Heat transfer and rivulet structures formation in a falling thin liquid film locally heated

Abstract

An experimental investigation of the heat transfer from a local heat source to a liquid film falling down a vertical plate is performed. The thermocapillary counterflow, induced by non-uniform heating, causes a deformation of the film surface having a horizontal bump-shape. This shape becomes unstable above a critical value of the imposed heat flux and deforms into vertical downstream rivulets. This variation of patterns is expected to modify significantly the heat transfer through the film. Experiments are carried out at atmospheric pressure with three varying parameters: the streamwise heater length, the Reynolds number and the imposed heat flux density. Velocimetry, shadowgraphy and infrared thermography are used to study the behavior of the interface and the heat transfer. We put in evidence the presence of a thermocapillary counter flow producing a stagnation line at the upper edges of the horseshoe structures, beyond the instability threshold, and observe a decrease of the heat transfer with the Reynolds number.