Thermal capacity effect on transient mixed convection over heated components

The effect of the surface thermal capacity upon the transient mixed convection flow over heated electronic modules is studied. The convection field is composed of an upward buoyancy induced flow generated by discrete heated components, and an opposed weak downflow resulting from an adverse pressure field. This circumstance may arise in electronic packaging and in regions where cooling is intended to rely on natural convection, however an adverse pressure field may occur due to forced convection cooling in other parts of the system. Several parameters are investigated in the current study, including the surface thermal capacity and the magnitude of the adverse pressure field. The computational technique selected to solve the equations in the current study is an Eulerian-Langrangian finite difference scheme. The model is verified by comparison of the results to previous known solutions, whereby excellent agreement is found. The effect of thermal capacity is predicted to be very significant in determining the transient flow regime and duration, as well as the existence and magnitude of temperature overshoots during the transient. For surfaces with low thermal capacity, significant temperature overshoots and oscillations are found, while for surfaces with large thermal capacity the temperatures are observed to increase gradually with very little or no overshoots. The component thermal capacity is also found to profoundly influence the net average volume flow rate in the channel.