Cooling components more effectively to make electric cars cheaper

(03-02-2022) In his doctorate, Ilya T'Jollyn investigated how two-phase cooling of components can be further optimised.

To combat climate change, greenhouse gas emissions must be greatly reduced in all sectors. In the transport sector, various options for reducing CO2 emissions are being considered, such as combustion engines running on hydrogen or biofuels. For vehicles, the most common strategy is to switch to electric propulsion with batteries that can be charged with renewable electric energy.

Electric cars currently have several disadvantages compared to combustion engine vehicles, such as a lower driving range and higher cost. These disadvantages can be countered by making the electric powertrain (motor, power electronics and battery) more compact and cheaper without losing power. One of the bottlenecks here is the cooling, which has to ensure that the components do not overheat. Better cooling systems are therefore required.

"In my PhD, I investigated two-phase cooling. In this form of cooling, a liquid (phase 1) coolant comes into contact with components that generate heat. The coolant will start boiling and transition into a gas (phase 2). The boiling process in the coolant provides better cooling compared to single-phase liquid cooling (immersion in a liquid with a high boiling point, the liquid will not boil in this form of cooling and therefore will not evaporate)." says Ilya.

"However, two-phase cooling also involves a risk. If the heat transfer from a component to the coolant rises above a maximum value (the critical heat flux), a layer of gaseous coolant will cover the entire surface of the component. This layer acts as thermal insulation, drastically decreasing the heat transfer and resulting in overheating and failure of the component.", Ilya continues.

Although heat transfer during boiling has been studied for a long time, there is no consensus yet about which heat transfer mechanisms are dominant. This lack of fundamental knowledge makes it difficult to predict heat transfer and design two-phase cooling systems.

"In my research, I chose to study the coolant FK-649, a fluoroketone. The results prove that two-phase cooling with FK-649 is feasible, but that it is not yet an improvement over current state-of-the-art cooling methods. A modelling study shows that alternative refrigerants operating at higher pressure have even more potential for cooling than FK-649."

"My research contributes to more effective two-phase cooling of components, which can also reduce the sales price of electric cars." concludes Ilya.

Read a more detailed summary or the entire PhD

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PhD Title: Assessment of Nucleate Pool Boiling Heat Transfer and Critical Heat Flux for Power Electronics Cooling with a Low-GWP Refrigerant

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Contact: Ilya T'Jollyn, Michel De Paepe

Ilya T'Jollyn

Ilya T'Jollyn (°1992) obtained his Master's degree in Electromechanical Engineering at the University of Ghent in 2014. He joined the research group Sustainable Thermo-Fluid Energy Systems as a project engineer and subsequently worked on several research projects. In 2016, he spent four months at the University of Girona for a research stay. From 2017, he started in a new position as teaching assistant and PhD student in the same research group.

His research is on heat transfer in electrical machines and systems, with a focus on two-phase cooling of power electronics and innovative cooling methods for electric motors. During his research activities, he has authored six publications in international journals (one as first author and five as coauthor) and 22 conference papers. He is also co-inventor of a patent on heat transfer in underground marine cables.

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Editor: Jeroen Ongenae - Final editing: Ilse Vercruysse - Illustrator: Roger Van Hecke