Hydrodynamic mixing

Gleeson, ). P., West, )., Magneto-hydrodynamic mixing, in Proceedings of the 5th International Conference on Modeling and Simulation of Microsystems, San )uan, Puerto Rico, 22-25 April 2002, Computational Publications, Boston, pp. 318-321 (2002). 

Figure 8. The relationship between biological, hydrodynamic, mixing, and transport phenomena in three-phase fluidized bed bioreactors.

The literature of fluidization phenomena and technology is extensive. A good although dated bibliography is in Ullmann s Encyclopedia (1973, Vol. 3, pp. 458-460). The book by Chere-misinoff and Cheremisinoff (1984) has more than 500 abstracts of articles on fluidization hydrodynamics, mixing and heat transfer, but little on reactor technology. Other literature on fluidization is cited in the References of Chapter 6. 

Basically, using these technologies one would like to move forward to the theoretical optimum of a chemical process, which is that there are no other limitations than chemical kinetics. Normally a chemical process is influenced by more than just kinetics hydrodynamics (mixing), heat transfer, and mass transfer determine the quality of the process. Process intensification focuses on removing these three limitations to reaching the goal of kinetically limited processes. This is schematically depicted in Figure 2. 

I. Burghardt, K. B. Moller, G. Parlant, L. S. Cederbaum and E. R. Bittner. Quantum hydrodynamics Mixed states, dissipation and new hybrid quantum-classical approach. Int. J. Quantum Chem., 100 1153-1162, 2004. 

Hydrodynamic mixing, either by rotating the working electrode or by mechanical stirring of the solution, is preferred, since this makes the analyte concentration as isotropic as possible in the bulk solution the flow of analyte is chaotic, while close to the electrode laminar flow will dominate. 

The fluidized bed coal gasifier computer model is designed to provide a description of the hydrodynamic mixing and coupled chemistry within the reactor. This model should permit a designer to predict bubble size,... 

Bubble columns have been widely used in chemical and petroleum industries. This paper presents a brief overview on the present state of art of vertically sparged bubble columns. Hydrodynamics, mixing and transport characteristics of the bubble column are briefly evaluated. Recommendations for the future experimental work are also made. 

It should be specially noted that average values of reaction rates are needed because under no circumstances can photons be very well mixed consequently, since in the radial direction in particular the photon concentration is normally non-uniform, usually, the reaction rate will be a strong function of the radial position. This consideration is also important if the reaction involves highly reactive intermediates, because very often their reaction characteristic time is much smaller than the hydrodynamic mixing time and the well-mixed condition cannot be extended to all the species participating in the reaction. Hence, even in approximate models, as is the case for the plug flow simplification, the radiation field non-uniformities cannot be ignored. 

A potential solution to prevent fouling is to develop fouling release membranes that do not resist the adhesion of foulants, but have an active layer with a low surface energy so that adhered foulants can be readily washed away by hydrodynamic mixing in the membrane module [21] provided the water flux and salt rejection of the resulting membrane are not compromised. 

There are several industrially important gas-liquid-solid reactions such as carbonation of lime,coal liquefaction etc.,where solids take part in the reaction.The common type of reactor for these reactions is normally a gas-liquid-suspended solid column with or without mechanical agitation.An extensive literature is already available on the hydrodynamic,mixing,mass transfer,and heat transfer characteristics of these reactors,and critical reviews have been published in recent years(1-3). 

One unique reactor is the preheater in the DCL process. It is a long coiled tube where the slurry is heated to the reactor temperature and as described later, for swelling coals, it may possess a peculiar thermo-hydraulic behavior. While, as described later in Table 5, available literature for various hydrodynamic, mixing, and transport parameters can be applicable to the reactors, their applicability to the preheater is questionable. More work is needed in understanding the hydrodynamic, mixing and transport characteristics of the preheater. 

Many reaction-transport models treat parcels of fiuid as if they are slugs flowing in a plug flow reactor. In real systems, hydrodynamic mixing and diffusion (Aris, 1956 Taylor, 1953) cause dispersion of species among the slugs. Gelhar et ah (1992) review the factors that affect dispersion in aquifer systems. 

The hydrodynamics, mixing, and contacting patterns in the fluidized bed are complex, with the result that it is difficult to predict accurately the performance of fluidized-bed reactors. The resulting uncertainty causes unwelcome risk relative to packed-bed reactors and other reactors which can be characterized more accurately and with greater security. 

Levich, V. G., V. S. Markin and Y. A. Chrismadzkev. On Hydrodynamic Mixing in a Model of a Porous Medium with Stagnant Zones. Chem. Eng. Science 22 (1967) 1357. 

Greenberg et al. compared the effects of IF addition in oil under three lubrication regimes hydrodynamics, mixed and limit [44]. They based the lubrication mechanism of IF on a film formation on surfaces and showed that the IF are most effective at mixed Inbrication because all conditions for a good efficiency of IF are combined, hi the hydrodynamic regime, fullerenes do not have interactions with surfaces. In a boundary Inbrication regime, film formed on surfaces is quickly removed, due to contact severity. 

---