Experimental study on time-series characteristics in Marangoni condensation for ethanol-water mixtures on a horizontal surface

Abstract

In this paper, an experimental system for condensation on a horizontal surface was designed and built to study the Marangoni condensation of ethanol-water mixtures. The time-series characteristics, including heat transfer characteristics and condensation modes, were experimentally studied herein. In the case of pure steam, the condensation mode was film-wise during the time-series process. As the condensation was processed, the heat transfer coefficient decreased first and then stayed stable. And the heat transfer coefficient increased with the increase both in the impinging cooling water temperature and vapor velocity. In the case of ethanol-water mixtures, the condensation modes at the starts of the time-series processes presented film-wise, film-wise with dropwise and dropwise under different conditions. As the impinging cooling water temperature and ethanol vapor concentration increased, the vapor-to-surface temperature difference and the heat transfer coefficient both showed smooth, periodic, fluctuated and slow variations during the time-series process. Increase in the vapor velocity promoted the transformation towards the periodic variation. Four typical condensation styles, including the filming style, periodic-dropwise style, irregular-dropwise style and slow-growth-dropwise style, were concluded based on the time-series characteristics, and the condensation styles distribution was obtained. As the impinging cooling water temperature increased, the condensation style presented filming, periodic-dropwise, irregular-dropwise and slow-growth-dropwise successively. The corresponding vapor-to-surface temperature difference, whose range was divided into four parts accordingly. As the ethanol vapor concentration increased, the ranges for the periodic-dropwise style increased first and then decreased. The ranges for the periodic-dropwise style increased with increasing the vapor velocity.