Author: Rebecca Lynn Winter Publisher: ISBN: Category : Amphiphiles Languages : en Pages : 118
Book Description
Condensation plays a fundamental role in our lives, from the way our climate functions to our ability to generate and use energy. The large amount of energy typically involved in phase change processes means that small improvements in efficiency could translate to impactful energy savings. Condensation can be significantly enhanced by changing the roughness and material of a surface to reduce thermal resistance. Notably, the use of hydrophobic and superhydrophobic materials enhance droplet shedding, which has been found to greatly improve performance. However, neither the most state-of-the-art, nor the simplest and most thoroughly studied of these hydrophobic designs are broadly implemented in real-world systems. These surfaces are often fragile, costly to manufacture, suffer from short usable lives, and can exhibit problematic failure modes. Here, amphiphilic surfaces, characterized by features with both hydrophilic and hydrophobic materials, demonstrate a new approach to the manipulation of wetting behavior and heat transfer.This work focuses on the experimental and analytical study of amphiphilic surfaces for use in condensation. First, an analytical foundation for the wetting behavior and heat transfer on amphiphilic surfaces is developed. The formation and stability of efficient thin filmwise condensation on microamphiphilic and hierarchical amphiphilic surfaces are presented. Next, this work is expanded to use in thermally conductive filmwise condensation on macroscale finned amphiphilic surfaces. A novel dewetting phenomenon is identified and characterized, which promotes cyclical dropwise condensation without the need for an ultrathin hydrophobic coating. Finally, the macroamphiphilic work is extended to use on cylindrical tubes in a controlled condensing environment. Both a stable conductive filmwise mode and a dynamic cyclical drainage mode are identified and characterized on tubes. Both are found to exhibit efficient condensing performance using completely distinct fundamental behaviors, and the cylindrical geometry is determined to offer additional stability to both condensing modes. The use of macroscale features with simple geometries, small dependence on coating thickness, and robustness of wetting dynamics make the work presented here particularly relevant to optimization for real-world application.
Author: David Milton Anderson Publisher: ISBN: Category : Amphiphiles Languages : en Pages :
Book Description
Condensation of water vapor is an everyday phenomenon which plays an important role in power generation schemes, desalination applications and high-heat flux cooling of power electronic devices. Continuous dropwise condensation is a desirable mode of condensation in which small, highly-spherical droplets regularly form and shed off the surface before a thick liquid is formed, thereby minimizing the thermal resistance to heat transfer across the condensate layer. While difficult to induce and sustain, dropwise condensation has been shown to achieve heat and mass transfer coefficients over an order of magnitude higher than its filmwise counterpart. Superhydrophobic surfaces have been extensively studied to promote dropwise condensation with mixed results; often surfaces that are superhydrophobic to deposited droplets formed in the gas phase above the surface do not retain this behavior with condensed droplets nucleated and grown on the surface. Recently, nanostructured superhydrophobic surfaces have been developed that are robust to vapor condensation; however, these surfaces still are not ideal for condensation heat transfer due to the high thermal resistance of the vapor layer trapped underneath the droplets and the reduced footprint of direct contact between the highly-spherical droplets and the underlying substrate. This work has two main objectives. First, a comprehensive free energy based thermodynamic model is developed to better understand why traditional superhydrophobic surfaces often lose their properties when exposed to condensed droplets. The model is first validated using data from the existing literature and then extended to analyze the suitability of amphiphilic (e.g. part hydrophobic and part hydrophilic) nanostructured surfaces for condensation applications. Secondly, one of the promising amphiphilic surfaces identified by the thermodynamic model is fabricated and tested to observe condensation dynamic behavior. Two complementary visualization techniques, environmental scanning electron microscopy (ESEM) and optical (light) microscopy, are used to probe the condensation behavior and compare the performance to that of a traditional superhydrophobic surface. Observations from the condensation experiments are used to propose a new mechanism of coalescence that governs the temporal droplet size distribution on the amphiphilic nanostructured surface and continually generates fresh sites for the droplet nucleation and growth cycle that is most efficient at heat transfer.
Author: Sameer Khandekar Publisher: Springer Nature ISBN: 3030484610 Category : Science Languages : en Pages : 462
Book Description
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: Sameer Khandekar Publisher: Springer Science & Business Media ISBN: 1461484472 Category : Science Languages : en Pages : 155
Book Description
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: Emmanuel E. Simpri Publisher: ISBN: Category : Languages : en Pages : 30
Book Description
Condensation is a process utilized by about 85% of power plants in their power generation cycles. Superhydrophobic surfaces can potentially improve the heat transfer due to condensation when compared to the untreated surfaces typically used in condensers. This can improve the efficiency of power plants by up to 3%. These surfaces are made by combining nanoscale roughness with chemical hydrophobicity, and can promote the mode of condensation that has the least resistance to heat transfer. However, it is unclear how long these surfaces will last under industrial conditions. This thesis is focused on testing the robustness of the surfaces in multiple experiments and analyzing the data gathered from these experiments, along with theorizing the mechanism behind any surface functionality deterioration that may be seen. Hydrophobic and superhydrophobic surface samples that have been prepared previously were subjected to water immersion and continuous condensation tests. For the water immersion tests, samples were submerged in water under neutral (pH = 7) and basic (pH = 10) conditions at room (~25°C) and elevated (~50°C) temperatures. The continuous condensations tests were run at a steam temperature of 27°C as well as 100°C. To understand the change in surface properties over the duration of the tests, the surface contact angle was chosen as the metric to be measured. The contact angles of water droplets on the samples were taken beforehand and throughout the tests using a micro-goniometer in order to quantify the change in surface functionality. The data gathered from these experiments were processed in Matlab to produce plots of the change in contact angle over the duration of each test. These plots showed significant contact angle decreases for the hydrophobic surfaces but little change in the contact angle for the superhydrophobic surfaces. This suggests that the addition of nanostructures on the surface, and thus the promotion of super- hydrophobicity, inhibits the surface functionality deterioration mechanism that is seen with the hydrophobic surfaces.
Author: J. Fraissard Publisher: Springer Science & Business Media ISBN: 9400990790 Category : Science Languages : en Pages : 709
Book Description
In 1976, on the occasion of the Centennial of the Ameri can Chemical Society, H. A. RESrnG and C. G. WADE organized an international symposium on magnetic resonance in collo1d and in terface science which brought together a large number of scien tists from the United States and from abroad. The aim of this symposium was to include all experimental inorganic, organic and biochemical systems in which molecules are bound to interfaces and to show the contribution of various techniques based on ma gnetic resonance to the knowledge of these systems. This ambi tious program resulted into a very interesting gathering that initiated a more interdisciplinary approach to the problem of interfaces. Because of the success of this symposium it was sug gested that a similar meeting should be organized in Europe within the next three years. Professor J. FRAISSARD accepted this task but, conside ring the rapid developments in the theory and in the applica tions of the magnetic resonance spectroscopies, the organ1z1ng committee decided to arrange the meeting to be held in MENTON (France) in two parts, the first being a School and the second the Symposium proper. The former was' intended to review and to teach theoretical aspects as well as to discuss the experimental results derived from these advanced methods; the Symposium was to be for the discussion of the latest results at the highest level.
Author: Arthur T. Hubbard Publisher: CRC Press ISBN: 9780849389115 Category : Science Languages : en Pages : 950
Book Description
This exciting new handbook investigates the characterization of surfaces. It emphasizes experimental techniques for imaging of solid surfaces and theoretical strategies for visualization of surfaces, areas in which rapid progress is currently being made. This comprehensive, unique volume is the ideal reference for researchers needing quick access to the latest developments in the field and an excellent introduction to students who want to acquaint themselves with the behavior of electrons, atoms, molecules, and thin-films at surfaces. It's all here, under one cover! The Handbook of Surface Imaging and Visualization is filled with sixty-four of the most powerful techniques for characterization of surfaces and interfaces in the material sciences, medicine, biology, geology, chemistry, and physics. Each discussion is easy to understand, succinct, yet incredibly informative. Data illustrate present research in each area of study. A wide variety of the latest experimental and theoretical approaches are included with both practical and fundamental objectives in mind. Key references are included for the reader's convenience for locating the most recent and useful work on each topic. Readers are encouraged to contact the authors or consult the references for additional information. This is the best ready reference available today. It is a perfect source book or supplemental text on the subject.
Author: Phuong Pham Publisher: BoD – Books on Demand ISBN: 1789851998 Category : Technology & Engineering Languages : en Pages : 295
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: Rebecca Lynn Winter
Author: David Milton Anderson
Author: Sameer Khandekar
Author: Alex Wu
Author: Sameer Khandekar
Author: Emmanuel E. Simpri
Author: J. Fraissard
Author: Arthur T. Hubbard
Author: Phuong Pham
Author: