tutorial4 - Indian Institute of Technology Kharagpur...

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1 Indian Institute of Technology Kharagpur Department of Mechanical Engineering Thermodynamics ME22002 Tutorial 4 (The Second Law of Thermodynamics) 1. A coal-burning steam power plant produces a net power of 300 MW with an overall thermal efficiency of 32 percent. The actual gravimetric air fuel ratio in the furnace is calculated to be 12 kg air/kg fuel. The heating value of the coal is 28,000 kJ/kg. Determine (a) the amount of coal consumed during a 24-hour period and (b) the rate of air flowing through the furnace. Answers: (a) 2.89 × 10 6 kg, (b) 402 kg/s 2. A household refrigerator that has a power input of 450 W and a COP of 2.5 is to cool five large watermelons, 10 kg each, to 8°C. If the watermelons are initially at 20°C determine how long it will take for the refrigerator to coo them. The watermelons can be treated as water whose specific heat is 4.2 kJ/kg · °C. Is your answer realistic or optimistic? Explain. Answer: 2240 s 3. Refrigerant-134a enters the evaporator coils placed at the back of the freezer section of a household refrigerator at 120 kPa with a quality of 20 percent and leaves at 120 kPa and -20°C. If the compressor consumes
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tutorial4 - Indian Institute of Technology Kharagpur...

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