Applied Heat past Examination Questions
1. An Ammonia refrigerator is to produce 2 tonne 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 horse power 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%
a. Indicated horse power;
b. Shaft horse power, and
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.
a. The relative velocity of the steam at inlet, and
b. The blade inlet angle.
4. An engine consumes fuel of calorific value 44MJ/Kg at a rate of 45tonne/day. It the indicated thermal efficiency is 39% and break thermal efficiency is 33%.
a. The indicated power,
b. The brake power, and
c. 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, 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 0.25 stroke,
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 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. 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 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 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...
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