Printed circuit boards (PCBs) with uniform surface temperature and uniform wall heat flux are ideal to study. However, in reality, the heating conditions existing on the PCB surfaces are much different from the ideal ones. Present attempts have been made to study different combinations of uniform heat flux (UHF) and uniform wall temperature (UWT) heating conditions on a single surface and to develop more realistic relationships between various flow and thermal parameters for evaluating the local and averaged Nusselt number. Both the numerical and experimental investigations were undertaken to study partial and mixed UHF and UWT heating conditions on a buoyancy assisted convection cooling of simulated PCB forming one wall of the vertical channel while, the other wall was kept insulated. The current work considers moderate to high flow Reynolds number $(14.1×103≤Re≤2.35×105)$ in the channel and range of heat fluxes near that occurring in electronic cooling applications using air as a coolant $(0.0. Data for heat flux and Nusselt number occurring at various locations of the plate surface under different heating conditions are presented to analyze variation patterns; and an empirical relation is put forward which is capable of predicting Nu under the heating conditions mentioned. The empirical expression obtained can be used for getting an optimized layout of the PCBs inside the equipment cabinet, thus resulting in better design for more reliable and safe operation under potentially harsh environment and/or maximum load condition.

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