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International Heat Transfer Conference 16

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

SURFACE DESIGN FOR DROPWISE CONDENSATION: A THEORETICAL APPROACH

Marieke Ahlers
Chair of Separation Science and Technology, TU Kaiserslautern, Kaiserslautern, Germany

H.-J. Bart
Chair of Separation Science and Technology, TU Kaiserslautern, Kaiserslautern, Germany

DOI: 10.1615/IHTC16.cod.023802
pages 2275-2282


KEY WORDS: condensation, heat transfer enhancement, numerical simulation, dropwise condensation, surface design

Abstract

Different theoretical models have been introduced in the past decades to find structure designs for hydrophobic surface geometries. While describing the wetting characteristics of sessile drops on homogenously structured surfaces reasonably well, they do not account for droplet growth phenomena during dropwise condensation. Hence, experimentally determined wetting behavior is often found incoherent with theory. In this contribution, a new theoretical model is developed to determine the wetting probability on a given surface structure. The proposed model takes the nucleation density, surface geometry, and intrinsic contact angle into account. To simplify the mathematical treatment, the critical nucleation radius, the nucleation density, and contact angles are assumed to be independent of each other. As a case study, parallel 2D pillar structures are used to investigate the resulting droplet type characteristics. These characteristics include: the probabilities for wetting or suspended droplet growth and coalescence. In this regard, an axisymmetric growth of the droplets is assumed between the pillars. The surface structure (ratio and scale) is found to have a substantial effect on the droplet wetting characteristics. In addition to this, the minimum contact angle value, at which suspended droplets are still likely to grow on intrinsically hydrophilic surfaces, is indicated.

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