Electro-hydrodynamic effects

ELECTRO-OPTiC APPLICATIONS OF LIQUID CRYSTALLINE POLYMERS 321 Electro-hydrodynamic Effects... 

The electro-optic effects described above all refer to director reorientation induced through the dielectric properties (Af) of the polymer. If, however, a change in the optical properties is induced by a current flow resulting from the anisotropic electrical conductivity (A a) of the material, then the so-called electro-hydrodynamic effects are observed. ... 

There is another important factor, namely the buffer flow inside the buffered substrate, which influences migration. This flow has three main sources evaporation partially caused by heat production from electrical energy the hydrodynamic result of the level of the buffer vessels with respect to one another and to the level of the paper and the electro-endosmotic effect, the interaction between the electrical forces and the buffered substrate. 

Szpyrkowicz, L. (2005) Hydrodynamic effects on the performance of electro-coagulation/electro-flotation for the removal of dyes from textile wastewater. Ind. Eng. Chem. Res. 44,7844-7853. 

In the middle of cells and in faces that are perpendicular to the flowing direction, the borders are branched, which means that the effective number of borders, equivalent to that in a real system, is different from five. The number of independent borders with constant by height radius and length L can be determined by the electro-hydrodynamic analogy between current intensity and liquid flow rate through borders, both being directly proportional to the cross-sectional areas [6,35]. This analogy indicates that the proportionality coefficients (structural coefficients B = 3) in the dependences border hydroconductivity vs. foam expansion ratio and foam electrical conductivity vs. foam expansion ratio, are identical [10]. From the electrical conductivity data about foam expansion ratio it follows... 

Figure 4 shows the most important feature of the electro-optical effect in a suspension, stabilized by polyelectrolyte adsorption. This is the appearance of an additional LF effect near the range of particle rotation (102-104 Hz) that resembles the LF effect in free polyelectrolyte solutions. The analogy is so impressive that we supposed the same origin of the LF effect in both systems. Polarization of tightly bound counterions with lower mobility in comparison to that of the free ions is proposed to explain the LF effect in stabilized suspensions [12-18], since it cannot be found in suspensions of bare oxide particles. The overlap (full or partial) of the frequency intervals of particle hydrodynamic relaxation (RF effect) and the relaxation of this additional LF effect means that the tightly bound counterions have close mobility to that of the whole colloid-polymer complex. A saturable ionic induced dipole moment probably arises due to the polarization of these coun-... 

The dynamics of the electroclinic effect is, in fact, the dynamics of the elastic soft mode. From Eqs. (13.18) and (13.19) follows that the switching time of the effect is defined only by viscosity and the term a(T — T ) and is independent of any characteristic size of the cell or material. It means that the relaxation of the order parameter amplitude is not of the hydrodynamic type controlled by term Kq (K is elastic coefficient). For the same reason Xg is independent of the electric field in agreement with the experimental data, shown in Fig. 13.9b. At present, the electroclinic effect is the fastest one among the other electro-optical effects in liquid crystals. 

If (5.20) is not valid other types of electrooptical effects take place and the modulated FVederiks transition cannot be observed in experiment. Figure 5.4 shows how doping liquid crystals with conducting and dielectric impurities can violate the inequality (5.20) and, consequently, the electro-hydrodynamic instabilities 1 and 5 (Table 5.1) are observed within the whole frequency range (curve B). Considerable change in the threshold voltage and inversion frequency also takes place for different values of the low-frequency dielectric anisotropy (curves A and C). 

R. Williams, Optical-Rotary Power and Linear Electro-Optic Effect in Nematic Liquid Crystals of p-Azoxyanisole, J. Chem. Phys., Vol. 50, p. 1324 (1969) and D. Meyerhofer, A. Sussman, and R. Williams, Electro-Optic and Hydrodynamic Properties of Nematic Liquid Films with Free Surfaces, J. Appl. Phys., Vol. 43, p. 3685 (1972). J. S. Smart, Effective Field Theories of Magnetism, W. B. Saunders Co., Philadelphia, Pa. (1966). 

In materials of positive dielectric anisotropy, most electro-optic phenomena are frequency independent field effects hydrodynamic effects, occurring with certain boundary conditions result in stable (laminar) flow, and no turbulent-flow reorientation is observed. ... 

A linear relationship exists between the ESA or CVP amplitude and the volume fraction of the suspended particles. At relatively high-volume fractions, hydrodynamic and electric double-layer interactions lead to a non-linear dependence of these two effects on volume fraction. Generally, non-linear behavior can be expected when the electric double-layer thickness is comparable to the interparticle spacing. In most aqueous systems, where the electric double layer is thin relative to the particle radius, the electro-acoustic signal will remain linear with respect to volume fraction up to 10% by volume. At volume-fractions that are even higher, particle-particle interactions lead to a reduction in the dynamic mobility. 

Rajagopalan and Tien (1976) have reported the results of a theoretical study of the effects of diffusion, fluid flow, gravity, hydrodynamic retardation, electro-... 

Dynamic pumps infuse energy to the fluid in a manner that increases either its momentum (centrifugal pumps) or its pressure (electroosmotic and electrohydro-dynamic pumps) as shown in Table 4. They involve centrifugal or hydrodynamic actuations and, more specifically, are driven by electro-/magneto-hydrodynamic [257], electroosmotic [254-256], electrokinetic [251-253], electrowetting [258], and acoustic forces [259]. Centrifugal pumps are typically less effective for fluids with low Reynolds numbers and have limitation in miniaturization. 

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