Application of TiO2 nanoparticles as a lubricant-additive for vapor compression refrigeration systems – An experimental investigation

The coefficient of performance of a refrigeration system can be improved if a reduction in the work of compression can be achieved by a suitable technique, for a specified heat removal rate. The present study investigates the effect of dispersing a low concentration of TiO2 nanoparticles in the mineral oil based lubricant, on its viscosity and lubrication characteristics, as well as on the overall performance of a Vapor Compression Refrigeration System using R12 (Dichlorodifluoromethane) as the working fluid. An enhancement in the COP of the refrigeration system has been observed and the existence of an optimum volume fraction noticed, with low concentrations of nanoparticles suspended in the mineral oil. The physics involved in the interaction of nanoparticles with the base fluid has been further elucidated by estimating the Optical Roughness Index using a Speckle Interferometer, by performing measurements on the pin surface following tests with a Pin-on-Disk tester.