滴状冷凝中液滴的脉动规律及分形分布模型中相邻两代液滴半径比参数

分析研究了滴状冷凝实验过程中液滴的随机运动行为以及液滴分布的分形特征,发现液滴的运动和分布与接触角及接触角滞后有关.得到了液滴分形分布模型中相邻两代液滴半径比与接触角滞后的关系式,该式计算结果与实验结果十分吻合.实验结果表明,在存在接触角滞后的表面上,液滴以脉动方式长大,导致液滴分布呈离散分代分布,并且,液滴脉动行为还受诱导因素的影响,在较强诱导因素作用的冷凝过程中,液滴分代呈明显的台阶分布;反之,在较弱的诱导条件下,分代特征不明显.液滴受接触角滞后影响而发生的脉动行为还表现为液滴偶然与随机的弹射.在液滴频繁脉动形成分代分布特征的过程中,液滴由接触角为前进角状态脉动到等体积下接触角为平衡角状态的可能性较大.

The Pulsating Feature of the Dancing Droplets and Droplet Radius Ratio of Adjacent Generations in the Fractal Model of Dropwise Condensation

The random motion of the droplets and the fractal characteristics of droplet sizes distribution during dropwise condensation were investigated. It is found that the motion and size distribution of droplets are related to the contact angles and the contact angle hysteresis. The relationship between the droplet radium ratio of adjacent generations in the fractal model of dropwise condensation and the contact angle hysteresis was obtained, and the calculated results agree well with the experimental data. On the surface existing contact angle hysteresis, the droplet grows up mainly by the pulsating motion, and it will cause the stepwise segment distribution of droplet sizes to occur. Furthermore, the pulsation of droplets is also affected by the inducing factors, such as the uneven distribution of the surface free energy over the condensing surface, etc., and the strong inducing effect leads to the obvious stepwise distribution of the droplet generation. The occasionality and randomicity of droplet ejections are also attributed to the droplet pulsation resulting from the contact angle hysteresis. In the formation of generation characteristic by the frequent pulsations of condensing droplets, the greater possibility is that the droplets transform from the stage with an advancing contact angle to the state with an equilibrium contact angle while the liquid volume keeps unchanged.