Sustainable Energy
2nd Edition
ISBN: 9781337551663
Author: DUNLAP, Richard A.
Publisher: Cengage,
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Chapter 17, Problem 10P
To determine
Find the average power requirement for the heat pump.
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A 50-L electrical radiator containing heating oil is placed in a 50-m³ room. Both the room and the oil in the
radiator are initially at 5°C. The radiator with a rating of 3 kW is now turned on. At the same time, heat
is lost from the room at an average rate of 0.3 kJ/s. After some time, the average temperature is measured
to be 20°C for the air in the room, and 60°C for the oil in the radiator. Taking the density and the specific
heat of the oil to be 950kg/m³ and 2.2kJ/(kg °C), respectively, determine how long the heater is kept on.
Assume the room is well-sealed so that there are no air leaks.
A closed tank containing hot air has an initial internal energy of 400 kJ. During the next 5 min, the tank loses heat to the surroundings at a rate of 1.5 kW, while an electrical element supplies 1000 W to the air. Find the final internal energy of the air.
A refrigerator is to remove heat from the cooled space at a rate of 300.74 kJ/min to maintain its temperature at -8 C. If the air surrounding the refrigerator is at 28.91 C, determine the minimum power input (kW) required for this refrigerator.
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