Mechanical and Aerospace Engineering


Analytical and Numerical Study of Filmwise Condensation on Periodic Asymmetrically Textured Surfaces

By: Shashank Natesh

Advisor: Professor Vinod Narayanan

Filmwise condensation on a horizontal surface with asymmetric millimeter-sized ratchets and periodically located film drainage pathways in the span-wise direction is analytically and numerically characterized in this research work. The central hypothesis of the proposed research work is that the asymmetry in the surface microstructures can induce a selfgenerated directional motion of the condensed vapor. Within the framework of this research work, the hypothesis is tested in three stages.

The first stage includes the numerical characterization of the initial transient growth of the condensate film inside a single periodic asymmetric ratchet. The second stage includes testing the validity of a net steady-state preferential drainage of the condensate on a small drainage-pathway-density surface through experimental visualization of the steadystate condensate film and development of a two-dimensional adiabatic analytical model describing the asymmetric steady-state characteristics of condensate film. The third stage comprises of analytical modeling of the condensate film drainage on arbitrarily-shaped periodic surfaces based on orthogonal curvilinear coordinates. The model is utilized to quantify the impact of structural asymmetry introduced to periodic surface profiles on net condensate drainage and surface heat transfer. An optimization of the two major objective functions (maximum net mass flux rate and maximum surface heat transfer) under the constraints of various surface and fluid parameters is carried out to engender best possible asymmetric surface topologies. Parametric studies are conducted in the first two stages of the research to evaluate the effects of ratchet pitch, ratchet angles, drainage-pathway-density, orientation of gravity, and Bond number on the condensate film profile. The results from the analysis of experimental visualization, analytical modeling, numerical simulations, and optimization studies in this research work have the potential to enable design of condenser surfaces with novel asymmetric textures, which can be employed in a passive (pump-less) closed-loop microgravity phase-change thermal management system.

Date(s) - 11/29/2017
2:30 pm - 3:30 pm

Bainer 2033


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