Saturday, July 14, 2012

Cooler Batteries Will Prevail

Published July 14, 2012

By Philippe Crowe

Have you ever wondered how EV batteries react to the intense heat found either under the hood or inside battery compartments?

German researchers from the Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT (UMSICHT) studied the matter.

Most of today’s batteries are vented, but hardly cooled at all; when cooled, they are more often than not air-cooled in a basic way.

Air, the researchers said, isn't a very efficient absorber of heat and its circulation needs wide spaces between the batteries. Water is a better heat conductor, but needs a large storage tank, which is impractical, especially when one considers the swappable battery systems some EVs rely on.

Batteries operating between 110 and 120 degrees Fahrenheit, as in a normal drive on a summer day, can halve their service life. It is important to know that the top end of a battery comfort zone is between 70 and 95 degrees Fahrenheit.

So, you guessed it; those clever German researchers found a solution. Enter CryoSolplus, a coolant developed by the Fraunhofer Institute researchers.

CryoSolplus is a mix of water, paraffin, anti-freeze and a stabilization agent. It can absorb between two and three times as much heat as water, depending on the temperature being used at and the mix chosen.

The novelty of the product is the use of paraffin a special stabilization agent developed by the team. The paraffin melts as it absorbs heat, contributing to a faster heat transfer. In turn the paraffin goes back to its solid state when cooled. The stabilization agent keeps the paraffin from clumping into one big blob within the liquid during the cooling process, which would otherwise clog cooling passages. It also prevents the droplets of paraffin from floating at the surface of the mix as paraffin is naturally lighter than water.

“The main problem we had to overcome during development was to make the dispersion stable,” explained Tobias Kappels, a scientist at UMSICHT.

More research is needed before we can see this product used in production. “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?” declared Kappels.

The UMSICHT team estimates the cost of integrating CryoSolplus at 50 to 100 euros, making it marginally more expensive than water cooling.

Researchers are currently studying CryoSolplus’ capacities in transferring heat, optimizing its flow capabilities and validating how it reacts to high heat levels.

Afterwards, the team will test CryoSolplus in an experimental vehicle.

Keeping electric vehicle batteries cool


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