Gas-liquid dispersions

The expression gas-liquid fluidization, as defined in Section III,B,3, is used for operations in which momentum is transferred to suspended solid particles by cocurrent gas and liquid flow. It may be noted that the expression gas-liquid-solid fluidization has been used for bubble-column slurry reactors (K3) with zero net liquid flow (of the type described in Sections III,B,1 and 1II,V,C). The expression gas-liquid fluidization has also been used for dispersed gas-liquid systems with no solid particles present. 

The Eulerian multiphase model is used to predict the dispersed gas-liquid flow in the airlift loop reactor. It involves a set of momentum and continuity equations for each phase. Model equation coupling is achieved through the pressure and interphase exchange coefBcdents [5],... 

An Eulerian-Eulerian (EE) approach was adopted to simulate the dispersed gas-liquid flow. The EE approach treats both the primary liquid phase and the dispersed gas phase as interpenetrating continua, and solves a set of Navier-Stokes equations for each phase. Velocity inlet and outlet boundary conditions were employed in the liquid phase, whilst the gas phase conditions consisted of a velocity inlet and pressure outlet. Turbulence within the system was account for with the Standard k-e model, implemented on a per-phase basis, similar to the recent work of Bertola et. al.[4]. A more detailed description of the computational setup of the EE method can be found in Pareek et. al.[5]. 

One of the purposes of giving Example 4.4 (on the chlorination of toluene) is to demonstrate the effect of different gas flowrates on the performance of a bubble column. The higher the gas flowrate, the larger the interfacial area a per unit volume of dispersion gas-liquid mass transfer will take place more readily and the concentration of the dissolved gas in the liquid will rise. Although the rate of reaction will increase, this is offset, as will be seen, by the disadvantage of a lower... 

Various types of sprayers and pneumatic nozzles which allow us to produce finely dispersed gas-liquid jets and aerosols with drops 500-10 pm in diameter are used to create coatings. Two ways of producing finely dispersed jets are known ... 

Delnoij E, Lammers FS, Kuipers JAM, van Swaaij WPM. Dynamic simulation of dispersed gas-liquid two-phase flow using a discrete bubble model. Chem Eng Sci 1997 52 1429-1458. 

Const, (power) dissipation energy per unit vessel volume Const, impeller discharge flow energy Turbulent dispersion Gas-liquid operation Reaction requiring microscale mixing... 

For dispersed gas-liquid flows it is further assumed that = Pc = P-The density of the continuous liquid phase is commonly assumed constant Pi constant, while the density of the gas phases is either given in accordance with the ideal gas law pg = or assumed constant. The viscosities of both phases are commonly given constant values. 

This is a first estimate for the height of the dispersion, gas + liquid. The total volume is 7.63 m. A better estimate for (C.4)out is obtained from Eq. (i) in which can now be better approximated ... 

A hierarchy of computational models is available to simulate dispersed gas-liquid-solid flows in three-phase slurry and fluidized bed reactors [84] continuum (Euler-Euler) method, discrete particle/bubble (Euler-Lagrange) method, or front tracking/capturing methods. While every method has its own... 

Delnoij, E., J.A.M. Kuipers and W.P.M. van Swaaij, 1998, Computational fluid dynamics (CFD) applied to dispersed gas-liquid two-phase flows. In Fourth European Computational Fluid Dynamics Conference ECCOMAS CFD 98, John Wiley Sons, Chichester, pp. 314-318. 

Deen NG, van Sint Annaland M, Kuipers JAM Multi-scale modeling of dispersed gas—liquid two-phase flow, Chem Eng Sd 59(8—9) 1853—1861, 2004. 

We will now briefly touch upon plate towers for dispersive gas-liquid absorption/stripping. The treatment of the plate tower dynamics will be given in greater detail in Section 8.1.3.5 on vapor-liquid distillation. A schematic ofthe plate tower with a sieve plate for countercurrent gas-liquid absorption/stripping has already been shown in Figure 8.1.5. 

For dispersed gas-liquid flows it is further assumed that Pm = Pc = P- The density of the continuous liquid phase is commonly assumed constant pi constant, while the density of the gas phases is either given in accordance with the ideal gas law pg = or assumed constant. The viscosities of both phases are commonly given constant values. The bubble wake effects are occasionally considered important describing the transversal movement of the bubbles [77, 232]. In these cases it is imagined that small bubbles are accelerated in the wake of larger ones and others are pushed aside. Hence, there is a considerable particle path dispersion on the bubble size... 

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