Computational fluid dynamic flow model

As computers become faster, the complexity of problem that can be usefully simulated increases. Areas of interest include combining computational fluid dynamics (CFD) modelling with chemical kinetics to investigate (and hence reduce) the effect of flow maldistributions on aftertreatment system efficiency, and simulating catalyst deactivation over the lifetime of the catalyst. 

Bridging the gap between micro- and macro-scale is the central theme of the first contribution. The authors show how a so-called Energy-Minimization Multi-Scale (EMMS) model allows to do this for circulating fluid beds. This variational type of Computational Fluid Dynamics (CFD) modeling allows for the resolution of meso-scale structures, that is, those accounting for the particle interactions, and enables almost grid-independent solution of the gas-solids two-phase flow. 

Care is needed when modeling compressible gas flows, flows of vapor-liquid mixtures, slurry flows, and flows of non-Newtonian liquids. Some simulators use different pipe models for compressible flow. The prediction of pressure drop in multiphase flow is inexact at best and can be subject to very large errors if the extent of vaporization is unknown. In most of these cases, the simulation model should be replaced by a computational fluid dynamics (CFD) model of the important parts of the plant. 

Any notable accumulation of gas was unlikely since the two fans inside the chassis create a flow rate of approximately 180 CFM of air through the system. This corresponded to more than 95 complete air changes or turnovers every minute (Heck and Manning, 2000). The most likely zone of gas escape would be above the microreactor due to a membrane failure. If this occurs, the control system should have interlocked and shutoff the flow of combustible gas to that reaction channel. The flammable gas that does escape would have been immediately diluted by air flowing over the microreactor at an estimated rate of 120 ft min (Heck and Manning, 2000). To provide a more detailed analysis of gas mixing in the immediate vicinity of a microreactor die, a computational fluid dynamics (CFD) model was constructed to simulate the gas flow hydrodynamics. This simulation quantifies that there is a recirculation zone above the reactor with an airflow rate... 

Kashid et al. studied the fiow patterns within the slugs and mass transfer between two consecutive slugs in liquid-liquid slug flow using a finite element-based computational fluid dynamics (CFD) model [51]. The model equations are implemented in the open-source software FEATFLOW (www.featflow.de). Figure 12.18 shows snapshots of the concentration profiles of the extract (acetic acid). These results are compared with experimental results and are consistent with them. 

With an effective thermal model of the cells, modules and overall system, an analysis of the performance under different situations and load conditions can be evaluated. This proves to be a very useful tool in the development of the pack as these thermal models can be input into computational fluid dynamic (CFD) models to determine how the cells will heat during operation. A good CFD model can be used to determine flow rates, turbulence, and heat transfer within a pack. In addition, it is possible to use a lumped parameter model to develop a simplified model where the external parameters are basically ignored and the model is designed using fully adjustable parameters to do high-level evaluations of the thermal effectiveness of a system. 

This paper reviews the detailed hydrodynamics of Outokumpu flotation cells by using Computational Fluid Dynamic (CFD) modelling. This includes different computational grid type dependency defining in the CFD model and examining the flow pattern induced in the cell as well as validating the model. 

A number of commercially available computational fluid dynamics (CFD) models could be used for the prediction of squat. At the core of any CFD problem is a computational grid or mesh where the solution is divided into thousands of elements. These elements are usually 2D quadrilaterals or triangles and three-dimensional (3D) hexahedral, tetrahedral, or prisms. Mathematical equations are solved for each element by the numerical model. For hydrodynamics the Navier-Stokes equations (NSEs) can be solved to include viscosity and turbulence. The NSEs provide detailed prediction (vortices) of the flow field, but require very thin meshes, high central processing unit (CPU) time, and memory storage. Its resolution is also quite difficult with numerical instabilities. Examples of commercial CFD models include Fluent and Fidap. 

The model presented here is a significant step forward in the simulation of fixed bed catalytic reactors. It is an early computational fluid dynamics (CFD) model of the continuum type. In recent years supercomputers have led to an increased application of CFD to studies of heat transfer in packed beds. In modeling the fluid flow in the voids confined by the catalyst particles, Nijemeisland and Dixon [2004] investigated the possibility of deriving values for the heat transfer coefficient between the bed and the wall in terms of the local properties of the flow field, but found no statistically valid correlation. They... 

Recently, robust developments in the capabilities of computers have led to the modeling of transient turbulent flows becoming much less challenging. The experimental analysis of PCD, which requires sophisticated measurements (e.g., LDA, PDA, pressure, temperature, noise, etc.) is difficult, hostile (e.g., high noise level, around 110-130 dB) and expensive to carry out in comparison with numerical simulations (Zbicinski, 2002). Computational fluid dynamics (CFD) models for a steady or transient flow, for example, as generated by the pulse combustor, differ... 

The use of film theory to describe solution mass transfer phenomena in pressure-driven membrane processes has a proven track record for aqueous systems. Under the flow conditions encountered in nanofiltration, the simplified film theory description of mass transfer has an accuracy close to solutions obtained by computational fluid dynamics (CFD) modeling (Zydney, 1997). The film theory, for component i, gives, for the total volumetric flux [see Peeva et al. (2004) for details] ... 

The simplest case of fluid modeling is the technique known as computational fluid dynamics. These calculations model the fluid as a continuum that has various properties of viscosity, Reynolds number, and so on. The flow of that fluid is then modeled by using numerical techniques, such as a finite element calculation, to determine the properties of the system as predicted by the Navier-Stokes equation. These techniques are generally the realm of the engineering community and will not be discussed further here. 

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