Faster charging times will juice electric vehicle adoption
Electric vehicles (EVs) are expected to become dominant in the automobile market in the foreseeable future. This development will require not only a network of charging stations along highways and roads but also faster charge-ups at those stations. In turn, quicker charge-ups will necessitate a significant increase in the electrical current passing through the charging cable — which unfortunately goes hand in hand with a tenfold or more increase in heat. We’ve developed a way to dissipate that heat for highly accelerated EV battery charging — boosting driving range; decreasing consumer anxiety; and avoiding large battery packs, thereby reducing vehicle size and weight and enhancing efficiency.
With our novel solution, consumers can simply charge their vehicles multiple times en route to their destinations while spending minimal time at charging stations — similar to how drivers fill up petroleum-based vehicles. People using our solution won’t have to plan to charge their vehicles ahead of time, or even think about it too much. Have a “low battery” alert? Just stop by a charging station, and recharge your car in a few minutes to drive a few hundred more miles.
Developments in modern technologies — like computers, data centers, hybrid and electric vehicles — and in aerospace and defense are becoming more dependent on the ability to remove enormous amounts of heat from increasingly tighter volumes. For decades, thermal management and heat dissipation were accomplished through a variety of air cooling schemes.
With the greater miniaturization of electronic and power devices, attention turned to liquid cooling, which relies on the superior cooling properties of liquids compared with air. But with ever more stringent requirements for heat dissipation in close quarters, even liquid cooling began to falter in its ability to maintain acceptable system temperatures.
This trend has prompted designers in recent years to transition from cooling systems using pure liquid to what is called a liquid-to-vapor phase change. With pure liquid cooling, the cooling captures the heat and itself incurs a temperature rise, and the coolant is then routed to a remote heat exchanger, where the heat is removed, returning the liquid temperature to its initial value and preparing for a new cooling cycle. With liquid-to-vapor phase change cooling, a coolant — initially in liquid state — captures the heat by capitalizing mostly on vaporization. This removes much larger amounts of heat while maintaining lower system temperatures.
With these enormous cooling benefits, it is possible to use a much smaller wire diameter inside the charging cable while dissipating an even higher current. The large increase in current flow translates to much faster charging of a vehicle at a station, as well as a reduction in wire weight so the charging cable, comprised of a bundle of these wires, is easier for customers to handle.
Building on my 37 years of research in developing liquid-to-vapor thermal solutions for consumer and aerospace applications, we are using this method to greatly decrease charging times for EVs. The liquid coolant is enclosed within the charging cable that carries the wires that deliver electrical current to the vehicle battery. The heat dissipated by the wires during charging increases the liquid coolant’s temperature, and some of the liquid is converted to vapor. This allows for very high rates of heat removal from the conductor wires — more than 10 times the rate of liquid cooling — while maintaining low wire temperatures.
And we’re not done yet. Aided by Purdue Engineering doctoral student Devahdhanush Vijayaraju Swathibanu and with contributions from former Purdue doctoral student Seunghyun Lee (now an assistant professor at South Korea’s Gwangju Institute of Science and Technology), we think we can increase the current even more by modifying both the state of incoming liquid and the design of the cooling space around the conductor wires in the charging cable.
Already, we have demonstrated the ability to tackle currents in excess of 2,400 amperes, compared with 500 amperes in competing advanced technologies. Our technology provides the capability to fully charge an EV in far less than the industry goal of five minutes.
Issam Mudawar, PhD
Betty Ruth and Milton B. Hollander Family Professor of Mechanical Engineering
School of Mechanical Engineering
College of Engineering, Purdue University