Mixers baffles

The setup is largely comprised of a continuous-flow, compensating calorimeter which consists of a flooded measuring kettle housed in an intermediate thermostat, which is enveloped by a base thermostat. The base thermostat and the intermediate thermostat are filled with a thermostat liquid. The base thermostat, the intermediate thermostat and the flow measuring kettle are each provided with a mixer, baffles and temperature sensors. The mixer of the base and intermediate thermostats are classic stirrers, and the mixer in the flooded measuring kettle is a circular pendulum mixer. Its bearing is protected from contamination with the reaction mixture by corrugated metal bellows, which is joined to the cover of the shaft to form a seal. 

The effective heat capacity C2 of the content in the flow measuring kettle comprises the heat capacity Cp of the reaction mixture and the effective heat capacity Cmi of the mixer, baffles, temperature sensor, wall of the measuring kettle, and so forth ... 

The General Mills mixer—settler (117), shown in Figure 13b, is a pump—mix unit designed for hydrometaHurgical extraction. It has a baffled cylindrical mixer fitted in the base and a turbine that mixes and pumps the incoming Hquids. The dispersion leaves from the top of the mixer and flows into a shallow rectangular settler designed for minimum holdup. 

Motionless inline mixers obtain energy for mixing and dispersion from the pressure drops developed as the phases flow at high velocity through an array of baffles or packing in a tube. Performance data on the Kenics (132) and Sul2er (133) types of motionless mixer have been reported. 

Wetox uses a single-reactor vessel that is baffled to simulate multiple stages. The design allows for higher destmction efficiency at lower power input and reduced temperature. Its commercial use has been limited to one faciHty in Canada for treatment of a complex industrial waste stream. Kenox Corp. (North York, Ontario, Canada) has developed a wet oxidation reactor design (28). The system operates at 4.1—4.7 MPa (600 to 680 psi) with air, using a static mixer to achieve good dispersion of Hquid and air bubbles. 

Axial-Flow Fluidfoil Impellers For vessel volumes of 4 to 200 m (1000 to 50,000 gal), a turbine mixer mounted coaxiaUy within the vessel with four or more baffles should be the initial choice. Here also the vessel straight-side-height-to-diameter ratio should be 0.75 to 1.5. Four vertical baffles should be fastened perpendicularly to the vessel wall with a gap between baffle and wall equal to Df/24 and a radial baffle width equal to Df/12. 

Portable or fixed mixers up to 5hp normally use propellers and run at either direct drive speeds of 1,150 or l,750rpm or at single reduction gear drive speeds between 300 and 420 rpm. They may either be clamped on the rim of open tanks or mounted with a fixed assembly for open or closed tank operation. These mixers are the most economical and are usually used in tanks without baffles. They are rugged and long-lasting. 

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. 

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. 

For turbine mixers that the width of a baffle should not exceed more than one-twelfth of the tank diameter and, for propeller mixers, no more than one-eighteenth the tank diameter. With side-entering, inclined or off-center propellers, as shown in Figure 13, baffles are not required. Instead, shrouded impellers and diffuser rings may be used to suppress vortex formation. These devices contribute to flow resistance and reduce circulation by creating intense shear and abnormal turbulence... 

Mixer a device for carrying out a mixing operation and which generally inclusively refers to an impeller, driver, baffle, and vessel combination. 

Dished bottom tank, center mounted mixer, 4 baffles... 

Baffles can be omitted when propeller mixers are top mounted at an angular off-center position (see Figure 5-23D) and vortex swirling is prevented. This is not recommended for large povver systems on large tanks, due to shaft fatigue. 

The effect on the process of a change in operation of the mixer system (impeller, baffles, etc.) is the final measurement of performance. Thus, operations such as blending, uniform particle suspension, reaction, gas absorption, etc., may be acceptable under one physical system and not so to the same degree under a slightly modified one. The ratio per unit volume on scale-up must be determined experimentally. 

Physical depth or height of turbine mixer, ft or in., consistent with other dimensions. Figure 5-34 = Impeller blade wndtii, ft = width of baffles in vertical tank. Figure 5-34. 

Surface in ter/after condenser, 349 System diagrams, 383 Mists, particle sizes, 225 Mixers, jet, 325, 326 Mixers, mechanical components, 289 Baffles, 311 Coils, 312... 

With injection mixers (Figures 10.52b,c), in which the one fluid is introduced into the flowing stream of the other through a concentric pipe or an annular array of jets, mixing will take place by entrainment and turbulent diffusion. Such devices should be used where one flow is much lower than the other, and will give a satisfactory blend in about 80 pipe diameters. The inclusion of baffles or other flow restrictions will reduce the mixing length required. 

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