Mixer Orientation

7-11 MOTIONLESS MIXERS OTHER CONSIDERATIONS 7-11.1 Mixer Orientation 

2 Density Ratio Effects in Dispersion. Again, the manufacturers recommend vertical arrangements. Horizontal arrangements will cause separation and increase coalescence, which will cut down on the interfacial area. The same criteria as used above in blending are therefore recommended. 

1 Turbulent Blending. The length downstream of the mixer is often referred to as the tailpipe. In laminar flow, no further mixing occurs in this region. 

2 Turbulent Dispersion Coalescence. After the dispersed phase leaves the motionless mixer, it will tend to coalesce to an equilibrium drop or bubble size characteristic of the shear field in the downstream piece of pipe. This coalescence is not just a phenomenon of the downstream tailpipe but is a process happening in parallel with dispersion. It is not as well understood. We do know that just like dispersion, coalescence is affected by volume concentration and is promoted by turbulence. Coalescence is strongly affected by surface chemistry effects. The role of many chemicals added to stabilize dispersions is to slow down the coalescence rate. 

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The material flow in an internal mixer is oriented vertically. On top of the internal mixer a more or less sophisticated feeding system can be found. Underneath the mixer a downstream device, such as a sheeting extruder with one or two tangential screws, or two roll mills are placed. 

Figure 2.45 Design of a multilamination mixer with hydrodynamic focusing (upper left) and flow pattern in such a mixer for a total volume flow of 10 ml h of water (lower left), taken from [141. The right side of the figure shows the orientation of liquid lamellae over a cross-section of the constriction for different Reynolds numbers [142].

Figure 2.48 The top shows the schematic design of a magneto-hydrodynamic mixer with equally spaced electrodes arranged In a micro channel and an external magnetic field oriented along the z-axis. On the bottom theoretical results for the evolution of two parallel liquid lamellae as a function of dimensionless time are shown [146].

The impinging-jet micro mixers are constructed as a cylindrical block comprising two feed tubes which become smaller towards the outlet [48]. Accordingly, the main characteristics of these mixers are the diameter of the outlet bore, the interspaces between the bores and the angle defined by the orientation of bores (relative to the normal). For one experimental study [48], nine impinging jet micro mixers were made which differ in these specifications. 

The interdigital feed can be fed in a counter-flow or co-flow orientation the first principle is realized in metal/stainless-steel devices [23, 25] and the latter in glass devices [24]. Glass mixers allow observation of hydrodynamics, e.g. for process control during reaction. To prolong residence time and/or to increase temperature, tubes are usually attached to interdigital micro mixers. These comprise millimeter dimensions or below, if necessary. 

All of the composites in this study were prepared in a Banbury internal mixer. After mixing, the curing ingredients and hexamethylenetetramine were added on a 10-inch rubber mill. This milling step causes molecular orientation or grain even in unfilled rubber although the effect is relatively small. 

Effect of Orientation on Distributive Mixing — Erwin s Ideal Mixer... 

Using this concept, Erwin [9] demonstrated that the upper bound for the ideal mixer is found in a mixer that applies a plane strain extensional flow or pure shear flow to the fluid and where the surfaces are maintained ideally oriented during the whole process this occurs when N = 00 and each time an infinitesimal amount of shear is applied. In such a system the growth of the interfacial areas follows the relation given by... 

In Erwin s ideal mixer, the amount of mixing increases in an exponential fashion, compared to a linear increase, if the orientation of the fluids interfaces remain undisturbed. 

In addition to grouping the mixers according to their mixing principles and their generic microstructure designs, a practically oriented classification refers to the complexity of the fluid network [25], So-called in-plane mixers rely on streams which are divided and mixed in a fluid network confined to one level (i.e. a pattern that can be projected on to a single plane) [25], In turn, out-of-plane mixers rely on a... 

The insertion of small static mixing elements (SME) is common to achieve swirls and eddies in pipe flow, albeit usually not being turbulent [71]. The flow obstacles are fairly small compared with the pipe diameter, unlike typical packings of static mixers which fully cover the diameter of the channel. Such mixing elements provide abrupt changes in surface orientation to result in flow separation and subsequent eddy production. 

This device achieves a horizontal orientation of the lamellae by alternate vertical stacking of plates, which carry one fluid each. This is different from the interdigital micro mixers described above having a vertical A-B-type orientation [40, 41]. 

Figure 1.101 Orientation of liquid lamellae in the mixing channel of the slitshaped interdigital micro mixer viewing direction is the flow direction [37]...

The latter is confirmed by CFD perpendicular-oriented velocity components are quickly compensated downstream [41]. After about 800 pm, parallel flow of the streams is attained as for the P-type mixer. 

Qualitative, numerical simulations were performed with the commercial tool FLUENT-5 to evaluate mixing efficiency [2], The simulations were oriented on concepts employed for conventional 3-D static mixing. The micro-mixer geometries were laid out using the GAMBIT predecessor as well as the meshing of surfaces and volumes and the specification of boundary conditions. Entrance and exit sections were also simulated. 

M 75] [P 66] 3-D twisting flow is found for a mixer design with an array of multiple obliquely oriented, straight grooves [44]. 

Table 1.8 List of parameters specifying the different impinging jet micro mixers diameter of the outlet boring d, the interspaces between the borings x and the angle a defined by the orientation of borings ([53] source IMM).

Jet mixer No. Diameter of outlet boring, dfrm) Interspaces between the borings, x (mm) Angle a defined by the orientation of borings (°)... 

The following example examines the SDF in drag flow between parallel plates. In this particular flow geometry, although the shear rate is constant throughout the mixer, a rather broad SDF results because of the existence of a broad residence time distribution. Consequently, a minor component, even if distributed at the inlet over all the entering streamlines and placed in an optimal orientation, will not be uniformly mixed in the outlet stream. 

Fig. 10.6 The single-stage FCM. (a) Size 15 FCM with chamber opened and rotated hydraulically (b) top view of staged apex twin rotors and the axial zones for carrying out the solids feed handling and the melting and mixing elementary steps (c) cross-sectional view of two rotor orientations, tip-to-tip (cx) and tip-to-flat (c2). [Reprinted by permission from E. L. Canedo and L. N. Valsamis, Farrel Continuous Mixer Systems for Plastics Compounding, in Plastics Compounding—Equipment and Processing, D. B. Todd, Ed., Hanser, Munich, 1998.]...

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