Bundle Droplet Shedding And Aggregation Fractal Analysis And Condensation Heat Transfer

There are two methods of steam condensation, that is, dropwise condensation and filmwisecondensation. The dropwise condensation is the method that has much higher heat transfer coefficientthan the filmwise condensation. In this paper, the mechanism of dropwise condensation wasinvestigated thoroughly. Compared with the copper tube bunch, the falling and congregating wasresearched through the experiment.First of all, from the basic viewpoint of adsorption theory, the mechanism of droplets formation duringthe dropwise condensation was analyzed. Based on the dropwise condensation photos under differentscales, the dropwise condensation is the classical fractal structure who meets the definition of fractalstructures, and the fractal model of dropwise condensation was formed. Meanwhile, the formula of itsfractal dimension was put forward. The physical signification of influencing factors and fractaldimension was brought forward for the first time. In addition, the fractal model of droplet falling andcongregating was formed basing on the fractal theory in this paper.Secondly, aimed to the characters of the horizontal-tube-bundle condensation, the falling diameter ofdroplet was researched, and the theoretical diameter formula was put forward.Finally, basing on the experiment between the ion implanted copper tube bundle and the commoncopper bundle, the influence of droplet falling and congregating was studied by the analyses of radialtube-wall temperature. Meantime, the influence of condensate submersion on the heat transfer wasexplored under different submersion levels.Based on the above researches, we can draw the conclusions as follows,(a) The dropwise condensation is the classical fractal structure, and its fractal dimension can reflect the ability of heat transfer. Compared with the dropwise condensation, The fractal dimension of filmwise condensation is the limiting case, that is, 2.(b) The droplet collision is the fractal phenomena. Its fractal model was put forward for the first time, and its fractal dimension is lower than 1 (it is 0.6309 during division times is 3).(c) The influence of droplet falling for the dropwise condensation and filmwisecondensation is different. For the former, the droplet falling and congregating is harmful for the dropwise condensation heat transfer. However, for the latter, it is useful to improve the heat transfer.(d) The influence of condensate submersion is same for the above condensation methods. It lower the whole ability of tube bundle heat transfer not only for the ion implanted copper bundle but for the common copper bundle. The influencing level is more visible for the ion implanted copper bundle.