THE UNIVERSITY OF MICHIGAN
Department of Mechanical Engineering
ME 235 Thermodynamics I / Winter 2014 / Section 002
HW 12 Solutions
Due date: Apr. 24 2014 5PM
9.89 A refrigerator receives 500 W of electrical power to the compressor driving the cycle flow of R-134a.
The refrigerator operates with a condensing temperature of 40°C and a low temperature of -5°C. Find the
COP for the cycle and its cooling capacity. 9.104 A small heat pump unit is used to heat water for a hot-water supply. Assume that the unit uses
ammonia 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.
10.67 A 4 stroke gasoline engine runs at