Download or read book Condensation on Superhydrophobic Copper Oxide Nanostructures written by Nicholas Gang Dou and published by . This book was released on 2012 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt: Condensation is an important process in many power generation and water desalination technologies. Superhydrophobic nanostructured surfaces have unique condensation properties that may enhance heat transfer through a mechanism driven by surface tension. The increased droplet removal rate and reduced size of departing droplets facilitates improvements over traditional filmwise and dropwise condensation. This work investigates copper oxide nanostructures as a potential substrate for superhydrophobic condensation. We first explored and refined a procedure for creating and functionalizing oxide nanostructures on copper surfaces. The condensation behavior of these samples was characterized using an optical microscope and an environmental scanning electron microscope by quantifying the distribution of nucleation sites and droplet growth behavior. Using the knowledge gained from these studies, an experimental test bed was designed and fabricated to measure macro-scale condensation heat transfer for flat and tubular sample geometries. Preliminary results validate previous theoretical and experimental studies of filinwise condensation and demonstrate heat transfer enhancement with dropwise condensation. The copper oxide nanostructures exhibited jumping, which shows the effectiveness of the synthesis procedure.

Download or read book Development and Characterization of Micro nano Structured Surfaces for Enhanced Condensation written by Nenad Miljkovic and published by . This book was released on 2013 with total page 185 pages. Available in PDF, EPUB and Kindle. Book excerpt: Micro/nanostructures have long been recognized to have potential for heat transfer enhancement in phase-change processes by achieving extreme wetting properties, which is of great importance in a wide range of applications including thermal management, building environment control, water harvesting, desalination, and industrial power generation. This thesis focuses on the fundamental understanding of water vapor condensation on superhydrophobic surfaces, as well as the demonstration of such surfaces for enhanced condensation heat transfer performance. We first studied droplet-surface interactions during condensation on superhydrophobic surfaces to understand the emergent droplet wetting morphology. We demonstrated the importance of considering local energy barriers to understand the condensed droplet morphologies and showed nucleation-mediated droplet-droplet interactions can overcome these barriers to develop wetting states not predicted by global thermodynamic analysis. To minimize these droplet-droplet interactions and ensure the formation of favorable morphologies for enhanced condensation heat transfer, we show that the structure length scale needs to be minimized while ensuring the local energy barriers satisfy the morphology dependent criteria. This mechanistic understanding offers insight into the role of surface-structure length scale and provides a quantitative basis for designing surfaces optimized for condensation in engineered systems. Using our understanding of emergent droplet wetting morphology, we experimentally and numerically investigated the morphology dependent individual droplet growth rates. By taking advantage of well-controlled functionalized silicon nanopillars, the growth and shedding behavior of both suspended and partially wetting droplets on the same surface during condensation was observed. Environmental scanning electron microscopy was used to demonstrate that initial droplet growth rates of partially wetting droplets were 6 times larger than that of suspended droplets. A droplet growth model was developed to explain the experimental results and showed that partially wetting droplets had 4-6 times higher heat transfer rates than that of suspended droplets. Based on these findings, the overall performance enhancement created by surface nanostructuring was examined in comparison to a flat hydrophobic surface. These nanostructured surfaces had 56% heat flux enhancement for partially wetting droplet morphologies, and 71% heat flux degradation for suspended morphologies in comparison to flat hydrophobic surfaces. This study provides fundamental insights into the previously unidentified role of droplet wetting morphology on growth rate, as well as the need to design nanostructured surfaces with tailored droplet morphologies to achieve enhanced heat and mass transfer during dropwise condensation. To create a unified model for condensation capable of predicting the surface heat transfer for a variety of surface length scales, geometries, and condensation conditions, we incorporated the emergent droplet wetting morphology, individual droplet heat transfer, and size distribution. The model results showed a specific range of characteristic length scales (0.5 - 2 ptm) allowing for the formation of coalescence-induced jumping droplets with a 190% overall surface heat flux enhancement over conventional flat dropwise condensing surfaces. This work provided a unified model for dropwise condensation on micro/nanostructured superhydrophobic surfaces and offered guidelines for the selection of ideal structured surfaces to maximize heat transfer. Using the insights gained from the developed model and optimization, a scalable synthesis technique was developed to produce functionalized oxide nanostructures on copper surfaces capable of sustaining superhydrophobic condensation. Nanostructured copper oxide (CuO) films were formed via chemical oxidation in an alkaline solution resulting in dense arrays of sharp CuO nanostructures with characteristic heights and widths of -1 pm and -300 nm, respectively. Condensation on these surfaces was characterized using optical microscopy and environmental scanning electron microscopy to quantify the distribution of nucleation sites and elucidate the growth behavior of individual droplets with characteristic radii of -1 to 10 pm at supersaturations

Download or read book Handbook of Phase Change written by S.G. Kandlikar and published by Routledge. This book was released on 2019-01-22 with total page 786 pages. Available in PDF, EPUB and Kindle. Book excerpt: Provides a comprehensive coverage of the basic phenomena. It contains twenty-five chapters which cover different aspects of boiling and condensation. First the specific topic or phenomenon is described, followed by a brief survey of previous work, a phenomenological model based on current understanding, and finally a set of recommended design equa

Download or read book Fabrication and Robustness Testing of Superhydrophobic Nanostructured Surfaces for Enhanced Jumping Condensation written by Jean Hope Sack and published by . This book was released on 2015 with total page 58 pages. Available in PDF, EPUB and Kindle. Book excerpt: Increasing worldwide and domestic demands for power and clean water will require advanced heat transfer materials. Superhydrophobic micro- and nano-structured surfaces which promote a jumping droplet mode of condensation have been shown to enhance heat transfer over conventional film wise condensation surfaces, but limited robustness testing has been reported validating feasibility of industrial implementation. This thesis seeks to quantify the robustness of a variety of nanostructures, substrates and coatings by analyzing contact angle measurements and SEM imaging over the course of accelerated robustness testing. This testing was enabled through the design and construction of three custom-built setups intended to accelerate the onset of failure mechanisms. These setups consist of a flow setup to observe resistance to shear flows from internal condensation steam flow, a droplet impingement setup to test mechanical durability, and an elevated temperature condensation chamber to characterize thermal stability. Methods for fabricating nanostructures were also developed, and scalable zinc oxide nanowires (ZnO) and copper oxide nanoblades (CuO) were used. CuO nanoblades were etched into copper, and ZnO nanowires were grown on silicon, low carbon steel, titanium, stainless steel, and electroplated nickel. Hydrophobic coatings tested on these surfaces included stearic acid and two polymer coatings: P2i (40nm) and Semblant. Observed failure mechanisms were coating degradation and poor nanostructure adhesion. Nanostrucure adhesion issues were observed as delamination of ZnO nanowires primarily on stainless steel substrates. Adhesion was improved through the addition of an electroplated nickel layer before nanowire growth, but delamination was still observed. This is likely the result a large mismatch in coefficient of thermal expansion between the ZnO nanowires and the substrate. The etched CuO nanostructures with a fluorinated polymer coating (P2i) showed very little change in performance throughout robustness testing. Characterization methods included contact angle measurements to monitor surface uniformity and durability, and scanning electron microscope (SEM) imaging to observe nanostructure degradation and delamination. Preliminary work was also done to functionalize the inside of tubes and design a dedicated test setup to characterize heat transfer measurements for internal jumping condensation. This setup will allow for extended robustness testing over a range of temperatures, pressures, and geometries, and give baseline heat flux values for comparison with dropwise or filmwise internal condensation. While ZnO nanowires still require additional testing and development, CuO nanoblades are good candidates for internal heat transfer measurements and scaled up robustness testing. Assuming this characterization confirms the expected benefits of jumping condensation from increased droplet removal and nucleation density, this technology has the potential to significantly improve power plant efficiency and output worldwide.

Download or read book Ice Adhesion written by Chang-Hwan Choi and published by John Wiley & Sons. This book was released on 2020-11-13 with total page 704 pages. Available in PDF, EPUB and Kindle. Book excerpt: This unique book presents ways to mitigate the disastrous effects of snow/ice accumulation and discusses the mechanisms of new coatings deicing technologies. The strategies currently used to combat ice accumulation problems involve chemical, mechanical or electrical approaches. These are expensive and labor intensive, and the use of chemicals raises serious environmental concerns. The availability of truly icephobic surfaces or coatings will be a big boon in preventing the devastating effects of ice accumulation. Currently, there is tremendous interest in harnessing nanotechnology in rendering surfaces icephobic or in devising icephobic surface materials and coatings, and all signals indicate that such interest will continue unabated in the future. As the key issue regarding icephobic materials or coatings is their durability, much effort is being spent in developing surface materials or coatings which can be effective over a long period. With the tremendous activity in this arena, there is strong hope that in the not too distant future, durable surface materials or coatings will come to fruition. This book contains 20 chapters by subject matter experts and is divided into three parts— Part 1: Fundamentals of Ice Formation and Characterization; Part 2: Ice Adhesion and Its Measurement; and Part 3: Methods to Mitigate Ice Adhesion. The topics covered include: factors influencing the formation, adhesion and friction of ice; ice nucleation on solid surfaces; physics of ice nucleation and growth on a surface; condensation frosting; defrosting properties of structured surfaces; relationship between surface free energy and ice adhesion to surfaces; metrology of ice adhesion; test methods for quantifying ice adhesion strength to surfaces; interlaboratory studies of ice adhesion strength; mechanisms of surface icing and deicing technologies; icephobicities of superhydrophobic surfaces; anti-icing using microstructured surfaces; icephobic surfaces: features and challenges; bio-inspired anti-icing surface materials; durability of anti-icing coatings; durability of icephobic coatings; bio-inspired icephobic coatings; protection from ice accretion on aircraft; and numerical modeling and its application to inflight icing.

Download or read book Bioinspired Design of Materials Surfaces written by Yongmei Zheng and published by Elsevier. This book was released on 2019-08-23 with total page 340 pages. Available in PDF, EPUB and Kindle. Book excerpt: Bioinspired Design of Materials Surfaces reviews novel methods and technologies used to design surfaces and materials for smart material and device applications. The author discusses how materials wettability can be impacted by the fabrication of micro- and nanostructures, anisotropic structures, gradient structures, and heterogeneous patterned structures on the surfaces of materials. The design of these structures was inspired by nature, including lotus, cactus, beetle back and butterfly wings, spider silk, and shells. The author reviews the various wettability functions that can result from these designs, such as self-cleaning, directional adhesion, droplet driving, anti-adhesion, non-wetting, liquid repellent properties, liquid separation, liquid splitting, and more. This book presents a key reference on how to fabricate bioinspired structures on materials for desired functions of materials wettability. It also discusses challenges, opportunities and many potential applications, such as oil-water separation devices, water harvesting devices and photonic device applications. Introduces the fundamentals of both bioinspired materials design and the theory behind dynamic materials wettability Reviews the latest methods and technologies used to create functional surfaces and structured materials that impact and potentially control wettability Provides a snapshot of potential device applications, such as oil-water separation, water harvesting, fluid transport, photonic applications, and much more

Download or read book Advances in Coatings Deposition and Characterization written by MDPI and published by MDPI. This book was released on 2020-12-29 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt: Coatings offer the unique opportunity to create architectures that combine the functionality of two or more materials, conferring unique properties to objects with an extremely large palette of solutions. For this flexibility, thick and thin films have terrific impacts on the most relevant societal challenges. Computers, food packaging, airplanes, and cars, to mention a few familiar objects from everyday life, rely heavily on coatings. To celebrate the key role that coatings have in society, and in science and technology, this book collects a selection of relevant reviews and original research articles published in “Coatings” in 2017 and 2018. Papers have been selected based on their broad impact and balancing between the two major aspects of coatings science and technology: deposition and characterization.

Download or read book Condensation and Wetting Dynamics on Micro Nano Structured Surfaces written by Emre Olceroglu and published by . This book was released on 2017 with total page 258 pages. Available in PDF, EPUB and Kindle. Book excerpt: Because of their adjustable wetting characteristics, micro/nanostructured surfaces are attractive for the enhancement of phase-change heat transfer where liquid-solid-vapor interactions are important. Condensation, evaporation, and boiling processes are traditionally used in a variety of applications including water harvesting, desalination, industrial power generation, HVAC, and thermal management systems. Although they have been studied by numerous researchers, there is currently a lack of understanding of the underlying mechanisms by which structured surfaces improve heat transfer during phase-change. This PhD dissertation focuses on condensation onto engineered surfaces including fabrication aspect, the physics of phase-change, and the operational limitations of engineered surfaces. While superhydrophobic condensation has been shown to produce high heat transfer rates, several critical issues remain in the field. These include surface manufacturability, heat transfer coefficient measurement limitations at low heat fluxes, failure due to surface flooding at high supersaturations, insufficient modeling of droplet growth rates, and the inherent issues associated with maintenance of non-wetted surface structures. Each of these issues is investigated in this thesis, leading to several contributions to the field of condensation on engineered surfaces. A variety of engineered surfaces have been fabricated and characterized, including nanostructured and hierarchically-structured superhydrophobic surfaces. The Tobacco mosaic virus (TMV) is used here as a biological template for the fabrication of nickel nanostructures, which are subsequently functionalized to achieve superhydrophobicity. This technique is simple and sustainable, and requires no applied heat or external power, thus making it easily extendable to a variety of common heat transfer materials and complex geometries. To measure heat transfer rates during superhydrophobic condensation in the presence of non-condensable gases (NCGs), a novel characterization technique has been developed based on image tracking of droplet growth rates. The full-field dynamic characterization of superhydrophobic surfaces during condensation has been achieved using high-speed microscopy coupled with image-processing algorithms. This method is able to resolve heat fluxes as low as 20 W/m2 and heat transfer coefficients of up to 1000 kW/m2, across an array of 1000's of microscale droplets simultaneously. Nanostructured surfaces with mixed wettability have been used to demonstrate delayed flooding during superhydrophobic condensation. These surfaces have been optimized and characterized using optical and electron microscopy, leading to the observation of self-organizing microscale droplets. The self-organization of small droplets effectively delays the onset of surface flooding, allowing the superhydrophobic surfaces to operate at higher supersaturations. Additionally, hierarchical surfaces have been fabricated and characterized showing enhanced droplet growth rates as compared to existing models. This enhancement has been shown to be derived from the presence of small feeder droplets nucleating within the microscale unit cells of the hierarchical surfaces. Based on the experimental observations, a mechanistic model for growth rates has been developed for superhydrophobic hierarchical surfaces. While superhydrophobic surfaces exhibit high heat transfer rates they are inherently unstable due to the necessity to maintain a non-wetted state in a condensing environment. As an alternative condensation surface, a novel design is introduced here using ambiphilic structures to promote the formation of a thin continuous liquid film across the surface which can still provide the benefits of superhydrophobic condensation. Preliminary results show that the ambiphilic structures restrain the film thickness, thus maintaining a low thermal resistance while simultaneously maximizing the liquid-vapor interface available for condensation.

Download or read book Ice Adhesion written by K. L. Mittal and published by John Wiley & Sons. This book was released on 2020-12-15 with total page 704 pages. Available in PDF, EPUB and Kindle. Book excerpt: This unique book presents ways to mitigate the disastrous effects of snow/ice accumulation and discusses the mechanisms of new coatings deicing technologies. The strategies currently used to combat ice accumulation problems involve chemical, mechanical or electrical approaches. These are expensive and labor intensive, and the use of chemicals raises serious environmental concerns. The availability of truly icephobic surfaces or coatings will be a big boon in preventing the devastating effects of ice accumulation. Currently, there is tremendous interest in harnessing nanotechnology in rendering surfaces icephobic or in devising icephobic surface materials and coatings, and all signals indicate that such interest will continue unabated in the future. As the key issue regarding icephobic materials or coatings is their durability, much effort is being spent in developing surface materials or coatings which can be effective over a long period. With the tremendous activity in this arena, there is strong hope that in the not too distant future, durable surface materials or coatings will come to fruition. This book contains 20 chapters by subject matter experts and is divided into three parts— Part 1: Fundamentals of Ice Formation and Characterization; Part 2: Ice Adhesion and Its Measurement; and Part 3: Methods to Mitigate Ice Adhesion. The topics covered include: factors influencing the formation, adhesion and friction of ice; ice nucleation on solid surfaces; physics of ice nucleation and growth on a surface; condensation frosting; defrosting properties of structured surfaces; relationship between surface free energy and ice adhesion to surfaces; metrology of ice adhesion; test methods for quantifying ice adhesion strength to surfaces; interlaboratory studies of ice adhesion strength; mechanisms of surface icing and deicing technologies; icephobicities of superhydrophobic surfaces; anti-icing using microstructured surfaces; icephobic surfaces: features and challenges; bio-inspired anti-icing surface materials; durability of anti-icing coatings; durability of icephobic coatings; bio-inspired icephobic coatings; protection from ice accretion on aircraft; and numerical modeling and its application to inflight icing.

Download or read book Icephobic Materials for Anti De icing Technologies written by Yizhou Shen and published by Springer Nature. This book was released on with total page 524 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Principles and Practice of Variable Pressure Environmental Scanning Electron Microscopy VP ESEM written by Debbie Stokes and published by John Wiley & Sons. This book was released on 2008-12-22 with total page 247 pages. Available in PDF, EPUB and Kindle. Book excerpt: Offers a simple starting point to VPSEM, especially for new users, technicians and students containing clear, concise explanations Crucially, the principles and applications outlined in this book are completely generic: i.e. applicable to all types of VPSEM, irrespective of manufacturer. Information presented will enable reader to turn principles into practice Published in association with the Royal Microscopical Society (RMS) -www.rms.org.uk

Download or read book 21st Century Surface Science written by Phuong Pham and published by BoD – Books on Demand. This book was released on 2020-11-26 with total page 295 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Dropwise Condensation on Inclined Textured Surfaces written by Sameer Khandekar and published by Springer Science & Business Media. This book was released on 2013-09-06 with total page 155 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Bioinspired Engineering of Thermal Materials written by Tao Deng and published by John Wiley & Sons. This book was released on 2018-06-11 with total page 274 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive overview and summary of recent achievements and the latest trends in bioinspired thermal materials. Following an introduction to different thermal materials and their effective heat transfer to other materials, the text discusses heat detection materials that are inspired by biological systems, such as fire beetles and butterflies. There then follow descriptions of materials with thermal management functionality, including those for evaporation and condensation, heat transfer and thermal insulation materials, as modeled on snake skins, polar bears and fire-resistant trees. A discussion of thermoresponsive materials with thermally switchable surfaces and controllable nanochannels as well as those with high thermal conductivity and piezoelectric sensors is rounded off by a look toward future trends in the bioinspired engineering of thermal materials. Straightforward and well structured, this is an essential reference for newcomers as well as experienced researchers in this exciting field.

Download or read book Thermal Characterization of Dropwise Condensation on Nanoengineered Copper Superhydrophobic Surfaces written by Ruiyuan Ma and published by . This book was released on 2012 with total page 75 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Superhydrophobic Surfaces written by Mehdi Khodaei and published by . This book was released on 2020-07 with total page 132 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Theory of Heat Pipes written by T. P. Cotter and published by . This book was released on 1965 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt: A heat pipe is a self-contained structure which achieves very high thermal conductance by means of two-phase fluid flow with capillary circulation. A quantitative engineering theory for the design and performance analysis of heat pipes is given.