Estimate the rate of heat transfer from the compressor. Assume for air that 
and that enthalpy is independent of pressure.
Fifty (50) kmol per hour of air is compressed from 
= 1.2 bar to 
= 6.0 bar in a steady-flow compressor.
Delivered mechanical power is 98.8 kW. Temperatures and velocities are:
The energy balance, including kinetic energy contributions, for a steady flow system gives us
The mass flow rate (in and out) is 50 kmol 
?29 kg/kmol = 1450 kg/hr = 0.40278 kg/s
The enthalpy change is
The kinetic energy change is
So, as is so often the case, the change in kinetic energy is negligible.
So, the energy balance becomes
from which Q = –9.9 kW. That is, 9.9 kW of heat flows from the system (the air) to the surroundings, or 9.9 kW of the input mechanical energy leaves the compressor as heat.
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