How to Calculate the Change of Enthalpy

Enthalpy, h, is a thermodynamic property of fluids used extensively when analyzing flow problems in fields such as fluid dynamics or aerodynamics. It is defined as u' + p/(rho), where u' is specific internal energy. Enthalpy is used to define two other fluid properties--specific heat at constant pressure, cp, and specific heat at constant volume, cv. Using the perfect gas law, p = (rho)RT, and algebraic manipulation, you can derive a simple equation to determine enthalpy, h = (cp)T.

Instructions

1. Determine the temperature change at one location in the fluid you are analyzing.

2. Look up the specific heat at constant pressure, cp, for the fluid you are analyzing. Thermodynamic property tables can most easily be found in thermodynamics textbooks as an appendix. One good source is "Fundamentals of Heat and Mass Transfer" by Incropera and DeWitt.

3. Multiply the value for specific heat at constant pressure by the change in temperature recorded earlier. That value is the change in enthalpy.