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Cooling technique could boost motor lives and efficiencies

05 March, 2020

Researchers at the University of Sheffield in the UK have embarked on a two-year project aimed at developing a novel liquid cooling technology for electrical machines that could cut end-winding temperatures by more than 30°C compared to forced-air-cooled machines with rotor-mounted fans. The technique could boost machine efficiencies and prolong their lives.

The research, backed by a £461,859 ($596,000) grant from the Engineering and Physical Sciences Research Council (EPSRC), will focus on cooling end-windings which are often the hottest part of a machine and thus have the biggest impact on efficiencies, power densities and lifespans.

Existing cooling methods such as spray cooling or flooding the stator can be effective because the cooling fluid is in direct contact with the windings. But spray-cooling suffers from reliability and robustness issues due to corrosion and erosion of the nozzles. And both techniques also need a closed-circuit liquid supply involving pumps and filters that add to the capital and running costs, while also reducing power densities.

The researchers from Sheffield’s Department of Electronic and Electrical Engineering are therefore hoping to develop a novel thermomagnetic liquid cooling technology based on an electrically non-conductive, temperature-sensitive ferro-fluid, consisting mainly of ferromagnetic nanoscale particles such as iron, cobalt and nickel, suspended in a liquid carrier such as synthetic oil.

When these liquids experience variations in temperature under the influence of an external magnetic field, they behave as smart fluids with higher magnetisation in the cooler region (further away from the heat source) than in the hotter region. As a result, a net magnetic force is produced, causing the fluid to flow towards the hotter area. This, the researchers hope, will result in a self-regulating, pumpless and maintenance-free method of cooling that could be extremely cost-effective.

As well as achieving a significant cooling effect, the technique could the extend the lives of electrical machines because a 10°C decrease in temperature can double the lifespan of winding insulation and have a similar effect on bearing lives.

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