Effect of binary mixed-surfactants and hybrid nanofluid on spray cooling heat transfer

The present study emphasizes the spray-cooling enhancement of a copper heater block of 10 mm² cross-sectional area with binary mixed surfactant based fluid and hybrid nanofluid using a pressure swirl nozzle with an orifice size of 0.51 mm. The experiments have been carried out at two distinct fluid input temperatures of 27 °C and 42 °C, with a volumetric flux of 3.50 cm³/cm²s. Polyvinyl pyrrolidone (polymer surfactant), Sodium dodecyl sulfate (an anionic surfactant), Tween-20 (a nonionic surfactant) have been used as binary mixed surfactant systems in distilled water. The best performance has been obtained with SDS:Tween-20, which resulted in a maximum heat flux of 264 W/cm² and a heat transfer coefficient of 3.59 W/cm²K. When compared to distilled water, the heat transfer coefficient increased by 32.2%, but only by 25.2% and 18.1% with PVP:Tween-20 and SDS:PVP surfactant solutions. Further, the effect of a hybrid nanofluid, which is a colloidal mixture of Titanium dioxide (TiO₂) and MWCNTs (multi-walled carbon nanotubes) in distilled water, has been studied to better understand spray cooling heat transfer enhancement. Heat transfer was first enhanced by the hybrid nanofluid and then decreased as the volume concentration was increased from 0.1% to 0.3%. A maximum heat flux of 234 W/cm² and a heat transfer coefficient of 3.15 W/cm²K has been achieved, with a heat transfer coefficient improvement of nearly 27.3% compared to distilled water. However, the mixed surfactant system outperformed, giving nearly 12.8% improvement in heat flux values. It has been observed that low surface tension resulted in high heat transfer rates. Furthermore, the effect of 15 °C subcooling on heat transfer performance has been investigated. A new correlation to find Nusselt number is proposed in terms of Reynolds number, Weber number and Prandtl number with a mean absolute error of 7.16%.