Models CFD flow

ANSYS, Inc. CFD flow modeling software solutions from fluent - website (2007), http //www.fluent.coin... 

The logical extension of this approach is to divide the crystallizer into many compartments. This is known as the network of zones approach and has been used suceessfully by Mann (1993). Here, the exchange flows between compartments are not modeled but applied separately, either from a knowledge of the overall flow pattern achieved from experimental measurements or from a CFD flow model. Additionally, rules are applied which describe the turbulent transport of particles and species between zones. 

This feattire conducts water and salt removal. The vanes, which are constructed from corrosion-resistant marine grade aluminum (other materials are available), are produced with a profile that allows the maximum removal of salt and water, yet produces an extremely low pressure loss. This optimal profile has been achieved by the very latest design methods, and in particular by utilizing a Computational Fluid Dynamics (CFD) flow modeling system. Hydra also incorporates a unique and novel method of separating water droplets from the air stream, and this has led to improvements in bulk water removal compared with conventional methods. 

Sophisticated computer models help to reduce the size of separator vessels and ensure that Uqtdd/vapor separation is achieved to specification. The CFD flow model pictured in Fig L-13 depicts the final design of a vertical gas separator for an LNG fadlity- This graphic provides the engineer with visual confirmation of gas flow paths and that the separator face velocities meet established design criteria. 

It must be reemphasized that the value of a flow model s reeom-mendations depends on how well the model represents the real proeess situation. The reaetor and the proeess streams must be deseribed aeeurately, as must the relationship between the fluid dynamies and the proeess performanee. Often, proeess engineers are tempted to rely on eommereial CFD programs for the fluid dynamies equations. However, any eommereial program may have partieular limitations for simulating eomplex proeess equipment. On the other hand, almost all... 

The probability density function of u is shown for four points in Fig. 11.16, two points in the wall jet and two points in the boundary layer close to the floor. For the points in the wall jet (Fig. 11.16<2) the probability (unction shows a preferred value of u showing that the flow has a well-defined mean velocity and that the velocity is fluctuating around this mean value. Close to the floor near the separation at x/H = I (Fig. 11.16f ) it is hard to find any preferred value of u, which shows that the flow is irregular and unstable with no well-defined mean velocity and large turbulent intensity. From Figs. 11.15 and 11.16 we can see that LES gives us information about the nature of the turbulent fluctuations that can be important for thermal comfort. This type of information is not available from traditional CFD using models. 

Al-Rashed etal. (1996) and Al-Rashed and Jones (1999a,b) presented a CFD-based model to prediet the effeets of mixing during bateh-wise gas-liquid reaetive preeipitation in the flat interfaee eell used by Waehi and Jones, 1991b. A 2D flow simulation was developed for the ehemieal reaetion with... 

Andersson, R. (2005) Dynamics of fluid particles in turbulent flows CFD simulations, model development and phenomenological studies. Chemical and Biological Engineering, Chalmers University of Technology, Gothenburg, p. 89. 

When running a CFD simulation, a decision must be made as to whether to use a laminar-flow or a turbulent-flow model. For many flow situations, the transition from laminar to turbulent flow with increasing flow rate is quite sharp, for example, at Re — 2100 for flow in an empty tube. For flow in a fixed bed, the situation is more complicated, with the laminar to turbulent transition taking place over a range of Re, which is dependent on the type of packing and on the position within the bed. 

In order to compare various reacting-flow models, it is necessary to present them all in the same conceptual framework. In this book, a statistical approach based on the one-point, one-time joint probability density function (PDF) has been chosen as the common theoretical framework. A similar approach can be taken to describe turbulent flows (Pope 2000). This choice was made due to the fact that nearly all CFD models currently in use for turbulent reacting flows can be expressed in terms of quantities derived from a joint PDF (e.g., low-order moments, conditional moments, conditional PDF, etc.). Ample introductory material on PDF methods is provided for readers unfamiliar with the subject area. Additional discussion on the application of PDF methods in turbulence can be found in Pope (2000). Some previous exposure to engineering statistics or elementary probability theory should suffice for understanding most of the material presented in this book. 

For canonical turbulent flows (Pope 2000), the flow parameters required to complete the CRE models are readily available. However, for the complex flow fields present in most chemical reactors, the flow parameters must be found either empirically or by solving a CFD turbulence model. If the latter course is taken, the next logical step would be to attempt to reformulate the CRE model in terms of a set of transport equations that can be added to the CFD model. The principal complication encountered when following this path is the fact that the CRE models are expressed in a Lagrangian framework, whilst the CFD models are expressed in an Eulerian framework. One of the main goals of this book... 

Bakker, R. A. and H. E. A. van den Akker (1996). A Lagrangian description of micromixing in a stirred tank reactor using 1 D-micromixing models in a CFD flow field. Chemical Engineering Science 51, 2643-2648. 

To understand the mechanisms of solids slug flows, a two-dimensional coupled DEM/CFD numerical model was built to simulate the motion of a pre-formed slug (ca. 0.3 m long) in a 1 m long horizontal 50 mm bore pipe as shown in Fig. 1. The pipe was initially filled with a layer of particles, approximately 15 mm thick at the bottom. (The thickness of this stationary layer was determined based on experience from previous experiments and computer test runs). 

Virtually all CFD fire models assume low Mach number flow, which is adequate in typical fire application, but not for high velocity cases and explosions. Inclusion of the compressibility effects in fire simulations would increase the computational cost considerably. One of the few compressible fire models is the Uintah Computational Framework developed at C-SAFE project of the University of Utah [7],... 

Concermng our problem of the modelling of the flow process, even if the CFD seems to be the most complete approach, the use of flow models for its characterization is sustained by the following statements ... 

The M2UE is a Computational Fluid Dynamics (CFD) 3D obstacle-resolved air flow model (Nuterman et al. 2008)... 

The theoretical and numerical basis of computational flow modeling (CFM) is described in detail in Part II. The three major tasks involved in CFD, namely, mathematical modeling of fluid flows, numerical solution of model equations and computer implementation of numerical techniques are discussed. The discussion on mathematical modeling of fluid flows has been divided into four chapters (2 to 5). Basic governing equations (of mass, momentum and energy), ways of analysis and possible simplifications of these equations are discussed in Chapter 2. Formulation of different boundary conditions (inlet, outlet, walls, periodic/cyclic and so on) is also discussed. Most of the discussion is restricted to the modeling of Newtonian fluids (fluids exhibiting the linear dependence between strain rate and stress). In most cases, industrial... 

It is necessary to develop an appropriate methodology to harness the potential of CFD tools for engineering analysis and design despite some of the limitations. Computational flow modeling (CFM) includes such overall methodology and all the other activities required to use CFD to achieve the engineering objectives. 

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