Researchers at the Fraunhofer Institute for Environmental, Safety and Energy Technology are working on a super coolant by the name of CryoSolplus. It is a dispersion that mixes water and paraffin along with stabilizing tensides and a dash of the anti-freeze agent glycol.
CryoSolplus advantage is it can absorb three times as much heat as water, and functions better as a buffer in extreme situations. Water has about 4 times the heat capacity of air, on the basis of mass or weight and 3000 times more on basis of volume, a more relevant relationship when the weight s a consideration.
Those values would be increased to beyond 12 by mass and 9000 by volume using the CryoSolplus material. That offers impressive engineering advantages.
The motive the Fraunhofer group is keyed upon is the damage heat has on the batteries of electric vehicles. Just driving fast on the freeway in summer temperatures can overheat the battery pack.
If batteries are to have a long service life, overheating must be avoided. Most batteries’ longevity and productive range lies between 20°C and 35°C. So an EV drive in the midday heat of summer can push a battery’s temperature well beyond that range. The long-term damage caused can be serious: operating a conventional battery at a temperature of 45°C instead of 35°C cuts its service life by half.
EV batteries are expensive; a new one can cost as much as half the price of the entire vehicle purchase price. That’s why it is so important to keep them cool. It’s a very good motive.
Conventional cooling systems have not reached their full potential: either the batteries are not cooled at all – which is the case with ones that are simply exchanged for a fully charged battery at the “service station” – or they are air cooled.
But air can absorb only a small amount of heat and is also a poor conductor of it. Moreover, providing air-cooling requires big spaces between the cells in the battery pack to allow sufficient fresh air to circulate between them. Water-cooling systems are still in early development. Though the water 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.
The Fraunhofer group is working at their option being available for keeping batteries cool. Along with the mass carrying and volume advantage for managing heat, the holding tank for the coolant can be much smaller than those of water-cooling 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.
The added costs are estimated at just 50 to 100 euros, making the new cooling system only marginally more expensive than water-cooling.
The technology of CryoSolplus is as it absorbs heat; the solid paraffin droplets within it melt, storing the heat in the first stage of the process. At the second stage when the solution cools, the droplets revert to their solid form. Quite simple in an explanation.
Scientists call such substances “phase change materials” or PCMs.
Dipl.-Ing. Tobias Kappels, a scientist at Fraunhofer explains, “The main problem we had to overcome during development was to make the dispersion stable.” The individual solid droplets of paraffin had to be prevented from agglomerating (clumping up into large masses) and, as they are lighter than water, from collecting on the surface of the dispersion. They also need to be evenly distributed throughout the water. The 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?” said 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.
Other useful points would be the new coolant would add a mass reserve of heat that would allow an insulated battery a longer wait time and a more efficient means of operating in cold conditions.
The hard part is to keep the paraffin in that small flowing droplet type of solution. If that can be managed at low cost at a wide range of temperatures for a long lifetime the potential of the new coolant is huge. Clumping up or clogging simply has to be solved in a permanent way. Once that is solved the coolant also offers itself as a means to move heat and the energy it contains.
The first market choice looks like the EV market. But if the technology is good enough a lot of other markets are going to needing the technology as well.
The group needs encouraged. Homogenizing paraffin into water and keeping it that way is not an easy task, but it sure looks worthwhile. Good luck over there.