Influence of surface topography on heat transfer in shear-driven liquid films

Thin gas-driven liquid films find numerous industrial applications. They are used for fuel preparation in airblast atomizers of modern gas turbines. Strong shear forces at the gas-liquid interface destabilize the liquid-gas interface and lead to development of interfacial waves. In this study, the heat transfer in liquid films driven by turbulent gas flow is investigated experimentally over a wide range of parameters. A liquid film is formed on vertical heated unstructured and micro-structured tubes. The Reynolds number of the gas flow is varied between 10⁴ and 10⁵, and the Reynolds number of the liquid film flow is varied between 80 and 800. Wall heat fluxes up to 30 W/cm² are applied. The heat transfer coefficient strongly depends on the gas and liquid Reynolds numbers. Using the micro-structured tube leads to a heat transfer enhancement of up to 80 %.