Session: 17-15-01: Society-Wide Micro/Nano Poster Forum

Paper Number: 99735

99735 - Quasi-Liquid Surface With Patterned Wettability for Condensation 

Massive efforts in research concern the development of low-cost water harvesting systems and optimization of heat-transfer processes for thermal applications like power generation and water desalination. With an improvement in heat-transfer efficiencies, there is potential to reduce wasting energy and overall costs. Specifically, surface engineering to change wettability and promote dropwise condensation has been widely studied to improve existing systems, but solutions suffer from poor heat transfer performance at high heat flux conditions due to inefficient droplet removal. With insufficient droplet removal, a surface tends to collapse from dropwise condensation to a filmwise condensation. It is widely understood during filmwise condensation there is a thick condensate layer, which provides a large thermal resistance and prevents droplet nucleation on the surface, thus adversely affecting heat-transfer performance. Drawing inspiration from the Namib desert beetle, patterned surfaces were made to leverage the advantages of each and improve heat-transfer performance. Current beetle-inspired surfaces suffer from poor droplet removal due to droplet pinning on the hydrophilic domains. Here, we present a chemically patterned hydrophilic and hydrophobic quasi-liquid surface to improve heat transfer performance. We use a PEGylated polymer to make hydrophilic quasi-liquid surface patterns and siloxane to make hydrophobic quasi-liquid surface patterns with an overall ultralow contact angle hysteresis. We present our novel PEGylated quasi-liquid surface which maintains hydrophobicity and slipperiness with the addition of PEG to also enhance nucleation. Utilizing these quasi-liquid surfaces with patterned wettability, we take the beetle-inspired surfaces to their upper limit of condensation heat transfer performance, resulting in a heat-transfer coefficient 70% higher than a beetle-inspired surface with conventional coatings. To overcome the inherent limitations of droplet pinning on the beetle-inspired surface we design a continuous channel pattern to facilitate droplet removal The hydrophilic slippery domains behave like a slippery bridge that facilitates droplet coalescence. As a result, the droplets rapidly grow large enough to shed off from both hydrophilic and hydrophobic domains. Moreover, we investigate the necessity of a slippery hydrophilic pattern to avoid filmwise condensation and a contact angle gradient (i.e. hydrophilic and hydrophobic) to achieve the highest performance. Through quantitative analysis of droplet removal, we determine that the droplet removal frequency accounts for the improvement in heat-transfer performance. Through experimental investigation, we have also determined the optimal pattern size and ratio for condensation. We demonstrate that the quasi-liquid surface with chemical channel patterns shows a heat-transfer coefficient 225% higher than a beetle-inspired surface with conventional coating. Through parametric studies and quantitative analysis concerning droplet removal, we provide design criteria to optimize condensation heat transfer using quasi-liquid surfaces with patterned wettability.

Presenting Author: Dylan Boylan University of Texas at Dallas

Presenting Author Biography: Ph.D candidate in Mechanical Engineering at the University of Texas at Dallas. Concentration is in thermal fluid sciences. Research interests include condensation heat-transfer, surface engineering utilizing polymer coatings, water harvesting, and micro/nano fabrication.

Authors:

Dylan Boylan University of Texas at Dallas
Deepak Monga University of Texas at Dallas
Li Shan University of Texas at Dallas
Xianming Dai University of Texas at Dallas
Zongqi Guo University of Texas at Dallas