INDIAN INSTITUTE OF TECHNOLOGY KANPUR
ESO 201A: Thermodynamics
(2023-24 I Semester)
Instructor: Dr Avinash Kumar Agarwal
Tutorial -12
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Question 1: A space is kept at -15°C by a vapor-compression refrigeration system in an
ambient at 25°C. The space gains heat steadily at a rate of 3500 kJ/h and the rate of heat
rejection in the condenser is 5500 kJ/h. Determine the power input, in kW, the COP of the
cycle and the second-law efficiency of the system.
(Ans: Power input = 0.5556 kW, COP = 1.75, II law efficiency = 27.1%)
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Question 2: Bananas are to be cooled from 28°C to 12°C at a rate of 1140 kg/h by a
refrigerator that operates on a vapor-compression refrigeration cycle. The power input to
the refrigerator is 8.6 kW. Determine: (a) the rate of heat absorbed from the bananas, in
kJ/h, and the COP, (b) the minimum power input to the refrigerator, and (c) the second-
law efficiency and the exergy destruction for the cycle. The specific heat of bananas above
freezing is 3.35 kJ/kg·°C.
(Ans: (a) 61,100 kJ/h, 1.97, (b) 0.463 kW, (c) 5.4 %, 8.14 kW)
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Question 3: A heat pump that operates on the ideal vapor-compression cycle with
refrigerant-134a is used to heat water from 15 to 45°C at a rate of 0.12 kg/s. The condenser
and evaporator pressures are 1.4 and 0.32 MPa, respectively. Determine the power input
to the heat pump.
(Ans: 2.97 kW)
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Question 4: A gas refrigeration cycle with a pressure ratio of 4 uses helium as the
working fluid. The temperature of the helium is -6°C at the compressor inlet and 50°C at
the turbine inlet. Assuming isentropic efficiencies of 85 percent for both the turbine and
the compressor, determine (a) the minimum temperature in the cycle, (b) the coefficient
of performance, and (c) the mass flow rate of the helium for a refrigeration rate of 25 kW.
(Ans: (a) 206.1 K, (b) 0.525, (c) 0.0791kg/s)
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Question 5: Propal alcohol (C3H7OH) is burned with 50 percent excess air. Write the
balanced reaction equation for complete combustion and determine the air-to-fuel ratio.
(Ans: A/F ratio = 15.51)
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Question 6: Heat is supplied to an absorption refrigeration system from a geothermal
well at 110°C at a rate of 5 × 105 kJ/h. The environment is at 25°C, and the refrigerated
space is maintained at -18°C. Determine the maximum rate at which this system can
remove heat from the refrigerated space.
(Ans: 6.58 × 105 kJ/h)
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