Performance of a hydrocarbon driven domestic refrigerator based on varying concentration of SiO2 nano-lubricant
Abstract This experimental work studies the performance of varying concentrations of SiO2 nanoparticle in mineral oil lubricant using LPG refrigerant, as a retrofit to R134a in a domestic refrigeration system. The test rig is fitted with thermocouple K, pressure gauges and a watt-meter to monitor the suction, discharge, the condensing temperatures, pressures and power consumption in accordance with ISO 8187 recommendations. Performance parameters investigated included: pull down time, compressor power consumption and input, coefficient of performance and thermal conductivity and viscosity. Findings showed that all the selected charges of LPG refrigerant infused with varying concentrations of nano-lubricants, achieved equal values of -3 °C (ISO 8187), or lower values of evaporator air temperatures at lower refrigerant charges, than the baseline R134a refrigerant. All the selected nano-lubricants based refrigerants resulted in improved Coefficient of Performance (COP) than R134a refrigerant, with COP values ranging from 2.05 with 50 g charge of LPG using 0.4 g/L nano-lubricant to 2.65 with 60 g of LPG using 0.2 g/L SiO2 based lubricant. Lower power input was recorded by the compressor for all the selected charges of SiO2-lubricant based LPG than R134a refrigerants, having 28.81 W (with 60 g charge of LPG using 0.2 g/L) and 39.21 W (with 100 g charge of R134a refrigerant using pure compressor oil lubricant). In addition, at low concentration of nanoparticle in the lubricants based LPG refrigerant, reduction in power consumption of the compressor was observed, whereas higher concentration of nanoparticle in the lubricant, resulted in a rise in power consumption. Furthermore, thermal conductivity values were found to be low at the suction and discharge ends of the compressor for R134a using pure mineral oil lubricant, whereas the values were high for retrofit working fluid (pure LPG refrigerant, and LPG with varying concentrations of nano-lubricants), at the suction and discharge ends of the compressor.