Multiphase flow reacting

F. Ham, S. V. Apte, G. laccarino, X. Wu, M. Herrmann, G. Con-stantinescu, K. Mahesh, and P. Moin. Unstructured LES of reacting multiphase flows in realistic gas turbine combustors. In Annual Research Briefs, pages 139-160. Center for Turbulence Research, NASA Ames/Stanford Univ., 2003. 

Fox, R. O. 2007 Introduction and fundamentals of modeling approaches for polydisperse multiphase flows, in Computational Models for Turbulent Multiphase Reacting Flows, Vienna Springer, pp. 1 0. 

It is well known that multiphase flow in tubular canals is accompanied by fibering. Phase disengagement leads to reduction of specific surface of reacted flows and consequently to additional diffusion limitations under fast chemical and mass-exchange physical process realization under polymers synthesis. This determines the expediency of determination of boundary condition of homogeneous and fibered regions of reaction mixture flow formation in tubular turbulent apparatus. 

CFD models for turbulent multiphase reacting flows do not solve the laminar two-fluid balances (Eqs. 164 and 165) directly. First, Reynolds averaging is applied to eliminate the large-scale turbulent fluctuations. Using Eq. (164) as an example, we can apply Reynolds averaging to find (with pg constant)... 

Computational fluid dynamics (CFD) is rapidly becoming a standard tool for the analysis of chemically reacting flows. For single-phase reactors, such as stirred tanks and empty tubes, it is already well-established. For multiphase reactors such as fixed beds, bubble columns, trickle beds and fluidized beds, its use is relatively new, and methods are still under development. The aim of this chapter is to present the application of CFD to the simulation of three-dimensional interstitial flow in packed tubes, with and without catalytic reaction. Although the use of... 

Current and future combustor applications require increased energy release with reduced chamber volume, increased equilibrium temperature, multiphase reacting flows with radiative heat transfer, and sometimes even with electric and magnetic fields. A thorough understanding of the basic physical and chemical... 

In multiphase reactors we frequently exploit the density differences between phases to produce relative motions between phases for better contacting and higher mass transfer rates. As an example, in trickle bed reactors (Chapter 12) liquids flow by gravity down a packed bed filled with catalyst, while gases are pumped up through the reactor in countercurrent flow so that they may react together on the catalyst surface. 

This situation describes an emulsion reactor in which reacting drops (such as oil drops in water or water drops in oil) flow through the CSTR with stirring to make the residence time of each drop obey the CSTR equation. A spray tower (liquid drops in vapor) or bubble column or sparger (vapor bubbles in a continuous liquid phase) are also segregated-flow situations, but these are not always mixed. We wiU consider these and other multiphase reactors in Chapter 12. 

Example 4.8 Chemical reactions and reacting flows The extension of the theory of linear nonequilibrium thermodynamics to nonlinear systems can describe systems far from equilibrium, such as open chemical reactions. Some chemical reactions may include multiple stationary states, periodic and nonperiodic oscillations, chemical waves, and spatial patterns. The determination of entropy of stationary states in a continuously stirred tank reactor may provide insight into the thermodynamics of open nonlinear systems and the optimum operating conditions of multiphase combustion. These conditions may be achieved by minimizing entropy production and the lost available work, which may lead to the maximum net energy output per unit mass of the flow at the reactor exit. 

The formulation that has been given here is not the only approach to the description of two-phase flows with nonequilibrium processes. Many different viewpoints have been pursued textbooks are available on the subject [43], [44], and a reasonably thorough review recently has been published [45]. Combustion seldom has been considered in this extensive literature. Most of the work that has addressed combustion problems has not allowed for a continuous droplet distribution function but instead has employed a finite number of different, discrete droplet sizes in seeking computer solution sets of conservation equations [5]. The present formulation admits discrete sizes as special cases (through the introduction of delta functions in fj) but also enables influences of continuous distributions to be investigated. A formulation of the present type recently has been extended to encompass thick sprays [25]. Some other formulations of problems of multiphase reacting flows have been mentioned in Sections 7.6 and 7.7. 

Marchisio, D. L. Fox, R. O. 2007 Multiphase Reacting Flows Modelling and Simulation. Udine Springer. 

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