A novel approach of using TiO2 and SiO2 nanoparticles and hydrocarbon refrigerant R600a in retrofitted vapour compression refrigeration system for environment protection and system performance enhancement

The environment effect of conventional refrigerants can be improved by adopting eco-friendly hydrocarbon (HC) refrigerants in a vapour compression refrigeration (VCR) system. In this work, various factors such as neutral ozone depletion potential (ODP) and low global warming potential (GWP), use of a lesser quantity of refrigerant, power saving, and retrofitting to the existing VCR system, are encouraged by opting for the HC refrigerant R600a. The mono and the hybrid nano-lubricants prepared by dispersing different concentrations of metallic oxide (TiO₂) and non-metallic oxide (SiO₂) nanoparticles in POE oil were used as the compressor lubricant. The morphology and crystal structure of each nanoparticle were analysed with the FE-SEM and XRD analysis. The performance parameters of the VCR system were analysed to study the effect of different nano-lubricants. In contrast to the better performance of TiO₂ in mono form, a combination of 25% TiO₂ and 75% SiO₂ in hybrid form performed better amongst all the tested lubricant samples. As compared to the base lubricant (POE oil). This hybrid nano-lubricant combination reduced the compressor power consumption by about 8% and enhanced the refrigeration effect by more than 13%. It resulted in the enhancement in COP by more than 23%. The compressor suction and delivery characteristics (such as pressure) and the pull-down temperature were also studied to evaluate the effect of different nano-lubricants. Furthermore, the viscosity and thermal conductivity analysis at various temperatures were also conducted to observe the tribological and thermo-physical property influence of the mono and hybrid forms of nano-lubricants on VCR system performance.