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.

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.

This book presents select proceedings of the National Conference on Advancement in Materials Processing Technology (AMPT 2020). It covers the new trends in materials and mineral processing technologies along with an emphasis on engineering materials, composite materials, smart materials and nanomaterials. Topics covered include advanced, mineral processing, advanced processing, foundry technology, modelling and simulation, recycling and waste recovery. Given the contents, this book will be useful for researchers, engineers and professionals working in the areas of chemical, mining, metallurgical and mechanical engineering and associated fields.

The Surface Wettability Effect on Phase Change collects high level contributions from internationally recognised scientists in the field. It thoroughly explores surface wettability, with topics spanning from the physics of phase change, physics of nucleation, mesoscale modeling, analysis of phenomena such drop evaporation, boiling, local heat flux at triple line, Leidenfrost, dropwise condensation, heat transfer enhancement, freezing, icing. All the topics are treated by discussing experimental results, mathematical modeling and numerical simulations. In particular, the numerical methods look at direct numerical simulations in the framework of VOF simulations, phase-field simulations and molecular dynamics. An introduction to equilibrium and non-equilibrium thermodynamics of phase change, wetting phenomena, liquid interfaces, numerical simulation of wetting phenomena and phase change is offered for readers who are less familiar in the field. This book will be of interest to researchers, academics, engineers, and postgraduate students working in the area of thermofluids, thermal management, and surface technology.

This book focuses on droplets and sprays and their applications. It discusses how droplet level transport is central to a multitude of applications and how droplet level manipulation and control can enhance the efficiency and design of multiphase systems. Droplets and sprays are ubiquitous in a variety of multiphase and multiscale applications in surface patterning, oil recovery, combustion, atomization, spray drying, thermal barrier coating, renewable energy, and electronic cooling, to name but a few. This book provides two levels of details pertaining to such applications. Each chapter delves into a specific application and provides not only an overview but also detailed physical insights into the application mechanism from the point of view of droplets and sprays. All chapters provide a mix of cutting-edge applications, new diagnostic techniques and modern computational methodologies, as well as the fundamental physical mechanism involved in each application. Taken together, the chapters provide a translational perspective on these applications, from basic transport processes to optimization, and from design to implementation using droplets or sprays as fundamental building blocks. Given its breadth of coverage, the book will be of interest to students, researchers, and industry professionals alike.

This thesis investigates the use of three classes advanced materials for promoting dropwise condensation: 1. robust hydrophobic functionalizations 2. superhydrophobic textures 3. lubricant-imbibed textures We first define the functional requirements of a hydrophobic functionalization for promoting dropwise condensation and use these guidelines to investigate two subclasses of materials: rare-earth ceramics and fluoropolymer films deposited via initiated chemical vapor deposition (iCVD). We show how both materials exhibit robust dropwise behavior, and further subject an iCVD film to an accelerated endurance trial to show how it sustains dropwise condensation throughout a 3-month equivalent trial. Next we combine hydrophobic functionalization with rough texture to obtain superhydrophobic surfaces and identify a self-similar depinning mechanism governing adhesion on surfaces with multiple roughness length scales. We introduce the metric of pinned fraction to show how these surfaces must be designed to minimize adhesion. We then show how dropwise condensation on superhydrophobic surfaces and the ensuing "jumping" behavior consists of not only binary coalescences, but multiple-drop coalescences with tangential departure that result in increased departing mass flux. However, we find that although this mode of condensation is readily achievable when condensing working fluids with high surface tension, such as water, even re-entrant structures that are known to support millimetric droplets of low-surface tension liquids in a superhydrophobic state are not sufficient to promote the dropwise mode of condensation for working fluids with low surface tension. Finally, we extend the applicability of textured surfaces by imbibing solid textures with a lubricant stabilized by capillary wicking. We show how these surfaces, when both solid texture and lubricant are properly designed, can promote dropwise condensation and reduce departing diameter of not only steam, but also of low-surface tension working fluids. In summary, we find that all three classes of surfaces provide significant increases in vapor-side heat transfer coefficient. However, when considering the overall heat transfer coefficient of a surface condenser, we find that most of the benefits of dropwise condensation can be realized by hydrophobic functionalization.