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Lecture

# MECHENG 235 Lecture Notes - Thermal Efficiency, Heat Capacity, Thermodynamics

Department
Mechanical Engineering
Course Code
MECHENG 235
Professor
Donald Siegel

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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 -C. Find the
COP for the cycle and its cooling capacity.

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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 1800 RPM with a total displacement of 3L and a compression
ratio of 10:1. The intake is at 290 K, 75 kPa with a mean effective pressure of 600 kPa. Find the cycle
efficiency and power output.
Solution: