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flux Contents Convective heat flux is a flux depending on the
temperature difference between the body and the adjacent fluid
(liquid or gas) and is triggered by the *FILM card. It takes the
form where is the a flux normal to the surface, is the film
coefficient, is the body temperature and is the environment
fluid temperature (also called sink temperature). Generally, the
sink temperature is known. If it is not, it is an unknown in the
system. Physically, the convection along the surface can be
forced or free. Forced convection means that the mass flow rate
of the adjacent fluid (gas or liquid) is known and its
temperature is the result of heat exchange between body and
fluid. This case can be simulated by CalculiX by defining
network elements and using the *BOUNDARY card for the first
degree of freedom in the midside node of the element. Free
convection, for which the mass flow rate is a n unknown too and
a result of temperature differences, ca