Physically-motivated Figure of Merit (FOM) assessing the cooling performance of fluids suitable for the direct cooling of electrical components

High heat fluxes occurring in modern electrical systems require direct cooling methods in which the electrical components come in direct contact with the cooling fluid. Hence electrically non-conductive fluids with thermal properties inferior to the ones of water have to be applied. In order to assess the cooling performance of such fluids a physically-based Figure of Merit (FOM) is presented based on the ratio of the achieved heat flux and the required pumping power in an exemplary cooling application under laminar flow conditions. This application is the direct cooling of windings in an electrical engine by feeding a cooling fluid through the channels between the stator teeth. Due to the high viscosities of most cooling fluids combined with small geometrical dimensions of modern electronics and the applied coolers, the assumption of a laminar flow is often justified. The FOM which is derived analytically through generally accepted correlation functions is solely a function of the thermal fluid properties and is hence applicable in any other cooling configuration with laminar flow conditions. The results of a combined experimental and numerical study of the considered cooling case are used to assess the accuracy of the FOM.