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Title:A comprehensive model of electric-field-enhanced jumping-droplet condensation on superhydrophobic surfaces
Author(s):Birbarah, Patrick
Advisor(s):Miljkovic, Nenad
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Electric field enhanced
jumping droplet
heat transfer
Abstract:Superhydrophobic micro/nanostructured surfaces for dropwise condensation have recently received significant attention due to their potential to enhance heat transfer performance by shedding positively charged water droplets via coalescence-induced droplet jumping at length scales below the capillary length, and allowing the use of external electric fields to enhance droplet removal and heat transfer, in what has been termed electric-field-enhanced (EFE) jumping-droplet condensation. However, achieving optimal EFE conditions for enhanced heat transfer requires capturing the details of transport processes that is currently lacking. While a comprehensive model has been developed for condensation on micro/nanostructured surfaces, it cannot be applied for EFE condensation due to the dynamic droplet-vapor-electric field interactions. In this work, I developed a comprehensive physical model for EFE condensation on superhydrophobic surfaces by incorporating individual droplet motion, electrode geometry, jumping frequency, field strength, and condensate vapor-flow dynamics. As a first step towards my model, I simulated jumping droplet motion with no external electric field, and validated my theoretical droplet trajectories to experimentally obtained trajectories, showing excellent temporal and spatial agreement. I then incorporated the external electric field into my model and considered the effects of jumping droplet size, electrode size and geometry, condensation heat flux, and droplet jumping direction. My model suggests that smaller jumping droplet sizes and condensation heat fluxes require less work input to be removed by the external fields. Furthermore, the results suggest that EFE electrodes can be optimized such that the work input is minimized depending on the condensation heat flux. To analyze overall efficiency, I defined an incremental coefficient-of-performance and showed that it is very high (~10e6) for EFE condensation. I finally proposed mechanisms for condensate collection which would ensure continuous operation of the EFE system, and which can scalably be applied to industrial condensers. This work provides a comprehensive physical model of the EFE condensation process, and offers guidelines for the design of EFE systems to maximize heat transfer.
Issue Date:2016-04-28
Rights Information:Copyright 2016 Patrick Birbarah
Date Available in IDEALS:2016-07-07
Date Deposited:2016-05

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