When modeling multiphase flow with CFX that involves a dispersed solid phase, and the material for the solid phase is solid material, the following error message will be encountered in CFX-Pre: “In Analysis -Domain : The following materials require Viscosity to be defined: ” Solid materials have no specification for dynamic viscosity. To resolve this: 1.) Duplicate the solid material under Materials and rename the material 2.) Change the Material Group to “User” 3.) Change the Thermodynamic State from Solid to Liquid. 4.) Specify a value for dynamic viscosity 5.) Refer to the new material name in the domain fluid specifications Swiching the Thermodynamic State of the material to Liquid from Solid will retain the pertinent solid properties (density, thermal conductivity, etc) but will also allow dynamic viscosity to be specified. Enter an arbitrary value for dynamic viscosity greater than zero. Dynamic viscosity must be specified but won’t be used since the phase is specified as “Dispersed Solid” under the morphology option in the domain Fluid and Particle Definitions. Note that dynamic viscosity is also not used in the case where the phase is specified as “Dispersed Fluid”