Experimental study on thermal characteristics of a state of art hairpin winding permanent magnet motor for automotive applications

This study investigates the thermal characteristics of the end-windings of a state-of-the-art hairpin winding permanent magnet motor designed for automotive applications. Hairpin windings offer advantages in terms of higher fill factors and automated manufacturing processes, making them ideal for high-performance motors. Water jacket cooling is used in the present study as it is one of the cost-efficient, reliable and commonly used techniques for mass-production. The experiments are conducted over a wide range of Reynolds numbers ( Re DH = 425–3610) covering a typical range of flow rates used in automotive industries. The influence of coolant fluid properties on the thermal characteristics of end-windings is investigated by varying Prandtl number ( Pr = 12.5 to 91). The results demonstrate that cooling characteristics are strongly influenced by gravitational forces. A distinct pattern of heat transfer is noticed for co-current (where gravity and flow direction are same) and counter-current direction (where gravity opposes the flow direction). This leads to variation in the heat transfer in the circumferential direction. A due consideration of the gravitational forces while designing the water jacket can minimize these thermal gradients. Heat transfer increases with the increment in the flow Reynolds number but rate of increment is higher towards the lower Reynolds number. Fluid properties have a significant influence on the heat transfer characteristics. A higher thermal diffusivity fluid leads to better heat transfer despite the higher Prandtl number.