0 bar 27°C. If the pressure ratio is 5 to 1, calculate:

• a. The index of compressionю
• b. Power absorbed by the compressor.

15. A single-acting opposed piston 6 cylinder two-stroke engine has a mechanical efficiency of 86% when running at 105 rpm with mean effective pressure of 7. 24 bar, produces brake power of 4326 kW. The mass of the top piston with its connecting parts is 25% greater than that of the bottom piston and the combined stroke is 2340 mm. If the stroke of the piston varies inversely as the masses of the reciprocating parts.

Calculate: (i) The stroke of the top and bottom pistons, (ii) The cylinder diameter.

16. The mass analysis of fuel is 86% carbon, 11. 5% hydrogen, and 2. 5% oxygen. If for complete combustion 25% excess air is supplied per kg of fuel burnt, calculate

• a. The mass of flue gases
• b. The volume of air at 1. 0 bar and 15°C. Take R for air = 0. 287 kJ/kg.

17. The diameter of an air compressor cylinder is 140 mm, the stroke is 180 mm, and the clearance volume is 77cm. he pressures in the cylinder at the beginning of the stroke is 1. 0 bar and during delivery is constant at 4. 8 bar. Taking the law of compression as pV1. 25=Constant, calculate; the distance moved by the piston during the delivery period and express this as a fraction of the stroke.

18. A turbine plant consists of H. P. and L. P. stages and is supplied with steam at 15 bar 300°C. The steam is expanded in the H. P. and leaves at 2. 5 bar 0. 97 dries. Some of the steam is bled off to the feed heater and the remaining passes to L. P. where it is expanded to 0. 15 bar 0. 84 dries. If the same quantity of work transfer takes place in each unit, calculate the amount of steam bled off expressed as a percentage of the steam supplied.

19. 7. 08 liters of air at a pressure 1. 79 bar and temperature of 333°C is expanded according to the law PV 1. 3 = constant and the final pressure 1. 206 bar, calculate:

• a. Volume at the end of expansion
• b. Work transfer from the air c. The temperature at the end of an expansion.

20. Steam leaves the nozzle and enters the blade wheel of a single-stage impulse turbine at a velocity of 840 m/s and at an angle of 20° to the plane of rotation. The blade velocity is 350 m/s and the exit angle of the blade is 25°12’. Due to friction, the steam loses 20% of its rotational velocity across the blades, calculate;

• a. The blade inlet angle
• b. The magnitude and the direction of the absolute velocity of steam at the exit.

21. In a Freon-12 refrigerating plant, Freon leaves the condenser with a specific enthalpy of 50kJ/kgK. The pressure in the evaporator is 1. 826 bars and the refrigerant leaves the evaporator at this pressure at a rate of 0. 4 Kg/s and a temperature of 0°C.

Calculate:

• a. Dryness fraction of Freon at the inlet of the evaporator,
• b. The refrigerating effect per minute.

22. A glass tube of the uniform bore is closed at on end and open at the other. It contains air imprisoned by a column of mercury 42. 7 mm long. When the tube is held vertically with the close end at the bottom, the length of the air column is 227. 6mm. Taking 1mm of mercury = 133. 5N/m2 and atmospheric pressure = 101. 5 kN/m2. Calculate the length of the air column if the tube is held vertically with the closed end at the top.

23. A single-acting gas engine of bore 190 mm and stroke 380 mm has an indicated power of 13 kW when developing brake power of 9 kW there being 125 explosions per minute. The consumption of gas of calorific value 1. 76 MJ/m3 is 6. 8m3/hour. Calculate the mechanical and indicated thermal efficiencies and the mean effective pressure.

24. A six-cylinder, four-stroke, the internal combustion engine is required to develop a brake of 176 kW under the following conditions: Speed 200rev/min, brake m. e. p. 8 bars, stroke/bore ratio 1. 25/1. Break specific fuel consumption 0. 262 Kg/KWh.

Calculate:

• a. The cylinder dimensions,
• b. Fuel consumption kg/h

25. Carbon dioxide leaves a refrigeration condenser with a total heat of 156kJ/kg. After throttling it passes through the evaporator from and it leaves with a dryness fraction of 0. 98. At the evaporator pressure, the liquid heat is 12kJ/kg and the latent heat is 280kJ/kg. If 13. 8 kg of refrigerant circulates per minute, calculate:

• a. The dryness fraction at the inlet to the evaporator
• b. The heat absorbed in the evaporator in 24 hours.

26. Steam is generated from feed water at a temperature of 93. 3° C as follows: In-plant A the steam generated is 17. 25 bar dry saturated. In-plant B the steam generated is 17. 25 bar 0. 9 dries and, In-Plant C the steam generated is 17. 5 bar 82°C superheat. Calculate the percentage change in the consumption using plant A as the base.

27. A hydrocarbon fuel cell is completely burned with 12. 5 percent excess air. Calculate the Volume of air used to burn 1Kg of fuel, measured at 1. 01 bars and 18°C. Air contains 23 percent oxygen by mass. Atomic mass relationship: Hydrogen=2, Carbon=12, Oxygen=16.

28. An oil engine has a volumetric compression ratio of 13:1. At the commencement of compression the air in the cylinder is at 1 bar and 15. 6°C. Calculate the temperature and pressure at the end of compression if the index of compression is 1. 8.

29. A single-acting air compressor working without clearance has a 220mm bore and 200mm stroke. The suction conditions are 1 bar 27°C and running speed is 10 rev/sec. if compression is according to the law pV1. 3=Constant and the discharge pressure is 10 bar.

Calculate:

• a. The mass of air compressed per hour
• b. The discharge temperature.

30. Calculate the final temperatures and final total heat of both (a) and (b).

• a. Water at 65. 6 °C having a mass of 45. 36 kg is cooled by placing 4. 536 kg of ice at -8. 9°C into the water.
• b. Water at 65. 6°C having a mass of 54. 1 kg is cooled by the addition of 22. 68 kg of water at 26. 7°C.

31. An impulse steam turbine operates at 50rev/sec. The mean blade tip diameter is 0. 6m. The blade exit angle is 30° and the velocity of the stream relative to the blade at the blade exit is 300 m/s. Calculate or determine by any other means the kinetic energy of steam leaving the blades per kilogram of steam flow.

32. A perfect gas at 3. 1 bar and 30°C is compressed according to the law pV1. 3=constant until its temperature increases to 215°C. Sketch the process on a p-V diagram.

Calculate:

• a. The pressure at the end of compression.
• b. The changes in enthalpy and internal energy per kilogram of gas.

33. In an ideal constant volume cycle, the temperature at the beginning of compression is 50°C. the volumetric compression ratio is 5:1. If the heat supplied during the bible is 930 KJ/Kg of working fluid

Calculate:

• a. The maximum temperature attained on the cycle
• b. Work is done during the cycle/kg of working fluid
• c. The thermal efficiency of the cycle. Take ?=1. 4 and Cv= 0. 1717 KJ/Kg K.

34. Fuel has a mass analysis of carbon 87 percent, hydrogen 5. percent, and remainder ash. The calorific value of carbon and hydrogen is 34MJ/kg and 145 MJ/kg respectively.

Calculate for one kilogram of fuel:

• a. The calorific value
• b. The mass of exhaust gas if 35 percent of excess air is supplied. When burning fuel, why is excess air used? Air contains 23 percent oxygen by mass Atomic mass relationships: hydrogen=1, oxygen=16, carbon=12.

35. One kilogram of dry saturated steam at 4 bars is contained in a cylinder fitted with a piston. The steam rejects 320 KJ of heat energy at constant pressure is 1. 4 bars.

Calculate:

• a. The condition of the steam on completion of cooling at constant pressure.
• b. The condition of the steam on completion of cooling at constant volume.
• c. The quantity of heat energy rejected during constant volume cooling.

36. A steam turbine that operates at 50rev/s has a mean blade-ring diameter of 1m at a certain stage. The blades are designed for 50 percent reaction and have the exit and inlet angles at 30° and 50° respectively. The turbine is supplied with steam at a ratio of 166. 67kg/s and the stage efficiency is 85 percent.

Calculate or determine by any other means:

• a. The power output of the stage.
• b. The specific enthalpy drop in the stage.

37. In the Ammonia refrigeration plant, the refrigerant leaves the condenser at 22°C as saturated liquid. The evaporator pressure is 2. 077bar and the refrigerant leaves the evaporator 0. 98 dry saturated. For a cooling load of 40kW.

Calculate:

• a. The rate of circulation of the refrigerant (kg/s).
• b. The effective swept volume of the compressor (m3) if its speed is 1 rev/s.

38. A copper bar of 75mm diameter, 13m long is heated by a direct current flowing through the bar. The steady electrical input to the bar is 500W. Assuming the bar is well-insulated and neglecting conduction heat losses at the leads, calculate the wires taken for the temperature of the bar to increase from 5°C to 365°C.

39. A single-stage double acting air compressor deals with 18. 2m3 of air per minute measured at conditions of 1. 61325 bar 15°C. The condition at the beginning of compression is 0. 965 bar 27°C and the discharge pressure is 4. 82 bars. The compression is according to the law pV1. 32=constant. If the mechanical efficiency of the compressor is 0. 9 calculate the input power required to drive the compressor.

40. In a steady flow process, the working fluid enters and leaves a horizontal system with negligible velocity. The temperature drop from inlet to outlet is 480°C and the heat losses from the system are 10KJ/kg of fluid. Determine the power output from the system for a fluid flow of 1. 7kg/s. For fluid Cp=900 J/kgK.

41. A four-stroke single cylinder engine working on constant volume cycle develops 7. 5 KW(Brake) at 60 rev/s, the mechanical efficiency being 0. 8. The pressure at the “beginning of compression” is 0. 97 bar. The engine has a volumetric compression ratio of 7 and the maximum pressure reached in the cycle is 34 bar. If both compression and expansion are according to the law pV1. 38=constant.

Calculate:

• a. The indicated mean effective pressure
• b. The diameter of the cylinder if the stroke/bore ratio is 1. 25.

42. A boiler generates steam at 40 bar 400°C and supplied to a steam turbine at the rate of 14 kg/s. due to frictional and heat losses, the steam at the turbine inlet is at 37 bar 350°C. If the steam velocity leaving the boiler is 30 m/s and the change in the kinetic energy of steam is negligible.

Calculate:

• a. The diameter of the steam supply pipe
• b. The heat loss from the steam supply pipe.

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