Natural Convection...

Pro/MECHANICA is a conduction heat transfer code and will only calculated the heat flow through solids. The effect of fluid flow for heating or cooling is applied as a boundary constraint. The user is required to calculate and provide the convection coefficient and fluid temperature. For natural convection cases this can be somewhat tricky. The film coefficient for natural convection is dependant on many parameters such as the temperature differential between the surface and the ambient fluid. This requires that the user make an estimate of the surface temperature to calculate the convection coefficient and then run the Pro/MECHANICA analysis comparing the estimate with the calculated value. Several iterations may be required. Also, the surface may have to be broken up into several regions since the surface temperature (and convection coefficient) will be different across the surface. The fluid temperature may also change as it is heated or cooled by the convection process. Natural convection is also dependent on gravity thus the orientation, shape and size of the surface is important. As you may deduce, for many cases Pro/MECHANICA is only going to provide a very crude estimate for natural convection. Even with computer codes that handle fluid flow this calculation is very difficult and may not result in answers that are any more accurate.

The following equations were empirically derived for use in calculating convection heat loads on buildings and piping systems in air. For structures that are significantly smaller in dimension these equations may be less accurate. Be careful of the units used here.

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