Tribological and Thermal Properties of Ionic Liquids

Increasing the efficiency of existing refrigeration systems is possible if a new alternative refrigerant can be selected. An ideal refrigerant would be CO2 because it is a natural refrigerant with an extremely high efficiency. In an effort to use CO2 as a refrigerant, ionic liquid lubricants were considered to carry the CO2 and act as the working fluid. The thermal conductivity, viscosity, and pressure-viscosity coefficient were measured for several ionic liquids using a Unitherm Thermal Conductivity Measurement System, a viscometer, and an Elastohydrodynamic Lubrication (EHL) rig, respectively. The ionic liquids tested are 1-butyl-3-methylimidazolium-trifluoromethanesulfonate, tributyl(dodecyl)phosphonium 1,2,3-triazolide and trihexyl(tetradecyl)phosphonium 1,2,3-triazolide. Tests were also performed on paraffin, hexadecane, and dodecane for comparison. Results show that ionic liquids have the potential to be suitable lubricants.