Improvement in the thermal conductivity and stability of rare-earth metal oxide nanofluids using the stabilizing action of nano CaCO3 in comparison with the stabilizing action of sodium dodecyl sulphate

Abstract

The stabilizing action of inorganic CaCO3 nanoparticles to increase the thermal conductivity of nanofluids containing nanoparticles of yttrium oxide (Y2O3), zirconium oxide (ZrO2), and yttria-stabilized zirconia (YSZ) prepared from their respective micron size metal oxide precursor through gel combustion method is reported in this work. The nanoparticles obtained through the gel-combustion method after calcination yield nano-size rare earth metal oxide particles. The morphology and composition of the constituents’ nanoparticles thus prepared were explored through XRD, FESEM with EDX, and elemental mapping analysis to confirm the purity and the particle sizes. Thermal conductivities of the nanofluids prepared using the above-mentioned nanoparticles were found to be superior to that of the base fluid, but their stabilities were lesser. Commercially available stabilizers like sodium dodecyl sulphate (SDS) were used to improve the stability but their addition reduces the thermal conductivity of the nanofluids. The nano-CaCO3 particle as a stabilizer provides better stability than SDS was reported. The stability of all the nanofluids was evaluated through the results obtained from zeta potential measurements and the mixture with the highest stability was evaluated. Based on the visual inspection and through UV–vis spectral measurements, the settling ability of the nanoparticles present in the nanofluid was also evaluated. Remarkably, Y2O3 + CaCO3 suspended nanofluid exhibits a commendable thermal conductivity of 29.18 % higher than the base fluid. Such fluids possessing higher stability with good thermal conductivity can be effectively utilized in heat exchanger applications.