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Author: Kuok Kong Cheng Publisher: ISBN: Category : Electronic books Languages : en Pages : 236
Book Description
Wettability of a solid surface with liquids could be tuned based on surface morphologies. This is significant in condensation heat transfer. Condensation is a critical heat transfer mechanism in industrial processes; Dropwise (DWC) and Filmwise (FWC) condensation processes are important and are focus of this study. There are few studies on surface morphology effect on wetting behavior of a solid in relation to condensation heat transfer. We conducted these studies to understand the phenomenon. Condensation heat transfer is affected by condensate droplets properties on the surface. Condensate drop sizes and mobility relationships are important to condensation heat transfer. Droplet sizes and mobility affect population density and condensation heat transfer coefficients directly. The goal of this study is to acquire the fundamental understanding of condensation heat transfer with relation to condensate droplet behavior. In order to achieve this goal, a liquid droplet wetting dynamic model was initially developed for predicting single drop behavior on different surfaces. Heat fluxes were then estimated by combining liquid droplet behavior models and heat transfer model. Condensation experiments were conducted to verify effectiveness of the model. Experimental results coupled with condensation models revealed relationships between wetting behaviors and condensation heat transfer. Contact angle hysteresis (CAH) remains low at both high and low droplet contact angle, i.e. whether the surface is hydrophilic or hydrophobic. CAH increases with degree of wetting, but coating thermal conductance also increases. Details of drop (DWC) and film-wise (FWC) condensation are presented.
Author: Kuok Kong Cheng Publisher: ISBN: Category : Electronic books Languages : en Pages : 236
Book Description
Wettability of a solid surface with liquids could be tuned based on surface morphologies. This is significant in condensation heat transfer. Condensation is a critical heat transfer mechanism in industrial processes; Dropwise (DWC) and Filmwise (FWC) condensation processes are important and are focus of this study. There are few studies on surface morphology effect on wetting behavior of a solid in relation to condensation heat transfer. We conducted these studies to understand the phenomenon. Condensation heat transfer is affected by condensate droplets properties on the surface. Condensate drop sizes and mobility relationships are important to condensation heat transfer. Droplet sizes and mobility affect population density and condensation heat transfer coefficients directly. The goal of this study is to acquire the fundamental understanding of condensation heat transfer with relation to condensate droplet behavior. In order to achieve this goal, a liquid droplet wetting dynamic model was initially developed for predicting single drop behavior on different surfaces. Heat fluxes were then estimated by combining liquid droplet behavior models and heat transfer model. Condensation experiments were conducted to verify effectiveness of the model. Experimental results coupled with condensation models revealed relationships between wetting behaviors and condensation heat transfer. Contact angle hysteresis (CAH) remains low at both high and low droplet contact angle, i.e. whether the surface is hydrophilic or hydrophobic. CAH increases with degree of wetting, but coating thermal conductance also increases. Details of drop (DWC) and film-wise (FWC) condensation are presented.
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: Sanjay Adhikari Publisher: ISBN: Category : Languages : en Pages :
Book Description
Dropwise condensation (DWC) is a high intensity heat transfer phenomenon, with heat fluxes up to an order of magnitude higher than in filmwise condensation. Many industrial applications like desalination, thermal management, power generation and fog water harvesting may benefit from employing DWC. Considerable work has been done in this field and yet there are some challenges which remain open for research and further investigation. High resolution numerical studies that capture the complex hydrodynamics of larger droplets as they coalesce and move on the surface, effectively refreshing it for renucleation, have still not been realized as the drop size distribution spans six orders of magnitude. A new Volume of Fluid (VOF) based multi-scale approach, which resolves the grid scale larger droplets O(50 [mu]m) and models the heat transfer for the subgrid scale smaller droplets, is proposed in this dissertation. To supplement this approach, heat transfer models for individual droplets (Chapter 1) and droplet interaction (Chapter 2) are presented. Modeling work described in chapter 2 also solves many challenges associated with resolving grid scale droplets in VOF simulations. The proposed multi-scale approach also requires a transient heat transfer closure model for the subgrid scale droplets. Experimental studies have so far focused only on the steady state behavior of DWC. The startup period is still not well understood. Transient phenomena in DWC startup may significantly affect the performance of proposed applications like vapor chambers subjected to pulsed heat fluxes, or refrigeration cycles operating intermittently. This dissertation provides first characterization of fast transients during startup (chapter 4). A unique experimental facility and instrumentation are developed for measurements. Inverse numerical methods are employed to extract data (q" and HTC) from these measurements. Three distinct phases during DWC startup have been identified, which further highlight the importance of characterizing this period. The experimental data can be coupled with the numerical work described in this dissertation to formulate a robust, widely applicable simulation framework.
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: Kuok Kong Cheng
Author: Kuok Kong Cheng
Author: 
Author: Sameer Khandekar
Author: Turgut Sarpkaya
Author: Sanjay Adhikari
Author: Harding Bliss
Author: Ronald Luther Reisbig
Author: C. Saturnino
Author: Sameer Khandekar
Author: