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A STUDY ON MARANGONI CONDENSATION (MEASUREMENT AND OBSERVATION FOR WATER AND ETHANOL VAPOR MIXTURE)

Yoshio Utaka
Yokohama National University, Department of Mechanical Engineering, Tokyo Institute of Technology 2-12-1 0-okayama, Meguro-ku Tokyo 152 JAPAN

Tatsuya Kenmotsu
Department of Mechanical Engineering and Materials Science Faculty of Engineering Yokohama National University 79-5 Tokiwadai, Hodogaya, Yokohama 240-0067 Japan

Shunya Yokoyama
Department of Mechanical Engineering and Materials Science Faculty of Engineering Yokohama National University 79-5 Tokiwadai, Hodogaya, Yokohama 240-0067 Japan

Abstract

The "Marangoni Dropwise Condensation" which is driven by the surface tension difference due to the concentration distribution at the condensate surface appears in the "positive system" of the condensation of vapor mixture. The observation and measurement were performed for water and ethanol vapor mixture. The processes of initial droplets formation from thin condensate film and drop departure were taken by using a high speed digital camera simultaneously with the heat transfer measurement. As a result, the variations of the initial drop distances exhibited U-shapes with the minimum values against the surface subcooling. Their minima were in the range of 0.03 mm ~ 0.15 mm depending upon the surface subcooling and the ethanol concentrations. The surface subcoolings at the minimum initial drop distances and at the minimum departing drops coincided with those at the maximum heat transfer coefficients. It indicates the possibility that the increase of driving force of Marangoni effect give the reduction of the thickness of the thin condensate film among the drops together with the decrease of the initial drop distance and the increase of the drop height.

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