Amirkabir University of Technology Amirkabir Journal of Mechanical Engineering 2008-6032 55 7 2023 09 23 Experimental investigation of the effect of pH on the stability and thermal conductivity of metal oxide nanofluids Experimental investigation of the effect of pH on the stability and thermal conductivity of metal oxide nanofluids 857 874 5266 10.22060/mej.2023.22193.7578 FA Behrouz Raei Department of Chemical Engineering, Mahshahr Branch, Islamic Azad University, Mahshahr, Iran 0000-0001-6031-4245 Journal Article 2023 02 11 The pH level of nanofluids plays an important role in stability and thermal conductivity. However limited studies have been done in this field. In this research, the effect of pH on the stability and thermal conductivity of ZnO-EG nanofluid at concentrations of 0.05 and 0.75% volumetric fraction and MgO-W at concentrations of 0.05 and 0.5% volumetric fraction were investigated. Experimental measurements of the thermal conductivity were performed by a thermal properties analyzer device at a constant temperature of 25 °C. The results showed that the pH strongly affected the stability of nanofluids so that at the pH of the isoelectric point (IEP), complete aggregation and sedimentation were observed. The thermal conductivity of nanofluids has the lowest value at the pH of the isoelectric point, but as the pH moves away from the isoelectric point, the thermal conductivity  increases. The highest enhancement in the thermal conductivity of ZnO-EG nanofluid was 63%, which was obtained at a volume fraction of 0.75% and pH = 12. However, the highest enhancement in the thermal conductivity of MgO-W nanofluid was 49%, which was obtained at a volume fraction of 0.5% and pH = 12. Finally, using the experimental results and with the help of curve fitting, equations with good quality were presented to predict the effective thermal conductivity of metal oxide nanofluids. The pH level of nanofluids plays an important role in stability and thermal conductivity. However limited studies have been done in this field. In this research, the effect of pH on the stability and thermal conductivity of ZnO-EG nanofluid at concentrations of 0.05 and 0.75% volumetric fraction and MgO-W at concentrations of 0.05 and 0.5% volumetric fraction were investigated. Experimental measurements of the thermal conductivity were performed by a thermal properties analyzer device at a constant temperature of 25 °C. The results showed that the pH strongly affected the stability of nanofluids so that at the pH of the isoelectric point (IEP), complete aggregation and sedimentation were observed. The thermal conductivity of nanofluids has the lowest value at the pH of the isoelectric point, but as the pH moves away from the isoelectric point, the thermal conductivity  increases. The highest enhancement in the thermal conductivity of ZnO-EG nanofluid was 63%, which was obtained at a volume fraction of 0.75% and pH = 12. However, the highest enhancement in the thermal conductivity of MgO-W nanofluid was 49%, which was obtained at a volume fraction of 0.5% and pH = 12. Finally, using the experimental results and with the help of curve fitting, equations with good quality were presented to predict the effective thermal conductivity of metal oxide nanofluids. https://mej.aut.ac.ir/article_5266_59b85c256f758c22eae6fa45913205db.pdf