Say hello to ionocaloric cooling. It’s a new way to lower temperatures with the potential to replace existing methods of cooling things with a process that’s safer and better for the planet.
Typical refrigeration systems transport heat from a space through a liquid that absorbs heat as it evaporates into a gas, which is then transported through a closed tube and condensed back into a liquid. As effective as this process is, some of the best materials we use as refrigerants are extremely unfriendly to the environment.
However, there are multiple ways in which a substance can be forced to absorb and release heat energy.
A method unveiled last year, developed by researchers at Lawrence Berkeley National Laboratory and the University of California, Berkeley, takes advantage of the way energy is stored or released when a material changes phase, such as when solid ice turns into liquid water. example.
Increase the temperature of a block of ice and it will melt. What we may not see so easily is that melting absorbs heat from the environment, effectively cooling it.
One way to melt ice without having to turn up the heat is to add a few charged particles, or ions. Sprinkling salt on roads to prevent ice formation is a well-known example of this in practice. The ionocaloric cycle also uses salt to change the phase of a fluid and cool the environment.
“The refrigerant landscape is an unsolved problem,” mechanical engineer Drew Lilley of California’s Lawrence Berkeley National Laboratory said in January 2023.
“No one has successfully developed an alternative solution that makes things cold, works efficiently, is safe and doesn’t harm the environment. We think the ionocaloric cycle has the potential to meet all of these goals if realized properly .”
The researchers modeled the theory of the ionocaloric cycle to show how it could potentially compete with or even improve the efficiency of refrigerants in use today. A current flowing through the system would move the ions within it, shifting the material’s melting point and changing its temperature.
The team also conducted experiments using a salt made with iodine and sodium to melt ethylene carbonate. This common organic solvent is also used in lithium-ion batteries and is produced using carbon dioxide as an input. That could ensure that the system is not just GWP [global warming potential] zero but GWP negative.
A temperature shift of 25 degrees Celsius (45 degrees Fahrenheit) was measured by applying less than a single volt charge in the experiment, a result greater than what other caloric technologies have yet achieved.
“There are three things we’re trying to balance: the GWP of the refrigerant, the energy efficiency and the cost of the equipment itself,” says mechanical engineer Ravi Prasher of Lawrence Berkeley National Laboratory.
“From the first attempt, our data looks promising on all three of these aspects.”
The vapor compression systems currently used in refrigeration processes rely on high GWP gases, such as various hydrofluorocarbons (HFCs).
Countries that signed the Kigali Amendment have committed to reducing the production and consumption of HFCs by at least 80 percent over the next 25 years – and ionocaloric cooling could play an important role in this.
Now the researchers must take the technology out of the laboratory and into practical systems that can be used commercially and can be scaled up without problems. Ultimately, these systems could be used for both heating and cooling.
“We have a brand new thermodynamic cycle and framework that brings together elements from different fields, and we have shown that it can work,” says Prasher.
“Now it is time for experiments to test different combinations of materials and techniques to meet the technical challenges.”
The research was published in Science.
An earlier version of this article appeared in January 2023.
