December 1, 2016
ME331: THERMODYNAMICS
EXAM 3
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1. (30%) Air enters the diffuser of a jet engine at 400 °R and exits the diffuser at 480 °R.
The air exits the compressor at 1000 °R and enters the turbine at 3000 °R. The gases exit
the turbine and enter the nozzle where they expand to the surrounding pressure. Using the
air standard analysis and assuming the isentropic operation of the compressor and that a
100% of the power developed by the turbine is used to drive the compressor:
a) Calculate the velocity of the air at the diffuser inlet in ft/s
b) Calculate the ratio of the pressure at the compressor discharge to the pressure at
the compressor inlet
c) Determine the temperature of the air entering the nozzle in °R.
2. (40%) A vapor-compression refrigeration system, with ammonia as the working fluid,
has evaporator pressure of 2 bar and condenser pressure of 12 bar. At the compressor
inlet the temperature is -10 °C and at the exit is 140 °C. The heat transfer rate from
the working fluid passing through the condenser is 15 kW and at its exit ammonia is
at the saturated liquid state. Assuming that there is no significant heat transfer
between the compressor and its surroundings, determine:
a) The mass flow rate of the refrigerant, in kg/s
b) The refrigeration capacity, in tons
c) the compressor power input, in kW
d) the coefficient of performance
e) the isentropic compressor efficiency
f) the rate of entropy production, in KW/K, for the compressor
3. (30%) Moist air at 37 °C, 1 atm, and 50% relative humidity enters a dehumidifier
operating at steady-state. Saturated moist air and condensate exit in separate streams,
each at 22 °C. Determine:
a) the humidity ratio at the inlet and outlet
b) the amount of water condensed, in kg per kg of dry air
c) the heat transfer from the moist air to the cooling liquid, in kJ per kg of dry air