A new way to keep EV batteries cool

Car buyers may think they have seen their last radiator when they trade in their internal combustion engine vehicle for an EV. But not so fast. Many EV batteries must be cooled to avoid overheating when powering significant loads for long periods. And the high-energy batteries deployed in modern EVs may need liquid rather than air cooling to get the job done.

So a recently developed coolant by the name of CryoSolplus is interesting in that it is said to absorb three times as much heat as water. Created by researchers at the Fraunhofer Institute for Environmental, Safety and Energy Technology in Germany, it is a dispersion that mixes water and paraffin along with stabilizing tensides (dispersing and wetting agents) and a small amount of the anti-freeze agent glycol.

Because it has a high heat capacity, CryoSolplus can sit in a holding tank much smaller than those of water cooling systems. Researchers say the new cooling system is only marginally more expensive than water cooling.

As CryoSolplus absorbs heat, solid paraffin droplets within it melt, storing the heat in the process. When the solution cools, the droplets revert to their solid form. Scientists call such substances phase-change materials or PCMs.

“The main problem we had to overcome during development was to make the dispersion stable,” explains Dipl.-Ing. Tobias Kappels, a Fraunhofer scientist. The individual solid droplets of paraffin had to be prevented from agglomerating or – as they are lighter than water – collecting on the surface of the dispersion. They must be evenly distributed throughout the water. Tensides serve to stabilize the dispersion, depositing themselves on the paraffin droplets and forming a type of protective coating.

“To find out which tensides are best suited to this purpose, we examined the dispersion in three different stress situations: How long can it be stored without deteriorating? How well does it withstand mechanical stresses such as being pumped through pipes? And how stable is it when exposed to thermal stresses, for instance, when the paraffin particles freeze and then thaw again?” says Kappels.

Other properties of the dispersion that the researchers are optimizing include its heat capacity, its ability to transfer heat and its flow capability. The scientists’ next task will be to carry out field tests, trying out the coolant in an experimental vehicle.

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