Direct liquid cooling in compact machines: Advantages and limitations

The increasing demand for more efficient propulsion systems in electric and hybrid vehicles necessitates advanced thermal management in compact electric machines. This study investigates a novel direct liquid cooling (DLC) approach using Litz copper wires braided around a stainless steel tube to enhance heat removal. Analytical model, numerical simulations, and experimental testing were employed to evaluate the system's cooling efficiency, considering various conductor sizes and supply currents. The results show that direct liquid cooling significantly lowers winding temperatures compared to traditional cooling methods when operating at the same load. These temperature dependencies are explored in more detail in the paper using the developed analytical approach. The analytical model, which was verified with experimental results, also indicates that direct liquid cooling windings can support up to 277% more current than traditional water jacket-cooled windings while maintaining a maximum temperature of 70 °C. These findings demonstrate that direct liquid cooling windings are a highly effective method for enhancing thermal performance even in compact motors, enabling higher power densities.