Single Nozzle

The computation performed in this study is based on the model equations developed in this study as presented in Sections II.A, III.A, III.B, and III.C These equations are incorporated into a 3-D hydrodynamic solver, CFDLIB, developed by the Los Alamos National Laboratory (Kashiwa et al., 1994). In what follows, simple cases including a single air bubble rising in water, and bubble formation from a single nozzle in bubble columns are first simulated. To verify the accuracy of the model, experiments are also conducted for these cases and the experimental results are compared with the simulation results. Simulations are performed to account for the bubble-rise phenomena in liquid solid suspensions with single nozzles. Finally, the interactive behavior between bubbles and solid particles is examined. The bubble formation and rise from multiple nozzles is simulated, and the limitation of the applicability of the models is discussed. 

Simulations are then performed for gas bubbles emerging from a single nozzle with 0.4 cm I.D. at an average nozzle velocity of lOcm/s. The experimental measurements of inlet gas injection velocity in the nozzle using an FMA3306 gas flow meter reveals an inlet velocity fluctuation of 3-15% of the mean inlet velocity. A fluctuation of 10% is imposed on the gas velocity for the nozzle to represent the fluctuating nature of the inlet gas velocities. The initial velocity of the liquid is set as zero. An inflow condition and an outflow condition are assumed for the bottom wall and the top walls, respectively, with the free-slip boundary condition for the side walls. 

In order to verify the simulation results, experiments on bubble behavior in bubble columns are carried out under conditions similar to the simulations. A 3-D rectangular bubble column with the dimension of 8 x 8 x 20 cm3 is used for the experiments. Four nozzles with 0.4 cm I.D. and a displacement of 2.4 cm are designed in the experiments. For single-nozzle experiments, air is injected into the liquid bed through one of the orifices while the others are shut off. The outlet air velocity from the nozzle is approximated using the measured bubbling... 

Fig. 5. Simulation results of air-bubble formation from a single nozzle in water. Nozzle size 0.4 cm I.D. and nozzle gas velocity lOcm/s.

For steady injection of a liquid through a single nozzle with circular orifice into a quiescent gas (air), the mechanisms of jet breakup are typically classified into four primary regimes (Fig. 3 2)[4°][41][22°][227] according to the relative importance of inertial, surface tension, viscous, and aerodynamic forces. The most commonly quoted criteria for the classification are perhaps those proposed by Ohnesorge)40] Each regime is characterized by the magnitudes of the Reynolds number ReL and a dimensionless number Z ... 

For steady injection of a liquid through a single nozzle with circular orifice into a co-flowing gas (air), the breakup of the liquid... 

Even with the above-mentioned limitations, the indirect methods constitute the simplest way of evaluating bubble volumes from single nozzles, and hence are most extensively used. As these methods involve a knowledge of the two quantities Q and f the ways of measuring each of them are separately discussed below. 

To obtain a large transfer area between raffinate and extract phases, one of the two liquids must be dispersed into drops. Figure 9.2 demonstrates this process schematically at a single nozzle. Similar to a dripping water tap, individual drops periodically leave the nozzle when the volumetric flow rate of the dispersed phase is low. When the flow rate is higher, however, the liquid forms a continuous jet from the nozzle that breaks into droplets. Because of stochastic mechanisms, uniform droplets are not formed. If the polydispersed droplet swarm is characterized by a suitable mean drop... 

Fig. 9.3 Sauter mean diameter < 32 calculated from drop size measurements at single nozzles of liquid systems (a) toluene (dispersed phase d) water (continuous phase c) and (b) butanol d) water (c), is dependent on the mean velocity Vjv of the dispersed phase in the nozzle. (From Ref. 5.)... 

The top spray system has been used to coat materials as small as 100 microns. Smaller substrates have been coated, but agglomeration is almost unavoidable due to nozzle limitations and the tackiness of most coating substances. Batch sizes range from a few hundred grams to approximately 1,500 kg. Typically, a single nozzle wand with up to six liquid delivery ports is used, but multiple nozzle systems have been applied. 

Yu Y, Gu L, Zhu C, Van Aken PA, Maier J. Tin nanoparticles encapsulated in porous multichannel carbon microtubes preparation by single-nozzle electrospinning and application as anode material for high-performance Li-based batteries. J Am Chem Soc. 2009 131 15984-5. 

Ceramic suspensions can also be deposited by dispensing or extrusion from a nozzle. While printing is a parallel process, i.e., many nozzles per color or substance are involved — say 128 or more, dispensing and extrusion processes usually use a single nozzle. The rheological properties of the ceramic suspensions are different from those of inkjet inks they may be much more viscous, i.e., contain a... 

The nozzle body holds the strainer and tip in proper position. Several types of tips that produce a variety of spray patterns may be interchanged on a single nozzle body made by the same manufacturer. 

Cluster nozzles are used either without a boom or at the end of booms to extend the effective swath width. One type is simply a large flooding deflector nozzle which will spread spray droplets over a swath up to 70 feet wide from a single nozzle tip. Cluster nozzles are a combination of a center-discharge and two or more off-center-discharge fan nozzles. The spray droplets vary in size from very small to very large, so drifting is a problem. 

The available data were correlated by Ueyama and Miyauchi (U5), who found that the normalized velocity profile Eq. (3-18) represents the data reasonably well. Figure 28 illustrates the experimentally measured velocity profile of water containing bubbles from a single-nozzle gas-distributor (Y2). The bubble column was 25 cm in diameter operating in the recirculation flow regime at a superficial gas velocity Uq of 5.2 cm/sec. Estimated values of Mo = 45 cm/sec and mw = 26 cm/sec, arrived at by trial, give the best fit of the normalized profile data, and Eq. (3-18) provides a reasonable approximation. 

Fig. 39. Longitudinal dispersion coefficients of liquid in bubble columns (SN = single nozzle PP = perforated plate). The full circles are calculated with the use of Eq. (4-12).

Axial distribution of kobOb has been shown to have only a minor effect on the performance of fluid catalyst reactors (K14, M28). It has been shown in Section II that (a) bubbles from a single nozzle break up in rising a certain distance to attain a final size (b) bubbles from a perforated plate associate together when rising and (c) stays fairly constant axially thereafter. 

Orifices and Mixing Nozdes Both liquids are pumped through constrictions in a pipe, the pressure drop of which is partly utilized to create the dispersion (see Fig. 18-34). Single nozzles or several in series may be used. For the orifice mixers, as many as 20 orifice plates... 

FIG. 21-154 Impact of single nozzle location on granule-size distribution and bulk density for disc granulation, 3-ft diameter, 200 Ib/h. Reprinted from Design and Optimization of Granulation and Compaction Processes for Enhanced Product Performance, Ennis, 2006, with permission ofE G Associates. All rights reserved.)... 

---