Assignment 2 (1)

DKK 2333 1
Thermodynamics (Sem20182019/1)
Due date for submission of Assignment 2 is on 12 December 2018 (Wednesday)
1. Air enters a 28-cm diameter pipe steadily at 200 kPa and 20oC with a velocity of 5 m/s.
Air is heated as it flows, and leaves the pipe at 180 kPa and 40oC. Determine (a) the
volume flow rate of air at the inlet, (b) the mass flow rate of air, and (c) the velocity
and volume flow rate at the exit.
2. Steam at 3 MPa and 400oC enters an adiabatic nozzle steadily with a velocity of 40 m/s
and leaves at 2.5 MPa and 300 m/s. Determine (a) the exit temperature and (b) the ratio
of the inlet to exit area A1/A2.
3. An adiabatic air compressor is to be powered by a direct-coupled adiabatic steam
turbine that is also driving a generator (as shown in Figure 1). Steam enters the turbine
at 12.5 MPa and 500oC at a rate of 25 kg/s and exits at 10 kPa and a quality of 0.92.
Air enters the compressor at 98 kPa and 295 K at a rate of 10 kg/s and exits at 1 MPa
and 620 K. Determine the net power delivered to the generator by the turbine.
Figure 1
DKK 2333 2
Thermodynamics (Sem20182019/1)
A Carnot heat engine receives 650 kJ of heat from a source of unknown temperature
and rejects 250 kJ of it to a sink at 24oC. Determine (a) the temperature of the source
and (b) the thermal efficiency of the heat engine.
An inventor claims to have devised a cyclical engine for use in space vehicles that
operates with a nuclear-fuel-generated energy source whose temperature is 510K and a
sink at 270 K that radiates waste heat to deep space. He also claims that this engine
produces 4.1 kW while rejecting heat at a rate of 15,000 kJ/h. Is this claim valid?
An air-conditioner with refrigerant-134a as the working fluid is used to keep a room at
23oC by rejecting the waste heat to the outdoor air at 34oC. The room gains heat through
the walls and the windows at a rate of 250 kJ/min while the heat generated by the
computer, TV, and lights amounts to 900 W. The refrigerant enters the compressor at
400 kPa as a saturated vapor at a rate of 80 L/min and leaves at 1200 kPa and 70oC.
Determine (a) the actual COP, (b) the maximum COP, and (c) the minimum volume
flow rate of the refrigerant at the compressor inlet for the same compressor inlet and
exit conditions.