Abstract
This work presents the results of experimental investigation of the thermophysical properties of Al₂O₃– EG:water nanofluid for its application in geothermal heat pumps. The experiment was conducted at temperatures ranging from 0 to 10 °C and nanoparticle concentrations of 1, 3, and 5 vol.%. The results showed that at 1% concentration, thermal conductivity increased by 8.2%, at 3% – by 17.4%, and at 5% – by 27%, compared to the base EG:water (60:40) solution. However, at 5% concentration, viscosity increased by 45%, leading to higher hydrodynamic losses. The optimal concentration of 3% increases thermal conductivity by 17.4% while raising viscosity by only 21%, providing a balance between heat transfer efficiency and pumping costs. The calculated performance evaluation criterion (PEC) confirms that the best balance is achieved at 3% Al₂O₃, where PEC = 1.23. Further research should investigate the impact of nanoparticles on corrosion, long-term stability, and interaction with system components. The obtained results may contribute to the development of more efficient heat transfer fluids for geothermal heating and reduction of energy consumption in heat pumps.