THE UNIVERSITY OF MICHIGAN Department of Mechanical ...
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 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:
10.69 A 4 stroke 2.4 L gasoline engine runs at 2500 RPM has an efficiency of 60%. The state before compression is 40 kPa, 280 K and after combustion it is at 2400 K. Find the highest T and P in the cycle, the specific heat transfer added, the cycle MEP and the total power produced. Solution:
10.90 A diesel engine has a state before compression of 95 kPa, 290 K, and a peak pressure of 6000 kPa, a maximum temperature of 2400 K. Find the volumetric compression ratio and the thermal efficiency.
10.94 A diesel engine has a bore of 0.1 m, a stroke of 0.11 m and a compression ratio of 19:1 running at 2000 RPM. Each cycle takes two revolutions and has a mean effective pressure of 1400 kPa. With a total of 6 cylinders find the engine power in kW and horsepower in hp.
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 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:
10.69 A 4 stroke 2.4 L gasoline engine runs at 2500 RPM has an efficiency of 60%. The state before compression is 40 kPa, 280 K and after combustion it is at 2400 K. Find the highest T and P in the cycle, the specific heat transfer added, the cycle MEP and the total power produced. Solution:
10.90 A diesel engine has a state before compression of 95 kPa, 290 K, and a peak pressure of 6000 kPa, a maximum temperature of 2400 K. Find the volumetric compression ratio and the thermal efficiency.
10.94 A diesel engine has a bore of 0.1 m, a stroke of 0.11 m and a compression ratio of 19:1 running at 2000 RPM. Each cycle takes two revolutions and has a mean effective pressure of 1400 kPa. With a total of 6 cylinders find the engine power in kW and horsepower in hp.
