Experimental Insights Into the Role of Rhamnolipid as a Bio‐Surfactants on Thermo‐Physical Behavior of Alumina

ABSTRACT

Although bio‐surfactants have attracted growing interest, their application in heat transfer enhancement remains less explored than synthetic surfactants, particularly, regarding their effects on nanofluid thermophysical properties. This study investigates the influence of the bio‐surfactant rhamnolipid (RHL) on the density, specific heat capacity, viscosity, and thermal conductivity of Al ₂ O ₃ /distilled water nanofluids. Nanofluids containing 0.02–0.3 wt% Al ₂ O ₃ nanoparticles were prepared with RHL concentrations ranging from 200 to 600 ppm to improve short‐term stability. Experimental results showed that density exhibited only marginal changes with nanoparticle concentration, indicating a negligible effect of RHL on mass‐related properties. The addition of RHL slightly reduced specific heat capacity due to improved nanoparticle dispersion and interfacial interactions. A significant reduction in viscosity was observed, with a maximum decrease of 29.41% at 0.1 wt% Al ₂ O ₃ and 550 ppm RHL. Thermal conductivity increased substantially, reaching a maximum enhancement of 6.95% at the same concentration, attributed to improved dispersion stability and reduced thermal resistance. These findings demonstrate that RHL is a promising eco‐friendly surfactant for improving the thermophysical characteristics and heat transfer potential of Al ₂ O ₃ ‐based nanofluids.