Library Subscription: Guest
Home Archives Thermal Letter Officers Future meetings Assembly for International Heat Transfer Conferences
International Heat Transfer Conference 15

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

Influence of Drop Shape and Coalescence on Dropwise Condensation over Textured Surfaces

Praveen M. Somwanshi
Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India

Krishnamurthy Muralidhar
Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India

Sameer Khandekar
Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur (UP) 208016, India

DOI: 10.1615/IHTC15.kn.000013
pages 251-270

Abstract

The authors of the present study have developed a mathematical model of dropwise condensation on the underside of horizontal and inclined surfaces [1-2]. The model is general enough to deal with a variety of fluids ranging from water to liquid sodium. The condensation process is seen to be quasi-periodic, starting from nucleation to growth and coalescence1, followed by the movement of unstable drops that initiates fresh nucleation on exposed portions of the substrate. From the distribution of drops of various sizes, the instantaneous surface averaged heat transfer coefficient and wall shear stress are computed. Heat transfer rate is high through small drops and small under large drops. The largest drop diameter achieved depends on gravitational stability with respect to the interfacial forces at the three-phase contact line. Drop instability controls the periodicity of the condensation process and as a result, the heat transfer coefficient and wall shear stress. The developed model (i) simplifies drop shapes as spheroidal and (ii) assumes droplet coalescence process as instantaneous. Including additional details in the multi-scale condensation model makes it computationally intractable. To examine the consequence of these two simplifications on the overall dropwise condensation process, the sensitivity of the heat transfer coefficient and wall shear stress to drop deformation and coalescence has been studied in the present work. The shape of the drop on the underside of an inclined surface has been determined using a software tool based on the principle of minimization of potential and surface energies. Velocity and timescales of droplet coalescence are determined from high speed imaging. With the drop shape correctly determined, results show that improved wall shear stress and heat transfer coefficient are both smaller but the overall integrated predictions are not severely sensitive to these additional details. With coalescence, large heat fluxes attained for short time duration do not contribute much to the surface-averaged value. On the other hand, large shear stresses are momentarily created and these can impact the life of surface coatings.

Purchase $25.00 Check subscription Publication Ethics and Malpractice Recommend to my Librarian Bookmark this Page