Dropwise condensation in the presence of non-condensable gas: Interaction effects of the droplet array using the distributed point sink method
Dropwise condensation in the presence of non-condensable gas: Interaction effects of the droplet array using the distributed point sink method
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DOI：
10.1016/j.ijheatmasstransfer.2019.06.068
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发表时间：
2019-10
影响因子：
5.2
通讯作者：
Shaofei Zheng;F. Eimann;C. Philipp;T. Fieback;U. Gross
中科院分区：
文献类型：
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作者：
Shaofei Zheng;F. Eimann;C. Philipp;T. Fieback;U. Gross
由于 NCG 的存在，在逐滴冷凝过程中必须考虑从环境到汽/液界面的蒸汽扩散。从历史上看，模拟滴状冷凝通常假设液滴以孤立的方式生长。然而，周围液滴的阻挡效应会极大地影响蒸汽的空间分布，最终决定与孤立液滴生长模型不同的凝结率。因此，对滴状凝结的准确预测必须包括邻居的阻挡效应（即相互作用效应）。一些经典方法，包括将液滴视为单点汇的点汇方法（PSM）、构造无限系列点汇以满足某些边界条件的图像方法（MOI），与不考虑液滴之间相互作用的孤立液滴生长模型相比，提供了显着的改进。为了捕捉滴状冷凝过程中由于大量液滴和液滴间距较近而产生的强相互作用，提出了分布式点汇方法（DPSM）。就像在格林函数方法中，总质量“汇”负责蒸汽浓度分布一样，冷凝液滴被分解为许多质量点“汇”。为了保证边界条件，对于每个液滴，一系列点汇以平均方式球形分布在液滴内部。点汇的强度通过矩阵公式求解，该矩阵公式需要一定的边界条件和从点汇映射的液滴表面的目标点。考虑一些简单的液滴阵列和逐滴冷凝中的一般液滴阵列，然后将 DPSM 的解决方案与使用 PSM 和 MOI 的解决方案进行比较。基于唯一性定理，精确满足的边界条件说明了DPSM解决强相互作用的能力。最后，DPSM 用于通过逐滴冷凝实验预测特征液滴阵列的液滴相互作用。
With the presence of NCG, the vapor diffusion from ambient to the vapor/liquid interface must be considered during dropwise condensation. Historically, modeling dropwise condensation often makes the assumption that the droplet is growing in an isolated way. However, the blocking effect of surrounding droplets will tremendously influence the spatial distribution of vapor, which finally determines a different condensation rate comparing with that by the isolated-droplet growth model. Consequently, an accurate prediction for dropwise condensation must include the blocking effect of neighbors (namely the interaction effect). Some classical methods, including the point sink method (PSM) treating the droplet as single point sink, the method of images (MOI) constructing an infinite series of the point sinks in order to satisfy certain boundary conditions, provide a significant improvement comparing the isolated droplet growth model without considering the interaction between droplets. For capturing the strong interaction during dropwise condensation because of a large number of the droplets and the closer inter-droplet spacing, a distributed point sinks method (DPSM) is proposed. Just like in the method of Green’s function with a total mass “sink” responsible for the vapor concentration profile, the condensation droplets are resolved into many mass point “sinks”. For guaranteeing the boundary conditions, for each droplet a series of point sinks are spherically distributed inside the droplet using an average manner. The strengths of the point sinks are solved through a matrix formulation which requires certain boundary conditions and the target points of the droplet surface mapped from the point sinks. Considering some simple droplet arrays and a general droplet array in dropwise condensation, the solutions of DPSM are then compared with those using PSM and MOI. Based on the uniqueness theorem, the exactly satisfied boundary conditions state the ability of DPSM in solving the strong interaction. Finally, the DPSM is used to predict the droplet interactions of a characteristic droplet array from dropwise condensation experiments.