Shear pulses

Fig. 5.2. Time evolution of 2D depolarized light scattering (DPLS) pattern from iPS during the annealing process at various temperature after applying a pulse shear with shear rate 30 and shear strain 12000 %. Note that the nominal melting temperature of iPS is 223 0...

Fig. 5.5. (a) spotted scattering pattern observed at 230 C at 16 min after pulse shear, (b) schematic sketch of two cylinders in an incident beam area, (c) FFT image of two cylinders... 

The analysis mentioned above predicts that the long anisotropic oriented structure has a several tens pm in width. Such large anisotropic oriented structures can be observed using polarized optical microscope (POM). Then, we tried to see such structure in POM observations. Some examples of the POM pictures at 230"C are shown in Fig. 5.7 after enhancement of the contrast. At 6s after a pulse shear we observed a very large cylinder-like structure with about 60 pm diameter, but the radius fluctuated along the cylinder... 

Fig. 5.6. DPLS intensity normal to the flow direction at 230 C at 16 min after pulse shear. Solid thin line is a horizontal component of form factor of a cylinder aligned along the vertical direction...

Fig. 5.7. Polarized optica] microscope (POM) images from iPS during the annealing process at 230 0 after pulse shear (upper row) and the corresponding FFT images (lower row), (a), (b) at 6 s, (c), (d) at 20 min, (e), ( ) at 20 min after pulse shear...

The transmission coefficient Cl (Qj,t), considering transient (broadband) sources, is time-dependent and therefore accounts for the possible pulse deformation in the refraction process. It also takes account of the quantity actually computed in the solid (displacement, velocity potential,...) and the possible mode-conversion into shear waves and is given by... 

Rota.ry Lobe Pumps. Rotary lobe pumps are similar to gear pumps in principle. These pumps have an added advantage of noncontacting metal parts by use of external gears, which reduces the wear, but adds complexity. Low wear and improved shear characteristics make these pumps apphcable to the food industry, where cleanliness and absence of contamination are required. These pumps produce a strong pulsing flow that must be addressed. 

When subjected to a step function loading, solid samples respond in one of the characteristic response modes described in Chap. 2. Often it is desired to investigate materials response to structured loading or even to shear-pulse loading. Both of these loadings can be achieved with the use of an intervening disk of a solid material placed between the loading and the sample. 

The response of the overall structure may be determined by the same techniques described above. The difference between directly loaded elements and supporting elements is the force amplitude and pulse shape of the applied loading. The loading on the overall stmctural system is determined from the reaction force time histories from directly loaded elements. Note that the loads on supporting members, frames, or shear walls, in some cases, may comprise reaction forces from pressures acting on the front and back faces of the structure simultaneously, taking into account the different arrival times of the blast wave. 

Effectiveness of a crude oil demulsifier is correlated with the lowering of shear viscosity and dynamic tension gradient of the oil-water interface. Using the pulsed drop technique, the interfacial dilational modulii with different demulsifiers have been measured. The interfacial tension relaxation occurs faster with an effective demulsifier. Electron spin resonance with labeled demulsifiers indicate that the demulsifiers form reverse micelle like clusters in bulk oil. The slow unclustering of the demulsifier at the interface appears to be the rate determining step in the tension relaxation process. 

Konrad was the first to address the issue of pulsed piston transport using the properties of the solids as they slide through the pipe in a plug-like motion. The friction generated in such systems often can be likened to bin and hopper flow and design, requiring shear stress measurements such as carried out by the Jenike shear stress unit. The final expression using the Konrad approach can be written for horizontal flow as... 

Finally, the shear modulus, GQ, was measured using a pulse shearometer (Rank Bros, Bottisham, Cambridge) as described before (21,22). G was measured as a function of Na SO concentration for 25 w/w latex B with the particles fnlly-coated with PVA. 

To (obtained from extrapolation of the ascending part of the flow curve) as a function of C. The shear modulus, GQ, measured using the pulse shearometer, is also shown as a function of C in the same figure. A measurable x and GQ is obtained above a critical value of C, which in both cases is -0.22 mol dm 3. As we will see later, this electrolyte concentration should be taken as the critical flocculation concentration (CFC) for the concentrated dispersion. Above the CFC, xg increases rapidly with increasing C whereas G initially increases gradually with increasing C until C = 0.3 mol dm 3, above which there is a more rapid increase of Gq. 

The final 2D spectra obtained by shearing or by using the split-/, pulse sequence can benefit from a proper scaling of the isotropic and anisotropic dimensions in order to facilitate comparisons between various experiments [171, 176-179]. In our opinion, the most convenient way to reference such 2D spectra is to define a ppm scale using, in the isotropic dimension, an apparent Larmor frequency depending on the given experiment and defined as... 

The best values of the parameter Cj are 1.51, 1.36, and 2.01 for no mass transfer, d and c direetion of transfer respectively. The product af is considered as the agitation variable in the equation, since the fit could not be improved if a and / were treated separately. The average absolute value of the relative deviation in the predicted values of d 2 from the experimental points is 16.3%. Even in packed columns, the separation can be substantially improved by pulsing of the continuous phase resulting from greater shear forces that reduce the drop size and increase the interfacial area [1, Chapter 8]. 

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