The engine that powers a crane burns fuel at a temperature of 1500 oC. It is cooled by air at a temperature of 20 oC. The crane is used to lift a 1000 kg steel girder 30 m into the air. If the engine is 40 % as efficient as a Carnot engine, what is it's thermal efficiency in %?

Explanation:

Given that,

Warm temperature TH = 1500°C

K= °C +273

TH=1500+273=1773K

Cold temperature TL = 20°C

TL = 20+273

TL = 293K

The efficiency of a Carnot engine is given as

η = 1 — (TL/TH)

η = 1 — (293/1773)

η = 1 — 0.165

η = 0.8347

Then, in %

η = 0.8347×100

η = 83.47%

Thermal efficiency is 83.47%

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explanation:

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