The aim of this research is to develop an algorithm to simulate droplets nucleation and growth during dropwise condensation in order to study the droplets spatial distribution. The proposed algorithm starts with droplets distributed based on the Poisson point process and investigates the spatial distribution of droplets using Ripley's L function method. Also, the effects of substrate temperature (T w) and initial density (N D) on the percentage of area occupied by droplets (φ) are studied. Good agreement between model predictions and experimental data for the rate of growth and changes in droplets density (N t) as well as spatial distribution of droplets verifies the validity of the simulating model.
Controlling condensation conditions by surface topography is of prime interest. The aim of this work is to investigate the behavior of water droplets condensing on oriented sub-micrometric structures representing ripples with wavelengths around 800 nm. Droplet behavior was studied on different ripples heights and on untextured surfaces. It was specifically looked at how the presence of ripples creates geometrical confinement, and how that influences the deformation and the orientation of single droplets. Results show that the condensed droplets follow the orientation of textured features, especially with high structures height (150 nm). This is shown by the decreasing of droplet roundness with ripples height. The relative number of circular droplets (roundness near to 1) is around 0.6 for 70 nm high ripples and decrease to around 0.2 for 150 nm high ripples. The corresponding relative number on untextured surface is around 0.5. A mechanism, based on droplets pinning and hysteresis, is proposed to explain the influence of the ripples orientation in a vertical plane, onto the droplet deformation during coalescence step. Finally, the presence of ripples is shown to barely impact breath figure dynamics. Number of droplets and mean droplet radius for the textured and untextured surfaces present a comparable evolution.
In polymer protection pieces, polycarbonate is often used for its transparency and its high impact resistance. However, when dew appears it degrades light transmission and thus transparency. To solve this problem, anti-fogging surfaces are developed. To further understand the dew formation in natural environment in order to design high efficiency anti-fogging surfaces on polycarbonate, a recently designed dew tracking setup giving dew pictures and a digital imaging procedure allowing reliable and highly accurate droplet measurements were developed. Thanks to this setup, dew formation conditions such as relative humidity level and air temperature can be chosen and studied. Particular attention is paid to the evolution of the number of droplets according to the relative humidity and how it explains the droplet growth rate. The influence of the relative humidity (RH) on the growth rate of non-coalescing dropwise condensation has already been observed. This paper is based on these existing results as a comparison to validate the experimental setup and the post-processing analysis. We shall also use the number of droplets to further explain the role of the RH on condensation dynamics. Moreover, by applying a light subcooling, the growth kinetics were slowed down in order to observe every characteristic phase in detail and even particular intermediate phases.
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