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.

The following analysis types support the usage of this boundary condition:

The heat transfer on each element of the assigned surfaces will be given by the difference between the local temperature:

$$ \kappa (\nabla T \cdot \vec{n}) = h(T – T_{ref}) $$

Where:

- \( \kappa \) 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 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 to apply known heat transfer gradients on the boundary faces.

Maximum Number of Table Parameters

Due to numerical difficulties, the underlying structural solver (Code_Aster) only supports table function definitions of one or two variables. If you need to define a function of the three spatial coordinates (X, Y, Z), or even combine it with time, you must create an analytical formula for it.

- Tutorial: Thermal Analysis of a Differential Casing
- Tutorial: Thermomechanical Analysis of an Engine Piston
- Validation Case: Convective Heat Transfer of a Sphere
- Validation Case: Thermal Effects in High Power LED Packaging.

Last updated: May 20th, 2021

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