Geometry baffles

Clearly, the fluid flow pattern depends critically upon the impeller/vessel/ baffle geometry, and the liquid rheology. Thus in selecting the appropriate... 

For slatted baffles the head loss can be assessed using the flow past fixed blades where the relative velocity is the liquid flow-through velocity through the slat gaps, and the drag coefficient is given by the baffle geometry, as in section 4.10.1. 

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The forces applied by an impeller to the material contained in a vessel produce characteristic flow patterns that depend on the Impeller geometry, properties of the fluid, and the relative sizes and proportions of the tank, baffles and impeller. There are three principal types of flow patterns tangential, radial and axial. Tangential flow is observed when the liquid flows parallel to the path described by the mixer as illustrated in Figure 7. 

FIGURE 10.46 Capture of lime dust from a clamshell unloading operation. Geometry of final configuration where baghouse flow is drawn from the back of the hopper under a single baffle, which is raised off of the grizzly,... 

Gas-Fired water heaters are also made more efficient by a variety of designs that increase the recov-ei y efficiency. These can be better flue baffles multiple, smaller-diameter flues submerged combustion chambers and improved combustion chamber geometry. All of these methods increase the heat transfer from the flame and flue gases to the water in the tank. Because natural draft systems rely on the buoyancy of combustion products, there is a limit to the recovery efficiency. If too much heat is removed from the flue gases, the water heater won t vent properly. Another problem, if the flue gases are too cool, is that the water vapor in the combustion products will condense in the venting system. This will lead to corrosion in the chimney and possible safety problems. 

Power curves for many different impeller geometries, baffle arrangements, and so on are to be found in the literature/10111719 2I but it must always be remembered that though the power curve is applicable to any single phase Newtonian liquid, at any impeller speed, the curve will be valid for only one system geometry. 

Jana. S. C., Tjahjadi, M., and Ottino, J. M., Chaotic mixing of viscous fluids by periodic changes in geometry—baffled cavity flow. AlChE J. 40, 1769-1781 (1994b). 

The work by group of Kozyuk [84—87] has illustrated the use of hydrodynamic cavitation for obtaining free disperse system in liquids, particularly in liquid hydrocarbons. It has been found that, there is substantial improvement in the quality of the obtained free dispersion, even in the absence of any catalyst. Also the geometry of a flow-constricting baffle body [84] effectively increases the degree of cavitation to substantially improve the quality of obtained free disperse system. 

The classical CRE model for a perfectly macromixed reactor is the continuous stirred tank reactor (CSTR). Thus, to fix our ideas, let us consider a stirred tank with two inlet streams and one outlet stream. The CFD model for this system would compute the flow field inside of the stirred tank given the inlet flow velocities and concentrations, the geometry of the reactor (including baffles and impellers), and the angular velocity of the stirrer. For liquid-phase flow with uniform density, the CFD model for the flow field can be developed independently from the mixing model. For simplicity, we will consider this case. Nevertheless, the SGS models are easily extendable to flows with variable density. 

The factors that can affect the rate of heat transfer within a reactor are the speed and type of agitation, the type of heat transfer surface (coil or jacket), the nature of the reaction fluids (Newtonian or non-Newtonian), and the geometry of the vessel. Baffles are essential in agitated batch or semi-batch reactors to increase turbulence which affects the heat transfer rate as well as the reaction rates. For Reynolds numbers less than 1000, the presence of baffles may increase the heat transfer rate up to 35% [180]. 

Bacteriological sulfur, 23 577-578 Bacteriophages, 3 135 12 474 in fermentation, 11 46 Bacteriorhodopsin, 20 826, 840 photochromic material, 6 603 Bacteriosins, 12 76. See also Bacteriocins Bacteriostatic water, 18 714 Bacterium lactis, 11 7 Baculovirus expression system, 5 346 Baddeleyite, 21 489 26 623-624 colorants for ceramics, 7 346t Badische Anilin und Soda Fabrik (BASF) terpenoid manufacture process, 24 481 Baeyer-Villiger oxidation reactions, 14 592 chiral recognition by enzymes, 3 675 microbial, 16 401 Baffled shellside flow, 13 262 Baffles, in stirred tank geometries,... 

Figure 9 Power characteristics for three slowly rotating stirrers (leaf, frame, cross-beam stirrers) installed in a vessel with and without baffles. Stirrer geometry and the installation conditions are given in Figure 10. (From Ref. 13.)...

From the numerical value of 112 the stirrer type and baffling conditions can be read off the abscissa. The diameter of the stirrer and the installation conditions can be determined from data on stirrer geometry in the sketch. 

An impeller in a tank functions as a pump that delivers a certain volumetric rate at each rotational speed and corresponding power input. The power input is influenced also by the geometry of the equipment and the properties of the fluid. The flow pattern and the degree of turbulence are key aspects of the quality of mixing. Basic impeller actions are either axial or radial, but, as Figure 10.4 shows, radial action results in some axial movement by reason of deflection from the vessel walls and baffles. Baffles contribute to turbulence by preventing swirl of the contents as a whole and elimination of vortexes offset location of the impeller has similar effects but on a reduced scale. 

The required heat-transfer area of 19.5 m2 is based on an overall heat-transfer coefficient of 102 W/(m2 K). The best exchanger geometry for this application includes six internal baffles, one shell-side pass and two tube-side passes. The shell is fabricated from standard carbon steel piping of nominal pipe size 30, schedule number 80. The 112 tubes required are each 1.83 m long and 38.1 mm (1.5 in.) o.d. (BWG 12). The tubes must be fabricated from stainless steel type 250 for reasons of temperature tolerance. 

The presence of internals in a bed, such as baffles and heat exchangers, or variation in geometric configurations, such as tapered geometry, can affect the flow behavior. The classification scheme in Fig. 9.3 is, however, generally applicable to these situations. 

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