Page 36 - Climate Control News Dec-Jan 21

Compressors, Condensers & Evaporators
Future of cooling: No refrigerants
RESEARCHERS AT THE Polytechnic Universi- ty of Catalonia and the University of Cambridge have performed a series of simple experiments that could have huge implications for cooling and refrigeration.
An article published in MIT Technology Review said scientists are identifying promising caloric materials that undergo big temperature changes when placed under pressure.
They placed plastic crystals of neopentyl gly- col – a common chemical used to produce paints and lubricants – into a chamber, added oil, and cranked down a piston. As the fluid compressed and applied pressure, the temperature of the crystals rose by around 40 ˚C.
Alleviating the pressure has the opposite ef- fect, cooling the crystals dramatically. The re- search team said the results highlight a promis- ing approach to replacing traditional refrigerants, potentially delivering “environmentally friendly cooling without compromising performance”.
The temperature change in the materials was comparable to those that occur in the hydro- fluorocarbons that drive cooling in standard air conditioning systems and refrigerators. Hydro- fluorocarbons, however, are powerful green- house gases.
The work is based on a long-known phenome- non, in which so-called caloric materials release heat when placed under pressure or stressed. Submitting certain materials to magnetic and
electrical fields, or some combination of these forces, also does the trick in some cases.
Scientists have been developing magnetic re- frigerators based on these principles for decades, though they tend to require large, powerful, and expensive magnets.
Research teams are pinpointing numerous ca- loric materials that undergo large temperature shifts and putting them to work in prototype heating and cooling devices.
“A CRITICAL DIFFERENCE WITH THIS TECHNOLOGY IS THAT THE MATERIALS REMAIN IN A SOLID STATE.”
Materials and devices that can release and transfer large amounts of heat using electricity, strain and pressure are already catching up with the performance achieved through decades of work in magnet-based cooling devices.
In addition to reducing the need for hydro- fluorocarbons, the hope is the technology could eventually be more energy efficient than stand- ard cooling devices.
A critical difference with this technology is that the materials remain in a solid state while
traditional refrigerants work by shifting between gas and liquid phases.
The key to delivering competitive commercial de- vices is identifying affordable materials that under- go large temperature shifts, and withstand extend- ed cycles of these changes without breaking down.
Maryland Energy & Sensor Technology has developed a prototype cooling device that com- presses and releases tubes made from nickel tita- nium to induce heating and cooling.
Water running through the tubes absorbs and dissipates heat during the initial phase, and the process then runs in reverse to chill water that can be used to cool a container or living space.
The company plans to produce a wine cooler, which doesn’t require the same cooling power as a large refrigerator or window AC unit, as an ini- tial product, using an unspecified but less expen- sive material.
Another company, Barocal, which is based in the UK, has developed a prototype heat pump re- lying on plastic crystals that are related to neo- pentyl glycol but is better, the company said.
There are now up to a dozen companies work- ing to commercialise products based on materi- als that change temperature in response to force and stress.
They expect products to be released in the next five to 10 years although it will take much longer for prices to become competitive.
With MIT Technology Review
Research teams are already putting prototype heating and cooling devices to work.
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