Thermal Conductivity Models for Polymer ‎Stabilized Hybrid Nanofluids Prepared by ‎One-Step Method

Polyvinyl alcohol (PVA)-ZnO hybrid nanofluid (HNF) was prepared by a one-step chemical method. The structure of PVA-ZnO nanocomposite was concluded by XRD analysis. The stability of HNF was investigated by spectral absorbency analysis and photographic capture methods. 1 wt% PVA capped ZnO nanofluid was stable for 45 days. Zeta potential measurements confirmed that the enhanced stability of PVA-ZnO HNF is due to steric stabilization offered by the polymer. The thermal conductivity of HNFs was predicted by applying the Mixture rule to the conventional Maxwell and Xue models. The theoretical values predicted by the above models were in good agreement with the experimental values. However, it increased steeply with the onset of percolation and it exhibited an additive behaviour under percolation. Thermal conductivity of the prepared hybrid nanofluids increased with temperature and maximum thermal conductivity of the hybrid nanofluids was observed at 60oC with 0.009 weight% of solid dispersant. Theoretical models were used to explain the thermal conductivity of hybrid nanofluids in contrast to most of the reported work which has used empirical correlations. The additive model satisfactorily explained the thermal conductivity of hybrid nanofluids under percolation. TEM micrograph showed the formation of heat conducting path due to onset of percolation in PVA-ZnO HNF resulting 22.5% increase in thermal conductivity due to synergistic effect.