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More than a dozen chemical blends could serve as alternative refrigerants that won't heat the atmosphere as much as today's refrigerants do, or catch fire, according to a new computational study by the National Institute of Standards and Technology (NIST).
The NIST study identified the 22 "best" nonflammable or marginally flammable blends with lower global warming potential (GWP)—a measure of how much heat a gas will trap if released into the atmosphere—than the current standard refrigerant for vehicle air conditioning (AC), called R-134a (tetrafluoroethane).
Blends - Refrigerants
Most of the identified blends combine R-134a with one or two other commercial refrigerants.
The new NIST analysis, which was conducted for the U.S. military but also applies to civilian applications such as AC systems for homes and cars, is a follow-up to a 2017 NIST study that found that all single-component, climate-friendly refrigerants were at least marginally flammable. That study suggested blends might offer the optimal solutions.
Military - Blends - Applications - Mixtures - NIST
"The military is insistent about wanting non-flammable blends, but the civilian applications are moving more and more toward at least marginally flammable mixtures," NIST mechanical engineer and study lead author Ian Bell said.
To help reduce global warming, nearly 200 nations, including the United States, agreed in 2016 to amend the Montreal Protocol to phase down by mid-century the refrigerants used in most AC systems. The partial phasedown, rather than a complete phaseout, recognized the complicated choices that will need to be made to select replacements.
Study - NIST - Researchers - Fluids - Range
For the new study, NIST researchers selected 13 fluids within a range of pressure, flammability, and GWP values that might produce a blend with the desired characteristics. All fluids were low in toxicity and commercially available. The researchers conducted an extensive evaluation of all possible combinations of two or three of the 13 fluids.
The fluids included hydrofluoroolefins, which have very low GWP but are mildly flammable; nonflammable hydrofluorocarbons...
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