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The power density of electric machines is a critical factor in various applications, i.e. like the power train. A major factor to improve the power density is boosting the electric current density, which increases the losses in the limited volume of the electric machine. This results in a need for an optimized thermal design and efficient cooling. The dissipation of heat can be achieved in a multitude of ways, ranging from air cooling to highly integrated cooling solutions. In this paper, this variety is shown and analyzed with a focus on water cooling. Further various structures in electric machines are presented. A planar testbench is built to systematically analyze water cooling geometries. The focus lies in providing different power loss distributions along cooling channels, accurate temperature readings in a multitude of locations, as well as the pressure drop across the channel.

Cooling is a critical factor for improving power density in electrical appliances, especially in integrated drives for mobile applications. However, the issue of distributed losses in electric machines can lead to hotspots and temperature gradients within the electric drive. Traditional cooling jackets use unidirectional flow without or with evenly distributed cooling structures. This often aggravates the issue of hotspots, resulting in thermal derating and thus limiting the operation range. As well, a non-demand oriented distribution of cooling structures leads to unnecessary pressure losses. This problem is addressed with a newly elaborated method for distributing cooling elements, i.e., pin fins with varying density distribution inside the cooling channel. Results from previous work, numerical simulations, and measurement data from a planar test bench are used. The approach segments the cooling channel by using a loss profile.