Background: Adding nanoparticles to working fluids such as compressor oil can be a
solution to ameliorate the efficiency of refrigeration systems. Using the mixture of nanoparticles and
oil that is called nanolubricant (or nanofluid) can augment the heat removal in refrigeration systems,
however, in the same time, the pumping power will be increased as the viscosity of nanolubricants is
higher than that of usual oils. Therefore, the measurement of nanolubricant viscosity is a prerequisite
to estimating the pumping power in refrigeration systems.
Methods: Experiments section has been divided into three sections. First, the functionalization method
of MWCNTs is presented. Then, the preparation of nanolubricants is explained. Finally, the viscosity
measurement approach is explained.
Results: To increase the dispersibility of MWCNTs in compressor oil, functionalization of
MWCNTs was done through attaching −OH and −COOH groups with the aid of 65 wt% nitric acid
solution. It was observed that with increasing the viscosity of the base oil, the stability of MWCNTs
based nanofluids improves. Then, the viscosity of nanofluids has been measured at a temperature
range of 15°C to 50°C. It was found that at 50°C and mass concentration of 0.1%, viscosity enhances
between 40 and 90%, depends on the type of base compressor oil.
Conclusion: Four correlations involving plane, paraboloid, Gaussian, and Lorentzian functions were
suggested for the viscosity of nanolubricants. In the near future, it is expected from the results of this
study that refrigeration systems will have included their Freon based refrigerants with nanoparticles.