Multi-phase Simulations

As mentioned earlier, work on validation of computational approaches to simulating multi-phase systems under realistic momentum and heat-transfer conditions is growing PEPT represents one of very few ways of doing this convincingly. 

The model is capable of simulating multi-phase internal corrosion processes that are governed by solid-state diffusion in the bulk metal. Oxidation experiments in laboratory air and He-02-H20 mixtures revealed that internal corrosion of low-alloy steels occurs along grain boundaries as part of the inward oxide growth process. Since the low-alloy boiler steels contain small amounts of Cr, the phase composition of the iimer layer exhibits a gradual... 

In most cases the only appropriate approach to model multi-phase flows in micro reactors is to compute explicitly the time evolution of the gas/liquid or liquid/ liquid interface. For the motion of, e.g., a gas bubble in a surrounding liquid, this means that the position of the interface has to be determined as a function of time, including such effects as oscillations of the bubble. The corresponding transport phenomena are known as free surface flow and various numerical techniques for the computation of such flows have been developed in the past decades. Free surface flow simulations are computationally challenging and require special solution techniques which go beyond the standard CFD approaches discussed in Section 2.3. For this reason, the most common of these techniques will be briefly introduced in... 

Haedt, S., Schonfeld, F., Simulation of hydrodynamics in multi-phase microreactors, in Proceedings of the 5th World Congress on Computional Mechanics, WCCM, 7-12 July 2002, Vienna... 

Zhang K., W.Y.S., et al. Parallel computing techniques for large-scale reservoir simulation of multi-component and multi-phase fluid flow. In Proceeding of the 2001 SPE reservoir simulation synposium, Texas.2001 SPE. 

The PDF codes presented in this chapter can be (and have been) extended to include additional random variables. The most obvious extensions are to include the turbulence frequency, the scalar dissipation rate, or velocity acceleration. However, transported PDF methods can also be applied to treat multi-phase flows such as gas-solid turbulent transport. Regardless of the flow under consideration, the numerical issues involved in the accurate treatment of particle convection and coupling with the FV code are essentially identical to those outlined in this chapter. For non-orthogonal grids, the accurate implementation of the particle-convection algorithm is even more critical in determining the success of the PDF simulation. 

We hope to have demonstrated that computer simulation of transport and transformation processes on digitally reconstructed multi-phase media can be beneficial to practical chemical engineering applications. We believe that as chemical engineering becomes more product-oriented, the need to model phenomena that control material microstructure formation will gain in importance. We hope that this chapter will provide a useful starting point for those who wish to familiarize themselves with the relevant computational techniques. 

P. Moin. Large eddy simulation of multi-phase turbulent flows in realistic combustors. Prog. Comput. Fluid Dynamics, 4 237-240, 2004. 

FIGURE 14 Computer simulation of bench scale spray drying process 3D, turbulent flow with multi-phase heat and mass transfer simulation. 

Sha Z, Laari A, Turunen I (2006) Multi-Phase-Multi-Size-Group Model for the Inclusion of Population Balances into the CFD Simulation of Gas-Liquid Bubbly Flows. Chem Eng Technol 29(5) 550-559... 

Vcrheggen, T.M.M. (ed.). 1992. Numerical methods for the simulation of multi-phase and complex flow. Springer-Verlag, New York. 

Sommers, J. A., and P.C. Rem. 1992. Obtaining numerical results from the 3D FCHC-lattice gas. p. 59-78. In T.M.M. Verheggen (ed.) Workshop for numerical methods for the simulation of multi-phase flow, Amsterdam. 30 May-1 June 1990. Springer, Berlin. 

Batch or semi-batch reactors can be simulated as stand-alone or coupled with a continuous process. Specification may include cycle operation with buffer tanks, as well as reactions in single and multi-phases. 

The two-phase flow option in FLAG allows numerical modelling of the flow of two immiscible fluids through porous media. A description of the concepts involved in the mathematical description of multi-phase flow may be found in reference books such as Fundamentals of Numerical Reservoir Simulation (Peaceman, D. W., 1977). Some of these concepts are addressed below. 

Processes that may need to be considered in these multi-phase problems are (i) partitioning of solutes, (ii) electro-dissolution of one phase into the other, (iii) the electrochemical conversion of a solute in phase to another redox level accompanied by ion exchange, and (iv) processes involving material adsorbed at the interface between the two phases. In view of the inherent complexity, data analysis based on numerical simulation is almost invariably necessary for detailed quantitative information to be gained. 

The simulations of the gas-liquid flow are based on the Eulerian two fluid model originally derived by Ishii [21]. In this approach, each phase is treated as a continuum. After averaging the general transport equations, we get the following set of multi-phase conservation equations [19,22] ... 

Lutsko, J.F., Boon, J.P., and Somers, J.A., Lattice gas automata simulations of viscous fingering in a porous medium, in T.M.M. Verheggen Numerical Methods for the Simulation of Multi-Phase and Complex Flow, Springer-Verlag, Berlin, 124-135, 1992. 

The interplay of phase separation and polymer crystallization in the multi-component systems influences not only the thermodynamics of phase transitions, but also their kinetics. This provides an opportunity to tune the complex morphology of multi-phase structures via the interplay. In the following, we further introduce three aspects of theoretical and simulation progresses enhanced phase separation in the blends containing crystallizable polymers accelerated crystal nucleation separately in the bulk phase of concentrated solutions, at interfaces of immiscible blends and of solutions, and in single-chain systems and interplay in diblock copolymers. In the end, we introduce the implication of interplay in understanding biological systems. 

In this section, we look at some examples of multi-phase flows from the simulation perspective. These have very important applications in wide range of microtechnologies. 

---