Locally heated shear-driven liquid films in microchannels and minichannels

The flow of a locally heated liquid film moving under the friction of gas in a channel is considered through theoretical and numerical modeling and conducting experiments. Theoretical investigation predicts that at Rel/Reg < 0.35 the main driving force for the film is the friction at the liquid-gas interface. In experiments it was revealed that a liquid film driven by the action of a gas flow in a channel is stable in a wide range of liquid/gas flow rates. A map of isothermal flow regimes was plotted and the lengths of smooth region and region of 2D waves were measured. It was found that the critical heat flux at which an initial stable dry patch forms for a shear-driven liquid film can be several times higher than that for a vertical falling liquid film, which makes shear driven liquid films more suitable for cooling applications. Temperature distribution at the film surface was measured by an infrared scanner and it was found that thermocapillary tangential stresses may exceed tangential stresses caused by the friction of the gas, which indicates a significant Marangoni effect on the film dynamics.