Direct Cooling of Stator End-Windings Using Ferrofluids: An Exploratory Experimental Study on Flow Dynamics and Heat Transfer

Efficient cooling is essential for electrical machines working with high power density. Ferrofluids offer a high potential to be served as an efficient coolant. However, they have not yet been studied for cooling purposes in an impinging jet flow and in the presence of alternating magnetic fields. In such a configuration, the ferrofluid flow can be strongly influenced by the magnetic field, which a strong interaction with ferrofluid flows can considerably enhance the cooling process. Alternating magnetic fields are present around the motor coils of a stator. In this regard, an experimental setup is built to investigate the cooling performance of two configurations of ferrofluid jet impingement onto the end-winding of a single coil: 1) the horizontal jet configuration impinging perpendicularly onto the end-winding, and 2) the vertical jet configuration impinging on the top of the end-winding. Both configurations exhibit similar cooling performances indicating the more pronounced influence of the ferrofluid flow interaction with the magnetic field compared to the influence of the impingement direction. A promising improvement of the cooling performance (up to a doubling) is found if magnetic flux densities on the side of the end-winding becomes larger than 10 mT and the alternating frequencies are sufficiently small to stimulate strong interactions between the ferrofluid flow and the magnetic fields at the end-winding.