scholarly journals Dropwise condensation on bioinspired hydrophilic-slippery surface

RSC Advances ◽  
2018 ◽  
Vol 8 (69) ◽  
pp. 39341-39351 ◽  
Author(s):  
L. Guo ◽  
G. H. Tang
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Water Transport ◽  
Nucleation Rate ◽  
Copper Surface ◽  
Dropwise Condensation ◽  
Sliding Angle ◽  
Small Contact Angle ◽  
Slippery Surface

A hydrophilic-slippery copper surface is fabricated, reconciling two required factors, enhanced condensation and efficient water transport. Nucleation rate, droplet mobility and heat transfer are enhanced by the small contact angle and sliding angle.

A Heat Transfer Model of Dropwise Condensation Underneath a Horizontal Substrate

2011 ◽  
Vol 199-200 ◽  
pp. 1604-1608
Author(s):  
Yun Fu Chen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Contact Angle ◽  
Fractal Model ◽  
Condensation Heat Transfer ◽  
Droplet Growth ◽  
Transfer Model ◽  
Dropwise Condensation ◽  
Small Contact Angle ◽  
Horizontal Substrate

For finding influence of the condensing surface to dropwise condensation heat transfer, a fractal model for dropwise condensation heat transfer has been established based on the self-similarity characteristics of droplet growth at various magnifications on condensing surfaces with considering influence of contact angle to heat transfer. It has been shown based on the proposed fractal model that the area fraction of drops decreases with contact angle increase under the same sub-cooled temperature; Varying the contact angle changes the drop distribution; higher the contact angle, lower the departing droplet size and large number density of small droplets; dropwise condensation translates easily to the filmwise condensation at the small contact angle ;the heat flux increases with the sub-cooled temperature increases, and the greater of contact angle, the more heat flux increases slowly.

The possibility for realizing dropwise condensation with small contact angle

2003 ◽  
Vol 52 (10) ◽  
pp. 2427
Author(s):  
Cao Zhi-Jue ◽  
Xia Bo-Li ◽  
Zhang Yun
Keyword(s):  
Contact Angle ◽  
Dropwise Condensation ◽  
Small Contact Angle

Study on Condensation Heat Transfer on Micro Structured Surfaces (Effect on Condensation Heat Transfer of Metal Sputtering Surfaces)

2013 ◽  
Author(s):  
Kohei Yamazaki ◽  
Hiroyasu Ohtake ◽  
Koji Hasegawa
Keyword(s):  
Heat Transfer ◽  
Metal Film ◽  
Copper Surface ◽  
Thin Metal Film ◽  
Thin Metal ◽  
Condensation Heat Transfer ◽  
Dropwise Condensation ◽  
Transfer Coefficients ◽  
Structured Surfaces ◽  
Heat Transfer Coefficients

The present study was intended to examine how the condensation heat transfer, especially the dropwise condensation, was affected by modifying the surface nature. In the present study, condensation heat transfer experiments for steam were performed by using mirror-finished copper surface and some very thin metal-film surfaces by using sputtering on mirror-finished copper block. That is, the effects on pattern of condensation heat transfer, i.e., dropwise or film-wise condensation, of metal-sputtered surfaces were examined experimentally and qualitatively. The present experimental results showed that the condensation on sputtered metal surfaces of Copper (Cu), Chromium (Cr) and Lead (Pb), became dropwise condensation. The heat transfer coefficients were ten times higher than the Nusselt equation. The condensation on sputtered metal surface of Titanium (Ti) became filmwise condensation. High contact angle was trended to be dropwise condensation on very thin metal-film surfaces by using sputtering.

The Effect of Thermal Resistance for Dropwise Condensation on Hydrophobic Micro-Pillared Structures

2012 ◽  
Author(s):  
Sara S. Beaini ◽  
Hector Mendoza ◽  
Van P. Carey
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Surface Energy ◽  
Thermal Resistance ◽  
Droplet Growth ◽  
Dropwise Condensation ◽  
Textured Surfaces ◽  
Critical Question ◽  
Low Surface Energy ◽  
The Continuum

Superhydrophobic/hydrophobic surfaces, developed to promote dropwise condensation, can be produced by modifying the surface chemically with low surface energy films, and/or structurally by fabricating micro-textured surfaces. Some research has reported the increased thermal resistance from the added chemical layer and its effect on condensation heat transfer. A critical question of interest is the thermal resistance due to micro-pillared structures and their influence on droplet growth during condensation as compared to smooth or non-textured surfaces. Though idealized, this paper presents a theoretical and computational model for evaluating and quantifying the effects of the pillared structures thermal resistance, as well as the continuum versus non-continuum mechanisms affecting droplet growth during dropwise condensation. The model is used to compare different micro-pillared surfaces, cited in the literature, and to predict which micro-pillar dimensions contribute to slower condensate growth despite the higher contact angle advantage during dropwise condensation.

Submicron Superhydrophobic Surface Treatment Suitable for High Performance Condensers: A Modeling

2009 ◽  
Author(s):  
Sunwoo Kim ◽  
Kwang J. Kim ◽  
John M. Kennedy ◽  
Jiong Liu ◽  
Ganesh Skandan
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Theoretical Model ◽  
Size Distribution ◽  
Drop Size ◽  
Drop Size Distribution ◽  
Condensation Heat Transfer ◽  
Dropwise Condensation ◽  
Superhydrophobic Coating ◽  
Single Droplet

The effect of the drop-contact angle on dropwise condensation heat transfer of saturated steam on a single horizontal copper tube with the superhydrophobic coating was investigated theoretically. The theoretical model is established by combining heat transfer through a single droplet with a well-known drop size distribution theory. The analysis of single droplet heat transfer incorporates resistances due to vapor-liquid interface, drop curvature, conduction through the drop, and conduction through the superhydrophobic coating layer. Each resistance is expressed as a function of the contact angle. The total resistance for a drop with a fixed radius increases as the contact angle increases. A population balance model is used to develop a drop distribution function for the small drops that grow by direct condensation. Drop size distribution for large drops that grow mainly by coalescence is obtained from the empirical equation proposed by Le Fevre and Rose (1966). The results indicate that the contact angle has a strong correlation with the maximum drop radius, which plays a pivotal role in determining drop size distribution. A high contact angle leads to a significant reduction in the radius of the largest drop that is about to fall down due to gravity and sweep away drops in its path. Thus, there are more areas on the condensing surface for small drops, allowing for greater heat transfer. Also, it is shown that surface wettability affects the performance of dropwise condensation heat transfer and our theoretical model successfully predicts this phenomenon.

Dropwise Condensation Heat Transfer Model: Effect of the Liquid-Solid Surface Free Energy Difference

2006 ◽  
Author(s):  
Xue-Hu Ma ◽  
Zhong Lan ◽  
Yu Zhang ◽  
Xing-Dong Zhou ◽  
Tian-Yi Sun
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Free Energy ◽  
Heat Transfer Coefficient ◽  
Energy Difference ◽  
Interfacial Interaction ◽  
Condensation Heat Transfer ◽  
Dropwise Condensation ◽  
Free Energy Difference ◽  
Simulation Results

Dropwise condensation heat transfer performance depends not only on the condensing conditions, but also on the interfacial interaction between condensate and condensing surface material. Based on the well-established Rose’s model, a modified model of dropwise condensation heat transfer is proposed by considering the interfacial interaction between liquid and solid, and established by rebuilding the space conformation of drop distributing into time conformation. The simulation results indicate that the heat transfer coefficient increases with the surface free energy difference increasing and the contact angle hysteresis decreasing. The larger contact angle and the smaller departure drop size result in the higher heat transfer coefficient. Different interfacial effect gives rise to the different heat transfer curves. For the identical solid-liquid-vapor system, the simulation results agree very well with the present experimental data and those reported in literature. The controversy among experimental results in literature might be well understood with the concept of the present paper.

scholarly journals Effect of Contact Angle on Steam Dropwise Condensation: A Simulation Approach

2012 ◽  
Vol 2012 ◽  
pp. 1-7
Author(s):  
Milad Nahavandi ◽  
Arjomand Mehrabani-Zeinabad
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Distribution Coefficient ◽  
Size Distribution ◽  
Atmospheric Pressure ◽  
Simulated Data ◽  
Condensation Process ◽  
Dropwise Condensation

Dropwise condensation process on surface of a vertical polytetrafluouroethylene (PTFE) plate at atmospheric pressure was simulated. Comparison of simulated data with experimental and theoretical results indicates that performed simulation results confirm experimental data, although they deviated from existing proposed correlations. For calculation of heat transfer coefficient and droplets size distribution, simulation of condensation process over vertical copper and PTFE surfaces at atmospheric pressure was performed. By considering the effect of contact angle on heat transfer resistances of droplets, the gained data were optimized in order to evaluate droplets size distribution coefficient. This distribution coefficient was used in a new correlation for prediction of heat transfer coefficient for dropwise condensation process. Comparison of experimental results with the correlation shows a good agreement, 11% relative error.

scholarly journals Droplet sweeping to enhance heat transfer during dropwise condensation

2021 ◽  
Vol 2116 (1) ◽  
pp. 012013
Author(s):  
M Tancon ◽  
M Mirafiori ◽  
S Bortolin ◽  
A Martucci ◽  
D Del Col
Keyword(s):  
Heat Transfer ◽  
Sol Gel ◽  
Saturation Temperature ◽  
Copper Surface ◽  
Aluminum Surface ◽  
Transfer Model ◽  
Dropwise Condensation ◽  
Transfer Coefficients ◽  
Vapor Velocity ◽  
Heat Transfer Coefficients

Abstract It is well known that dropwise condensation (DWC) can achieve heat transfer coefficients (HTCs) up to 5-8 times higher as compared to filmwise condensation (FWC). The interaction between the condensing fluid and the surface defines the condensation mode. Coatings that present low surface energy and high droplet mobility are a solution to promote DWC instead of FWC on metallic substrates. In the present paper, the effect of vapor velocity during DWC has been investigated over a sol-gel coated aluminum surface and a graphene oxide coated copper surface. Heat transfer coefficients and droplets departing radii have been measured at constant saturation temperature and heat flux, with average vapor velocity ranging between 3 m s−1 and 11 m s−1. A recent method developed by the present authors to account for the effect of vapor velocity on the droplet departing radius is here presented. The results of the proposed method, when coupled with the Miljkovic et al. [1] heat transfer model, are compared against experimental data.

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