While every electric vehicle (EV) owner deals with the so-called drive range anxiety, the idea of charging their EVs swiftly, as in way faster than any currently available chargers, could be the equalizer. No less than the US National Aeronautics and Space Administration (NASA) recently reported it was undertaking a project involving an advanced temperature control technique. The project was developed for future NASA missions and can also make charging EVs faster and more accessible, potentially paving the way for increased adoption of electric cars.
Future NASA space missions will involve complex systems that must maintain specific operating temperatures. These systems—including nuclear fission power systems for missions to the moon, Mars, and beyond, vapor compression heat pumps to support lunar and Martian habitats, and systems to provide thermal control and advanced life support onboard spacecraft—will require advanced heat transfer capabilities to execute the needed thermal management.
A team sponsored by NASA’s Biological and Physical Sciences Division is developing new technology that will achieve not only orders-of-magnitude improvement in heat transfer to enable these systems to maintain proper temperatures in space, but also significant reductions in the size and weight of the hardware. Moreover, this same technology may make owning an electric-powered car here on Earth easier and more feasible.
Applied on the ISS
Led by Issam Mudawar, Purdue University’s Betty Ruth, and Milton B. Hollander, Family Professor of Mechanical Engineering, the team has developed the Flow Boiling and Condensation Experiment (FBCE). It will enable two-phase fluid flow and heat transfer experiments in the long-duration microgravity environment on the International Space Station (ISS).
The FCBE’s Flow Boiling Module includes heat-generating devices mounted along the walls of a flow channel into which coolant is supplied in a liquid state. As these devices heat up, the temperature of the liquid in the channel increases, and eventually, the liquid adjacent to the walls starts to boil. The boiling liquid forms small bubbles at the walls that depart from the walls at high frequency, constantly drawing liquid from the inner region of the channel toward the channel walls. This process efficiently transfers heat by taking advantage of the liquid’s lower temperature and the change of phase from liquid to vapor. This process is greatly enhanced when the liquid supplied to the channel is in a subcooled state (well below the boiling point). This new “subcooled flow boiling” technique results in significantly improved heat transfer effectiveness compared to other approaches and could be used to control the temperatures of future systems in space.
FBCE was tested and delivered to the ISS in August 2021 and began providing microgravity flow boiling data in early 2022. Results from the FBCE will enable the design of future space systems that require temperature control. However, this technology also has applications on Earth—specifically, on EV charging.
Faster, safer electric vehicle charging
Before electric cars can become widely used, specific challenges must be overcome. First, a network of charging stations must be deployed along highways and roads to enable EV charging. Second, the time required to charge a vehicle must be reduced. Currently, charging times vary widely, from 20 minutes at a station alongside a roadway to hours using an at-home charger. Lengthy charging times and charger location have been cited as major issues hindering EV ownership.
An EV charging system contains a charging cable ending with a plug inserted into the vehicle’s charging inlet. The electrical current supplied through the charging cable is delivered to the battery inside the vehicle, which powers the vehicle’s electric motor. The passage of electrical current through any conductor results in a finite amount of heat generation, and the higher the current, the greater the heat generated. A charging station conductor typically consists of a bundle of wires. Due to temperature limits, charging cables for conventional, 350-ampere, “fast charging” systems require sizable conductors, rendering the charging cable quite heavy and inconvenient for customers to maneuver. The cable weight is also increased by the large charging connector and liquid coolant passing through the cable to remove the heat.
Reducing the charging time for EVs to five minutes (an industry goal) will require charging systems to provide current at 1,400 amperes. Advanced chargers only deliver currents up to 520 amperes, and most chargers available to consumers support currents less than 150 amperes. Charging systems providing 1,400 amperes will generate significantly more heat than current systems, however, and will require improved methods to control temperature.
That’s where the FBCE comes in. Mudawar’s team applied the “subcooled flow boiling” principles learned from NASA’s FBCE to the EV charging process. As such, dielectric (non-electrically conducting) liquid coolant is pumped through the charging cable, where it captures the heat generated by the current-carrying conductor. Subcooled flow boiling allows the team to deliver 4.6 times the current of the fastest available EV chargers on the market today by removing up to 24.22 kw of heat. Purdue’s charging cable can provide 2,400 amperes, far beyond the 1,400 amperes required to reduce the time needed to charge an electric car to five minutes.
Applying FBCE has reduced the time necessary to charge an EV to unprecedented levels, and if put to widespread use, may remove one of the critical barriers to worldwide EV adoption. (Story and photos courtesy of NASA Glen Research Center and Purdue University/Jared Pike)