Mixed Convection

In many electronic cooling applications, the heated or cooled air is blown but may contain local temperature gradients that will cause some appreciable buoyancy effects. This type of heat transfer is known as mixed convection, since it has features of both natural and forced convection. There is not a good way to tell prior to the analysis if the heat transfer is mixed or forced. To check, you should run a mixed convection analysis after the forced convection analysis is finished:

1. Get a converged flow solution with Heat Transfer set to Off on the Solve dialog and Fixed fluid properties on the Materials dialog.
2. Disable Flow, enable Heat Transfer on the Solve dialog, and run 50 iterations. If the temperatures are unrealistically high, continue to the next step, but on the Solve dialog, continue from the iteration after Step 1 (select from the Continue From field on the Solve dialog).
3. On the Solve dialog, enable Flow and Heat Transfer, and specify the Gravity vector. To allow the properties to vary with temperature, click Edit... on the Environment line. On the Material Environment dialog, select Variable, and click OK.
4. Run 100 more iterations and examine the results for changes.