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Why Do Compressed Air Cans Get Cold?

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 Physics   |   Science
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This video is about compressed air cans (aka gas dusters) and why they get cold when you spray them. They cool off because the refrigerant inside (1,1-difluoroethane) is under pressure and boils off when the pressure lowers, and energy lost to the latent heat of vaporization cools the can a lot. Difluoroethane normally boils at -25°C (-13°F), but under ~6 atm (6 bar, 600 kpa) it is a liquid at room temperature. The gas also cools off slightly due to the Joule-Thompson effect of fluid expansion through a throttled valve. Difluoroethane is heavier than air and water soluble, so it is recommended to use it in a ventilated environment to clean your keyboard, etc. Also, 1,1-difluoroethane is a potent greenhouse gas. It is also known as Freon 152a, Ethylidene difluoride, Ethylidene fluoride, HFC-152a, R-152a, and DFE.

Thanks to Tino and Hannah!

REFERENCES

CRC Air Duster Safety Data Sheet
http://docs.crcindustries.com/msds/5185.pdf

Latent Heat of vaporization
https://en.wikipedia.org/wiki/Latentheat

1,1-difluoroethane chemical and physical properties
https://webbook.nist.gov/cgi/cbook.cgi?ID=C75376&Mask=3FFF

1,1-difluoroethane on wikipedia
https://en.wikipedia.org/wiki/1,1-Difluoroethane

Free Expansion of Real Gases, Goussard, 1993
http://dx.doi.org/10.1119/1.17417

Joule-Thompson Expansion Course Notes
http://tccc.iesl.forth.gr/education/local/Labs-PC-II/JT.pdf

Properties of 1,1-difluoroethane
http://www.inchem.org/documents/sids/sids/75376.pdf
https://pubchem.ncbi.nlm.nih.gov/compound/11-difluoroethane

Medical Effects of difluoroethane
https://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+5205


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Created by Henry Reich

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