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Volume 3 addresses special topics in condensation: dropwise condensation, theoretical and numerical models for microchannel condensation, altered wettability of condensation surfaces, and flow pattern based models for condensation in horizontal tubes.
Contents:https://doi.org/10.1142/9789814623285_fmatter03
The following sections are included:
https://doi.org/10.1142/9789814623285_0018
Dropwise condensation is a nucleation phenomenon analogous to nucleate boiling except that the active nucleation sites are much smaller and the nucleation site density is much larger. The smallest “primary” drops are almost in contact with their neighbours and coalescences take place soon after nucleation. Thereafter, drops grow by condensation and coalescence with neighbours and primary drops nucleate at sites exposed by coalescences until the region of the condensing surface is swept by a falling droplet and the process begins again. This complex sequence of events is treated in a quasi-static manner. An expression is obtained for the heat transfer though a drop of give size and this is combined with an effective steady mean distribution of drop sizes to give the heat flux for the whole surface. Owing to the wide range of drop sizes it is necessary to include the effect of surface curvature, (important for the smallest drops), vapor-liquid interface resistance (important for slightly larger drops) and conduction (important for large drops). An algebraic equation is obtained for the heat flux which correctly predicts the effects of vapor-surface temperature difference, pressure and maximum drop size.
https://doi.org/10.1142/9789814623285_0019
Annular flow has been observed to be the predominant mode of condensation in small channels. A theory of condensation in microchannels with laminar flow of the condensate, based only on the Nusselt approximations and with no empirical input, is described. As well as gravity and surface shear stress from the flowing vapor, the theory takes account of the transverse flow resulting from the pressure difference across the curved vapor-liquid interface. For non-circular channels this causes condensate to be driven towards the corners leaving a thin film along channel sides. Owing to the curvature term, the resulting differential equation for the condensate film thickness is of fourth order in the transverse direction. Solutions can be found for any channel section with a vertical axis of symmetry where the first and third derivatives of film thickness with respect to the transverse coordinate are zero at the upper and lower positions of symmetry, providing the necessary four boundary conditions. The position of onset of condensation, where the film thickness is zero around the perimeter of the channel, provides the required streamwise boundary condition. The theory is described in detail and examples of solutions are given.
https://doi.org/10.1142/9789814623285_0020
The following sections are included:
https://doi.org/10.1142/9789814623285_0021
Condensation is a ubiquitous natural process often harnessed in many industrial processes such as power generation, desalination, thermal management, and building environmental control. Recent advancements in surface engineering have offered new opportunities to enhance condensation heat transfer by drastically changing the wetting properties of the surface. Specifically, the development of superhydrophobic surfaces has been pursued to enhance dropwise condensation heat transfer, where the low droplet surface adhesion and small droplet departure sizes increase the condensation heat transfer coefficient. In this review, we provide theoretical and experimental insights gained to tailor these superhydrophobic surfaces for enhanced condensation heat transfer with consideration of structure geometry, surface chemistry, departure characteristics, and droplet size distribution. In addition, we discuss new modes of condensation, including jumping-droplet, liquid infused, and immersion condensation, which have demonstrated heat transfer enhancements by as much as 100% over classical dropwise condensation on a smooth surface. Finally,we identify challenges and new opportunities to advance these surfaces for broad implementation in thermo-fluidic systems.
https://doi.org/10.1142/9789814623285_0022
The process of film condensation on the fins and in the channels is studied theoretically and experimentally. The equation describing evolution of vapor condensed film on a curved surface is derived for thin liquid layer. The model accounts for both bulk and surface forces (gravity, surface tension, shear stress), and generalizes several well-known classical models. The numerical method of solution to the evolution equation is described. The shape of two-dimensional curved fins is generalized for film condensation of pure vapor; for this purpose, the curvature function, determining the profile of an optimal fin, is found through variation method. The influence of the level of inter-fin valleys filled with condensed liquid on condensation intensity is analyzed. Condensation of pure vapor moving in a round tube is investigated numerically. The effect of tube diameter, vapor flow rate, temperature difference and angle of tube inclination relative to the horizon are studied.Times of stationary condensation stabilization in the round tubes at a sudden transition from the Earth's gravity to microgravity, and vice versa are calculated. The calculated time of stationary condensation stabilization in a round tube at transition to the microgravity conditions is larger than the transition to terrestrial gravity, when the tube diameter is larger than the capillary length.
https://doi.org/10.1142/9789814623285_0023
A pragmatic model for numerical simulation of laminar annular flow condensation in microchannels was previously developed by Nebuloni and Thome (2010). Presently, their condensation model has been extended in three directions, first by including turbulent flows, secondly by introducing adiabatic flows and thirdly by adding evaporating flows. Notably, a 1-d turbulent model has been added to extend the previous laminar onlymodel to nowinclude turbulent annular liquid films. The turbulent model was then compared and validated versus experimental microchannel condensation data. The adiabatic simulations were compared here with established solutions of the Navier-Stokes equations in annular flows, whilst the evaporation simulations were validated against a selection of experimental flow boiling data. Particular emphasis was placed on the analysis of the fluid flow and heat transfer differences between condensation and evaporation. The liquid film thickness distribution and liquid film velocities yielded different optimal geometries for evaporation and condensation.
https://doi.org/10.1142/9789814623285_0024
The principles of condensation in horizontal tubes are presented with special attention to the prediction of local heat transfer coefficients as a function of the local flow pattern. The influence of flow pattern, especially flow stratification or not, is shown to be very important in accurately predicting local condensation heat transfer coefficients. In addition to condensation of pure vapors (and azeotropic mixtures), condensation of zeotropic mixtures are also addressed along with condensation of superheated vapor and the subcooling of condensate. Principle focus is on the flow pattern model of El Hajal et al. (2003) and on the flow pattern based heat transfer model of Thome et al. (2003). For additional models on intube condensation, the reader is referred to Volume 2 of Set 1 of this series by Garimella and Fronk (2015).
John Rose has been Professor of Mechanical Engineering at Queen Mary, University of London since 1985. He is a Fellow of the UK Institution of Mechanical Engineers and of the American Society of Mechanical Engineers. He has held sabbatical appointments at MIT, US Naval Postgraduate School and the Universities of Tokyo and Kyushu. His research interests are mainly in the field of condensation heat transfer in which he has published some 200 theoretical and experimental papers. He is presently UK editor of International Journal of Heat and Mass Transfer, International Communications in Heat and Mass Transfer and Experimental Heat Transfer.
Dr Hua Sheng Wang is Senior Lecturer in Future Energy at Queen Mary, University of London, UK. He has held previous posts at Xi'an Jiaotong University, China, and Kyushu University, Japan. His research interests include convection heat transfer, liquid/solid phase change, refrigeration, air-conditioning, two-phase flow, boiling, condensation, magnetic refrigeration, energy storage, molecular dynamics and multiscale simulations. He was awarded the Prize and Medal by the Japan Society of Mechanical Engineers as co-author of "JSME Outstanding Paper of 2002" (Wang, Honda and Nozu, 2002).
Davide Del Col is associate professor at University of Padova, Italy, where he teaches Energy Science and Refrigeration Technology at the School of Engineering. He got his PhD on Energy Science at University of Padova in 1999. He was visiting scholar at Pennsylvania State University, USA. He is Member of Commission B1 of International Institute of Refrigeration, Paris; member of the Steering Committee of UIT (Italian Union of Thermal-Fluidynamics), associate of INFN (Istituto Nazionale di Fisica Nucleare) in the framework of the Program ALICE at CERN, Geneve. Responsible of the "Laboratory of Two-Phase Heat Transfer" and the "Laboratory of Solar Energy Conversion", at the Department of Industrial Engineering of University of Padova. He has authored more than 200 scientific publications, fifty of them on international peer reviewed journals.
Stefano Bortolin is a post-doctoral researcher at the Department of Industrial Engineering, University of Padova, Italy. He received his PhD from the University of Padova in 2010. His research interests include microscale heat transfer, new refrigerants, computational fluid dynamics and condensation over nano-engineered surfaces. Dr Bortolin has co-authored more than 40 papers in refereed journals and conference proceedings.
Enrico Da Riva is professor of thermal engineering at the University of Applied Sciences Western Switzerland at Yverdon-les-Bains. He got his PhD at the University of Padova, Italy, and was a visiting scholar at the Purdue University, Indiana, USA. He has been working as the technical coordinator of the CFD Team at the European Organization for Nuclear Research (CERN), Geneva, Switzerland. His main research topics are heat pump systems, microscale heat transfer, computational fluid dynamics, and modelling of two-phase flow and heat transfer.
Nenad Miljkovic is currently an Assistant Professor of Mechanical Science and Engineering at the University of Illinois at Urbana-Champaign, where he leads the Energy Transport Research Laboratory. Previous to this, he was a Postdoctoral Associate in the Nano Engineering Lab, in the Department of Mechanical Engineering at the Massachusetts Institute of Technology. He earned his PhD and MS degrees in the Device Research Laboratory at the Massachusetts Institute of Technology in 2013 and 2011, respectively. His PhD work focused on the design and characterization of micro/nanostructured surfaces for enhanced condensation heat transfer.
Daniel J Preston completed his MS and is currently working on his PhD in the Device Research Laboratory at the Massachusetts Institute of Technology. He studies enhancement of condensation heat transfer achieved through scalable superhydrophobic surface coatings, application of electric fields, and use of lubricating intermediate fluids on micro- and nanostructured surfaces. He received his BS from The University of Alabama, where he investigated industrial-scale energy saving measures with the Alabama Industrial Assessment Center.
Evelyn N Wang is an Associate Professor in the Mechanical Engineering Department at MIT. She received her BS from MIT in 2000 and MS and PhD from Stanford University in 2001, and 2006, respectively. From 2006–2007, she was a postdoctoral researcher at Bell Laboratories, Alcatel-Lucent. Her research interests include fundamental studies of micro/nanoscale heat and mass transport and the development of efficient thermal management, water desalination, and solar thermal energy systems. Her work has been honored with awards including the 2008 DARPA Young Faculty Award, the 2011 Air Force Office of Scientific Research Young Investigator Award, the 2012 Office of Naval Research Young Investigator Award, the 2012 ASME Bergles-Rohsenow Young Investigator Award in Heat Transfer, as well as best paper awards at 2010 and 2014 ITherm and 2012 ASME Micro and Nanoscale Heat and Mass Transfer International Conference.
Igor V Marchuk is senior researcher of the Kutateladze Institute of Thermophysycs, Novosibirsk, Russia. He graduates the Novosibirsk State University at 1991. The main interests are heat and mass exchange, multiphase flows, condensation and evaporation, liquid film flows, infrared thermography.
Professor, PhD Oleg A Kabov graduated from the Tomsk Polytechnic State University, Russia, in 1978 and received the Ph.D. degree from the Institute of Thermophysics, Siberian Branch of Russian Academy of Sciences (IT) in 1987. In 1999 he received the degree of Doctor of Sciences in Physics and Mathematics (habilitation) from the same institute. In 2007 he has been granted the diploma of Professor on thermal physics and thermal fluids science of Russian Academy of Sciences. Since 1987, he has been the Head of Laboratory of Enhancement of Heat Transfer in IT (Novosibirsk). His current research interests include: shear-driven and falling liquid films and rivulets, two-phase flows in microgravity and hypergravity, drop spreading and drop evaporation, condensation, evaporative and thermocapillary convection. From 1997 till 2012 he was in a research staff of the Universite Libre de Bruxelles and has been managing the "Two-Phase Systems Group" of the Microgravity Research Center of ULB. He was involved as a coordinator and researcher in the several experiments performed under microgravity conditions (Parabolic Flights, Sounding Rockets, International Space Station). Experiments in 10 parabolic flights campaigns of the European Space Agency have been performed. He has authored and coauthored 271 papers in referred journals and conference proceedings, 7 patents, has delivered 60 keynotes, plenary, and invited lectures at technical conferences and institutions. He is a member of National Committee on Heat and Mass Transfer of Russian Academy of Sciences. In 2006 Prof. Kabov initiated the permanent yearly Workshop on Two-Phase Systems for Ground and Space Applications. Since 2013 he is serving as Editor-in-Chief of the Journal "Interfacial Phenomena and Heat Transfer" published by Begell House.
Nicolas's current research area focuses on numerical and physical modeling of evaporating and condensing flows in microchannels with emphasis on pragmatic and industrially realistic modeling. He continued the development of an annular flow condensation code and extended it to include evaporation, turbulent flows and elongated bubbles/slug flows.
Nicolas obtained his PhD from the Heat and Mass Transfer Laboratory of the Swiss Federal Institute of Technology, Lausanne under the supervision of Professor John R Thome.
Ricardo J Da Silva Lima received his PhD in Energy at the EPFL in Lausanne in 2011, where he investigated two-phase flow in U-bends (flow visualization and pressure drops). He moved to the Fribourg's University of Applied Sciences and then in 2013 he was appointed lecturer at the Geneva's University of Applied Sciences for energy courses and post-doctoral researcher at LTCM (EPFL) where currently he conducts two-phase flows research.. He is also the developer of a widely used two-phase flow pattern, heat transfer and pressure drop calculation tool, the "Excel Data Book III Calculator". In 2013 Ricardo Lima has been distinguished by ASHRAE with the Homer Addams Award.
John R Thome is Professor of Heat and Mass Transfer at the Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland since 1998, where he directs the two-phase flow and heat transfer research laboratory (LTCM) with 20 some post-docs and PhD students, see http://ltcm.epfl.ch/. His work focuses on visual investigations of the fundamental phenomena of microchannel two-phase flows (in channels as small as 85 microns), new experimental and image processing techniques for microscale two-phase flows, mechanistic two-phase flow pattern based heat transfer and pressure drop models for microscale evaporating and condensing flows, computerized flow control of two-phase microcooling systems, the development of multi-microchannel evaporators for electronics cooling with up to 1200 parallel microchannels, and the numerical modeling of two-phase phenomena. He received his PhD at Oxford University, England in 1978.