表面形貌对初始滴状冷凝的影响

Effects of Surface Topography of Condensation Surface on Initial Dropwise Condensation

鉴于镁能与热水(冷凝液)反应,反应后镁表面的化学成分将发生变化,初始冷凝液核的形态将被保留在镁表面上,所以本实验采用金属镁作为冷凝表面。同时为了研究冷凝表面微观形貌同滴状冷凝之间的关系,在相近的冷凝条件下,选取不同磁控溅射条件下制备的镁膜作为冷凝表面,采用分形理论对镁表面冷凝前表面形貌的复杂程度进行量化研究,运用差分计盒维数法计算镁表面冷凝前表面形貌的分形维数。结果表明冷凝试件的表面形貌特征对初始滴状冷凝的液核数有较大影响,其分形维数不同,冷凝后镁表面初始液核数也不同。在实验的基础上,建立了能够反映表面分形维数对成核中心密度影响的定量关系式。

Since the magnesium can react with hot water（condensate） and change its chemical compositions,via the magnetic-controlled sputter coating method the magnesium-coating surface was used as the condensation surface in this study,thus making the formation of initial condensation nucleuses detectable.The magnesium-coating surfaces with different topographies were prepared via varying the operating parameters of the sputter coating process,and then the differential box-counting method was used to calculate the fractal dimension of these prepared magnesium-coating surfaces.After that,initial dropwise condensation experiments on these magnesium-coating surfaces were carried out under almost the same experimental parameters,and the relationships between the surface topography and dropwise condensation were analyzed.The results show that when the surface fractal dimensions are different,the numbers of nucleation sites for dropwise condensation on the surface are different too,and the surface topography effects the initial dropwise condensation significantly.Based on the experimental results,a new formula was proposed to evaluate quantitatively the relation between the fractal dimension of the condensation surface and the nucleation site density of the dropwise condensation.