Ionic Liquids as Thermal Fluids

Abstract

The general properties of ionic liquids match many of the physical and chemical properties required of liquids used as heat transfer fluids. The properties of the ionic liquids 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) that are relevant to their use as thermal fluids were measured or compiled from the literature. The properties where the ionic liquids compare favorably with established fluids are heat storage capacity, vapor pressure, liquidus range, boiling point, and freezing point. They compare unfavorably in cost. They compare roughly equally in viscosity, thermal stability, and thermal conductivity. Comparison data are still lacking for flammability, toxicity, thermal expansion, volume change at melting and freezing, surface tension, maximum film temperature, and critical point quantities.