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New phase change material battery coolant absorbs 3x as much heat as water

13 July 2012

Cryosolplus
CryoSolplus is a dispersion that can absorb three times as much heat as water, and can prevent batteries from overheating. Click to enlarge.

Researchers at the Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT in Oberhausen have developed a new phase-change material (PCM) coolant that conducts heat away from a traction battery for electric vehicles three times more effectively than water, keeping the battery temperature within an acceptable range even in extreme driving situations.

Avoiding overheating EV battery packs is important to maintaining long service life; operating a battery at a temperature of 45°C instead of 35°C halves its service life. Conventional cooling systems have not reached their full potential, Fraunhofer suggests:

  • Air cooling systems are limited, FraunhoferÚ says, because air can absorb only very little heat and is also a poor conductor of it. What’s more, air cooling requires big spaces between the battery’s cells to allow sufficient fresh air to circulate between them.

  • Water-cooling systems are still in their infancy. Though their thermal capacity exceeds that of air-cooling systems and they are better at conducting away heat, their downside is the limited supply of water in the system compared with the essentially limitless amount of air that can flow through a battery.

Fraunhofer researchers have developed a coolant they call CryoSolplus—a dispersion that mixes water and paraffin along with stabilizing tensides (also known as surfactants: chemical species that act as wetting agents to lower the surface tension of a liquid)—and a dash of the anti-freeze agent glycol. The advantage is that CryoSolplus can absorb three times as much heat as water, and functions better as a buffer in extreme situations such as trips on the freeway at the height of summer.

This means that the holding tank for the coolant can be much smaller than those of watercooling systems—saving both weight and space under the hood. In addition, CryoSolplus is good at conducting away heat, moving it very quickly from the battery cells into the coolant. With additional costs of just €50–100, the new cooling system is only marginally more expensive than water cooling.

As CryoSolplus absorbs heat, the solid paraffin droplets within it melt, storing the heat in the process. When the solution cools, the droplets revert to their solid form (i.e., phase change materials).

The main problem to be overcome during development of CryoSolplus was making the dispersion stable, said Dipl.-Ing. Tobias Kappels, a scientist at UMSICHT. 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 need to 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?

—Tobias 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.

July 13, 2012 in Batteries | Permalink | Comments (8) | TrackBack (0)

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Comments

Hope it helps, but what is the effect of solidifying on flow in cold temperatures? The below freezing mountain top is sometimes only a short drive away.

it looks as fluid as creamy mammoth sc_m...

How do you cool this coolant once it heats up?.. water is reusable is you flow it thru a radiator so you dont need to store much of it.

@Herm,
This is an emulsion of water and wax particles. This "creamy mammoth scvm", as Treehugger so humourously puts it, actually has a consistency similar to milk, so that it will easily flow in and out of a radiator. Whether the wax (paraffin) particles is solid or liquid has no bearing on the flow property of the emulsion. The trick is to keep it in emulsion all the time. If the wax particles aggregrate and clog-up the flow channels of the radiator, then you'll have a big problemhe. So far, the fat droplets in milk stays pretty much emulsified in the milk even after weeks of sitting still.

Water has 4 times more heat capacity than air, on a per pound basis, 3000 times more on a volume basis, which is more relevant.

These values are increased to 12 and 9000 with the CryoSolplus. Very good.

But more air is required through a radiator for the battery-to-cold plate-to-water-to-radiator-to-air system.

An air cooled battery system is simply; battery-to-air; but the battery surface (unless finned) is a poor match to air and cell spacing must be increased.

So water cooling is much more complex (and a battery system does not need to address local hot spots to the degree that an ICE system does).

Is a CryoSolplus system as simple/ troublesome as an ICE cooling system?
So what’s the answer?
- - Watch what the auto makers do.

They know a WHOLE lot more than me about this and more reason to find out what’s most cost effective and marketable.

Very few people currently use water to cool the vehicle ICE. Would this be more effective than common place ant-freeze and sustain +50C to -40C?

@TT,
This technology has not yet been tested in a real vehicle. What remains to be seen is how long can the wax particles stay in emulsion without separating and clog up the cooling channels.

I think that a more practical solution is the use of batteries with lower internal resistance, for example, moving from 20C battery to 40-50 C batteries will produce much less heat, ergo much less cooling needs.

Very few ICEs (except for air cooled motorcycles) use anything BUT a 50/50 water/antifreese mix for coolant.

The mix provides a lowered freezing point and raised boiling point with somewhat less heat capacity (than water alone).

Batteries with lower internal resistance have always been needed for their higher efficiency - heat is wasted energy.

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