Mass transfer computation fluid dynamics

Computational fluid dynamics (CFD) is the analysis of systems involving fluid flow, energy transfer, and associated phenomena such as combustion and chemical reactions by means of computer-based simulation. CFD codes numerically solve the mass-continuity equation over a specific domain set by the user. The technique is very powerful and covers a wide range of industrial applications. Examples in the field of chemical engineering are ... 

Computational fluid dynamics (CFD) is the numerical analysis of systems involving transport processes and solution by computer simulation. An early application of CFD (FLUENT) to predict flow within cooling crystallizers was made by Brown and Boysan (1987). Elementary equations that describe the conservation of mass, momentum and energy for fluid flow or heat transfer are solved for a number of sub regions of the flow field (Versteeg and Malalase-kera, 1995). Various commercial concerns provide ready-to-use CFD codes to perform this task and usually offer a choice of solution methods, model equations (for example turbulence models of turbulent flow) and visualization tools, as reviewed by Zauner (1999) below. 

Another important modeling aspect is the simulation of catalytic process parameters and reactor configurations. Such models are typically associated with process engineering, and involve computational fluid dynamics and heat- and mass-transfer calculations. They are essential in the process planning and scale-up. However, as this book deals primarily with the chemical aspects of catalysis, the reader is referred to the literature on industrial catalysis and process simulations for further information [49,56]. 

Egorov, Y., Menter, F., Kloeker, M., Kenig, E.Y. Hydrodynamik und Stofftransport in katalytischen Packungen detaillierte CFD Berechnung und Prozesssimulation. Proc. GVC-Conf. Heat and Mass Transfer" and CFD Computational Fluid Dynamics", Weimar, 2002. 

Mathematical models have been developed by considering classical flow models. At the same time, the capacity of computational fluid dynamics to be coupled with heat and mass transfer processes and with a reaction has been considered. 

Computational fluid dynamics involves the analysis of fluid flow and related phenomena such as heat and/or mass transfer, mixing, and chemical reaction using numerical solution methods. Usually the domain of interest is divided into a large number of control volumes (or computational cells or elements) which have a relatively small size in comparison with the macroscopic volume of the domain of interest. For each control volume a discrete representation of the relevant conservation equations is made after which an iterative solution procedure is invoked to obtain the solution of the nonlinear equations. Due to the advent of high-speed digital computers and the availability of powerful numerical algorithms the CFD approach has become feasible. CFD can be seen as a hybrid branch of mechanics and mathematics. CFD is based on the conservation laws for mass, momentum, and (thermal) energy, which can be expressed as follows ... 

Computational fluid dynamics simulations were used by Li et al. [68] to determine mass transfer coefficients and power consumption in channels filled with non woven net spacers. The geometric parameters of a non woven spacer were found to have a great influence on the performance of a spacer in terms of mass transfer enhancement and power consumption. The results from the CFD simulations indicated that an optimal spacer geometry exists. 

Takeuchi et al. 7 reported a membrane reactor as a reaction system that provides higher productivity and lower separation cost in chemical reaction processes. In this paper, packed bed catalytic membrane reactor with palladium membrane for SMR reaction has been discussed. The numerical model consists of a full set of partial differential equations derived from conservation of mass, momentum, heat, and chemical species, respectively, with chemical kinetics and appropriate boundary conditions for the problem. The solution of this system was obtained by computational fluid dynamics (CFD). To perform CFD calculations, a commercial solver FLUENT has been used, and the selective permeation through the membrane has been modeled by user-defined functions. The CFD simulation results exhibited the flow distribution in the reactor by inserting a membrane protection tube, in addition to the temperature and concentration distribution in the axial and radial directions in the reactor, as reported in the membrane reactor numerical simulation. On the basis of the simulation results, effects of the flow distribution, concentration polarization, and mass transfer in the packed bed have been evaluated to design a membrane reactor system. 

Cockx, A., Do-Quang, Z., Line, A. and Roustan, M. (1999), Use of computational fluid dynamics for simulating hydrodynamics and mass transfer in industrial ozonation owers, Chem. Eng. Sci., 54, 5085-5090. 

The approach developed by Newman for the treatment of both mass-transfer and electric-field effects in boundary-layer flows has had considerable success.L2 6 However, many flows of practical interest have separation and recirculation regions, features not amenable to a boundary-layer analysis. Fortunately, there has been significant progress in the heat-transfer and other communities in computational fluid dynamics (CFD), providing numerical methods applicable to problems important to electrochemistry. The pioneers in using CFD for electrochemical applications are Alkire and co-workers, who have been largely interested in flow effects in localized corrosion. The literature is briefly reviewed in the next section. 

In industrial electrolytic processes, including metal electrodeposition and preparation reactions, mass transfer and fluid flow are usually of central importance, especially in scaleup from laboratory-scale experimentation. In the final chapter of this volume. West and co-authors give the essential aspects of computer analysis and modeling of such processes in terms of fluid dynamics and mass transfer. 

It is useful to mention another class of problems related to those referred to in the previous paragraphs, but that is not considered here. We do not try to answer the ques- tion of how fast a system will respond to a change in constraints that is, we do not try to study system dynamics. The answers to such problems, depending on the system and its constraints, may involve chemical kinetics, heat or mass transfer, and fluid mechanics, all of which are studied elsewhere. Thus, in the example above, we are interested in the final state of the gas in each cylinder, but not in computing how long a valve of given size must be held open to allow the necessary amount of gas to pass from one cylinder to the other. Similarly, when, in Chapters 10, 11, and 12, we study phase equilibrium and, in Chapter 13, chemical equilibrium, our interest is in the prediction of the equilibrium state, not in how long it will take to achieve this equilibrium state. —... 

S. Jayanti and G. F. Hewitt, Hydrodynamics and Heat Transfer in Wavy Annular Gas-Liquid Flow A Computational Fluid Dynamics Study, Int. J. Heat Mass Transfer (40) 2445-2460,1997. 

Utilize computational fluid dynamics (CFD) models to rmderstand and address heat and mass transfer issues and reactor performance for steady-state and transient analysis. 

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