The basis for thermal analysis is a heat balance equation obtained from the principle of conservation of energy. (For details, see the Mechanical APDL Theory Reference.) The finite element solution calculates nodal temperatures and uses them to obtain other thermal quantities.
The program handles all primary modes of heat transfer: conduction, convection, mass transport (advection), and radiation.
You specify convection as a surface load for the boundary condition on conducting solid elements or shell elements. You specify the convection film coefficient and the bulk fluid temperature at a surface, which are used to calculate heat transfer across that surface. If the film coefficient depends upon temperature, you specify a table of temperatures along with the corresponding values of film coefficient at each temperature.
The convection element named LINK34 is available for use in finite element models with conducting bar elements (which do not allow a convection surface load), or in cases where the bulk fluid temperature is not known in advance.
A mass transport option is available for the current-technology elements, SOLID278 and PLANE292, and the legacy elements, PLANE55 and SOLID70, to simulate the heat transfer by a mass flow with a prescribed velocity field in your analysis. The current-technology elements can be used to simulate all flow conditions without restriction while the legacy elements are limited to the condition that the ratio of the rate of advective heat transport to the rate of diffusive heat transport (Peclet number) is less than one. For details on this and setting up an analysis that includes mass transport, see Mass Transport (Advection) and Mass Transport (Advection) in the Theory Reference.
Radiation problems, which are nonlinear, can be solved using any of these methods:
For detailed information on these methods, see Radiation.
In addition to the three modes of heat transfer, you can account for special effects such as change of phase (melting or freezing) and internal heat generation (due to Joule heating, for example). For instance, you can use the thermal mass element MASS71 to specify temperature-dependent heat generation rates.
Far-field elements allow you to model the effects of far-field decay without having to specify assumed boundary conditions at the exterior of the model. A single layer of elements is used to represent an exterior sub-domain of semi-infinite extent. For more information, see Far-Field Elements in the Low-Frequency Electromagnetic Analysis Guide.