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International Heat Transfer Conference 15

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

A Numerical Study of Condensation on Asymmetric Microstructures

DOI: 10.1615/IHTC15.cds.009958
pages 631-644

Shashank Natesh
Oregon State University

Vinod Narayanan
Oregon State University

Sushil Bhavnani
Auburn U


KEY WORDS: Condensation, Thermal management, passive, microstructuers

Abstract

Preferential movement of the condensate due to asymmetry in surface microstructure is explored in this paper. A two-dimensional numerical model to predict the growth of liquid condensate and the associated heat transfer rate on a single asymmetric ratchet is presented. The 80 micrometer ratchet surface, which is maintained at a subcooled temperature, consists of two walls inclined at 30º and 60º to the horizontal respectively. Volume of Fluid (VOF) method is used to track the liquid-vapor interface and the mass and energy source terms are deduced from the Hertz-Knudsen equation. Surface tension force is evaluated by the Continuum Source Force (CSF) concept. The numerical simulations are performed in ANSYS Fluent 14.5 and a code is developed using user-defined functions (UDFs) to calculate the source terms for the governing equations. One-dimensional Stefan problems and laminar condensation over a symmetric ratchet are solved as benchmark tests to validate this numerical model. A small hemispherical droplet of radius 4 micrometers is placed at the trough of the ratchet to initiate the condensation process. A single-phase natural convective vapor precursor solution of the entire computational domain is obtained before introducing the embryo droplet. Sensitivity tests are performed to characterize the effect of the initial droplet size on the growth of the condensate on the walls. Surface tension force plays a significant role in pulling the condensate strongly towards the crest of the steeper wall. Velocity vectors and pressure contour plots are depicted to explain this preferred motion of the condensate.

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