Abstract
Hairpin windings and spray cooling are becoming an increasingly popular combination in the field of high-performance electrical machine design. Machines adopting hairpin windings can achieve higher torque and power densities while enabling them to be manufactured automatically on a large scale to meet the rapid market growth of electric transport. Spray cooling is an effective way for high heat flux removal, which has shown great potentials in electrical machine applications. Although spray cooling has been studied for decades in different engineering applications, the focus had been on investigating its performance on regular surfaces using low-viscosity liquids, such as water. In addition, many existing models for spray cooling heat transfer were built on spray parameters that are difficult to obtain without specialist equipment. Thus, most results from previous studies are difficult to be interpreted and directly applied to electrical machine applications. Practical and economical approaches for estimating the heat transfer coefficients (HTCs) of spray cooling on hairpin windings are needed. This article proposes and validates an experimental approach based on reduced-parameter models that can be applied to predict the HTC of spray cooling setups on hairpin windings.
Highlights
RECENT developments in transport electrification have increased the need for electrical machines with improved performance metrics [1, 2]
As can be seen for some cases, there are some deviations, which may be due to the randomness of the spray distribution
The study has shown that in typical electrical-machine-design environments, reducedparameter models can be established based on specific design constraints, which enable the use of simple experimental setups to determine the constants in the model
Summary
RECENT developments in transport electrification have increased the need for electrical machines with improved performance metrics [1, 2]. The United States Department of Energy (DoE) has established a series of goals to achieve a power density target of 33kW/L and a cost target of $6/kW for a 100 kW electric traction drive system by 2025 [4] To achieve such goals, one of the main trends, especially in the electrification of road transport is to use electrical machines with directly-cooled hairpin windings. The regular geometry of hairpin windings can contribute to heat dissipation when combined with direct oil cooling, where oil is in direct contact with the windings and can flow through the gaps between the hairpins Such combinations show great potential in benefiting the performance-metrics of the machine, there is only a relatively small amount of literature that has been published regarding this topic. The key performance parameters such as HTC (heat transfer coefficient) are not reported
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