Increased heat transfer using interrupted convection in back iron laminations
Thompson, Nicholas (Engineer)
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The need for more efficient electrical power generation components is growing as technologies mature while improvements on these technologies make smaller gains over previous versions. Improvements in cooling methods are required in order to avoid increased temperatures and decreased reliability and efficiency. An area that has room for rapid growth is cooling optimization of electromagnetics. Direct air flow is the simplest cooling method. It is well documented that the heat transfer coefficient of a fluid can be increased by adding fins to the surface of the heat generating component. Using lamination layers allows for the achievement of more complex fin design geometries while limiting induction losses. Optimization of these fin dimensions as well as clocking positions allows for the system designer to choose the amount of flow interruption by using variable hydraulic diameters and flow paths for the fluid, thus controlling pressure drop and heat transfer coefficient for a given system. This flexibility of parameters also allows for the elimination of localized hot spots. This research investigates the effect of changing fin patterns as well as changes in fin distances between laminations on convection. It is hypothesized that by forcing periodic redevelopment of the boundary layer, local heat transfer will increase, thus temperature of the component will decrease. Results show a direct correlation between hydraulic diameters versus pressure drops as well as heat transfer coefficient versus tooth surface area. Results also showed that flow impingement increases pressure drop by a larger factor than the increase in heat transfer due to the flow impingement. Experimental data, confirmed by numerical computation, showed that increased fluid flow proportionally affected effective heat transfer coefficient. Experimentally, the design using 0.15" finless spacer between finned laminations and zero degree clocking performed the best. Conversely, both 180 degree clocked designs performed poorly due to fluid stagnation on the front and rear fin walls, overcoming any benefit due to increased wetted surface area.