### 5.6.4. Solids Bulk Viscosity

#### 5.6.4.1. Constitutive Equation Models

Most simple constitutive equation models ignore the solids bulk viscosity. However, it is possible for you to specify a model for this, using a CEL expression, if required. Note that, as for solids shear viscosity (see Solids Shear Viscosity), the full dependence of the solids bulk viscosity on solid phase volume fraction must be included in the CEL expression.

#### 5.6.4.2. Kinetic Theory Models for Solids Bulk Viscosity

There is general agreement on the correct kinetic theory form for the solids bulk viscosity (Lun et al. 1984 [99]).

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