Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session A10: Multiphase Flows: Modeling and Theory I |
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Chair: Vladimir Ajaev, Southern Methodist University Room: Georgia World Congress Center B215 |
Sunday, November 18, 2018 8:00AM - 8:13AM |
A10.00001: A Mechanistic Model for the Initiation of Bubble Centering in Horizontal Gas-Liquid Slug Flow Sean Perkins, Huazhou Li Slug flow is a commonly observed, complex flow pattern in two-phase horizontal pipe flow. It is characterized by alternating flow of aerated liquid slugs and elongated bubbles which form a stratified-type flow with a thin liquid film as the bottom layer. Accurate modeling and understanding of slug flow is paramount to the design of a flowing system which may encounter the flow pattern. Bubble centering in horizontal slug flow is infrequently discussed in the current state of literature. Typically, the elongated bubble is assumed to flow along the upper wall of the pipe due to gravity segregation. At some conditions, however, the bubble is seen to travel closer to the centerline of the pipe. Until now, there has not existed a model which can offer clear insight into what causes this mechanism. A novel model which predicts the initiation of the bubble centering mechanism is presented. The model is mechanistic and thus focuses on characterizing and capturing all physical processes involved. Prediction of initial bubble detachment matches reasonably well with available air-water data. The presentation of this research includes an overview of slug flow, model development, and results. |
Sunday, November 18, 2018 8:13AM - 8:26AM |
A10.00002: Cluster-Based Reduced-Order Modeling of Dispersed and Slug Flows Bianca Viggiano, Naseem Ali, Murat Tutkun, Raúl Bayoán Cal Two-phase dispersed and slug flows in a pipe are investigated using a cluster-based reduced-order analysis technique. The data are obtained via 2-D construction of X-ray computed tomography measurements. Moving-average is used to obtain the fluctuating phase fraction of the periodic slug flow field. Flow fields are analyzed and reduced-order descriptions are achieved. A cluster-based reduced-order model algorithm is implemented on the phase fraction field and the proper orthogonal decomposition time coefficients. The algorithm partitions the basis into clusters, minimizing distances between the data points inside a cluster and maximizing the distances between the clusters. Cluster-based reduced-order model links a cluster analysis and a Markov chain model. The dynamical model is presented based on the transition process between the extracted clusters. Results display coherent features near the center of the pipe, the liquid-liquid interface, for the dispersed flow case while the slug flow shows coherent structures that correspond to the periodic formation of the slug. |
Sunday, November 18, 2018 8:26AM - 8:39AM |
A10.00003: A two-phase eleven-equation model for numerical simulations of aerated slug flow in horizontal and nearly horizontal pipelines Arianna Bonzanini, Marco Ferrari, Alberto Di Lul, Gianni Arioli, Pietro Poesio In this work, we propose a new model for the description of a one-dimensional two- phase flow. This model consists in a derivation of the hyperbolic, one-dimensional, five-equation, two-fluid model developed in previous work, which proved to be a good model to automatically capture the transition to slug flow regime adopting a flow description consistent with stratified conditions. The model presented here is built on eleven equations, namely four mass and four momentum conservation equations and three equations to describe the advection of the three interfaces. It is shown that this model owns the same hyperbolicity properties found for the five-equation system. The explicit form of the eigenstructure of the eleven-equation system allows to apply the high resolution extension of Godunov’s method with Roe linearization at cell interfaces. This model can describe stratified and wavy flow in pipeline; nevertheless, to numerically simulate slug flow, a slug criterion is developed and implemented to describe the disappearance of the field composed by continuous gas and droplets in some regions of the pipeline. Particular care is paid to the description of bubble entrainment and deposition in the slug body. |
Sunday, November 18, 2018 8:39AM - 8:52AM |
A10.00004: Sub-Filter Turbulent Velocity Reconstruction for a Volume-of-Fluid Dual-Scale approach at Turbulent Phase Interface Dynamics Dominic Kedelty, James Uglietta, Marcus Herrmann Advances to a dual-scale modeling approach are presented to describe turbulent phase interface dynamics in a LES spatial filtering context. Spatial filtering of the governing equations introduce several sub-filter terms that require modeling. Instead of developing individual closure models for the interface associated terms for LES, the dual-scale approach uses an exact closure by explicitly filtering a fully resolved realization of the phase interface. This resolved realization is maintained using a Refined Local Surface Grid approach (Herrmann, 2008) employing an unsplit geometric Volume-of-Fluid method (Owkes and Desjardins, 2014). The advection equation for the phase interface on this DNS scale requires a model for the fully resolved interface advection velocity. This velocity is the sum of the LES filtered velocity and modeled sub-filter velocity contributions. In this work, results from the dual-scale LES model using sub-filter turbulent eddy reconstruction by techniques including fractal interpolation (Scotti and Meneveau, 1999) and spectral differential filtering (Bassenne et al. 2017) are compared to DNS results for a material interface in a homogeneous isotropic turbulent flow. |
Sunday, November 18, 2018 8:52AM - 9:05AM |
A10.00005: An extended lubrication model for fluid flow in narrow gaps Jingchen Gu, Shintaro Takeuchi, Takeo Kajishima In this paper, to extend the applicable range of the lubrication theory, an extended lubrication equation is derived by considering the velocity component in surface-normal direction. The proposed equation is applied to the following two cases: the induced flows between a fixed flat plate and a curved object and by a sphere approaching to a plate. For the former case, the characteristics of the pressure distribution, particularly in the surface-normal direction, are reproduced successfully. For the latter case, the proposed equation is employed to model the flow between the sphere and plate. The effectiveness of the proposed equation is confirmed. A wider applicable range of the proposed equation comparing to that of the Reynolds lubrication equation is verified. The proposed equation predicts an applicable result for the ratio of the clearance width to the sphere radius being less than 0.5, while the Reynolds lubrication equation holds for a smaller range of the ratio being less than 0.1. This extended applicable range of the proposed equation is attributed to taking account of the velocity component in the surface-normal direction. |
Sunday, November 18, 2018 9:05AM - 9:18AM |
A10.00006: A porous media approach to the evaporation of droplets containing particles Christos Varsakelis, Sandrine Dessoy In this talk, we present a mathematical model for the evaporation of droplets containing particles based on continuum and thermodynamically consistent theories for porous media-clear fluid flows. According to our approach, a collection of particles, when homogenized appropriately, can be treated as porous medium that is nevertheless prone to compaction. With this premise, the two phases (liquid and porous medium) can be treated as thermodynamic continua that are allowed to interact with each other in the form of mass, momentum and energy exchanges. We will at first delineate the theoretical foundations and give a brief derivation of the mathematical equations. Particular emphasis will be paid to the compaction equation that governs the porosity evolution and the analogies that can be drawn from continuum theories of granular mixtures. The talk will conclude with a first characterization of the resulting governing equations and a discussion on numerical and theoretical implications. |
Sunday, November 18, 2018 9:18AM - 9:31AM |
A10.00007: Heat and mass transfer in a cylindrical heat pipe with a circular-capillary wick under small imposed temperature differences Pramesh Regmi, Harris Wong Previous models of heat pipes use the heat rate through the pipe as an input parameter, and therefore lack predictive capabilities. Here, we demonstrate, using a simple heat pipe, that if the evaporation and condensing kinetics are properly modeled, then the heat rate is predicted. We consider a cylindrical heat pipe with the inner wall lined with a circular-capillary wick. The capillaries are filled with a partially wetting liquid, and the center of the pipe is filled with its vapor. The equilibrium vapor pressure at the hot end is higher than that at the cold end, and this pressure difference drives the heat transfer in the heat pipe. We assume that the wick’s pore size is infinitesimal compared with the pipe dimensions. Thus, pore-level events can be treated separately from pipe-level events. Analytic solutions are obtained for the pipe temperature, vapor pressure, and all the other variables. For maximum evaporative heat transfer, we find an optimal pipe length for fixed pipe cross-sectional dimensions, and an optimal wick thickness for a fixed pipe length. These optimal pipe length and wick thickness can help to improve the design of heat pipes and are found for the first time. |
Sunday, November 18, 2018 9:31AM - 9:44AM |
A10.00008: Contact line motion on heated surfaces with spatially non-uniform properties Vladimir Ajaev, Elizaveta Gatapova Modeling of evaporation near contact lines is important for a number of applications such as pool boiling and micro heat pipes. Recent data from Constrained Vapor Bubble heat pipe experiment in microgravity provided new insights into physics of evaporation and flow near contact lines in confined systems, but mathematical models of such systems are still incomplete. Motivated by recent experiments, we develop a model of a moving contact line incorporating the effects of evaporation, Marangoni stresses, and two-component disjoining pressure and apply it to study contact line motion over heated surfaces with either temperature or wettability gradients. Conditions for local increase in the evaporative flux are identified. |
Sunday, November 18, 2018 9:44AM - 9:57AM |
A10.00009: Coupled dynamics of solid-liquid-vapour systems with mass transfer David N Sibley, Pablo Llombart, Eva G Noya, Andrew J Archer, Luis G MacDowell The dynamics of droplets on surfaces has received vast attention theoretically due to the interest in the moving contact line problem, and due to applications in inkjet printing, creation of super-hydrophobic surfaces, efficient irrigation methods and more. Many studies explore a conserved regime where a droplet of non-volatile liquid spreads on a fixed solid. Others study a similarly fixed solid with volatile liquid. Here, we explore a material existing in the three phases of solid, liquid and vapour, and consider dynamics where vapour can condense to liquid which in turn can freeze to solid throughout a droplet spreading process. By developing a thin-film model capturing phase-change, surface tension, density contrast, and interfacial potentials, a rich phase diagram will be explored---and complex dynamics such as layered solid growth driven by forces at the contact lines described. |
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