存在温度梯度的竖直壁面Marangoni 凝结换热特性研究

对水-酒精混合蒸气在表面存在温度梯度的竖直壁面上的Marangoni凝结换热特性进行了实验研究,并观测了混合蒸气的凝结形态.实验结果表明:凝结表面不同位置的换热系数不同,温度梯度大的位置凝结换热系数较大;当酒精蒸气的质量分数wv=0.5%,1%时,凝结换热系数随过冷度单调减小;当wv≥2%时,凝结换热系数与过冷度的关系为含有最大值的非线性特性关系;在相同条件下,wv=1%时的凝结换热系数最高,wv=0.5%时的次之,wv≥2%以后,凝结换热系数随酒精含量的升高而减小.与仅由浓度梯度引起的Marangoni凝结相比,本实验中由浓度梯度和温度梯度共同驱动的凝结换热更强.初步的理论分析也表明,凝结表面上的浓度梯度和温度梯度共同作用使水-酒精凝结液表面的表面张力梯度增大,Marangoni对流加强,凝结换热进一步强化.

Marangoni Condensation Heat Transfer Characteristics on Vertical Surface with Temperature Gradients

Marangoni condensation heat transfer of water-ethanol mixtures on a vertical surface with temperature gradients were studied experimentally,and the variation of condensation modes was observed.The results show that the local heat transfer coefficients at different locations on condensing surface were different,and at the local position with greater temperature gradient the heat transfer coefficient was higher.When the ethanol vapor concentration(mass fraction) was at low range(0.5%,1%),the heat transfer coefficient decreased with the increase of vapor-to-surface temperature difference. When the ethanol vapor concentration was higher,the characteristic curve was a nonlinear one with a maximum.The highest heat transfer coefficient existed at a ethanol vapor concentration of 1%.The heat transfer coefficient decreased with the increase of vapor concentration when the ethanol vapor concentration was more than 2%.Compared with the solutal Marangoni condensation,the present Marangoni condensation driven by concentration and temperature gradients had stronger heat transfer.The preliminary analysis also shows that,under the coaction of concentration and temperature gradients,the surface tension gradient on the condensate surface is greater,leading to the condensation heat transfer to be further enhanced.