UT Dallas research team creates fridge with a twist


Tuesday, January 28, 2020

By twisting small fibers, UT Dallas researchers have created a new device for producing changes in temperature. Years from now, it may change the way we cool things down.



Interested in research? Fascinated by chemistry, engineering, and technology? Studying at the University of Texas Dallas (UTD) might be the perfect opportunity for you to be able to earn your bachelor’s, master’s, or doctoral degree (PhD) in chemistry. We’ll go through a UTD’s chemistry research team’s recent findings to show you why studying at UTD is the way to go.

Research scientists at the University of Texas Dallas have developed a new approach to cooling things down—by understanding that twisting and untwisting fibers can result in changes in temperature. 

Let’s look at an example. As a thin rubber strand is twisted tightly, the strand gets quite hot. As the rubber untwists, it cools down. UT Dallas researchers attached fibers such as rubber to a motorized twister that then applied torsional force. The scientists demonstrated their twist on rubber, fishing lines and nickel titanium wire—the same kind of wire used in dental braces.

A cooling effect has been observed in all of them. The UTD team collaborated with scientists at Nankai University in China in order to produce a cooling device prototype. They call it a “twist fridge.” The findings were recently published in the journal Science

This is the first time that research scientists have found that twisting and untwisting fibers can cause cooling. 

In the research paper, scientists demonstrated the effects of twist—also known as torsion—on a small scale. The cooling device is a thin tube as long as a ballpoint pen. A few nickel titanium fibers are contained within it.

The device can cool about one gram of water by almost 14 degrees Fahrenheit after one twist-untwist cycle. Today’s fridges keep contents around 40 degrees cooler than their surroundings. The research team is working on improvements to lower temperatures even further. In theory, they might be able to cool temperatures more by linking several devices together.

“We’ve already had inquiries from commercial manufacturers for refrigerators interested in our work,” shares Ray Baughman, a chemistry professor at UTD and one of the authors of the paper. Baughman teaches chemistry courses at the undergraduate and graduate level at UTD for students who are earning their bachelor’s, master’s, and doctoral degree (PhD) in chemistry.

Baughman estimates that in a few years, twist-untwist cooling may be used in special cases when conventional fridges can’t be made small enough to work. Applications could include portable coolers for camping and the cooling of electronic devices such as computers and cellphones. It will most likely be another decade before the twist fridge competes with conventional refrigerators found in kitchens. 

The UTD research finding is “definitely high-quality” says Jun Cui, a materials science professor at Iowa State University. Cui, who was not involved in the study says previous studies had explored stretching and unstretching metallic fibers to get a similar effect. 

However, stretching fibers poses a number of problems.
  1. Stretching takes much more effort than twisting to produce the same cooling effect.
  2. To get a reasonable cooling effect from stretching alone, there must be room to stretch rubber by four to six times its length.
UTD researchers stretched the rubber a bit after twisting but Baughman says that twisting the fiber reduces the extent to which it must be stretched by about a sixth. 

Twisting fibers is just the latest approach to replace today’s cooling methods in refrigerators and air-conditioning units. 

Typical refrigerators cool by evaporating a liquid into a gas to dissipate heat from inside the fridge. The gas is compressed then condensed into liquid through coils outside the fridge. This causes the heat siphoned from the refrigerator to be expelled outside.

Why does this UT Dallas' technology research matter?

Refrigeration and air conditioning, which rely primarily on this vapor-compression cooling, use a fifth of the world’s electricity. This usage is expected to grow as developing countries prosper and as the planet continues to warm, according to the International Institute of Refrigeration (IIR). 

“Conventional vapor-compression, I think, has reached the end of its potential,” says Cui. “If we want anything better, more efficient or less environmentally unfriendly, we really need a new platform.”

The twist fridge shows signs of being moderately more efficient than vapor-compression systems. Given the cooling industry’s immense electricity consumption, “if you can make a fridge that’s 7% more efficient than conventional fridges, what an impact it’d have,” shares Baughman. 

The twist fridge also cuts out conventional fridges’ most direct environmental impact: cooling fluid. Coolants used in refrigerators and air-conditioning units are hydrofluorocarbons—greenhouse gases that are often thousands of times more potent than carbon dioxide. 

These gases should remain sealed in the fridges’ coils, but there are paths of the system that can leak. For big systems with long paths along which the coolant must flow—such as those found in supermarkets—leaks here and there can amount to large emissions.

Household refrigerators tend to be leak-tight. However, these fridges are often discarded without regard for the coolants inside. As a result, refrigerants escape into the atmosphere.

The twist fridge has a promising start, but it will be difficult to reach commercial viability because, currently, it is most applicable for very small pieces of equipment.

There’s also lots of question about how long fibers can last when they are constantly being twisted. UT Dallas researchers have shown only that nickel titanium fibers can survive a thousand twists. In order to last the typical lifetime of a decade or so, the fibers will need to be twisted and untwisted much more.

Cui points out that damage to the fibers isn’t a dealbreaker. For a normal refrigerator, the water filter needs to be changed every so often. Sometimes it has to be changed every half year. That’s not damaged material! It’s normal.

For now, no one knows how long a twist fridge could run before the fibers must be switched out. Baughman says that will be the next problem that the UT Dallas science research team will seek to address.

“There are many possibilities for materials that provide even higher performance than we’ve already seen. This is the beginning of the story, not the end,” says Baughman.

Does this research appeal to you? UT Dallas could be the best university for you to apply to in order to earn a bachelor’s, master’s, or doctoral degree (PhD) in science, technology, engineering, or mathematics.  




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