I am trying to design an air heater. The heater will consist of a pipe of diameter approximately 10 inches and length unknown (any size is acceptable), an electric heat element will be inserted with an output of 2.5 kW. The pressurized air is entering at 120 psi and 70 deg F. I am interested in determining mainly the outlet temperature and pressure.

Can qdot=mdot*CP*deltaT used for a varying pressure system since obviously the pressure will increase due to temperature rise through the heater. My intuition says this is not acceptable in a pressurized system.