New amorpheous hydrogenated carbon films have been applied successfully to promote dropwise condensation (DWC) of steam on metallic surfaces at atmospheric pressure. The highest heat transfer ...coefficients have been measured for completely coated surfaces, maximum contact angle, largest thermal conductivity of the base material, vertically oriented wall and minimum wall height. The effect of these parameters on the DWC performance is evaluated quantitatively. The investigation of partly coated surfaces shows, that even for a small portion of coated surface (approx. 20 % DWC and 80 % filmwise condensation (FWC)) still nearly maximum heat transfer is achieved. This phenomenon is explained qualitatively by the application of numerical simulation of the local condensation process using the finite element method (FEM). Furthermore, this analysis technique also explains the dependence of DWC heat transfer on the thermal conductivity of the base material being coated.
De nouveaux films de carbone halogéné amorphe ont été utilisés avec succès pour favoriser la condensation en gouttes de vapeur sur des surfaces métalliques à la pression atmosphérique. Les coefficients de transfert thermique les plus élevés ont été mesurés pour des surfaces entièrement recouvertes par le film, un angle de contact maximum, une paroi de conductivité thermique élevée, orientée verticalement et de faible hauteur. L'effet de ces paramètres sur les performances de la condensation en gouttes est déterminé quantitativement. L'étude des surfaces partiellement recouvertes par le film montre que, même pour une faible partie de surface revêtue (approximativement 20 % pour la condensation en gouttes et 80 % pour la condensation en film), les transferts thermiques restent très élevés. Ce phénomène est expliqué qualitativement par simulation numérique du processus de condensation locale par une méthode d'éléments finis. De plus, cette technique d'analyse permet d'expliquer la variation des transferts thermiques en condensation en gouttes avec la conductivité thermique du matériau de la paroi recouverte.
The dynamic behaviors of water droplets on a slippery surface are significant to practical anti-icing applications. Herein, the impact and sliding behavior of water droplets on lubricant-infused ...surfaces (LISs) were investigated with a high-speed camera. LISs were prepared by infusing perfluoropolyether oils into anodized porous surfaces. The results show that the maximum spreading diameter and retraction velocity of the impact droplet increased with the We number. For LIS-100, the spreading factor at 2.5 ms increased from 2.00 to 3.88 with We increasing from 30 to 267. Low-viscosity lubricant facilitated the retraction speed and rebound of droplet impact on the surface, while high-viscosity lubricant contributed to the lubricant stability of the LIS. Additionally, high inclination angle (θ) facilitated the rapid shedding of water droplets on the surface. The velocity increased rapidly from 1.04 to 4.66 mm/s with θ increasing from 15° to 45°. The LIS prepared with low-viscosity lubricant had a high sliding velocity, and the sliding velocity of water droplets on LIS-100 was about seven times faster than that on LIS-104. This work reveals the impacting law of water droplets on LISs and provides useful information for the design of LISs under drop impact conditions.
