Question

In the compression stroke of a gas engine the work done on the gas by the piston is 70 kJ/kg and the heat rejected to the cooling water is 42 kJ/kg.
Estimate the change of specific internal energy stating whether it is a gain or a loss.

Answer 1

Answer

Using first law of thermodynamics

$\Delta Q=\Delta U+\Delta W$

$\Delta U=\Delta W+\Delta Q$

Heat is rejected so using positive sign here

So the change of specific internal energy

$\Delta U=70+42=112KJ/Kg$