液滴在纳米结构表面上的传热与生长模型

摘要

在传热学领域,滴状冷凝具有高效传热性能,比膜状冷凝的传热系数高出几十倍.若能在工业生产中实现滴状冷凝,所需的有效换热面积将会大为减少,产生可观的经济效益.为了更好地提高设备的传热性能,节约能源以及原材料,对利用仿生超疏水性表面实现滴状冷凝传热的过程进行了研究.通过建立单个液滴的冷凝传热模型,分析液滴的润湿状态,研究了液滴的2种生长模式:以恒定接触角增加底部润湿面积(CCA)模式和以恒定底部直径增加接触角(CB)模式,得出了液滴按照这2种模式生长的数学模型,进而分析冷凝液滴生长模式的影响因素.结果表明:当液滴按照CCA模式生长时,其半径生长速率与纳米锥导热率、尖端尺寸呈正相关,与高度、间距呈负相关,接触角对其是分段式的影响,即当θ<90°时呈负相关,反之,当θ>90°时呈正相关;当液滴按照CB模式生长时,与CCA模式不同的是,其生长速率与接触角呈负相关.综合液滴的2种生长模式可知,接触角的影响最为显著.本文所建立的理论模型与实验数据基本吻合,可为优化纳米锥结构表面提供理论参考.%In the field of heat transfer,dropwise condensation has high heat transfer performance,which is several times higher than that of filmwise condensation.If dropwise condensation can be realized in industrial production,the required effective heat exchange area will be greatly reduced,which will inevitably produce huge economic benefits.In order to improve the heat trans-fer performance of the equipment,save energy and raw materials,the process of droplet condensation heat transfer using bionic superhydrophobic surface is studied.the wetting state is analyzed and the two growth modes of the droplet are studied by estab-lishing the condensation heat transfer model of a single droplet.The two modes are increasing the bottom contact area with con-stant contact angle and increasing the contact angle with constant bottom diameter,respectively.Then the mathematical model of the droplet growth is obtained according to the two modes,and the influencing factors of the droplet growth mode are ana-lyzed.It is found that when the droplet grows according to the CCA mode,the radius of the growth rate is positively correlated with thermal conductivity of nanocone and tip size,but negatively correlated with height and spacing,and the contact angle shows stages influencing on it.That is,whenθ<90°,it has a negative correlation,while if not,it has a positive correlation.When the droplet grows in accordance with the mode of CB,unlike the CCA mode,its growth rate is negatively correlated with contact angle.Combined with the two growth modes of droplets,the influence of contact angle is the most significant.The fitting experiments show that the theoretical model established in this paper is in good agreement with the experimental data basically,and provides theoretical reference for optimizing the nanocone structure surface.