Equation for gas flow in a duct subject to heat exchange

5 Equation for gas flow in a duct subject to heat exchange 

The specific internal energy and the specific enthalpy of an ideal gas are dependent on temperature alone, and so equation (20.9) is valid for a gas as well as a liquid. Further, we may note that the specific heats at constant volume and constant pressure for a gas are given by  

Comparing equation (20.12) with equation (20.11), we see that the temperature front in a gas duct subject to heat exchange will travel at a velocity of yc, somewhat faster than the speed of the flowing gas. 

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