Journal
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
Volume 109, Issue -, Pages 187-199Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijheatmasstransfer.2017.01.119
Keywords
Dropwise condensation; Dropsize distribution; Sweeping; Heat transfer; Lubricant infused surface (LIS); Slippery liquid infused porous surface (SLIPS)
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Funding
- National Science Foundation Engineering Research Center for Power Optimization of Electro Thermal Systems (POETS) [EEC-1449548]
- Office of Naval Research (ONR) [N00014-16-1-2625]
- International Institute for Carbon-Neutral Energy Research [WPI-I2CNER]
- Japanese Ministry of Education, Culture, Sports, Science and Technology
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Condensation is a ubiquitous phenomenon in nature and industry. Heat transfer rates during dropwise condensation on non-wetting substrates can be 6-8X higher than heat transfer rates during traditional filmwise condensation on wetting substrates. Dropwise condensation on lubricant-infused surfaces (LIS, or SLIPS) is particularly interesting due to high droplet mobility on these surfaces. To accurately predict heat transfer rates during dropwise condensation, the distribution of droplet sizes must be known. Here we present condensation studies of water on aluminum-based lubricant-infused surfaces with a wide range of lubricant viscosities (12-2717 cSt) to determine droplet size distributions. Through optical imaging and microscopy, we show that the distribution of droplet sizes on LIS is independent of lubricant viscosity, and agrees well with the model developed by Rose for the distribution of droplet sizes on hydrophobic surfaces, especially in the range 10 < r < 100 mu m. Using artificial sweeping experiments and numerical modeling, we investigate the dependence of sweeping rates on the distribution of droplet sizes and on average heat transfer rates. The maximum size to which droplets grow before being swept decreases rapidly with only a modest decrease in sweeping period, from 750 to 62 mu m. Yet, the distribution of droplet sizes and heat transfer rates are nearly unaffected by the change in sweeping period, due to a relative insensitivity of heat transfer to droplets with radii r > 100 mu m due to a high conduction resistance within these droplets. Our work provides an experimental and analytical framework to predict heat transfer and sweeping rates for water condensation on a vertical plate coated with a LIS or SLIPS surface. (C) 2017 Elsevier Ltd. All rights reserved.
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