Dropwise Condensation on Hydrophilic Surfaces PDF Download

Author: Alex Wu
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author:
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Category :
Languages : en
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Book Description
Abstract : The objective of this work is to identify the fundamental mechanism of dropwise condensation on a smooth solid surface by probing the solid-vapor interface during phase-change to evaluate the existence and structure of the thin film and the initial nucleus that develop during condensation. In this work, an automated Surface Plasmon Resonance imaging (SPRi) instrument with the ability to perform imaging in intensity modulation and angular modulation is developed. The SPRi instrument is used to probe (in three dimensions) the adsorbed film that forms on the substrate during dropwise condensation. SPRi with a lateral resolution of ~ 4-10 μm, thickness resolution of 0.1-1nm, and temporal resolution of 200-10,000 frames per second can measure water films that are monolayer to multilayer in thickness. The governing mechanism of dropwise condensation is investigated in detail for stable dropwise condensation on a smooth hydrophilic substrate. The study shows nucleation is the first step in dropwise condensation and no film greater than a monolayer exists between droplets during stable dropwise condensation. Our result confirms previous experimental works in support of nucleation theory as the mechanism of dropwise condensation. Our observation of unstable dropwise condensation of steam on a smooth hydrophilic surface shows presence of a several nanometers thick water film between droplets during dropwise condensation. This data matches with previous experimental work in support of film rupture theory. In summary, our results indicate nucleation theory or film rupture theory may be valid for special experimental settings. And, neither of these two theories are a comprehensive theory than can explain the physics of dropwise condensation.

Author: Sameer Khandekar
Publisher: Springer Science & Business Media
ISBN: 1461484472
Category : Science
Languages : en
Pages : 155

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Dropwise Condensation on Textured Surfaces presents a holistic framework for understanding dropwise condensation through mathematical modeling and meaningful experiments. The book presents a review of the subject required to build up models as well as to design experiments. Emphasis is placed on the effect of physical and chemical texturing and their effect on the bulk transport phenomena. Application of the model to metal vapor condensation is of special interest. The unique behavior of liquid metals, with their low Prandtl number and high surface tension, is also discussed. The model predicts instantaneous drop size distribution for a given level of substrate subcooling and derives local as well as spatio-temporally averaged heat transfer rates and wall shear stress.

Author: Sameer Khandekar
Publisher: Springer Nature
ISBN: 3030484610
Category : Science
Languages : en
Pages : 462

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This book is an expanded form of the monograph, Dropwise Condensation on Inclined Textured Surfaces, Springer, 2013, published earlier by the authors, wherein a mathematical model for dropwise condensation of pure vapor over inclined textured surfaces was presented, followed by simulations and comparison with experiments. The model factored in several details of the overall quasi-cyclic process but approximated those at the scale of individual drops. In the last five years, drop level dynamics over hydrophobic surfaces have been extensively studied. These results can now be incorporated in the dropwise condensation model. Dropwise condensation is an efficient route to heat transfer and is often encountered in major power generation applications. Drops are also formed during condensation in distillation devices that work with diverse fluids ranging from water to liquid metals. Design of such equipment requires careful understanding of the condensation cycle, starting from the birth of nuclei, followed by molecular clusters, direct growth of droplets, their coalescence, all the way to instability and fall-off of condensed drops. The model described here considers these individual steps of the condensation cycle. Additional discussions include drop shape determination under static conditions, a fundamental study of drop spreading in sessile and pendant configurations, and the details of the drop coalescence phenomena. These are subsequently incorporated in the condensation model and their consequences are examined. As the mathematical model is spread over multiple scales of length and time, a parallelization approach to simulation is presented. Special topics include three-phase contact line modeling, surface preparation techniques, fundamentals of evaporation and evaporation rates of a single liquid drop, and measurement of heat transfer coefficient during large-scale condensation of water vapor. We hope that this significantly expanded text meets the expectations of design engineers, analysts, and researchers working in areas related to phase-change phenomena and heat transfer.

Author: Danuska Pathiranage
Publisher: GRIN Verlag
ISBN: 3346524698
Category : Technology & Engineering
Languages : en
Pages : 47

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Bachelor Thesis from the year 2020 in the subject Engineering - Aerospace Technology, grade: First Class, University of Brighton, course: BEng Aeronautical Engineering, language: English, abstract: This project investigates the effects of different wettability characteristics in drop wise condensation on smooth plates. It involves a Volume of Fluid (VOF) based Computational. Condensers are used in various energy intensive processing industries. Improving their efficiency plays a crucial role in optimization of energy consumption. Drop wise Condensation is a highly attractive form of heat transfer. Fluids Dynamics (CFD) model to carry out the simulations in OpenFOAM on smooth plates with various wettabilities. Different parameters such as receding angle, advancing angle and various radii of droplets have been used for investigation. A base case with droplets’ radius of 12.5μm, receding angle and advancing angles of (34°, 90°) was used. Three sets of simulations were performed. In Set 1, the angles were (34°, 90°). The radius of the first droplet was kept constant at 12.5μm and the radius of the second droplet changes 1:4 progressively. In Set 2, the angles are changed to (154°,162°) and the radius of the second droplet changes in the same manner above. In Set 3, the angles were kept at (107°, 117°). The radius changes as above. In some cases, the droplets merge and condense. In others, momentum created by merging of the droplets creates repeated oscillation or even a lift off, from the cooled plate.

Author: Karlen Elizabeth Ruleman
Publisher:
ISBN:
Category :
Languages : en
Pages : 24

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Dropwise condensation has the potential to greatly increase heat transfer rates. Heat transfer coefficients by dropwise condensation and film condensation on microstructured silicon chips were compared. Heat transfer coefficients are found to be seventy percent higher in the hydrophobic, dropwise condensation case relative to the hydrophilic, film condensation case. With this increased heat transfer coefficient, dropwise condensation using microstructures could improve many heat exchange applications, particularly electronics cooling.

Author: Phuong Pham
Publisher: BoD – Books on Demand
ISBN: 1789851998
Category : Technology & Engineering
Languages : en
Pages : 295

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Book Description
Surface sciences elucidate the physical and chemical aspects of the surfaces and interfaces of materials. Of great interest in this field are nanomaterials, which have recently experienced breakthroughs in synthesis and application. As such, this book presents some recent representative achievements in the field of surface science, including synthesis techniques, surface modifications, nanoparticle-based smart coatings, wettability of different surfaces, physics/chemistry characterizations, and growth kinetics of thin films. In addition, the book illustrates some of the important applications related to silicon, CVD graphene, graphene oxide, transition metal dichalcogenides, carbon nanotubes, carbon nanoparticles, transparent conducting oxide, and metal oxides.

Author: Yajing Zhao (S.M.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 62

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Condensation is a ubiquitous process often observed in nature and our daily lives. The large amount of latent heat released during the condensation process has been harnessed in many industrial processes such as power generation, building heating and cooling, desalination, dew harvesting, thermal management, and refrigeration. Condensation has two modes: dropwise mode and filmwise mode. Although it has been known for decades that dropwise condensation outperforms filmwise condensation in heat transfer owing to the droplet shedding effects which can efficiently reduce thermal resistance, filmwise condensation still dominates industrial applications currently due to the high costs, low robustness and technical challenges of manufacturing dropwise coatings. During water condensation, dropwise mode can be readily promoted with thin hydrophobic coatings. Superhydrophobic surfaces made out of hydrophobic coatings on micro-or-nano-engineered surfaces have shown further heat transfer enhancement in dropwise condensation of water; however, the applications of these micro- or nanoscale structured surface designs have been restricted by the high manufacturing expenses and short range of subcooling limit. Recent studies have shown that the combination of millimeter sized geometric features and plain hydrophobic coatings can effectively manipulate droplet distribution of water condensate, which provides opportunities to locally facilitate dropwise condensation at relatively low manufacturing expenses as compared to those delicate micro- and nano-structured hydrophobic surfaces. Low surface tension fluids such as hydrocarbons pose a unique challenge to achieving dropwise condensation, because common hydrophobic coatings are not capable of repelling low surface tension fluids. Recent development in lubricant infused surfaces (LIS) offers promising solutions to achieving dropwise condensation of low surface tension fluids by replacing the solid-condensate interface in conventional hydrophobic coatings with a smooth lubricant-condensate interface. However, only a few experimental studies have applied LIS to promoting dropwise condensation of low surface tension fluids (y as low as 15 mN/m). In this work, we investigated dropwise condensation of both water (y ~ 72 mN/m) and a low surface tension fluid, namely butane (y - 13 mN/m) on structured surfaces. For water condensation, we studied the effects of millimeter sized geometric structures on dropwise condensation heat transfer under two different environments: pure vapor and an air-vapor mixture. Our experimental results show that, although convex structures enable faster droplet growth in an air-vapor mixture, the same structures impose the opposite effect during pure vapor condensation, hindering droplet growth. We developed a numerical model for each case to predict the heat flux distribution along the structured surface, and the model shows good agreement with experimental results. This work demonstrates that the effects of geometric features on dropwise condensation are not invariable but rather dependent on the scenario of resistances to heat and mass transfer in the system. For butane condensation, based on a design guideline we recently developed for lubricant infused surfaces, we successfully designed an energy-favorable combination of lubricant and structured solid substrate, which was further demonstrated to promote dropwise condensation of butane. The fundamental understanding of dropwise condensation of water and low surface tension fluids on structured surfaces developed in this study provides useful guidelines for condensation applications including power generation, desalination, dew harvesting, and thermal management.

Author: John Arthur Bryant
Publisher:
ISBN:
Category :
Languages : en
Pages : 336

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Author: Daniel Beysens
Publisher: Springer Nature
ISBN: 3030904423
Category : Science
Languages : en
Pages : 458

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In this book, the author focuses on the physics behind dew, breaths figures, and dropwise condensation phenomena to introduce scientists, engineers and students to the many original processes involved in condensation. Consisting of 15 Chapters, 18 Appendices and over 500 references, the reader learns the needed theoretical backgrounds and formulae to understand the complexity of dropwise condensation. Heat and mass transfer, nucleation and growth on various substrates are considered (solid, liquid, plastic, undergoing phase change or micro-patterned substrates). The particular role of thermal or geometrical discontinuities where growth can be enhanced or reduced, dynamical aspects of self-diffusion, problems related to drop collection by gravity and the optics of dropwise condensation are all discussed. Although the content mainly deals with condensation from humid air, it can readily be generalized to condensation of any substance. The specificities of pure vapor condensation (e.g. steam) are also examined. Numerous images are provided within the text to illustrate the physics. This book is meant for those studying or researching dew and dropwise condensation, but also for individuals wishing to develop their knowledge on the subject.