nano-oil, refrigerant/nano-oil mixture, physical property, thermal conductivity
Refrigeration oil is generally used in refrigerant compressor for lubrication. Recently, a nano-oil, which is a suspension of base lubrication oil and nano-order particles, is proposed to pursue further improvement of refrigeration cycle efficiency. There are many advantages by using nano-oil as lubrication oil in refrigerant compressor; (a) improvement of thermophysical property of lubrication oil, (b) bearing effect at sliding part, and (c) sealing effect of leakage of refrigerant and so on. For actual application of nano-oil to refrigeration system, it is important to investigate the effect of addition of nano-particles to the physical properties of refrigeration oil and its mixture of refrigerant at first. In this study, we measured not only thermal conductivity, but also other physical properties such as viscosity and dielectric constant of nano-oil itself. In addition to nano-oil, such physical properties of refrigerant / nano-oil mixture were also measured and the effect of nano-particles was discussed. Nano-oil was prepared by dispersing CuO nano-particles into refrigeration oil with 0.5, 1.0 and 3.0 vol% of the volume fraction. We chose Polyvinyl ether (PVE) as a refrigeration oil in this study. Temperature of nano-oil was ranged from 30 to 100 °C. The results show that thermal conductivity, viscosity and dielectric constant of the nano-oil are larger than those of the base oil. The increase of these properties becomes large with increasing volume fraction of nano-particles. On the other hand, the physical properties of refrigerant / nano-oil mixture were measured in a pressure vessel. R410A was used as a refrigerant in this study. The temperature was kept at 30 °C. The concentration of refrigerant in nano-oil was measured by the sampling method. The results show that thermal conductivity, viscosity and dielectric constant of R410A / PVE-CuO nano-oil are larger than those of R410A / PAG for the small concentration of refrigerant. The tendency that the increasing level of these properties becomes small with increasing refrigerant concentration was observed.