To cool solidly without warming the planet

To cool solidly without warming the planet

The operation of vapor compression cycles requires energy, and is currently responsible for nearly 20 percent of the electricity consumption of buildings worldwide.

It’s a real dilemma how to keep cool on hot and humid summer days without turning to conventional air conditioning, which consumes huge amounts of electricity and emits strong climate-changing greenhouse gases. The answer potentially involves a new class of solid-state refrigerants that could enable energy-efficient and emission-free cooling. Researchers at Harvard University’s Department of Chemistry and Chemical Biology have developed an environmentally friendly mechanism that enables solid-state cooling using two-dimensional perovskites. Their results were presented in a new study published in the journal Nature Communications.”Moving away from vapor compression systems, which have been used for a very long time, is a key part of the overall drive towards a more sustainable future. We are focused on looking deeply into the intrinsic properties of these materials to see what is possible in terms of solid-state cooling as a sustainable alternative.” – said Jarad Mason, lead author of the study. Two-dimensional perovskites, also known as barocaloric materials, emit and absorb heat during their expansion and contraction in response to pressure changes. The effect is based on a phenomenon you may be familiar with if you’ve ever inflated a balloon and felt the material heat up with your lips. Similarly, these materials also give off heat when they are put under pressure or under tension. Without producing harmful emissions, this mechanism can conduct heat in the solid at low driving pressure.The new mechanism of solid-state cooling is able to overcome the limitations of traditional vapor compression cooling technology, which has remained largely unchanged since the beginning of the 20th century. Any cooling system goes through a cycle from a low-entropy state, when the material can absorb heat, thereby cooling the space, to a high-entropy state, when this energy can be released in a heat sink, where it is dissipated. Vapor compression air conditioners circulate a volatile liquid refrigerant that evaporates and condenses at varying pressures through metal coils to cool the enclosed space and release heat. The operation of vapor compression cycles requires energy, and is currently responsible for nearly 20 percent of the electricity consumption of buildings worldwide. Additionally, leaking refrigerants are more than 1,000 times more potent greenhouse gases than carbon dioxide. The research team identified two-dimensional perovskites as an ideal replacement material because they undergo phase transitions that can be operated reversibly under minimal pressure while remaining in the solid state. The more a substance can change its entropy, the more effective it can be in operating refrigeration cycles. Because organic bilayer materials are capable of large entropy changes when their hydrocarbon chains switch between ordered and disordered states, the research team expected that two-dimensional perovskites could serve as highly tunable solid-state refrigerants that could operate at lower pressures than previously thought possible. The team synthesized the materials in their laboratory and tested them in a high-pressure calorimeter to measure changes in heat flow in the material at different pressures and temperatures. These experiments show how much heat can be dissipated in a potential cooling circuit and how much pressure is required for reversible operation of the cycle.”Once we started testing the material, we realized that we could remove a very large amount of heat with a very small change in pressure. From then on, we knew we were going to have something interesting here,” Mason said. The researchers also performed high-pressure X-ray powder diffraction experiments to understand the phase changes at the molecular level. With the help of the X-ray synchrotron, the researchers were able to characterize how the structure of individual materials changes at different temperatures and pressures.”These materials are worth studying beyond their promising performance. They may also be useful for chemists to understand the fundamental properties that are critical to scale up this technology,” said the lab’s Jinyoung Seo. The Mason Lab next plans to build barocaloric refrigeration prototypes as it continues to investigate potential uses for different materials. “We will probably use next-generation materials for the prototype device. We will try to come up with new technologies to solve the cooling challenge,” Seo noted, according to the Harvard Gazette.

Hardware, software, tests, interesting and colorful news from the world of IT by clicking here!

Leave a Comment

Your email address will not be published.