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Linearized superposition using CFD for thermal and power characterization of electronic equipment with significant thermal radiation and natural convection

This paper presents a computational analysis for a PCB level natural convection system that is used to validate the principle of linearized superposition. The validated method is then used to rapidly predict the distribution of power in the PCB based on knowledge ofthe total input power and on discrete thermal probe data for the PCB. The principle of thermal superposition is fairly well documented for systems in which forced convection is dominant. This principle enables thermal characterization of systems and is particularly useful when used in conjunction with a design oriented CFD tool. This recent development makes it possible to complete most of the computational analysis before accurate electrical power information is available, with almost no compromise in accuracy. More recently, work has been performed to include non-linear thermal effects. Superposition breaks down as soon as there is significant thermal radiation and/or natural convection in the system. These two thermal phenomena are usually significant together because naturally cooled systems tend to have a higher percentage of heat dissipation by radiation due in part to hot spots and also the comparatively low convective ability. By linearizing the problem in the region of the best guess estimate for power levels, the principle of superposition can be harnessed to provide engineering solutions with considerable leeway for power modifications.