Experimental investigations on thermo-physical properties and stability of diamond-alumina based hybrid nanofluids.

In recent years, the demand of hybrid nanofluids (HNFs) is growing due to their quintessential thermo-physical properties (TPP) and good stability. In this work, nano-diamond (ND) (<10 nm) and nano-alumina (Al2O3) (<80 nm) based mono and HNFs are taken in to consideration. Good thermal conductivity (TC) of ND particles and good physical properties of Al2O3 particles combine to form better HNF when dispersed in water. In-depth and critical experimental investigation has been conducted on TPP and stability analysis of nanofluids. Particle characterization is performed with Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM) assisted with energy dispersive analysis of X-rays (EDAX). Two-step method is employed for constructing Al2O3/water, ND/water, ND-Al2O3/water nanofluids at different weight fractions (0.01–0.3 wt.%). KD2 Pro TC analyzer and Anton Paar MCR 302e rheometer are used for determining TC and viscosity of nanofluids, respectively. The maximum enhancement of 4.2%, 16.93%, and 22.93% are observed in TC at 80 °C for 0.3 wt.% of Al2O3/water, ND-Al2O3/water, and ND/water nanofluids, respectively in comparison with that of distilled water. Correlations are developed for TC and viscosity and compared with experimental values. For evaluating stability of nanofluids, three methods applied such as visual inspection, UV–vis spectroscopy, and zeta-potential (ZP) are used. Stability period of nanofluids represented as ND/water (55 days) > ND-Al2O3/water (45 days) > Al2O3/water (30 days). Both TPP and stability enhanced for ND-Al2O3/water (hybrid) nanofluid compared to Al2O3/water (mono) nanofluid, thus used in various thermo-fluidic industries. [ABSTRACT FROM AUTHOR]