Baffles applications

For laminar mixing other impellers are used, some laminar impellers are sketched in Fig. 7.4. To bring the fluid in the entire tank in motion, the diameter of these impellers usually approach the tank diameter since the laminar bulk flow is otherwise relatively low. Laminar impellers with diameter approaching the tank diameter are also called close-clearance impellers. Laminar mixers often have complex geometries, characterized by geometrical variables as the impeller diameter D, the blade width W, the pitch p, the impeller wall clearance C, and the off-bottom clearance Cb- In most applications, baffles are not needed and can in fact cause poor mixing behavior [87], Examples of laminar impellers are helical ribbons, screws, helical ribbon screws and anchor impellers. 

Another design, shown ia Figure 5, functions similarly but all components are iaside the furnace. An internal fan moves air (or a protective atmosphere) down past the heating elements located between the sidewalls and baffle, under the hearth, up past the work and back iato the fan suction. Depending on the specific application, the flow direction may be reversed if a propeUer-type fan is used. This design eliminates floorspace requirements and eliminates added heat losses of the external system but requires careful design to prevent radiant heat transfer to the work. 

Rietz Extruder This extruder, shown schematically in Fig. 18-49, has orifice plates and baffles along the vessel. The rotor carries nmlti-ple blades with a forward pitch, generating the head for extrusion through the orifice plates as well as battering the material to break up agglomerates between the baffles. Typical applications include wet... 

Vortex formation leads to a considerable drop in mixing efficiency and should be suppressed as much as possible in practical applications to increase the homogenizing effects of mixers. The preferable method of vortex suppression is to install vertical baffles at the walls of the mixing tank. These impede rotational flow without interfering with the radial or longitudinal flow. Figure 11 illustrates such a system. 

In heat transfer applications, this jacket is considered a helical coil if certain factors are used for calculating outside film coefficients. The equivalent heat transfer diameter, D, for a rectangular cross-section is equal to 4 w (w being the width of the annular space). Velocities are calculated from the actual cross-section of the flow area, pw (p being die pitch of die spiral baffle), and die effective mass flowrate W dirough die passage. The effective mass flowrate is approximately 60% of die total mass flowrate of die jacket. 

The efficiency of this type of unit varies, and is a function of the effectiveness of the impingement baffling arrangement. About 70% of separator applications can use the line-type unit the other 30% require the vessel construction. The preference of the designer and problems of the plant operator are important in the final selection of a unit to fit a separation application. 

This is considered applicable to all sizes of tanks using 6-blade flat blade turbines, even with baffles on wall or inside single helical coil, providing that tube diameters are of 0.018 = d/T = 0.036, with viscosity range probably... 

The design techniques of this system of baffling are not adequately published in literature, because they are proprietary information of Phillips Petroleum Co. and are licensed to design firms for specifically designing the units to ensure proper application details. Figures 10-73 and 10-74 illustrate... 

A principle of application relative to internals is to obtain as many 180° or (second preference) 90° turns of the gas flow after it enters the drum as reasonably possible. Plat plate pieces, baffles, etc., welded to the side or nozzles are not recommended, because the vibration forces tend to fatigue and crack the welds. Baffle plates have been known to break loose on one face and ratde around in the drum. This can be potentially dangerous. The vessel itself should be designed for rugged service. 

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. 

This result makes it clear that particle stress is strongly dependent on the interaction between the particles and the interface, so that electrostatic and also hydrophobic and hydrophilic interactions with the phase boundary are particularly important. This means that the stress caused by gas sparging and also by boundary-layer flows, as opposed to reactors with free turbulent flow (reactors with impellers and baffles), may depend on the particle system and therefore applicability to other material systems is limited. 

Baffles will normally be used in most applications. 

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