58 January/February 2024 | E-Mobility Engineering Nick Flaherty explains the advantages of immersion cooling and the various forms that approach can take Flow motion Immersive cooling can significantly improve the performance of e-mobility powertrain designs, allowing higher charging and discharging rates and extending the life of battery packs by keeping the temperature of battery cells under much tighter control. Immersive cooling technology is being adopted in the data centre, with dielectric fluids covering processor boards to carry heat away from higher performance chips. The same approach is being used for electronic control units (ECUs), battery packs and even motors in vehicle designs. This cuts out many elements of a traditional liquid cooling system, such as the cold plates that are inserted in battery packs or the heat sinks for power electronics, reducing the weight of the powertrain. The use of immersive cooling can also allow components to be closer together, reducing the overall size of the powertrain. There are several different ways of implementing immersive cooling. One of these is employing single phase dielectric fluids that can carry away heat from a battery pack, using a radiator to disperse the heat. Dual phase liquids close to their boiling point are also used to take the heat from cells to turn into a gas that is then recovered in a condenser. The move to using hydrogen also opens up the opportunities to use the liquid hydrogen as a coolant in battery packs and even in motors before being used by a fuel cell stack to produce power. The adoption of immersive cooling also puts more pressure on the design of the fluid conveyancing systems, whether by hoses or steel or aluminium pipes, around a vehicle. Single phase cooling Single phase cooling uses a dielectric fluid with a high thermal capacity to carry heat away. The fluid has to be insulating so that it can be used with the electronics in a battery pack such as temperature, voltage and current sensors, and also for the busbars that carry large amounts of current. The viscosity of the fluid is key for the ability to pump the dielectric around the pack and to the radiator. “We started almost five years ago with a couple of research projects,” said Andrew Ennever head of electrification at Ricardo which has developed several immersion systems. “Immersion cooling was an opportunity to improve thermal performance,” he explained. In 2021, Ricardo joined the Inception collaborative research project, led by Blue Bear Systems (now Green Jets). The Inception project’s objective was to develop a highly power-dense, zero emission, quiet and efficient aircraft propulsion module. “We developed a highly power dense immersion cooled battery pack, that wraps around the inner surface of the propulsion module nacelle. The pack is made up of 32 extremely lightweight bonded composite and foam modules, each module containing 48 Molicel cells,” added Ennever. The immersion cooling allows the significantly higher operating temperature of 75 C and faster charging at 6C rates if the cell chemistry allows without getting too far above the operating temperature. This higher charging rate is key for a fast operational turnaround on the ground to recharge the batteries of a UAV. Immersion cooling also extends battery lifetime due to even temperature distribution in the A dual phase cooling system (Image courtesy of Carrar)
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