A heat engine receives heat of 400kW from a heat source of 1100 K, and rejects the waste heat into a heat sink at 320K. It generates 120 kW of power output. Determine the 2nd law thermal efficiency of the heat engine.

Explanation:

efficiency of carnot engine operating between 1100 K and 320 K

= 1100 - 320 / 1100

= .709

efficiency of heat engine = 120 / 400 = .30

2 nd law thermal efficiency of heat engine = .30 x 100  / .709

= 42.31 % .

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