Synthesis of Stable PVA based Hybrid Metal Oxide Nanofluids and their Impact on Stability and Thermal Conductivity

Abstract

Nanofluids are a new generation of coolants with enhanced thermal performance that have the potential to address heat transfer problems in the industry. Excellent enhancement in thermal conductivity, heat transfer efficiency and improvement in heat flux can be attained by suitably suspending small volume concentration of nanometer sized particles in conventional heat transfer fluids. These fluids are termed as nanofluids and are capable of improving the efficiency, safety and durability of thermal systems. PVA based metal oxide HNF systems namely PVA-CuO and PVA-ZnO were successfully synthesized by simple one step chemical synthesis without involving sophisticated instruments and procedures. After characterization, it was concluded that among the PVA-CuO HNFs, with various PVA %, the nanofluid containing 0.5wt% PVA with 0.1 molar CuO resulted in highest stability of 12 months, in contrast to 3 months reported in literature. The thermal conductivity ratio Keff /Kbf was found to be 1.80 as compared to 1.08 (reported in literature) which is 58% higher.As the existing models for predicting the ratio of thermal conductivity Keff /Kbf for hybrid nanofluids yield much lower values compared to the experimental values, a modified model is proposed in this study by suitably combining Xue s model for high aspect ratio applied to surfactant (PVA) and Maxwell s model for CuO nanoparticle embedded in PVA which also serves as the matrix for the nanocomposite. These values indicate a synergisitic effect between PVA and CuO due to percolation at higher volume fraction of the dispersed phase. A separate study on the rate of precursor addition on HNF showed that both the samples slow addition (SA) and rapid addition (RA) are equally stable. Hence rapid addition is suitable for bulk synthesis, without sacrificing the stability.