You may assume all the lost power from the above 80W, 75% efficient motor is transferred in the form of heat to the surrounding air. Suppose the motor is enclosed in a box 3 feet by 2 feet by 4.5 feet and runs on an intermittent cycle for 2 minutes before a fan turns on. How much thermal energy (in units of calories) is released to the space surrounding the motor in two minutes? g

answer:

explanation:

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If the temperature goes on increasing with respect to the length (i.e temperature gradient)then it is called positive heat transfer. If the temperature gradient decreases then it is called negative heat transfer.

Explanation:

A Carnot heat engine receives heat from a reservoir at 900$^\circ{}$C at a rate of 800 kJ/min and rejects the waste heat to the ambient air at 27$^\circ{}$C. The entire work output of the heat engine is used to drive a refrigerator that removes heat from the refrigerated space at -5$^\circ{}$C and transfers it to the same ambient air at 27$^\circ{}$C. Determine (a) the maximum rate of heat removal from the refrigerated space and (b) the total rate of heat rejection to the ambient air. Answers: (a) 4982 kJ/min, (b) 5782 kJ/min