Good news!
"As the race to find alternative cooling tech heats up, researchers are exploring climate-friendly options such as elastocaloric cooling, a solid-state tech that moves heat through reversible phase transformations.
Now, researchers ... have announced the first elastocaloric device capable of reaching subzero Celsius temperatures, marking a milestone in the development of this promising refrigeration technology. The desktop prototype, described in a recent Nature paper, successfully froze 20 milliliters of water into ice within two hours, making it comparable to the performance of a domestic freezer. ..."
"... The features include:
(1) Super-elastic alloy: employing a binary low-transition-temperature nickel-titanium (NiTi) alloy with a high nickel content (51.2 at %) and lowering its austenite finish temperature (Af) to -20.8℃. This alloy maintains excellent super-elasticity and a substantial latent heat even at -20℃, with a peak adiabatic temperature change of 16.3℃ at 0℃ and a functional temperature window of 48.5℃.
(2) Freezing-resistant heat transfer fluid: using a 30wt% aqueous calcium chloride solution as the working fluid. Its low freezing point ensures that it remains fluid in sub-zero operation, while its good wettability on the NiTi surface enhances heat exchange efficiency.
(3) Cascaded tubular architecture: the regenerator operates on a compression-based active Brayton cycle and consists of eight cascaded units, each containing three thin-walled NiTi tubes. This design offers a high surface area-to-volume ratio (8.68 mm-1) and withstands a compressive stress of 900MPa without buckling, as verified by X-ray computed tomography.
..."
From the abstract:
"Elastocaloric cooling using shape-memory alloys (SMAs) is a promising greenhouse gas (GHG)-free alternative to conventional vapour-compression refrigeration that relies on high global warming potential (GWP) gas refrigerants. However, existing elastocaloric systems have not yet reached sub-zero Celsius temperatures, which restricts their application in various freezing scenarios. Here we constructed a compression-based, regenerative elastocaloric cooling device using low-transition-temperature tubular NiTi units in a cascaded configuration. The selected NiTi alloy exhibited superelasticity and substantial entropy changes down to −20 °C.
Moreover, low-freezing-point aqueous calcium chloride solution was used as the heat-transfer fluid, ensuring effective flow at low operational temperatures.
Our desktop device achieved a heat-source temperature of −12 °C from a room-temperature heat sink, paving the way for next-generation green elastocaloric freezing technologies."
HKUST Develops World’s First Sub-Zero Celsius Elastocaloric Green Freezer, Reshaping Freezing Industry with its Zero Emissions (original news release)
Sub-zero Celsius elastocaloric cooling via low-transition-temperature alloys (no public access, but article above has a link to paper)
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