Q6. In an Ideal diesel cycle the pressure and temperature at the start of compression are 1.0 bar and 57°C respectively. The volume compression ratio is 16:1 and the heat energy added at constant pressure is 1250 kJ/kg.
(a) Sketch the cycle on Pressure-Volume and Temperature-specific entropy diagrams.
(b) Calculate EACH of the following:
(i) The cycle efficiency
(ii) The mean effective pressure.
Note: For air Cp = 1.005 kJ/kg K and g = 1.4
Q7. Air enters an open cycle gas turbine plant at a pressure and temperature of 1.013 bar and 27°C respectively and is compressed to 12.5 bar. The hot gases Leave the combustion chamber and enter the turbine at a pressure of 12.5 bar and a temperature of 827°C expanding in two stages of equal pressure ratio to the initial pressure. The gases are reheated to 827°C between the turbine stages. The isentroic efficiency of the compressor is 0.8. The isentropic efficiency of each turbine stage is 0.85. The mass flow rate of fuel may be ignored. Sketch the cycle on a Temperature Specific entropy diagram. Calculate EACH of the following
(i) The compressor outlet temperature
(ii) The second stage turbine outlet temperature
(iii) The work ratio.
NOTE: For Air g = 1.4 and = 1.005 kJ/kgK
For the Hot Gas g = 1.33 and = 1.15 kJ/kgK
Q8. In a vapour compression refrigeration plant using refrigerant R134a, the refrigerant enters the compressor at a pressure of 1.0637 bar and after isentropic compression Leaves at a pressure and temperature of 7.7 bar 50°C respectively.
The refrigerant leaves the condenser at the rate of 20 kg/min with 5 K of sub-cooling.
(a) Sketch the cycle on EACH of the following:
(i) A p-h diagram indicating the refrigeration effect, compressor work and condenser heat rejection
(ii) A T-s diagram, indicating superheat and sub-cooling.
(b) Determine EACH of the following:
(i) The condition of the refrigerant at the compressor suction
(ii) The compressor power required
(iii) The heat rejection in the condenser
(iv) The coefficient of performance.
Q7. Dry saturated steam at 14 bar enters a steam pipe 50 m long with an outer diameter of 150 mm. The pipe is covered with ii Inner layer of moulded insulation 50 mm thick and an outer Layer of mineral felt 30 mm thick.
The mass flow rate of steam in the pipe is 500 kg/hr.
The air temperature surrounding the pipe is 15°C.
Calculate EACH of the following:
(a) The rate of heat loss from the pipe
(b) The mass of steam condensed per hour.
Note: Inner heat transfer coefficient of the pipe 1000 W/m2K
Thermal conductivity of moulded insulation = 0.075 W/m K
Thermal conductivity of mineral felt = 0. 15 W/mK
Outer heat transfer coefficient of the pipe = 13 W/m2K
Q6. A single cylinder single acting air compressor has a bore of 268 mm and stroke of 535 mm with a clearance volume of 1.7 Liters.
Air is induced at a pressure and temperature of 1 bar and 27°C respectively.
The Law for both expansion and compression process is pV1.3 C.
The temperature after compression is 225℃.
The compressor has a mechanical efficiency of 0.88 when delivering 650 kg/hr.
(a) Sketch the process on a p-V diagram, indicating ALL volumes.
(i) the delivery pressure
(ii) The volumetric efficiency
(iii) The input power at full Load
(iv) The full load speed.
Note: for air R = 0.287 kJ/kgK
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