Investigation of the effect of pH adjustment on the stability of nanofluid

Coagulation of the dispersed nanoparticles in the base fluid diminishes its thermo-physical and transport properties, leading to its low performances as a heat transfer medium for thermal applications. In this paper, Al2O3-water and CuO – water nanofluids were synthesized using NaOH, NH4OH and acetic acid as surface charge modifiers to improve the stability of the prepared nanofluids. The stability of the suspended nanoparticles was evaluated using, scanning electron microscope (SEM), transmission electron microscope (TEM), and optical microscope (OP). The results showed that Al2O3-water nanofluid stabilized at low pH value of 4.59 (within the acidic region) while CuO-water nanofluids showed poor stability compare to Al2O3-water nanofluid. It is a well-known fact that if the pH of a nanofluid is significantly less or substantially more than the isoelectric point (IEP), better stability will be observed. Therefore, by adjusting the pH of the suspension away from IEP, the repulsive force of the particles in the suspension become stronger, making the nanofluid stable.