Computational fluid dynamics software

As previously mentioned, the analysis of microfluidic systems can be rather difficult for a variety of reasons. The direct implementation of the Navier-Stokes equations toward surface-directed microfluidic systems requires careful attention when considering the advection of the free surface and the associated curvature of this surface. Consequently, sophisticated computational fluid dynamics software packages are required for a comprehensive three-dimensional analysis of the fluid transport within surface-directed microfluidic devices. However, a time-consuming comprehensive analysis may be beyond the requirements of designing and manufacturing functional surface-directed microfluidic platforms. Consequently, empirical approximations and scaling arguments are commonly used in the characterization of microfluidic physics. 

The preparation and splitting of emulsions are the key parameters in an emulsion liquid membrane process. A very stable emulsion which avoids any loss of emulsified droplets is a prior condition for the feasibility of the process. However, the more stable the emulsion, the more difficult to split it. So both steps are dependent on each other and have to be optimized, also with regard to cost optimization. In the present work, we try to calculate the flow pattern in the two steps using CFD (computational fluid dynamics) software in order to improve the design of the two steps. 

CEWES MSRC (n.d.). Computational fluid dynamics software data log, http //phase.go. jp/nhse/rib/repositories/cewes cfd/catalog/index.html. 

The Prandtl mixing length concept is useful for shear flows parallel to walls, but is inadequate for more general three-dimensional flows. A more complicated semiempirical model commonly used in numerical computations, and found in most commercial software for computational fluid dynamics (CFD see the following subsection), is the A — model described by Launder and Spaulding (Lectures in Mathematical Models of Turbulence, Academic, London, 1972). In this model the eddy viscosity is assumed proportional to the ratio /cVe. 

Computational fluid dynamics (CFD) emerged in the 1980s as a significant tool for fluid dynamics both in research and in practice, enabled by rapid development in computer hardware and software. Commercial CFD software is widely available. Computational fluid dynamics is the numerical solution of the equations or continuity and momentum (Navier-Stokes equations for incompressible Newtonian fluids) along with additional conseiwation equations for energy and material species in order to solve problems of nonisothermal flow, mixing, and chemical reaction. 

With the widespread use of software packages to assist with computational fluid dynamics (CFD) of polymer flow situations, other types of viscosity relationships are also used. For example, the regression equation of Klien takes the form... 

Individual process steps identified in a conceptual design (reactors or separation/purification units) are studied experimentally in the laboratory and/or by computer simulation (see simulation programs as given in SOFTWARE DIRECTORY or Computational Fluid Dynamics (CFD) programs for studying fluid dynamics, such as PHOENIX, FLUENT, and FIDAP). 

Using these methods, the elementary reaction steps that define a fuel s overall combustion can be compiled, generating an overall combustion mechanism. Combustion simulation software, like CHEMKIN, takes as input a fuel s combustion mechanism and other system parameters, along with a reactor model, and simulates a complex combustion environment (Fig. 4). For instance, one of CHEMKIN s applications can simulate the behavior of a flame in a given fuel, providing a wealth of information about flame speed, key intermediates, and dominant reactions. Computational fluid dynamics can be combined with detailed chemical kinetic models to also be able to simulate turbulent flames and macroscopic combustion environments. 

Since it will take several years to realize such an integral software toolbox, individual approaches with separate steps have to be applied to meet gradually the requirements of microreactor design. Standard software for computational fluid dynamics is directly applicable in this context, and there are also powerful software tools for the simulation of special steps in microfabrication processes. However, there has been rather little experience with materials for microreactors, optimization of microreactor design, and, in particular, the treatment of interdependent effects. Consequently, a profound knowledge of the basic properties and phenomena of microreaction technology just described is absolutely essential for the successful design of microreaction devices. 

Software tools are applied in every step of process development. Tools for individual reactor simulations such as computational fluid dynamic simulations are not the topic in this chapter. These tools supply only numerical data for specific defined reactor geometry and defined specific process conditions. A change of parameter would demand a complete recalculation, which is often a very time-consuming process and not applicable to a parameter screening. Methods for reactor optimization by CFD are described in detail in the first volume of this series. Tools for process simulation allow the early selection of feasible process routes from a large... 

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