In: Mechanical Engineering
2. A refrigeration machine has been designed based on R134a. The
design capacity is 15 tons. The evaporator coil design
temperature is 8 oC. The refrigerant enters the compressor as a
slightly superheated vapor at 15 oC. The condenser coil design
pressure is 14 bar. Refrigerant enters the expansion valve as a
compressed (subcooled) liquid at 44 C. Note that the temperature of
the air passing over the tubing in the evaporator coil will be
higher than 8 oC and the temperature of the air passing over the
condenser coil will be lower than the coil temperature. Use 80% for
the compressor isentropic efficiency.
a. Calculate the power required to run the compressor under these
design conditions and the required mass flow rate of R134a. (30
pts)
b. Find the rate of heat transfer for the condenser (high pressure
side) of the system. (15 pts)
c. Find the quality of the refrigerant as it enters the evaporator.
(10 pts)
3. A small gas turbine engine is used to produce power for
auxiliary systems. This is a simple gas turbine open to the
atmosphere. Air enters the compressor at 1 bar, 300 K. The
compressor pressure ratio is 3.5:1. After passing through the
combustion chamber, the air enters the turbine at a temperature of
1300 K. Determine the mass flow rate of air needed for the turbine
to produce 60 kW of power. Also determine the heat that must be
generated in the combustors. (30 pts) Solar collector …
For Question 2.....
process 1 to 2 is isentropic compression
process 1 to2' is actual compression
process 2' to 3 is isobaric heat rejection
process 3 to 4 is isenthalpic expansion
process 4 to 1 is isobaric heat addition