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EML4304C HW4

# EML4304C HW4 - cycle COP 3(11.129 A small heat pump unit is...

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EML4303C Homework Concept questions: 1C. A refrigerator in my 20 °C kitchen uses R-12, and I want to make ice cubes at -5 °C. What is the minimum high P and the maximum low P it can use? 2C. How many parameters are needed to completely determine a standard vapor-compression refrigeration cycle? Problems: 1. (11.126) The air conditioner in a car uses R-134a, and the compressor power input is 1.5 kW, bringing the R-134a from 201.7 kPa to 1200 kPa by compression. The cold space is a heat exchanger that cools 30 °C atmospheric air from the outside down to 10 °C and blows it into the car. What is the mass flow rate of the R- 134a, and what is the low-temperature heat-transfer rate? What is the mass flow rate of air at 10 °C? 2. (11.130) The refrigerant R-22 is used as the working fluid in a conventional heat pump cycle. Saturated vapor enters the compressor of this unit at 10 ° C; its exit temperature from the compressor is measured and found to be 85 ° C. If the compressor exit is 2 MPa, what is the compressor isentropic efficiency and the
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Unformatted text preview: cycle COP? 3. (11.129) A small heat pump unit is used to heat water for a hot-water supply. Assume that the unit uses R-22 and operates on the ideal refrigeration cycle. The evaporator temperature is 15 °C, and the condenser temperature is 60 °C. If the amount of hot water needed is 0.1 kg/s, determine the amount of energy saved by using the heat pump instead of directly heating the water from 15 to 60 °C. 4. (11.133) In an actual refrigeration cycle using R-12 as the working fluid, the refrigerant flow rate is 0.05 kg/s. Vapor enters the compressor at 150 kPa and -10 °C and leaves at 1.2 MPa and 75 °C. The power input to the nonadiabatic compressor is measured and found to be 2.4 kW. The refrigerator enters the expansion valve at 1.15 MPa and 40 °C and leaves the evaporator at 175 kPa and -15 °C. Determine the entropy generation in the compression process, the refrigeration capacity, and the coefficient of performance for this cycle....
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