QUESTION 1: A sealed, rigid vessel of 2 m3 contains R-134a at 10°C; at these conditions it is a saturated mixture of liquid and vapour. The liquid phase disappears when it is heated to 48°C. Determine:
a) The pressure at 48°C
b) The initial mass of liquid
c) The heat transfer required to cause the change from state 1 to state 2.
QUESTION 2: A heat exchanger cools 1.1 kg/s of water which enters at 10 kPa and 300°C and exits as a saturated liquid. The coolant is lake water that enters at 20°C and exits at 30°C. If all processes are isobaric, determine the required flow rate of lake water.
QUESTION 3: A heat engine which operates on the Carnot cycle receives 6 kW. If the high temperature reservoir is at 250°C and the low-temperature reservoir is at 30°C, determine:
a) The efficiency of the cycle
b) The heat transfer to the low-temperature reservoir
QUESTION 4: The compressor of a large gas turbine receives air from the ambient, quiescent surroundings at 95 kPa and 20°C. At the compressor discharge, air exits at 1.52 MPa and 430°C with a speed of 90 m/s and area of 2 m2. If the air in the compressor undergoes a polytropic process which has a polytropic coefficient of 1.3, determine:
a) The mass flow rate through the compressor
b) The power required to drive the compressor
c) The heat transfer
Include any necessary explanations or calculations to justify your answer.
QUESTION 5: An engine operates on the Diesel cycle, which is ideal except for the compression process, which has a polytropic coefficient of 1.2. The state prior to compression is 95 kPa, 290 K and 0.5 L, while the maximum temperature is 1800 K and the compression ratio is 20:1.
a) Sketch the P-v diagram for this cycle
b) Calculate the maximum pressure
c) Calculate the heat transfer in
d) Calculate the heat transfer out
e) Calculate the thermal efficiency
f) Calculate the Mean Effective Pressure
QUESTION 6: An ideal heat pump operating at 1.1 kW uses R-134a as the refrigerant. Saturated vapour enters the compressor at 10°C and the fluid exits the compressor at 1 MPa.
a) Sketch the T-s diagram for this process
b) Calculate the mass flow rate of the R-134a
c) Calculate the heat transfer rate out of the R-134a
d) Calculate the heat transfer rate into the R-134a
e) Calculate the COP.