Cooling and Tribological Performance Analyses of a Refrigeration System Using Nano-Fluids as Refrigerant and Lubricant

This experimental study investigates the effects of TiO₂ nano-particles on the cooling and tribological performance of a vapor compression refrigeration system running on R134a as refrigerant and polyolester oil (POE) as lubricant. Dynamic light scattering analysis was conducted to observe the dispersion of the nano-particles. The heat transfer rate in the evaporator and condenser was taken into consideration to observe the cooling performance of the system charged with combination of 0.1 vol% and 0.5 vol% TiO₂ incorporated nano-refrigerants (R0.1 & R0.5) and 0.1 vol% and 0.5 vol% TiO₂ incorporated POE nano-lubricants (P0.1 & P0.5). Coefficient of friction and wear rate analyses were also performed on the piston ring of the compressor by immersing the samples in two different lubricants (P0.1 & P0.5). The compressor’s suction-discharge characteristics were assessed to determine the impact of the nano-fluid combinations. Scanning electron microscopy was used to examine the morphology of the nano-particles and worn surfaces. Atomic force microscopy was utilized to observe the structure of the worn substrates. The chemical composition of the worn surfaces was analyzed using energy-dispersive X-ray and the thermal stability of the nano-additives was ascertained via thermogravimetric analysis and differential scanning calorimeter. The best cooling and tribological performance results were obtained when the system was run on a combination of R0.5 + P0.1. Compared to standard conditions (R134a + POE), the highest increase in COP was 35.86% for R0.5 + P0.1. With the same combination, the cooling time was reduced by 22.25% and the highest decrease in the average coefficient of friction was 8.02% for 0.1 vol% of TiO₂ incorporated POE lubricant (P0.1).