Effect of biopolymers on stability and properties of aqueous hybrid metal oxide nanofluids in thermal applications

Biopolymers like chitosan and Gum Arabica (GA) provide safe and effective options for improving the stability of nanofluids. The current work investigates the feasibility of water-based CuO, Fe3O4, and hybrid CuO + Fe3O4 nanofluids stabilized with Sodium Dodecyl Benzoic Sulfate (SDBS), chitosan, and GA dispersants, in heat transfer applications. Using the two-step method, water-based nanofluids are prepared with 0.1 wt% nanoparticles and 0.05–0.5 wt% dispersants. The Zeta potential of freshly prepared nanofluids is monitored together with turbidity monitoring for 60 days to study the stability of the prepared samples. Nanofluids with chitosan and GA showed stable behavior for the entire 60-day period, whereas SDBS stabilized nanofluids showed complete settlement in 10 days. Viscosity is seen to increase for all the nanofluids samples, compared to the basefluid and the increase is found to be a weak function of the nanoparticle material but strongly influenced by the type of dispersant employed. All the nanofluids show higher thermal conductivity than water, with CuO-water nanofluid showing the highest thermal conductivity, followed by hybrid CuO + Fe3O4 nanofluids and Fe3O4-water, irrespective of the dispersant employed. Contact angle measurements are carried out to determine the wettability characteristics. GA and chitosan dispersant showed minimal influence on the contact angle of nanofluids, while with SDBS, contact angle of nanofluids is seen to decrease with concentration. Thermal property analysis of the nanofluids showed that the higher viscosity of nanofluids with bio-dispersants affects their thermal performance at 0.5 wt% dispersant concentration. Our analysis shows that the nanofluids considered in the present work deliver superior performance compared to water in internal laminar flow applications. This research work demonstrates the utility of biopolymers in providing stable nanofluids, gives a detailed picture of their thermophysical behavior and evaluates their performance in cooling applications. [Display omitted]