The specific heat capacity must be defined when the energy equation is active. Ansys Fluent provides several options for definition of the heat capacity:
constant heat capacity
temperature- and/or composition-dependent heat capacity
kinetic theory
Each of these input options and the governing physical models are detailed in this section. In all cases, you will define the Cp in the Create/Edit Materials Dialog Box.
Setup → 
Materials
Specific heat capacity is input in units of J/kg-K in SI units or BTU/lbm-°R in British units.
Important: For combustion applications, a temperature-dependent specific heat is recommended.
For additional information, see the following sections:
If you want to define the heat capacity as a constant, check that constant is selected in the drop-down list to the right of Cp in the Create/Edit Materials Dialog Box, and enter the value of heat capacity.
The specific heat for the default fluid (air) is 1006.43 J/kg-K.
You can also choose to define the specific heat capacity as a function of temperature. Three types of functions are available:
You can input the data pairs (
), ranges and coefficients 
and 
, or coefficients 
that describe
these functions using the Create/Edit Materials Dialog Box, as described in Defining Properties Using Temperature-Dependent Functions.
If you are using the ideal gas law (as described in Density), you have the option to define the specific heat capacity using kinetic theory as
 | (8–67) |
where 
is the number of modes of energy
storage (degrees of freedom) for the gas species 
that you can input by selecting kinetic-theory from the drop-down list to the right
of Cp in the Create/Edit Materials Dialog Box. The solver will use your
kinetic theory inputs in Equation 8–67 to compute
the specific heat capacity. See Kinetic Theory Parameters for details about kinetic theory inputs.
If you are modeling a flow that includes more than one chemical species (multicomponent flow), you have the option to define a composition-dependent specific heat capacity. You can also define the heat capacity of the mixture as a constant value or a function of temperature, or using kinetic theory.
To define a composition-dependent specific heat capacity for a mixture, follow these steps:
For the mixture material, choose mixing-law in the drop-down list to the right of Cp.
Click .
Define the specific heat capacity for each of the fluid materials that make up the mixture. You may define constant or (if applicable) temperature-dependent heat capacities for the individual species. You may also use kinetic theory for the individual heat capacities, if applicable.
The solver will compute the mixture’s specific heat capacity as a mass fraction average of the pure species heat capacities:
 | (8–68) |