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Title:Liquid-infused slippery surfaces for air-conditioning and refrigeration applications
Author(s):Yu, Rong
Director of Research:Jacobi, Anthony M.
Doctoral Committee Chair(s):Jacobi, Anthony M.
Doctoral Committee Member(s):Hrnjak, Predrag S.; Miljkovic, Nenad; Dutton, Craig
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Liquid-infused surface
Surface wettability
Heat transfer
Droplet mobility
Air-conditioning and refrigeration applications
Water drainage
Air-side pressure drop
Surface modification
Wettability management
Heat exchanger performance
Frosting and defrosting
Abstract:Liquid-infused surfaces have drawn a lot of attention due to their excellent water repellency. A method is presented for creating a durable liquid-infused surface (LISs) on aluminum surfaces to minimize the water retention and enhance thermal-hydraulic performance for air-conditioning and refrigeration (AC&R) applications. The results demonstrate that the LISs has a sliding angle smaller than 5˚ and reduces the water retention ratio after defrosting by more than 75% compared to the baseline specimen. A delay of ice formation is also observed. These LISs can effectively drain condensate, retard frost formation, and reduce frost meltwater retention. Water droplet configuration on the LISs is explored. Droplets float on the surface and are surrounded by an annular ridge of lubricant. The excess surface energy released during the coalescence drives the droplets to move on the horizontal LISs and induces droplet jumping on a superhydrophobic surface. The changes in Gibbs energy (ΔG) of the condensation at the oil-air and oil-solid interfaces are also investigated to understand better the onset of condensation and thus lead to enhanced nucleation. Water prefers condensing at a higher relative humidity environment and on a more wettable substrate due to less ΔG at a metastable equilibrium. The onset of condensation can occur at the oil-air interface or the oil-solid interface depending on the relative humidity, the substrate wettability, and the water solubility. The longevity of surfaces is examined from periodic frosting and defrosting experiments. The oxalic acid-anodized LISs with nanostructures keep the water repellency after 60 frosting and defrosting cycles. The sulfuric acid-anodized LISs with hierarchical structures is not capable of locking the lubricant on the surface, so the performance deteriorates with increasing cycles. The hierarchical textured substrate has a smaller capillary pressure and a capillary pressure gradient, which causes an unstable lubricant layer and thus accelerates the oil depletion. Therefore, a substrate with uniform nanostructures is recommended for an LIS. A plain-fin-and-tube heat exchanger with LISs aluminum fins and the other heat exchanger with hydrophilic fins are built with the same fin-and-tube configuration. The effect of the liquid-infused fin surface design on the heat transfer and thermal-hydraulic performance is quantified experimentally under dry and wet conditions in a closed-loop wind tunnel. Surface wettability has more impact on the air-side pressure drop than it does on the heat transfer coefficient. Two heat exchangers have a comparable heat transfer coefficient under wet conditions, but the pressure drop of the slippery prototype is decreased by up to 27% due to better water drainage behavior than that of a hydrophilic baseline. Overall, the liquid-infused heat transfer surfaces show promise for AC&R applications.
Issue Date:2019-11-25
Rights Information:Copyright 2019 Rong Yu
Date Available in IDEALS:2020-03-02
Date Deposited:2019-12

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