EML4304C HW4 - cycle COP? 3. (11.129) A small heat pump...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
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
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

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....
View Full Document

This note was uploaded on 09/05/2011 for the course EML 4304C taught by Professor Abbitt during the Summer '09 term at University of Florida.

Ask a homework question - tutors are online