Download or read book Active Augmentation of Condensation written by Ali Mohammad A Alshehri and published by . This book was released on 2021 with total page 234 pages. Available in PDF, EPUB and Kindle. Book excerpt: Condensation is a very complicated subject to fully unveil as it constitutes a complex interplay of momentum, heat and species transport and interfacial physics. Drop-wise condensation (DWC) adds more layers of complexity by introducing droplet dynamics and the two-way interaction with droplets surrounding. DWC has been shown repeatedly for about a century to possess around an order of magnitude improved heat transfer rates. Additionally, it has been shown that DWC is limited by the maximum size of droplets a surface sustains. Since this realization, promoting DWC has been greatly steered towards developing stable hydrophobic coating techniques. However, attempts have not been feasible so far especially due to the extreme conditions encountered in condensation processes. Another concern that has not been resolved adequately is the deterioration of heat and condensation rates due to the presence of non-condensable gases (NCG). This dissertation aims at understanding the process of condensation especially in the presence of NCG. First, a numerical model of the process of vapor condensation on surfaces characterized by film-wise condensation with the presence of (NCG) is presented. State variables in both the condensate film and the diffusion layer were solved separately and the condensation interface was used to couple the two solutions. The solution of the condensate film was obtained using well-established solutions of laminar film condensation of pure vapor. In contrast to other models surveyed, this work provides a inexpensive and accurate predictions of heat and mass transfer characteristics. We validated the work against two classical condensation problems. The model was first validated against empirical correlations and experimental work, resulting in a very good agreement. We then assessed the applicability of ignoring the condensate film effect, as performed in previous models, on the condensation processes by observing the thermal resistances of both the condensate film and diffusion layer. Results indicated that for the studied cases of NCG mass fractions above 20\%, the condensate thermal resistance was at least an order of magnitude lower than that of the diffusion layer. However, the two thermal resistances seem to approach each other as NCG mass fraction becomes smaller. On another front, we observed that models that ignore the condensate film thermal resistance underestimate the interfacial temperature albeit accurately predicting the overall heat transfer rate. To simulate even lower NCG mass fractions, we validated our model to the classical analytical work of Sparrow and co-workers. Results showed an excellent agreement between the two solutions at different NCG mass fractions (0.5\%-10\%) and subcooling degrees (5$^o$F-40$^o$F). Finally, we found a good agreement between results of our model and the heat/mass transfer analogy. The heat/mass transfer analogy is a semi-empirical method therefore, is limited to the existing correlations and their uncertainties. On the other hand, our model does not use any empiricism and relies on the available solutions of laminar condensate film of pure vapor in predicting the liquid side heat transfer coefficient. Moreover, motivated by the improvement in heat transfer by frequently disturbing the thermal boundary layer in nucleate boiling phenomenon, we attempted making the analogy to DWC. We developed an initial theoretical model to predict the transience of the diffusion boundary layer in condensation problems with NCG presence. The problem of suddenly exposing a cooled surface to a humid environment was modeled as two semi-infinite gas and solid domains in contact with the condensate film as a coupling condition. Results showed that the transient behavior of heat and condensation rates start by very high values and then decrease to steady state rates. This suggested that if the diffusion layer is frequently disturbed by droplets of heights similar to the layer's thickness, the condensation rate is expected to improve. To realize this, jet impingement of humidified air was proposed as a means of thinning the diffusion layer as well as to provide better shedding capabilities of condensate droplets. Finally, Utilizing jet impingement technique as a means for continuous drop-wise condensation (CDC) was investigated. The technique showed an advantage of overcoming the necessity of using highly non-wetting surfaces while yet maintaining micron-sized droplets. By shifting focus from surface treatment to the force required to sweep off a droplet, we were able to utilize stagnation pressure of jet impingement to tune the shed droplet size. To demonstrate the effectiveness of this technique, we performed condensation experiments on a broad range of contact angle and contact angle hysteresis surfaces. The results showed that droplet size being shed can be tuned effectively by tuning the jet parameters namely the jet Reynolds number. Droplets as low as 20 $\mu$m in radius on a hydrophilic surface were shed with this technique surpassing the traditional gravity-assisted shedding mechanism by almost 80 folds. In terms of condensation rate improvement, we showed theoretically that CDC improves the condensation rate of pure steam, and hence heat transfer rate, by more than 300\% compared to gravity-assisted shedding DWC. Finally, our experimental observations showed that the effect of NCG, such as air in this work, is greatly alleviated by utilizing our technique. An improvement by at least six folds in mass transfer compactness factor compared to state-of-the-art dehumidification technology was possible. We illustrated the physics of droplet departure and mobility due to the stagnation flow condition by microscopically tracing a single droplet.

Download or read book Condensation Heat Transfer Enhancement written by V. G. Rifert and published by WIT Press (UK). This book was released on 2004 with total page 402 pages. Available in PDF, EPUB and Kindle. Book excerpt: In processes with condensation of steam-to-gas compositions or refrigerative agents an intensification of condensation is often required because thermal resistance on the condensation side can be greater than the thermal resistance of the heat transfer wall on the cooling side. In this work, a pair of researchers from the National Technical U. of Ukraine and the State Academy of Refrigeration (Ukraine) provide information about the enhancement of condensation, including research results from the former USSR they feel deserves wider dissemination as well as discussion of different theoretical models of the condensation process. The US office of WIT Press is Computational Mechanics. Annotation : 2004 Book News, Inc., Portland, OR (booknews.com).

Download or read book Heat Transfer in Condensation and Boiling written by Karl Stephan and published by Springer Science & Business Media. This book was released on 2013-06-29 with total page 342 pages. Available in PDF, EPUB and Kindle. Book excerpt: I welcome the opportunity to have my book translated, because of the great emphasis on two-phase flow and heat transfer in the English-speaking world, as related to research, university education, and industrial practice. The 1988 Springer-Verlag edition of "Warmeiibergang beim Kondensieren und beim Sieden" has been enlarged to include additional material on falling film evaporation (Chapter 12) and pressure drop in two-phase flow (Chapter 13). Minor errors in the original text have also been corrected. I would like to express my sincere appreciation to Professor Green, Asso ciate Professor of German at Rensselaer, for his excellent translation and co operation. My thanks go also to Professor Bergles for his close attention to technical and linguistic details. He carefully read the typescript and made many comments and suggestions that helped to improve the manuscript. I hope that the English edition will meet with' a favorable reception and contribute to better understanding and to progress in the field of heat transfer in condensation and boiling. February 1992 K. Stephan Preface to the German-Language Edition This book is a continuation of the series "Heat and Mass Transfer" edited by U. Grigull, in which three volumes have already been published. Its aim is to acquaint students and practicing engineers with heat transfer during condensa tion and boiling, and is intended primarily for students and engineers in mechanical, chemical, electrical, and industrial processing engineering.

Download or read book Enhanced Condensation with Active Methods written by Sudarshan Sarathy and published by . This book was released on 2016 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt: Condensation of low surface tension fluids is important in liquefied natural gas processing and refrigeration systems. Current state of the art low surface energy low hysteresis coatings are not able to achieve dropwise condensation below 10 mN/m. Surface acoustic waves are proposed as an active method to shed thin condensate films to reduce their thermal resistance and improve heat transfer coefficients. Interdigitated electrode patterns were fabricated on piezoelectric LiNbO3 wafers and SAW waves were generated with RF voltages in the 12.5 - 100 MHz regime. These were tested in the in-house condensation rig with Ethanol, Pentane, Hexane and Perfluorohexane. Heat transfer coefficients showed more than 2X improvement over standard filmwise condensation. Further, the effect of refrigerant side heat transfer enhancement in a condenser operating in a vapor compression refrigeration cycle is studied as a potential application.

Download or read book Theory of Laminar Film Condensation written by Tetsu Fujii and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 225 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since the petroleum crisis in the 1970s, a lot of effort to save energy was made in industry, and remarkable achievements have been made. In the research and development concerning thermal energy, however, it was clar ified that one of the most important problems was manufacturing con densing systems with smaller size and higher performance. To solve this problem we need a method which synthesizes selections_ of the type of con denser, cooling tube and its arrangement, assessment of fouling on the cooling surfaces, consideration of transient characteristics of a condenser, etc. The majority of effort, however, has been to devise a surface element which enhances the heat transfer coefficient in condensation of a single or multicomponent vapor. Condensation phenomena are complexly affected by a lot of physical property values, and accordingly the results of theo retical research are expressed with several dimensionless parameters. On the other hand, the experimental research is limited to those with some specified cooling surfaces and some specified working fluids. Hence, the basic research of condensation is necessary for criticizing the enhancement effect as well as for an academic interest.

Download or read book Augmentation of Condensation Heat Transfer with In line Static Mixers written by Shih-Teh Lin and published by . This book was released on 1975 with total page 212 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Augmentation of Condensation Heat Transfer with Electrohydrodynamics on Vertical Enhanced Tubes written by Edouard Motte and published by . This book was released on 1994 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effect of Condensation on Performance and Design of Extended Surfaces written by and published by DIANE Publishing. This book was released on with total page 59 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Augmentation of In tube Condensation of R 113 written by Minh Luu and published by . This book was released on 1980 with total page 918 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Dropwise Condensation as Affected by Vapor Diffusion and Molecular Sticking written by Salil Kumar Banerjee and published by . This book was released on 1974 with total page 181 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Handbook of Thermal Science and Engineering written by and published by Springer. This book was released on 2018-07-31 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This Handbook provides researchers, faculty, design engineers in industrial R&D, and practicing engineers in the field concise treatments of advanced and more-recently established topics in thermal science and engineering, with an important emphasis on micro- and nanosystems, not covered in earlier references on applied thermal science, heat transfer or relevant aspects of mechanical/chemical engineering. Major sections address new developments in heat transfer, transport phenomena, single- and multiphase flows with energy transfer, thermal-bioengineering, thermal radiation, combined mode heat transfer, coupled heat and mass transfer, and energy systems. Energy transport at the macro-scale and micro/nano-scales is also included. The internationally recognized team of authors adopt a consistent and systematic approach and writing style, including ample cross reference among topics, offering readers a user-friendly knowledgebase greater than the sum of its parts, perfect for frequent consultation. The Handbook of Thermal Science and Engineering is ideal for academic and professional readers in the traditional and emerging areas of mechanical engineering, chemical engineering, aerospace engineering, bioengineering, electronics fabrication, energy, and manufacturing concerned with the influence thermal phenomena.

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 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 Augmentation of Condensation Heat Transfer of R 113 by Internally Finned Tubes and Twisted Tape Inserts written by Salem Abdul-Hai Mohamed Said and published by . This book was released on 1982 with total page 814 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Recent Developments in Boiling and Condensation written by Edgar R. F. Winter and published by Wiley-VCH. This book was released on 1977 with total page 120 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Capillary driven Condensation for Heat Transfer Enhancement in Steam Power Plants written by Samuel Steven Cruz and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Condensation is a phenomenon that is ubiquitous in nature and used to effectively transfer heat in many important industrial applications including thermal management of electronics, steam power generation, and natural gas processing. Industry relies mainly on filmwise condensation, where the condensate forms an insulating, thick liquid film on the condensation surface, posing a large thermal resistance. For almost a century, much work has explored developing surfaces that can promote the nucleation, growth, coalescence and effective shedding of mobile condensing droplets from surfaces, called dropwise condensation, which is known to enhance the heat transfer up to an order of magnitude. However, the requirement for ultra-thin coatings has hampered the wide adoption of this form of condensation as thin hydrophobic coatings degrade over time in various industrial applications. In this thesis, we model, fabricate, optimize, experimentally demonstrate a proof-of-concept for a novel condensation approach which we term capillary-driven condensation. The method consists of a hierarchical structure consisting of a hydrophobic porous membrane attached on top of a wicking structure that is firmly bonded to the condenser surface. The wicking structure and the membrane can be separately tailored to maximize the fluid flow in the wick and its effective thermal conductivity, as well as the maximum capillary pressure that the membrane can sustain to push fluid through a viscous pressure drop in the porous wick to an exit port. The geometry can be optimized to reduce the thermal resistance of the structure, as well as maximize the amount of condensate that can be removed passively by capillarity. To demonstrate the viability of this condensation method, we fabricated the proposed structure with highly-defined geometry utilizing silicon microfabrication technique s. The result is a surface which is able to constrain a thin film of condensate within a high thermal conductivity wicking structure while the top condensation surface appears dry despite sustaining condensation rates above those of filmwise condensation. The thickness of this layer and geometry of the membrane can be rationally designed to maximize the heat transfer coefficient even beyond dropwise condensation. Heat transfer measurements indicate a potential range of enhancement of ~~ 40% to ~~ 400% which is to be confirmed by more sensitive experiments that reduce error. The results from this thesis show a proof-of-concept and support the promise of capillary-driven condensation surfaces for various heat transfer applications.

Download or read book The Surface Wettability Effect on Phase Change written by Marco Marengo and published by Springer. This book was released on 2022-10-30 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.