Question

A new automobile engine, working between the temperatures 319 C and 499 C is expected to produce 17.0 kW of power for 49.5 kW heat input. Evaluate these claims. If the claims are invalid, what is the minimum heat input needed if everything else remains the same?

Answer 1

maximum efficiency η = 1 - Tc/Th

Tc = temperature of cold reservoir in kelvin

Th = tempearture of hot reservoir in kelvin

η = 1- ( 319+273) /( 499+273) =0.233160622

efficiency = work done / heat input = 17 /49.5 =0.343434343

since efficiency > max efficiency the claims are invalid

if everything else remains the same

η = W/Q  

0.233160622   = 17 /Q

Q = 17 / 0.233160622 =72.911111 kW answer

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