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Development Of A General Purpose Subgrid Wall Boiling Model From Improved Physical Understanding For Use In Computational Fluid Dynamics
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Book Synopsis Development of a General Purpose Subgrid Wall Boiling Model from Improved Physical Understanding for Use in Computational Fluid Dynamics by : Lindsey Anne Gilman
Download or read book Development of a General Purpose Subgrid Wall Boiling Model from Improved Physical Understanding for Use in Computational Fluid Dynamics written by Lindsey Anne Gilman and published by . This book was released on 2014 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advanced modeling capabilities were developed for application to subcooled flow boiling through this work. The target was to introduce, and demonstrate, all necessary mechanisms required to accurately predict the temperature and heat flux for subcooled flow boiling in CFD simulations. The model was developed using an experimentally based mechanistic approach, where the goal was to accurately capture all physical phenomena that affect heat transfer and occur at the heated surface to correctly predict surface temperatures. The proposed model adopts a similar approach to the classical heat partitioning method, but captures additional boiling physical phenomena. It introduces a new evaporation term, to truly capture the evaporation occurring on the surface while also tracking the bubble crowding effect on the boiling surface. This includes evaporation from the initial bubble inception and evaporation through the bubble microlayer. The convection term is modified to account for increased surface roughness caused by the presence of the bubbles on the heated surface. The quenching term accounts for bringing the bubble dry spot back to the wall superheat prior to bubble inception. In addition to the changes to these three classic components, a sliding conduction term is added to capture the increased heat transfer due to bubble sliding on the heated surface prior to lift-off. The sliding conduction component includes all heat removal associated with transient conduction caused by disruption of the thermal boundary layer. The new method extends the generality and applicability of boiling models in CFD through a fully mechanistic representation. The new model also tracks the dry surface area during boiling for possible application in DNB predictions. A statistical tracking method for bubble location on the heated surface provides information on the bubble merging probability and prevents the active nucleation site density from reaching un-physical values. The model was implemented in the CFD software STAR-CCM+, and the wall temperature predictions were recorded and compared against the standard model's predictions and experimental data for a range of mass fluxes, heat fluxes, inlet subcoolings, and pressures. In general, the new model predicts wall temperatures closer to experimental data for both low and high pressures when compared against the standard model. The new model also converges at higher heat fluxes and greater subcoolings than the standard model.
Book Synopsis Modeling and Simulation of Liquid Microlayer Formation and Evaporation in Nucleate Boiling Using Computational Fluid Dynamics by : Alexandre Nicolas Guion
Download or read book Modeling and Simulation of Liquid Microlayer Formation and Evaporation in Nucleate Boiling Using Computational Fluid Dynamics written by Alexandre Nicolas Guion and published by . This book was released on 2017 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt: The transport of latent heat makes boiling one of the most efficient modes of heat transfer, allowing a wide range of systems to improve their thermal performance, from microelectronic devices to nuclear power plants. In particular, Boiling Water Reactors (BWR) use boiling as the primary mode of heat transfer in the reactor core to accommodate very high heat fluxes. In Pressurized Water Reactors (PWR) subcooled flow boiling can occur in hot sub-channels. As a bubble grows outside of a surface imperfection during nucleate boiling, viscous stresses at the wall can be strong enough to impede liquid motion and trap a thin liquid layer - referred to as microlayer, underneath the growing bubble. The contribution of microlayer evaporation to overall heat transfer and bubble growth can be large, in particular in the case of water1. In practice, numerical simulations of nucleate boiling resolve the macroscopic interface of the bubble and resort to subgrid models to account for the evaporation of the microlayer at the microscopic scale. The applicability of this subgrid modeling approach relies on the capacity to initialize the microlayer shape and extension, prior to its evaporation. However, existing models of microlayer formation are either physically incomplete2 or purely empirical3. In this work, we first confirm through a sensitivity study the need for accurate modeling of microlayer formation to initialize boiling simulations and to reproduce physical boiling dynamics (a). Then, we build the first generally applicable model for microlayer formation through direct computations of the hydrodynamics of bubble growth at the wall for a wide range of conditions and fluids, including water at 0.101MPa (lab experiments) and 15.5MPa (PWR), capillary numbers Ca [is element of] [0.001; 0.1], and contact angles [theta] [is element of] [10°; 90°] (b). In addition, we modify an existing experimental pool boiling setup to measure with unprecedented accuracy initial bubble growth rates needed to predict microlayer formation (c). Lastly, we develop a numerical procedure based on hydrodynamics theories to obtain mesh-independent results in moving contact line simulations for a wide range of contact angles and viscosity ratios (d). In particular, we use direct computations of the transition to a Landau-Levich-Derjaguin film in forced dewetting to inform the onset of microlayer formation in nucleate boiling. These contributions(a) (b) (c) (d) bridge a significant gap in our understanding of how boiling works and can be modeled at the microscopic scale, which represents a first step in designing surfaces with higher heat transfer performance and in building safer and more efficient energy systems.
Book Synopsis ASSESSMENT OF ANNULAR FLOW BOILING IN THE CONTEXT OF COMPUTATIONAL FLUID DYNAMICS (CFD) SIMULATIONS, EXPERIMENTS, AND EXISTING CORRELATIONS by :
Download or read book ASSESSMENT OF ANNULAR FLOW BOILING IN THE CONTEXT OF COMPUTATIONAL FLUID DYNAMICS (CFD) SIMULATIONS, EXPERIMENTS, AND EXISTING CORRELATIONS written by and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract : The main objective of the current work is to achieve a better understanding - through modeling and simulation/programming activities - of annular flow-boiling and its applications based on a synthesis of Computational Fluid Dynamics (CFD) simulations, existing correlations, and experiments. A unique and rigorous 2-D CFD simulations technique was developed for annular flow-boiling to propose a correlation for convective component of Heat Transfer Coefficient (HTC) - defined here as flow-boiling in the absence of nucleation. To provide a context for the correlation structure of convective component of HTC, flow-physics details of annular flow-boiling and correlation structure (based on fundamental considerations) for HTC have also been discussed. Further, other existing correlations for Nusselt number, void-fraction, flow-regime transition, and pressure-drop have been used to develop a general but first order engineering estimates-methodology for design of annular flow-boilers and flow-condensers. The first order estimates-methodology, thus developed for annular flow-boiler operations, was used to: (i) make a priori estimates of flow predictions towards choosing suitable instrumentations for the design of a particular test-section and associated flow-loop needed for a new high heat-flux flow-boiling experiments involving water as a working fluid), and (ii) define a range of experimental operating conditions - for a low heat-flux test-section and flow-loop (involving FC-72 as working fluid) facility from which experimental data needed to be obtained to throw light on the flow-physics being modeled by the CFD code. Furthermore, preliminary results from a different low heat-flux experiments are briefly discussed here and then compared with rigorous CFD simulations to achieve better understanding of the flow-physics.
Book Synopsis A One-dimensional Subgrid Near-wall Treatment for Reynolds Averaged Computational Fluid Dynamics Simulations by : Seth Hardin Myers
Download or read book A One-dimensional Subgrid Near-wall Treatment for Reynolds Averaged Computational Fluid Dynamics Simulations written by Seth Hardin Myers and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Prediction of the near wall region is crucial to the accuracy of turbulent flow computational fluid dynamics (CFD) simulation. However, sufficient near-wall resolution is often prohibitive for high Reynolds number flows with complex geometries, due to high memory and processing requirements. A common approach in these cases is to use wall functions to bridge the region from the first grid node to the wall. This thesis presents an alternative method that relaxes the near wall resolution requirement by solving one dimensional transport equations for velocity and turbulence across a locally defined subgrid contained within wall adjacent grid cells. The addition of the subgrid allows for wall adjacent primary grid sizes to vary arbitrarily from low-Re model sizing (y+ ~ 1) to wall function sizing without significant loss of accuracy or increase in computational cost.
Book Synopsis A One-Dimensional Subgrid Near-Wall Treatment for Reynolds Averaged Computational Fluid Dynamics Simulations by :
Download or read book A One-Dimensional Subgrid Near-Wall Treatment for Reynolds Averaged Computational Fluid Dynamics Simulations written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Prediction of the near wall region is crucial to the accuracy of turbulent flow computational fluid dynamics (CFD) simulation. However, sufficient near-wall resolution is often prohibitive for high Reynolds number flows with complex geometries, due to high memory and processing requirements. A common approach in these cases is to use wall functions to bridge the region from the first grid node to the wall. This thesis presents an alternative method that relaxes the near wall resolution requirement by solving one dimensional transport equations for velocity and turbulence across a locally defined subgrid contained within wall adjacent grid cells. The addition of the subgrid allows for wall adjacent primary grid sizes to vary arbitrarily from low-Re model sizing (y+ ~ 1) to wall function sizing without significant loss of accuracy or increase in computational cost.
Book Synopsis A New Mechanistic Model of Critical Heat Flux in Forced-convection Subcooled Boiling by :
Download or read book A New Mechanistic Model of Critical Heat Flux in Forced-convection Subcooled Boiling written by and published by . This book was released on 1997 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: Because of its practical importance and various industrial applications, the process of subcooled flow boiling has attracted a lot of attention in the research community in the past. However, the existing models are primarily phenomenological and are based on correlating experimental data rather than on a first-principle analysis of the governing physical phenomena. Even though the mechanisms leading to critical heat flux (CHF) are very complex, the recent progress in the understanding of local phenomena of multiphase flow and heat transfer, combined with the development of mathematical models and advanced Computational Fluid Dynamics (CFD) methods, makes analytical predictions of CHF quite feasible. Various mechanisms leading to CHF in subcooled boiling have been investigated. A new model for the predictions of the onset of CHF has been developed. This new model has been coupled with the overall boiling channel model, numerically implemented in the CFX 4 computer code, tested and validated against the experimental data of Hino and Ueda. The predicted critical heat flux for various channel operating conditions shows good agreement with the measurements using the aforementioned closure laws for the various local phenomena governing nucleation and bubble departure from the wall. The observed differences are consistent with typical uncertainties associated with CHF data.
Book Synopsis Efficient Simulation of Thermochemical Nonequilibrium Flows using Highly-Resolved H-Adapted Grids by : Christian Windisch
Download or read book Efficient Simulation of Thermochemical Nonequilibrium Flows using Highly-Resolved H-Adapted Grids written by Christian Windisch and published by Cuvillier Verlag. This book was released on 2014-07-08 with total page 234 pages. Available in PDF, EPUB and Kindle. Book excerpt: Accurate and easy to handle simulation tools are needed for the design and development of future space transportation systems. The simulation of hypersonic flow fields in thermochemical nonequilibrium is a challenging task, as a variety of flow features on various time and length scales needs to be properly resolved. With this purpose in mind, a general CFD solver framework is developed in this doctoral thesis. It combines the multiscale-based grid adaptation with the necessary physical models and numerical methods for the simulation of arbitrary reaction models in thermochemical nonequilibrium. The developed tools and methods are incorporated into the QUADFLOW solver, an integrated concept of grid generation, grid adaptation and finite-volume flow solver. The modified QUADFLOW solver is then applied to pertinent applications. The injection of various cooling gases into a supersonic boundary layer demonstrates the versatility of the QUADFLOW solver at the example of a low enthalpy configuration. The simulated high-enthalpy Edney type IV and type VII shock-shock interactions represent a complex and challenging flow configuration. A high resolution of the vortex structures in the inner flow field and of the boundary layer is achieved at the same time. Für die Auslegung und Entwicklung zukünftiger Raumtransportsysteme werden Simulationslösungen benötigt, die präzise und einfach in der Handhabung sind. Die Simulation hypersonischer Strömungen im chemischen und thermischen Nichtgleichgewicht ist eine anspruchsvolle Aufgabe, da eine Vielzahl von Strömungseffekten auf verschiedenen Zeit- und Längenskalen aufgelöst werden muss. In der vorliegenden Dissertation wird eine speziell für diese Aufgabe optimierte CFD Simulationslösung entwickelt. Hierzu wird eine multiskalen-basierte Gitteradaption mit den notwendigen physikalischen Modellen und numerischen Methoden kombiniert die erforderlich sind, um beliebige Reaktionsmodelle im chemischen und thermischen Nichtgleichgewicht zu simulieren. Die entwickelten Modelle und Methoden werden in QUADFLOW implementiert, einer integrierten Simulationslösung bestehend aus Gittergenerierung, Gitteradaption und Finite-Volumen Strömungslöser. Die modifizierte QUADFLOW Simulationslösung wird im Anschluss zur Simulation einschlägiger Anwendungsbeispiele eingesetzt. Die Kühlgaseinspritzung verschiedener Gase in eine Überschallgrenzschicht demonstriert eindrucksvoll die Vielseitigkeit von QUADFLOW am Beispiel einer Konfiguration mit geringer Enthalpie. Die simulierten Edney Typ IV und Typ VII Stoß-Stoß Interaktionen stellen komplexe und anspruchsvolle Konfigurationen mit hoher Enthalpie dar. In diesem Fall konnte eine hohe Auflösung sowohl der Wirbelstrukturen im inneren Strömungsfeld als auch der Grenzschicht erzielt werden.
Book Synopsis Extending Bubble-induced Turbulence Modeling Applicability in CFD Through Incorporation of DNS Understanding by : Benjamin Lawrence Magolan
Download or read book Extending Bubble-induced Turbulence Modeling Applicability in CFD Through Incorporation of DNS Understanding written by Benjamin Lawrence Magolan and published by . This book was released on 2018 with total page 213 pages. Available in PDF, EPUB and Kindle. Book excerpt: Precise knowledge and understanding of the multiphase flow distribution is essential for light water reactor design. Multiphase Computational Fluid Dynamics (M-CFD) modeling and simulation techniques provide three-dimensional resolution of complex flow structures, which can be used to improve operation and safety in current systems, while driving optimization and performance enhancement in next generation designs. Introducing bubbles into liquid flow dramatically modifies the turbulent kinetic energy profile. Examination of experimental and Direct Numerical Simulation (DNS) research reveals a complicated, incomplete, and conflicting picture of bubble-induced turbulence (BIT). Incorporating these physical mechanisms into a BIT model compatible within the Eulerian-Eulerian framework remains a formidable challenge. Two-equation BIT models share a general formulation, manifesting as additional source terms in traditional turbulence models to account for production and dissipation of bubble-induced turbulence. Existing formulations struggle with reliably predicting the turbulent kinetic energy profile, routinely yielding non-physical results that subsequently worsen mean flow predictions. The present work encompasses two research objectives that include (1) advancing the understanding of the complex effects bubbles pose on liquid turbulence, and (2) proposing an approach to incorporate these physical phenomena into a BIT closure relation. Greater understanding of two-phase turbulent mechanisms is advanced through statistical analysis of upward bubbly channel flow DNS data generated by Bolotnov and Lu/Tryggvason. The impact of bubble deformability on the resulting turbulent distributions, energy budgets, and scales are quantified and examined. A methodology that incorporates these fundamental mechanisms into a new BIT model is proposed. The closure comprises five components that include new turbulent viscosity and time-scale formulations in addition to optimized values for the modulation parameter, dissipation coefficient, and newly proposed turbulent viscosity multiplier. Model performance and improvement is confirmed through simulation of the entire Liu (1989) experimental database and comparison with existing closures. The model is incorporated into the Bubbly And Moderate void Fraction (BAMF) formulation (Sugrue et al., 2017) in order to deliver best practices and guidelines for application of momentum closures with BIT modeling. This is accomplished through redefinition of the Wobble number, calibration of expressions for the turbulent dispersion coefficient and lift inversion function, and assessment via simulation of experimental databases.
Book Synopsis Modeling Vertical Subcooled Boiling Flows at Low Pressures by : G. H. Yeoh
Download or read book Modeling Vertical Subcooled Boiling Flows at Low Pressures written by G. H. Yeoh and published by . This book was released on 2011 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt: An improved wall heat flux partitioning model at the heated surface was developed by Yeoh et al. This model, coupled with a three-dimensional two-fluid model and Multiple Size Group model, has led to satisfactory agreement being achieved between the model predictions and experimental measurements. Nevertheless, one shortcoming is the reliance on empirical correlations for the active nucleation site density in the wall heat flux partitioning model. This discrepancy brings about uncertainties, especially in appropriately evaluating the vapor generation rate, which greatly influences the model prediction on the axial and radial void fraction profiles within the bulk fluid flow. By considering the fractal model with the aforementioned subcooled boiling flow model in the absence of empirical correlations for the active nucleation site density, a comprehensive mechanistic model to predict vertically oriented subcooled boiling flows is developed. The proposed model is assessed against the experimental data of axial measurements of Zeitoun and Shoukri and the radial measurements of Yun et al. and Lee et al. for vertical subcooled boiling flows within annular channels. Improved model predictions are obtained when the model is compared against typically applied empirical correlations for active nucleation site density. Discussions on the agreement of other two-phase flow parameters are also presented.
Book Synopsis Computational Fluid Dynamics in Fire Engineering by : Guan Heng Yeoh
Download or read book Computational Fluid Dynamics in Fire Engineering written by Guan Heng Yeoh and published by Butterworth-Heinemann. This book was released on 2009-04-20 with total page 545 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fire and combustion presents a significant engineering challenge to mechanical, civil and dedicated fire engineers, as well as specialists in the process and chemical, safety, buildings and structural fields. We are reminded of the tragic outcomes of ‘untenable’ fire disasters such as at King’s Cross underground station or Switzerland’s St Gotthard tunnel. In these and many other cases, computational fluid dynamics (CFD) is at the forefront of active research into unravelling the probable causes of fires and helping to design structures and systems to ensure that they are less likely in the future. Computational fluid dynamics (CFD) is routinely used as an analysis tool in fire and combustion engineering as it possesses the ability to handle the complex geometries and characteristics of combustion and fire. This book shows engineering students and professionals how to understand and use this powerful tool in the study of combustion processes, and in the engineering of safer or more fire resistant (or conversely, more fire-efficient) structures. No other book is dedicated to computer-based fire dynamics tools and systems. It is supported by a rigorous pedagogy, including worked examples to illustrate the capabilities of different models, an introduction to the essential aspects of fire physics, examination and self-test exercises, fully worked solutions and a suite of accompanying software for use in industry standard modeling systems. Computational Fluid Dynamics (CFD) is widely used in engineering analysis; this is the only book dedicated to CFD modeling analysis in fire and combustion engineering Strong pedagogic features mean this book can be used as a text for graduate level mechanical, civil, structural and fire engineering courses, while its coverage of the latest techniques and industry standard software make it an important reference for researchers and professional engineers in the mechanical and structural sectors, and by fire engineers, safety consultants and regulators Strong author team (CUHK is a recognized centre of excellence in fire eng) deliver an expert package for students and professionals, showing both theory and applications. Accompanied by CFD modeling code and ready to use simulations to run in industry-standard ANSYS-CFX and Fluent software
Book Synopsis Modelling Subcooled Boiling Flows by : Guan Heng Yeoh
Download or read book Modelling Subcooled Boiling Flows written by Guan Heng Yeoh and published by . This book was released on 2009 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis NURESIM project deliverable D2.2.13.1b by : Boštjan Končar
Download or read book NURESIM project deliverable D2.2.13.1b written by Boštjan Končar and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Bubbly Flows written by Martin Sommerfeld and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 354 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book summarises the outcom of a priority research programme: 'Analysis, Modelling and Computation of Multiphase Flows'. The results of 24 individual research projects are presented. The main objective of the research programme was to provide a better understanding of the physical basis for multiphase gas-liquid flows as they are found in numerous chemical and biochemical reactors. The research comprises steady and unsteady multiphase flows in three frequently found reactor configurations, namely bubble columns without interiors, airlift loop reactors, and aerated stirred vessels. For this purpose new and improved measurement techniques were developed. From the resulting knowledge and data, new and refined models for describing the underlying physical processes were developed, which were used for the establishment and improvement of analytic as well as numerical methods for predicting multiphase reactors. Thereby, the development, lay-out and scale-up of such processes should be possible on a more reliable basis.
Book Synopsis The Finite Volume Method in Computational Fluid Dynamics by : F. Moukalled
Download or read book The Finite Volume Method in Computational Fluid Dynamics written by F. Moukalled and published by Springer. This book was released on 2015-08-13 with total page 799 pages. Available in PDF, EPUB and Kindle. Book excerpt: This textbook explores both the theoretical foundation of the Finite Volume Method (FVM) and its applications in Computational Fluid Dynamics (CFD). Readers will discover a thorough explanation of the FVM numerics and algorithms used for the simulation of incompressible and compressible fluid flows, along with a detailed examination of the components needed for the development of a collocated unstructured pressure-based CFD solver. Two particular CFD codes are explored. The first is uFVM, a three-dimensional unstructured pressure-based finite volume academic CFD code, implemented within Matlab. The second is OpenFOAM®, an open source framework used in the development of a range of CFD programs for the simulation of industrial scale flow problems. With over 220 figures, numerous examples and more than one hundred exercise on FVM numerics, programming, and applications, this textbook is suitable for use in an introductory course on the FVM, in an advanced course on numerics, and as a reference for CFD programmers and researchers.
Book Synopsis Wall Modeling Via Function Enrichment for Computational Fluid Dynamics by : Benjamin Krank
Download or read book Wall Modeling Via Function Enrichment for Computational Fluid Dynamics written by Benjamin Krank and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Development of physical models for boiling flow and implementation in the NURESIM-CFD code by : Boštjan Končar
Download or read book Development of physical models for boiling flow and implementation in the NURESIM-CFD code written by Boštjan Končar and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Computational Fluid Dynamics for Engineers by : Bengt Andersson
Download or read book Computational Fluid Dynamics for Engineers written by Bengt Andersson and published by Cambridge University Press. This book was released on 2011-12-22 with total page 203 pages. Available in PDF, EPUB and Kindle. Book excerpt: Computational fluid dynamics, CFD, has become an indispensable tool for many engineers. This book gives an introduction to CFD simulations of turbulence, mixing, reaction, combustion and multiphase flows. The emphasis on understanding the physics of these flows helps the engineer to select appropriate models to obtain reliable simulations. Besides presenting the equations involved, the basics and limitations of the models are explained and discussed. The book combined with tutorials, project and power-point lecture notes (all available for download) forms a complete course. The reader is given hands-on experience of drawing, meshing and simulation. The tutorials cover flow and reactions inside a porous catalyst, combustion in turbulent non-premixed flow, and multiphase simulation of evaporation spray respectively. The project deals with design of an industrial-scale selective catalytic reduction process and allows the reader to explore various design improvements and apply best practice guidelines in the CFD simulations.
