Mathematical Optimization of Electronic Enclosures

Abstract

The thermal design of electronic enclosures is becoming more important as the demand for smaller, lighter systems with better performance increases. The limiting factor on the lifetime of these systems is the maximum temperature of the electronic components. Nowadays in some systems, the thermal design is the limiting factor for performance increases. A simple yet effective design method that yields optimum designs is therefore required to design these systems. Traditionally, experimental methods were used in the design of electronic enclosures. More recently Computational Fluid Dynamics (CFD) has established itself as a viable alternative to reduce the number of experimentation required, resulting in a reduction in the time scales and cost of the design process. The CFD process is usually applied on a trial and error basis and relies heavily on the insight and experience of the designer to improve designs. Even an experienced designer will only be able to improve the design and does not necessarily guarantee optimum results. A more efficient design method is to combine a mathematical optimizer with CFD. In this study the mathematical optimization method, DYNAMIC-Q, is linked with the commercial CFD package, Icepak to optimize different electronic enclosures. The method is applied to the following design situations commonly found in electronics enclosures. The first case is that of the optimization outlet grille of a telecommunications rack to reduce the electromagnetic interference without exceeding a specified temperature in the rack. The second case involves the optimum placement of electronic components on a printed circuit board to minimize the maximum temperatures of the components. The third case deals with flow through an electronic enclosure cooled by fans placed on the wall of the enclosures. The geometrical arrangement of boards and components on the boards in these enclosures might result in unequal flow distribution between the boards. For this purpose air flow filters of varying free-area ratios are used to make the flow rates between the boards more uniform. The free-area ratios of three filters are determined in order to maximize the total flow rate through system with the added constraint that the flow rates through each of the three filters are within 5% of each other. The last case deals with flow through a simplified notebook where the CPU temperature is minimized by changing the position of two exhaust fans. The study shows that mathematical optimization is a powerful tool that can be combined with CFD to yield optimum designs.