The Korea Institute of Energy Research (KIER), based in Daejeon, South Korea, announced on August 27 that it has developed, for the first time in the country, a low-temperature refrigeration technology that uses air (R729) as a refrigerant and incorporates a “compander” system, which combines a compressor, heat exchanger and expander.
The research received support from the “Climate Change Response Technology Development Project” in the South Korean Ministry of Science and ICT (Information and Communication Technology).
The system cools air to below -60°C (-76°F) within one hour, said KIER, adding that when temperatures are below -50°C (-58°F), the system demonstrates higher efficiency than traditional vapor compression systems. Theoretically, it is capable of cooling down to -100°C (-148°F), and at that temperature, the refrigeration efficiency is expected to improve by more than 50% compared to vapor compression system, noted KIER.
“We are currently working on improving the system’s performance to enable the production of cold temperatures below -100°C,” said the lead researcher, Dr. Beom Joon Lee with the South Korean Ministry of Science and ICT. “We anticipate that this technology will be applied in fields that require ultra-low temperatures, such as semiconductor processes, pharmaceuticals, and biotechnology.”
KIER noted that f-gases are used in Korean export products such as air conditioners, automobiles, and semiconductor processes, but there is now “an urgent need to develop alternative technologies” given the phase out of f-gases taking place in the EU and other regions.
Using the reverse-Brayton cycle
KIER’s air-based cooling system leverages what is called the reverse-Brayton cycle. Unlike the traditional vapor-compression systems that involves evaporating a liquid, systems using this cycle compress a gas and then use heat exchange and expansion to produce a low-temperature gas. The compander, which combines compression, heat exchange and expansion, “must be designed with extreme precision due to the ultra-high-speed rotation during the cooling process,” said KIER. “For instance, the gaps between components and shaft displacement require a tolerance within 0.1mm.”
Under the reverse-Brayton cycle, air is compressed to a high temperature and high pressure; the compressed air is passed through a heat exchanger, where it is cooled down to a low temperature while maintaining high pressure; the cooled, high-pressure air is then expanded in an expander, reducing it to a low temperature and low pressure. The cooled air is then delivered to the required area for cooling.
To implement the reverse-Brayton cycle system, the research team devised a compander system that connects the compressor, expander, and motor on a single shaft. The shaft system design ensures stable operation even at ultra-high rotational speeds, further enhancing the reliability and performance of the system, said KIER.
Other systems using air as a refrigerant have been developed by Mayekawa and Mirai Intex. In 2019, Mirai Intex’s COLD 15 air-cycle refrigeration machine, capable of cooling down to -130°C (-202°F), won ATMOsphere’s Innovation of the Year award for Europe. ATMOsphere is the publisher of NaturalRefrigerants.com.
“We anticipate that this technology will be applied in fields that require ultra-low temperatures, such as semiconductor processes, pharmaceuticals, and biotechnology.”
Dr. Beom Joon Lee with the South Korean Ministry of Science and ICT
