Editing Compressed-air energy storage (section)

=== Near-isothermal ===
Near-isothermal compression (and expansion) is a process in which a gas is compressed in very close proximity to a large incompressible thermal mass such as a heat-absorbing and -releasing structure (HARS) or a water spray.<ref>{{Cite journal|last1=Guanwei|first1=Jia |last2=Weiqing|first2=Xu |last3=Maolin|first3=Cai |last4=Yan|first4=Shi |date=2018-09-01|title=Micron-sized water spray-cooled quasi-isothermal compression for compressed air energy storage|url=http://www.sciencedirect.com/science/article/pii/S0894177718304862 |journal=Experimental Thermal and Fluid Science|language=en |volume=96|pages=470–481 |doi=10.1016/j.expthermflusci.2018.03.032|bibcode=2018ETFS...96..470G |s2cid=126094265 |issn=0894-1777|url-access=subscription}}</ref> A HARS is usually made up of a series of parallel fins. As the gas is compressed, the heat of compression is rapidly transferred to the thermal mass, so the gas temperature is stabilized. An external cooling circuit is then used to maintain the temperature of the thermal mass. The isothermal efficiency (Z)<ref>{{cite web |url=http://www.fluidmechanics.co.uk/wp-content/uploads/2015/07/Calculating-Isothermal-Efficiency-V1.2.pdf |title=Calculating Isothermal Efficiency |date=2015 |website=www.fluidmechanics.co.uk |access-date=July 4, 2015 |archive-date=February 14, 2019 |archive-url=https://web.archive.org/web/20190214190805/http://www.fluidmechanics.co.uk/wp-content/uploads/2015/07/Calculating-Isothermal-Efficiency-V1.2.pdf |url-status=dead }}</ref> is a measure of where the process lies between an adiabatic and isothermal process. If the efficiency is 0%, then it is totally adiabatic; with an efficiency of 100%, it is totally isothermal. Typically with a near-isothermal process, an isothermal efficiency of 90–95% can be expected.