Thermal Expansivity (or coefficient of thermal expansion), , describes how a fluid expands with temperature. It is used in the Boussinesq approximation for buoyant flow and has dimensions of (where is temperature). For details, see Buoyancy in the CFX-Solver Theory Guide. This parameter will be used by the flow solver only if the fluid has a constant density. Otherwise, the full buoyancy model will be used, for which thermal expansivity is not a required parameter.