Types of Mixer

When abrasive solid particles must be suspended, maintenance costs for the submerged shaft seal of a side-entering propeller may become high enough to make this type of mixer an uneconomical choice. 

Stationaiy. shell or trough. There are a number of different types of mixers in which the container is stationary and material displacement is accomplished by single or multiple rotating inner mixing devices. 

Uniformity of Mixture The proper type of mixer shoiJd be chosen to assure the desired degree of batch homogeneity. This cannot be compromised for other conveniences. Information is given under Types of Solids-Mixing Machines about the special abilities of various lands of machines to blend different types of materials. 

Horsepower requirements of several types of mixers are hsted in Table 19-3. 

There are two primary types of mixers propeller/paddle and screw. Screw mixers can be further divided into two types batch and mixer-extruder. 

The mixer-extruder combination unit shown in Figure 38.5 combines the functions of a mixer and screw conveyor. This type of mixer is used for mixing viscous products. 

The shape of the mixer entry chute allows the feeding of raw materials in almost any trade form. Rubber bales, the most widely used trade form for mbbers and polymers, can be fed as one piece in an industrial-sized mixer. Feeding of material is very convenient, especially for tangential type of mixers. 

Fig. 2.1.10 Complete cell with a paddle with one row of holes (blade stirrer), mounted in a glass tube (left), a second paddle with two rows of holes (middle) and a propeller mounted on a rotation axis (right) used to study the velocity distribution in different types of mixers.

The rheo cells can easily be replaced by various types of mixers, propellers or paddles (Figure 2.1.10). It is then possible to analyze the temporal evolution of chemical/physical reactions of mixing, demixing and sedimentation of materials in process engineering, e.g., during the mash process or fermentation [28, 29]. The stirring mechanics and speed can be optimized for various materials of different particle sizes and viscosity. 

Internal mixers of various types are produced in a range of sizes such that the appropriate capacity can be achieved for any size of production facility. There are a number of producers of the conventional types of mixer. Some mixers come with special modifications to improve mixing ability and quality. 

A turbine type agitator is commonly used for liquid-solid systems. Mixing rates depend on the forces required to suspend all solid particles. Minimum levels can be determined for (1) lifting the particles, and (2) for suspending them in an homogeneous manner [200]. Similar requirements apply to liquid-liquid systems. For cases where two poorly miscible fluids of about equal volume are used in the reaction, the mixer is placed at the interface. For a bench-scale experimental system of about 2 liters capacity, the minimum rotational speed to obtain well-dispersed system is 300 to 400 rpm [201], depending on the type of mixer. This rotational value decreases as the vessel volume increases. 

Mixing of elastic liquids is very strongly dependent on the type of mixer and the tank geometry, as well as the rheological properties of the liquid so that at a particular value of ReM the power drawn may be lower or higher than that for a Newtonian liquid. 

Although the full history of this screw is unknown, the mixing pins appeared to have been added to the screw after the screw failed to mix and homogenize the extrudate. Pin mixers have been retrofitted to screws for many years as a way to improve the distributive mixing for an extruder. Here the pin mixers would distribute the solid polymer fragments evenly in the extrudate, hut the mixers lacked the ability to trap and disperse them. Pin mixers were clearly the wrong type of mixer to use for this application. Instead, a dispersive mixer such as a Maddock-style mixer would be preferred see Section 8.5.1. 

There are many variants on this simple theme. For instance, many other methods for mixing have found use. In a design offered by Lurgi, the phases are mixed in what is essentially an axial flow pump, and then pass down a relatively long pipe where the turbulence of flow keeps the phases mixed while the extraction takes place. In another design, the individual phases are pumped and then join and pass through a static mixer. There are no particular physicochemical reasons for preferring one type of mixer to... 

Three types of mixer are recognized, plus a miniature mixer which would provide just enough compound for a curemeter test and one sheet. Mixers types A] and A2 and the miniature device have non-interlocking (tangential) rotors whilst type B has interlocking rotors. Dimensions of the larger mixers are specified fairly precisely, including new and worn rotor clearances, and they are required to have temperature control, a system to record power or torque and a timer. The miniature mixer is only specified in terms of capacity, rotor speed and friction ratio but is required to control of temperature, indication of power and a timer. 

Type of mixer Mixing length for mixing residual of 0.05 (m) Mixing time for mixing residual of 0.05 (s)... 

The modular backbone introduced here allows both commercial and demonstration-type micro structured devices to be coupled in all three dimensions in a flexible and easy manner. Micro structured heat exchangers, reactors and mixers of different manufacturers are surface mounted on this backbone. Owing to the standardized interfaces, devices can easily be exchanged, for example, to evaluate different types of mixers. The backbone itself consists of elements which can be combined individually and flexibly in all directions, according to the demands of the plant to be built. The backbone provides the flow paths for fluids and electrical conduits for power supply and signal transmission of sensors and actuators. 

The second type of mixer uses two impinging jets exiting from two borings to contact the reactants (for more detailed information, see Section 1.3.33, Jet Collision Turbulent or Swirling-flow Mixing). 

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