When performing a similar type of analysis, consider the following hints and recommendations:
Create surface-effect elements that are much smaller than the fluid elements.
Doing so ensures that all fluid elements are coupled with the surface-effect elements.
Mapping the surface-effect elements onto the fluid elements (MSTOLE) creates the two extra nodes for the surface-effect element.
Three methods are available for mapping: Minimum Centroid Distance, Projection, and Hybrid.
Use MSTOLE with care.
As shown in this analysis, the MSTOLE command is applied to each hole. Using a single MSTOLE command for multiple holes is inefficient and can lead to incorrect mappings.
If a hole passage is straight, a single MSTOLE command should be sufficient.
If the passage has a serpentine path, several MSTOLE commands may be necessary to produce the correct mapping for that hole. For example, if the passage is a U-tube, use the MSTOLE command three times.
When higher-order elements are used for the solid region, the midside nodes on the convecting elements should be dropped.
The lower-order surface-effect element can then be used. Using higher-order surface-effect elements can sometimes lead to an unrealistic temperature distribution.