Energetic, exergetic, and thermoeconomic analyses of different nanoparticles-added lubricants in a heat pump water heater

The heat pumps are frequently used in domestic and industrial applications for hot water supply. The present paper aims to thermodynamically investigate the impacts of the nanoparticle-addition into the lubricants on the energetic, exergetic, and thermoeconomic aspects of a heat pump. In the experiments, air to the water heat pump is separately charged with various metal oxide-based nanoparticles (Al2O3, CuO, and TiO2)-added oils at a constant mass fraction of 0.5%. Polyolester (POE) and 134a are used as a lubricant, and refrigerant, respectively. The mass flow rates of the water passed through the condenser are varied from 10 to 25 g/s with an interval of 5 g/s. In the results, it is observed that the thermal conductivity value noteworthy increases with the presence of nanoparticles in POE. The highest increment in thermal conductivity is found to be 39% for POE + CuO in comparison with that of pure POE. Furthermore, with nanoparticles addition, it is noticed that the COP value generally improves, and the highest improvement for COP value is noticed to be 8% for POE + TiO2 nanolubricant at the mass flow of 25 g/s. Furthermore, exergy efficiency enhances by 3.6%, 1.8%, and 4.5% for POE + Al2O3, POE + CuO, and POE + TiO2, respectively. The lowest heating cost is calculated to be 3.465 c/kWh at 20 g/s flow rate for POE + Al2O3. In conclusion, this paper clearly reports that usage of nanoparticles along with lubricants is presenting better energetic, exergetic, and thermoeconomic results rather than the usage of lubricant alone in the heat pumps.