Striation thickness measurement

For such practical measurements, striation thickness is directly related to interfacial area [2], the simple relationship being  

Striation thickness can be measured using microtomed sections examined under a microscope using transmitted light. The thickness can be measured manually using a 

Image analysis is a less judgemental process for producing a representative value. Benkreira and co-workers [3] have described the method they used on samples removed from the extruder screw channel after rapid cooling to freeze the molten polymer, mainly at the stage where the polymer had just melted. 

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Assessment of Mixing Performance by Striation Thickness Measurement... 

Despite the wide use of the striation thickness concept in the early commercial literature, the CoV is now the most widely used mixing index. The following correlations are valid for viscosity ratios 0.01 < nBlnA < 100, feeding into the center of the pipe and with CoV measured 2dp downstream for Sulzer mixers, 3dp downstream for Kenics mixer. 

Another relatively simple measure for characterizing texture that is suggested in the polymer processing literature is the striation thickness, which is defined as the total volume divided by one-half the total interfacial surface (10)... 

Schrenk et al. [1963] analyzed the degree of mixing in a simple annular mixer, which might be helpful for understanding mixing in a SSE. To evaluate the mixedness of the two component polymers, the striation thickness was measured, when the inner shaft was rotated and the outer cylinder was stationary. Near the shaft, the thickness was substantially reduced, but only slightly near the external cylinder. 

When two viscous liquids are mixed, the interfacial area increases and the striation thickness decreases. Spencer and Wiley [201] have proposed to use the interfacial area as a quantitative measure of the goodness of mixing. Mohr et al. [189] used the striation thickness to describe the mixing process. If a surface element with arbitrary orientation is located in a simple shear flow field, the surface area A after a total shear strain of y can be demonstrated to be [201] ... 

The striation thickness is a commonly used measure of mixing. In simple shear the striation thickness reduces with the shear strain as follows ... 

Polymer mixtures containing deformable components tend to contain streaky or layered structures resulting from laminar shear flow. In such cases, the striation thickness (the distance between the streaks) can be measured to provide an indication of degree of mixing. As mixing progresses, a decrease in striation thickness is accompanied by an increase in interfacial area between the components. Reductions in striation thickness will depend on the level of imposed shear strain and the orientation of the components relative to the direction of shear [38]. 

In the second model an average striation thickness 8 is assumed, and with this the combined process of diffusion and reaction can be calculated as a function of time. For this one needs a set of combined differential equations such as eqs. (5.28a,b) (though with different boundary conditions see eqs. (5A.la-c) in the Appendix). The resulting concentration profiles are of the shape shown in figure 5.2 the distance between the peaks is the striation thickness. In principle, this striation thickness is a physical parameter that can be measured directly. For this model, a micro-mixing time could be defined by putting the Fourier- number for non-steady state diffusion equal to 0.1 (see eq. (4.8)) ... 

Scale of segregation is a measure of the average separation between regimes comprising the same component and may be correlated to the average striation thickness, which is the average distance between like interfaces in a mixture [11]. On other hand, intensity of segregation is a measure of concentration [11]. 

For measnrement of distributive mixing, striation thickness is a far more practical proposition than measuring surface area (see Chapter 3). In the above example the... 

When comparing mixing devices by measurement of striation thickness in the extrudate, under normal extruder arrangements the results are for overall mixing by both extruder screw and attached mixer. A particular variable is the influence of back pressure due to the mixer on both melting rate and mixing in the screw channel. 

Most of this handbook treats spatial mixing. Suppose that a sample of fluid is collected and analyzed. One may ask Is it homogeneous Standard measures of homogeneity such as the striation thickness in laminar flow or the coefficient of variation in turbulent flow can be used to answer this question quantitatively. In this chapter we look at a different question that is important for continuous flow systems When did the particles, typically molecules but sometimes larger particles, enter the system, and how long did they stay This question... 

In the preceding two sections, it was shown how to measure local micromixing intensity using intermaterial area distribution [H(log p)] and length scale distributions [H(logs)]. These tools are not directly applicable to 3D flows, because the resolution of the smallest length scales in 3D mixture structures is, to date, computationally prohibitive. In this section we present a predictive method for striation thickness distributions applicable to either 2D or 3D chaotic flows. 

Another important component of mixing processes, diffusion, remains to be included in the discussion. The ability to measure or predict striation thickness distributions in chaotic flows provides the link between mixing on the macroscopic and microscopic scales. Diffusion and stretching are intimately coupled because as material filaments are stretched by the flow, the rate of diffusion is... 

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