MARANGONI CONDENSATION HEAT TRANSFER OF WATER-ETHANOL MIXTURE VAPOR

Abstract

The heat transfer characteristics for condensation onto three plates (flat, taper fin, and flat fin) of water-ethanol vapor have been systematically investigated. A comparison of the three condensation heat transfer characteristics was made, and the effect of temperature gradients on the Marangoni condensation heat transfer was investigated. The results showed that the condensation modes on the surfaces with temperature gradients were usually a mixture of several different modes, while a single mode usually occurred on the condensing surface of the plat plate. The change of condensation modes on plates with fins was less marked and frequent than that on the flat plate. The mean heat transfer coefficients for the flat-fin plate, which had larger temperature gradients on the condensing surface, were greater than those on the surfaces with smaller temperature gradients. However, the degree of promotion of heat transfer by the temperature gradients depended on their values. Temperature gradients on the condensing surface made the vapor-to-surface temperature difference region, responsible for enhancing heat transfer, move to the lower region, and larger temperature gradients produced more significant movement. Moreover, the positive effect of both vapor velocity and pressure on the heat transfer was weakened by temperature gradients. The enhancement effect of vapor velocity and pressure on heat transfer was weaker when the temperature gradients on the condensing surface were larger.