An inventor proposed a contrivance which would take in a str

An inventor proposed a contrivance which would take in a stream of air, at a supercharged 2 bar, 350 K, and use it to generate electricity by undisclosed mechanical means, which we suspect involve some sort of heat transfer with the environment, which is at 300 K. After delivering 10 kJ or electricity for each kg of air ingested, the device discharges that air back into the atmosphere, at 1 bar, 280 K. Discuss whether the device has some technical merit, or rather it is a fake

Solution

Work input given per unit mass of air = 10 KJ

Now, heat transferred per kg of air using this work is = Cp x (350-280) = 1.005 x 70 = 70.35 KJ

So, it means the device has the technical advantage, since it is utilizing 10 Kj/kg of electricity work to obtain a heat transfer of 70.35 Kj/kg, which is an advantage.