HW08_Sol - at 200 kPa and leaving as saturated vapor. The...

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ME 3513 – Thermodynamics I Solutions to Homework Assignment # 8 – Chap. 7 - Second Law 1. A gasoline engine produces 20 hp using 35 kW of heat transfer from burning fuel. What is its thermal efficiency and how much power is rejected to the ambient? 2. A farmer runs a heat pump with a 2 kW motor. It should keep a chicken hatchery at 30°C, which loses energy at a rate of 10 kW to the colder ambient T amb . What is the minimum coefficient of performance that will be acceptable for the heat pump? 3. Assume a cyclic machine that exchanges 6 kW with a 250°C reservoir and has a. Q L = 0 kW, W . = 6 kW b. Q L = 6 kW, W . = 0 kW and Q L is exchanged with a 30°C ambient. What can you say about the processes in the two cases a and b if the machine is a heat engine? Repeat the question for the case of a heat pump.
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4. Sixty kilograms per hour of water runs through a heat exchanger, entering as saturated liquid
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Unformatted text preview: at 200 kPa and leaving as saturated vapor. The heat is supplied by a Carnot heat pump operating from a low-temperature reservoir at 16C. Find the rate of work into the heat pump. 5. A refrigerator keeping 5C inside is located in a 30C room. It must have a high temperature T above room temperature and a low temperature T below the refrigerated space in the cycle to actually transfer the heat. For a T of 0, 5 and 10C respectively calculate the COP assuming a Carnot cycle. 6. An ideal gas Carnot cycle with air in a piston cylinder has a high temperature of 1200 K and a heat rejection at 400 K. During the heat addition the volume triples. Find the two specific heat transfers (q) in the cycle and the overall cycle efficiency....
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HW08_Sol - at 200 kPa and leaving as saturated vapor. The...

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