With the convective heat flux boundary condition, a linear heat transfer model is applied between the boundary entities and the external environment. This is useful to model general heat losses or gains such as those due to natural/forced convection or conduction with adjacent bodies of relatively constant temperature.
The parameters of the boundary condition are:
Reference temperature: Temperature of the environment, used to compute the boundary heat transfer.
Heat transfer coefficient: Proportionality value used to compute the boundary heat transfer, with units of power \((W, Btu/h)\) divided by units of temperature \((K, °C, °F)\) and area \((m^2, in^2)\)
Assignment: Set of faces where the convective heat flux value will be applied.
Function or Table input
The values for the reference temperature and heat transfer coefficient in the settings panel for the convective heat flux boundary condition can also be input using the function or table capability.
Supported Analysis Types
The following analysis types support the usage of this boundary condition:
\( \kappa \) is the thermal conductivity of the material,
\( \nabla T \) is the local temperature gradient,
\( \vec{n} \) is the area normal vector of the element boundary surface,
\( h \) is the convection heat transfer coefficient,
\( T \) is the local temperature.
\( T_{ref} \) is the external reference temperature, and
Variable Convective Heat Flux
Variable heat flux values can be specified with the use of the formula or table inputs for the reference temperature and/or the heat transfer coefficient. The allowed functions are:
Time-dependent: The parameters vary with respect to time (variable t) in a transient heat transfer, nonlinear static or dynamic thermomechanical simulation. This is useful, for instance, to ramp up the load from zero in nonlinear simulations, where a sudden application of load leads to numerical divergence, or to define heat transfer curves.
Coordinate-dependent: The parameters vary with respect to the position in space (variables X, Y, Z). This is useful for applying known heat transfer gradients on the boundary faces.