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/cm(2) 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 %.