Simultaneous temperature and thickness measurements of falling liquid films by laser-induced fluorescence

Abstract

Thin wavy liquid films are used in many applications as heat and mass transfer promoters thanks to their great performances for a small liquid consumption. To evaluate the influence of the coupling between the wavy fluid dynamics and the heat transfer in a 2D waves regime, a pointwise laser-induced fluorescence technique has been developed. The technique enables a simultaneous measurement of both the thickness and the temperature of a wavy film flowing down an inclined plane with a high temporal resolution thanks to an optical probe placed directly above the liquid film. The fluorescence intensity is integrated over the thickness of the film, allowing a robust measurement of temperature and thickness for strongly perturbed wave fronts. This paper reports on the development of the technique and discuss the capabilities and limits of the current design. Water liquid films were investigated under two-dimensional waves conditions. The measurements, and the evaluation of the local heat transfer coefficient they permit, reveal the regions where mixing is enhanced by convective circulation zones.

Numerical simulation and modeling of the heat and mass transfer in a grooved flat falling film evaporator

“…Experimental studies also reported the appearance of complex phase-change mechanisms when condensing [17] water vapor or during boiling [22,23] of the falling films in soprtion systems. Despite a very strong interest in understanding the inner workings of heat and mass transfer in falling liquid films by the community, either theoretically [24,25,26,27] or experimentally [28,29,30,31], the literature concerning the component scale of the sorption systems remains scarce and further knowledge on the behaviour of the flows inside of falling films exchanger is required.…”