## 8.3.5 Incompressible Ideal Gas Law

In FLUENT, if you choose to define the density using the ideal gas law for an incompressible flow, the solver will compute the density as

 (8.3-5)

where,

 = the universal gas constant = the molecular weight of the gas = Operating Pressure

In this form, the density depends only on the operating pressure and not on the local relative pressure field.

Density Inputs for the Incompressible Ideal Gas Law

The inputs for the incompressible ideal gas law are as follows:

1.   Enable the ideal gas law for an incompressible fluid by choosing incompressible-ideal-gas from the drop-down list to the right of Density in the Materials panel.

Specify the incompressible ideal gas law individually for each material that you want to use it for. See Section  8.3.7 for information on specifying the incompressible ideal gas law for mixtures.

2.   Set the operating pressure by defining the Operating Pressure in the Operating Conditions panel.

Define Operating Conditions...

 By default, operating pressure is set to 101325 Pa. The input of the operating pressure is of great importance when you are computing density with the ideal gas law. See Section  8.14 for recommendations on setting appropriate values for the operating pressure.

3.   Set the molecular weight of the homogeneous or single-component fluid (if no chemical species transport equations are to be solved), or the molecular weights of each fluid material (species) in a multicomponent mixture. For each fluid material, enter the value of the Molecular Weight in the Materials panel.

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