Scientists develop a cool new method of refrigeration

This collage depicts elements related to ionocaloric refrigeration, a newly developed refrigeration cycle that researchers hope can help eliminate refrigerants that contribute to global warming. Credit: Jenny Nuss/Berkeley Lab

Adding salt to a road before a winter storm changes when ice will form. Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have applied this basic concept to develop a new method of heating and cooling. The technique, which they have dubbed “ionocaloric cooling,” is described in a paper published Dec. 23 in the journal Science.

Ionocaloric cooling takes advantage of the way energy or heat is stored or released when a material changes phase – such as the change from solid ice to liquid water. Melting a material absorbs heat from its surroundings, while solidifying it releases heat. The ionocaloric cycle causes this phase and temperature change through the flow of ions (electrically charged atoms or molecules) coming from a salt.

Researchers hope the method could one day provide efficient heating and cooling, which accounts for more than half of the energy used in homes, and help phase out current “vapor compression” systems, which use high-potential gases. of global warming as a coolant. Ionocaloric cooling would eliminate the risk of such gases escaping into the atmosphere by replacing them with solid and liquid components.

“The refrigerant landscape is an unsolved problem: No one has successfully developed an alternative solution that makes things cool, runs efficiently, is safe and doesn’t harm the environment,” said Drew Lilley, a graduate research assistant at Berkeley Lab and Ph.D. candidate at UC Berkeley who led the study. “We think ionocaloric cycling has the potential to accomplish all of those goals if done right.”

This animation shows the ionocaloric cycle in action. When a current is added, the ions flow and change the material from solid to liquid, causing the material to absorb heat from the surroundings. When the process is reversed and the ions are removed, the material crystallizes into a solid, releasing heat. Credit: Jenny Nuss/Berkeley Lab

Finding a solution that replaces current refrigerants is essential for countries to meet climate change goals, such as those in the Kigali Amendment (accepted by 145 parties, including the United States in October 2022). The agreement commits signatories to reduce the production and consumption of hydrofluorocarbons (HFCs) by at least 80% over the next 25 years. HFCs are potent greenhouse gases commonly found in refrigerators and air conditioning systems and can trap heat thousands of times more effectively than carbon dioxide.

The new ionocaloric cycle joins several other types of “caloric” cooling in development. These techniques use various methods—including magnetism, pressure, stretching, and electric fields—to manipulate solid materials so that they absorb or emit heat. Ionocaloric cooling varies by using ions to induce solid-to-liquid phase changes. Using a liquid has the added benefit of making the material pumpable, making it easier to get heat in or out of the system—something solid-state cooling has struggled with.

Lilley and corresponding author Ravi Prasher, a research associate in Berkeley Lab’s Energy Technologies Area and assistant professor of mechanical engineering at UC Berkeley, laid out the theory underlying the ionocaloric cycle. They calculated that it has the potential to rival or even exceed the efficiency of gaseous refrigerants found in most systems today.

They also demonstrated the technique experimentally. Lilley used a salt made of iodine and sodium, along with ethylene carbonate, a common organic solvent used in lithium-ion batteries.

“There is potential to have refrigerants that are not just GWP [global warming potential]-zero, but GWP-negative,” Lilley said. “Using a material like ethylene carbonate can actually be carbon negative because you produce it using carbon dioxide as an input. This could give us a place to use CO2 from carbon capture.”

The current flowing through the system moves the ions, changing the melting point of the material. When it melts, the material absorbs heat from its surroundings, and when the ions are removed and the material solidifies, it returns the heat. The first experiment showed a temperature change of 25 degrees Celsius using less than one volt, a greater temperature increase than demonstrated by other caloric technologies.

“There are three things we’re trying to balance: the GWP of the refrigerant, the energy efficiency and the cost of the equipment itself,” Prasher said. “From the first exam, our data looks very promising for all three of these aspects.”

While caloric methods are often discussed in terms of their cooling power, cycles can also be used for applications such as water heating or industrial heating. The ionocaloric team is continuing work on prototypes to determine how the technique can be scaled to support large amounts of cooling, improve the amount of temperature change the system can support, and improve efficiency.

“We have this whole new thermodynamic cycle and framework that brings together elements from different fields, and we’ve shown that it can work,” Prasher said. “Now, it’s time for experiments to test different combinations of materials and techniques to meet engineering challenges.”

Lilley and Prasher have received a provisional patent for the ionocaloric refrigeration cycle and the technology is now available for licensing.

More information: Drew Lilley et al, The Ionocaloric Refrigeration Cycle, Science (2022). DOI: 10.1126/science.ade1696

Provided by Lawrence Berkeley National Laboratory

Citation: Scientists develop new cool method of refrigeration (2023, January 4) Retrieved January 5, 2023 from https://phys.org/news/2023-01-scientists-cool-method-refrigeration.html

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