Impact of Employing Hybrid Nanofluids as Heat Carrier Fluid on the Thermal Performance of a Borehole Heat Exchanger

In this numerical study, 4 types of hybrid nanofluid, including Ag-MgO/water, TiO2-Cu/water, Al2O3-CuO/water, and Fe3O4-multi-wall carbon nanotube/water, have been considered potential working fluid in a single U-tube borehole heat exchanger. The selected nanofluid is then analyzed by changing the volume fraction Reynolds number. Based on results, Ag-MgO/water chosen as most favorable carrier fluid, among others, considering its superior effectiveness, minor pressure drop, appropriate thermal resistance compared to pure water. Moreover, it was indicated that all cases at various fractions (from 0.05 0.20) numbers 3200 6200) could achieve better effectiveness lower resistances, but higher drops corresponding Nevertheless, evaluated nanofluids present coefficient performance (COP)-improvement than unity which means applying them not economically viable because having drop transfer enhancement.