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research-article

DIRECTIONAL PASSIVE CONDENSATE FILM DRAINAGE ON A HORIZONTAL SURFACE WITH PERIODIC ASYMMETRICAL STRUCTURES

[+] Author and Article Information
Shashank Natesh

Mechanical and Aerospace Engineering University of California-Davis, One Shields Ave Davis, CA, 95616 USA
snatesh@ucdavis.edu

Eric Truong

Mechanical and Aerospace Engineering University of California-Davis, One Shields Ave Davis, CA, 95616 USA
hdtruong@ucdavis.edu

Vinod Narayanan

Mechanical and Aerospace Engineering University of California-Davis, One Shields Ave Davis, CA, 95616 USA
vnarayanan@ucdavis.edu

Sushil H. Bhavnani

Department of Mechanical Engineering Auburn University, Mary Martin Hall Auburn, AL, 36849 USA
bhavnsh@auburn.edu

1Corresponding author.

ASME doi:10.1115/1.4036708 History: Received October 14, 2016; Revised May 08, 2017

Abstract

Condensation of a highly wetting fluid on a horizontal surface with asymmetric millimeter-sized ratchets and periodically located film drainage pathways in the span-wise direction is characterized. The hypothesis to be tested is whether the geometry would result in a net steady state preferential drainage of the condensate film. Experiments are performed using PF5060 on a brass surface with ratchets of 3 mm pitch, and 75-15 degree asymmetry. Drainage pathways are varied in density as non-dimensional drainage pathways per meter depth ranging from 133 to 400. Experiments are performed at varied wall subcooling temperatures from 1-10°C. Results of the asymmetric ratchet are compared against a control test surface with 45 - 45 degree symmetric ratchets. Both global and film visualization experiments are performed to characterize the differences in condensation between the symmetric and asymmetric surfaces. Global mass collection results indicate that all characterized asymmetric ratchet surfaces exhibit a net directional drainage of condensate while the symmetric control surface exhibited no preferential drainage. Among the asymmetric ratchets, the total mass flux rate increase with decrease in drainage pathway density while the net mass flux rate increased with pathway density. Visualization of the condensate film was performed to explain the trends in net drainage with subcooling for different drainage pathway densities. For small drainage path density surfaces, a two-dimensional analytical model was developed to further characterize the effect of ratchet angle and Bond number on the net preferential drainage.

Copyright (c) 2017 by ASME
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