In the middle of the night, the low-pitched humming sound from the fridge compressor is likely the most common noise in every household. The fridge's cooling system compresses and circulates the refrigerant vapor, removing heat from inside the refrigerator.
But this traditional cooling technology is facing a challenger. In a study reported in the journal Science, a team of researchers at the University of Texas at Dallas (UT Dallas) has come up with a brand new refrigeration method that relies on twisted and coiled elastic fibers.
Although most of the current fridges and air conditioners no longer use Ozone depleting refrigerants such as chlorofluorocarbons (CFCs), but the coolants inside them can create a strong greenhouse effect and pose a health hazard if they leak. Moreover, traditional compression-based systems already reach their maximum cooling efficiency, which is about 60%.
According to the UT Dallas team and their collaborators in the U.S. and China, the innovative solid-state cooling system uses no liquid refrigerants but twisted fibers made out of elastic materials, such as natural rubber, nickel-titanium wires, and polyethylene fishing line. When the coiled fibers become untwisted and stretched, their surface temperature drops, creating a cooling effect due to the change in entropy of the materials. This so-called "twistocaloric" process can produce a theoretical cooling efficiency of up to 84%.
In an email interview, LabRoots reached out to Dr. Ray Baughman, a Chemistry Professor and the Robert A. Welch Distinguished Chair in Chemistry at UT Dallas, who is also the corresponding author behind the paper. He talked about what inspired them to look into solid-state cooling of twisted fibers.
"Our discovery of twistocaloric cooling was accidental. We had previously discovered that ordinary polymer fibers provide powerful artificial muscles that can be thermally driven," Baughman referred to one of their publications back 2014 which described artificial muscles made with fishing line and sewing thread.
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In the current study, the chemistry researchers successfully built a prototype fridge that's based on nickel-titanium fiber. It can cool flowing water by 7.7°C in a single cycle. But they won't just stop there. "We have already made improved prototypes that will be described in future publications, and our work on making improved coolers is continuing," said Baughman.
"Additionally, while our original work used fibers that are commercially available, we are presently optimizing twistocaloric properties by using specially prepared yarns and fibers," he added.
Material fatigue, the deterioration and weakening of structure, can happen to a material after it has performed repeated, cyclic work. "Material fatigue is a problem for previously investigated mechanocaloric materials, considering the enormous number of cycles needed for the over ten year lifetime for conventional refrigerators," said Baughman. "We have not yet encountered the fatigue problem since we have at present investigated only a few thousand cycles. However, we will thoroughly investigate this issue in future work, and correspondingly optimizes our selection of twistocaloric yarns and fibers."
In a press release, Dr. Baughman also commented on the prospective development and potential commercialization of their solid state fridge idea.
“Many challenges and opportunities exist on the path from these initial discoveries to (the) commercialization of twist fridges for diverse large- and small-scale applications,” he said. “Among the challenges are the need to demonstrate refined devices and materials that provide application-targeted cycle lifetimes and efficiencies by recovering part of the inputted mechanical energy. The opportunities include using performance-optimized twistocaloric materials, rather than the few presently studied commercially available candidates.”
Source: Ars Technica