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ISSN Online: 2377-424X

International Heat Transfer Conference 12
August, 18-23, 2002, Grenoble, France

Heat Transfer Analysis of Falling Film Evaporation on Structured Surfaces

Get access (open in a dialog) DOI: 10.1615/IHTC12.2530
6 pages

Résumé

Evaporation of thin films falling down smooth and rough/structured wall surfaces is a very important technological process. Using structured wall surfaces can strongly increase the evaporation rate and the stability of the process. However, the mechanism of influence of the surface micro - geometry on the heat transfer coefficient is not yet understood and theoretical models are not very accurate. Two ways of improvement of the earlier models can be suggested: (i) to account for the peculiarities of evaporation process in the vicinity of the evaporating contact line ("micro region") on the overall heat transfer; (ii) to account for the wavy motion of the falling film.
In the present work a model for steady fluid flow and heat transfer during evaporation of a liquid film falling down a grooved wall is developed, which accounts for the effect of the micro region on the overall heat transfer rate. The model takes into account the gravity driving the flow, the capillary forces, the disjoining pressure, conduction in the wall and in the liquid, and evaporation.
A stability analysis is performed to quantify the effect of the capillary structure on the film stability properties. It is shown that the presence of longitudinal grooves has a stabilizing effect on the falling films flow.
The developed model is used for the calculation of the heat transfer coefficient for different liquids and groove geometries as a function of the temperature, wall heat flux and the liquid mass flow rate.