Q1-2 = (segma) - n / (segma) - 1 * W1-2

where W1-2 is the work done during polytropic process.

If dQ is the small quantity of heat transfer during small change of pressure and volume, then

dQ = (segma) - n / (segma) - 1 * pdv

Rate of heat transfer per unit volume,

dQ / dv = (segma) - n / (segma) - 1 * p

and rate of heat transfer per second,

dQ / dt = dQ / dv * dv / dt = (segma) - n / (segma) -1 * p * dv / dt

where dv / dt is the swept volume of the piston per second.