July 15, 2012
Coolant Helps Keep Electric Vehicle Batteries Cooler
Brett Smith for redOrbit.com - Your Universe Online
The service life of electric car batteries is cut in half when operating between 110 and 120 degrees Fahrenheit, the temperature they reach on a typical a summer day.
To solve this problem, a team of German researchers at the Fraunhofer Institute for Environmental, Safety and Energy Technology developed a new coolant called CryoSolplus, which is capable of absorbing between two and three times as much heat as water.
CryoSolplus is a mix of water, anti-freeze and a stabilization agent. It also uses paraffin, which melts as it absorbs heat. This change from a solid form to a liquid form contributes to the coolant´s heat transfer capabilities. When the coolant system shuts down, the paraffin goes back to its solid state.
The stabilization agent is a key ingredient in CryoSolplus because it keeps the paraffin from clumping within the liquid and prevents the system´s cooling passages from becoming clogged.
“The main work of the research so far was to get a stable dispersion – that´s very critical and it wasn´t easy, because when it´s not at the right concentration, the paraffin tends to agglomerate and plug the pipes,” said project lead Tobias Kappels.
“If you have microencapsulated particles, it´s possible to damage the particles. Then the paraffin gets out into the water. But because we have surfactants, they always get back to the paraffin particle, and it´s refreshed, it´s stable and there will be no wear.”
In testing the new coolant, the research team had three main questions: “How long can it be stored without deterioration?”, “How well can it withstand mechanical stress from pumping through pipes?” and “How well can the paraffin droplets melt and solidify repeatedly?” said Kappels.
In addition to increasing the coolant´s shelf life, durability, and repeatability of use–the researchers are trying to optimize the heat capacity, its ability to transfer heat and its flow capability.
Currently, batteries are either not cooled at all or they are air-cooled. Batteries without cooling systems are often swapped out for a fully charged replacement at service stations.
According to the researchers, air isn't a very efficient absorber of heat because it needs wide spaces to circulate around the batteries. Water is a much better conductor of heat, but a water-based system needs a large storage tank and a way to keep the water from coming in contact with the battery´s electrodes. A water coolant system also has a limited supply of water to absorb heat.
Another positive aspect of the coolant is that less of it is needed to effectively cool the battery–only about 5.2 gallons, compared with around 15 gallons required for a water-based system. This means that the holding tank for the coolant can be much smaller, which saves both weight and space. Kappels acknowledges that the amount of coolant needed would add around $60 to $120 to the price of an electric car battery.
According to the researchers, they will begin field testing the new coolant and trying it out in an experimental vehicle.