Hot Spot Removal in Power Electronics by means of Direct Liquid Jet Cooling

This study examines the potential performance of submerged single phase direct impinging jet cooling and compares this cooling concept to a state of the art pin fin cooling systems. Submerged single impinging jets and arrays of impinging jets are characterized by high heat transfer coefficients. Especially in the stagnation region, in which the jet provides fresh cooling liquid to the surface, high heat removal rates occur. Thus, impinging jet arrays are a promising approach for hot spot removal as well as for thermal uniformity in large areas. In the present cooling concept, micro jets of approximately 1 mm diameter directly impinge onto the backside of a IGBT-semiconductor. In contrast to pin fin cooling, direct jet impingement cooling dispenses with the need for any kind of thermal interface materials (TIM) or heat spreader, and thus, minimizes the thermal resistance of the heat sink. A further advantage of submerged direct impinging jet cooling is hot spot removal. Once the exact location of heat generation is determined a small impinging jet can be directed at these hot spots. For this, local heat generation of the IGBT-semiconductor is first investigated by measuring the surface temperature on the top and bottom side by IR-thermometry. To observe the local heat generation the IGBT is operated for a very short time without any heat sink. This information is used in the development and design of the cooling chamber and the jet positioning. Finally, the cooling system is analyzed and compared to other common cooling systems. Both liquid cooling concepts are experimentally investigated with respect to heat transfer, pressure drop, and pumping power. A comparison and evaluation is provided with a special focus on applications in the automotive and electro-mobility sector.