Tangential streaming potential

Eievet, P., Sbal M., Szymczyk, A. and Vidonne, A. 2003. Determining the z-potential of plane membranes from tangential streaming potential measurements Effect of the membrane body conductance. J. Memh. Sci. 226 27-36. 

With respect to membrane transport/eleetrieal characteristics, both membranes have slightly electronegative character at neutral pH and the following values of the electrokinetic surface charge density (ae) and isoeleetrie point (ie.p.) were obtained from tangential streaming potential measurements [13, 62] ... 

In order to correlate chemieal analysis of aetivated membrane surface with other characteristic parameters, tangential streaming potential measurements at a constant NaCl concentration (5x10 " M) but different pHs were carried out with the DT200 sample and analysed using the local dissociation model [68-69], which allows the determination of the pKa and the munber of acid sites accessible on the membrane surface (N ), and their comparison with the same parameter for PAO polyamide/polysulfone composite membrane (the un-modified base membrane). The obtained values and surface roughness are ... 

Figure 9.5c shows tangential streaming potential with dense RgC and nanofiltration NF45 membranes, which characterizes the external membrane surface (instead of internal surface or pore wall/solution interface), as represented in Figure 9.5d. From the slopes of the straight lines shown in Figure 9.5a, c, the streaming potential coefficient Ogt = AtPst/ P was determined and zeta (Q potential was obtained from those values by using Equation (9.1).

Streaming potential measurements or tangential streaming potential in the case of dense membranes, but important transport information associated with hydro-dynamic permeation is missing in the latter cases. Other information related to different characteristic membrane material parameters (electrical/adsorption parameters) can also be obtained from these measurements. 

Figure 12.7b is a sketch of an apparatus that may be used to measure streaming potential. As was the case with electroosmosis, the capillary can be replaced by a plug of powdered material between perforated electrodes. An applied pressure difference p across the capillary causes the solution to flow through the capillary, thereby tangentially displacing the part of the double layer in the mobile phase from the stationary part. 

If a liquid moves tangential to a charged surface, then so-called electrokinetic phenomena arise [101]. Electrokinetic phenomena can be divided into four categories Electrophoresis, electro-osmosis, streaming potential, and sedimentation potential [102], In all these phenomena the zeta potential plays a crucial role. The classic theory of electrokinetic effects was proposed by Smoluchowski2 [103],... 

Lehmann, C., Mockel, D., and Staude, E., Permeation and tangential flow streaming potential measurements for electrokinetic characterization of hack-etched microfil-hation membranes, J. Membr. Sci., 159, 243, 1999. 

If the material to be removed is dust, the self-cleaning bypass filter with automatic blowback constitutes a potential solution, whereas in other instances, cyclone separators should be considered. In the former device (Figure 3.5), the process stream enters tangentially to provide a swirling action, and the cleaned sample is taken near the center. Transportation lag can be kept to less than 1 minute, and the unit is applicable to both gas and liquid samples. This type of centrifuge can also separate streams by gravity into their aqueous and organic constituents. 

The potential-flow solution for streaming motion past a circular cylinder was obtained earlier and given in terms ofthe streamfunctionin(10-17). To calculate the pressure gradient in the boundary layer, we first determine the tangential velocity function, ue, as defined in (10-37) ... 

In this regard, it is of interest to contrast the two problems of the streaming motion of a fluid at large Reynolds number past a solid sphere and a spherical bubble. In the case of a solid sphere, the potential-flow solution (10 155)—(10—156) does not satisfy the no-slip condition at the sphere surface, and the necessity for a boundary layer in which viscous forces are important is transparent. For the spherical bubble, on the other hand, the noslip condition is replaced with the condition of zero tangential stress, Tr = 0, and it may not be immediately obvious that a boundary layer is needed. However, in this case, the potential-flow solution does not satisfy the zero-tangential-stress condition (as we shall see shortly), and a boundary-layer in which viscous forces are important still must exist. We shall see that the detailed features of the boundary layer are different from those of a no-shp, sohd body. However, in both cases, the surface of the body acts as a source of vorticity, and this vorticity is confined at high Reynolds number to a thin 0(Re x/2) region near the surface. 

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