Capillary flow method apparatus

For the explanation of parameters A, C, and y, look into the theory of the boiling point method. The above equations consider diffusion and flow of vapor only through the exit capillary of the apparatus. The equations become very complex when the diffusion upstream through the entrance capillary is taken into account. Their application is not practical, as they contain too many unknown parameters. 

The hydrodynamic thicknesses were measured by observing the change in capillary flow due to adsorption on fritted disks prepared by sintering the powders used for adsorption. The results will be reported only for the glass disks. The data from the steel disks were poorly reproducible. For the operational method, see (10) and the dissertation by A. Kudish (11). However, their flew apparatus was modified so that the liquid could flow through the disks in both directions. This was found to reduce the time required to attain equilibrium and compensates for any one-way necks present in the pores. Poiseuille s equation was used in a modified form (12,13) assuming the disk to be a packet of parallel... 

The Poiseuille equation provides a method for measuring 77 by observing the time required for a liquid to flow through a capillary. The apparatus shown in Fig. 9.6 is an example of one of many different instruments designed to use this relationship. In such an experiment the time required for the meniscus to drop... 

The experiments initially conducted were designed to test the performance of the apparatus by determination of the effect of pressure on the viseosity/quality spectrum of a typical foaming agent when it flows through a straight capillary tube. The method used is based on a technique recently developed in the laboratories(7) for this purpose, at atmospheric pressure,... 

While the external electrical field approach is a method directly modifying the zeta-potential of the capillary wall, it is not applicable with commercial apparatuses. The back-pressure technique, on the other hand, has the disadvantage that the flat electroosmotic flow profile is disrupted by superposition of a pressure-driven laminar flow profile hence, the efficiency of separation deteriorates. 

The experimental apparatus consists essentially of a narrow vertical glass tube down the inner surface of which one liquid is made to flow, the other liquid emerges from a fine glass tip in the form of a narrow jet down the axis of the tube. The two solutions are connected with calomel electrodes employing potassium chloride or nitrate as junction liquids. The E.M.F. of the cell is measured by means of a sensitive quadrant electrometer. The greatest source of error in the method is the elimination of or the calculation of the exact values of the liquid-liquid junction potentials in the system. For electrolytes which are not very capillary active, the possible error may amount to as much as fifty per cent, of the observed E.M.F. 

As already mentioned in Chapter 1, there are mainly three geometries suitable for the measurement of flow birefringence, viz. those of the concentric cylinder apparatus, the adapted cone-and-plate apparatus and the slit-capillary with a rectangular cross-section. The general principles of the pertinent techniques have been described in the same chapter. The purpose of the present chapter is to give details of the design and construction in order to enable the reader to form a judgement as to the efficiency of the proposed methods, i.e. the relation between information and experimental effort. 

The method described by Grob and Zurcher (151 in which a very small amount of charcoal is used to collect volatile compounds has been modified slightly by P. S. Beevor and coworkers, Tropical Products Institute, London (1 61 to collect pheromones from insects. We have adapted and further modified this method. Briefly, it consists of a small charcoal filter prepared by sealing 3-5 mg of charcoal between two 325-mesh stainless steel frits in a 6 mm (0.D.1, 3.7 mm (I.D.l Pyrex tube (Figure 81. This filter is then placed at the exit end of an aeration chamber, and air is drawn through the aeration apparatus at a flow rate of 2.5 liters/min. When aeration is complete, the filter is rinsed with six aliquots (15-20 pi) of distilled dichloromethane the combined aliquots are concentrated to about 5-10 pi by gently warming, and isooctane or another solvent of choice for analysis by capillary GC with splitless injection is added. 

Basically two different types of experimental approaches have been used to study the boundary shp local (direct) [45,60] and effective (indirect) methods [49-52,61]. The first group of methods is based on apphcation of optical techniques using tracer particles or molecules to determine the flow field. These techniques have a resolution of less than lOOnm, so they cannot distinguish small differences in slip lengths. The effective methods assume the boundary conditions (Eq. 18) or similar ones to hold at the substrate surface and infer the slip length by measuring macroscopic quantities. These methods have been the most popular so far and they include atomic force microscopy (AFM), surface force apparatus (SEA), capillary techniques, and QCM. 

Particles consist of both internal and external surface area. The external surface area represents that caused by exterior topography, whereas the internal surface area measures that caused by microcracks, capillaries, and closed voids inside the particles. Since the chosen surface area technique should relate to the ultimate use of the data, not all techniques are useful for fine powders. The commonly used approaches are permeametry and gas adsorption according to the Brunauer, Emmet, and Teller (BET) equation [9]. Because of simplicity of operation and speed of operation, permeametry methods have received much attention. The permeametry apparatus consists of a chamber for placing the material to be measured and a device to force fluid to flow through the powder bed. The pressure drop and rate of flow across the powder bed are measured and related to an average particle size and surface area. Especially for porous powders, permeametry data include some internal surface area, thus decreasing their value. 

Electro osmosis This technique involves the movement of a liquid relative to a stationary charged surface (e.g. a capillary or porous plug) by the application of an electric field. Experimentally, zeta potentials may be measured by this method by means of an apparatus such as that shown in Figure 10.10. The potential is supplied by electrodes, as shown in the schematic, and the transport of liquid across the tube is observed through the motion of an air bubble in the capillary providing the return flow. For water at 25°C, a field of about 1500 V/cm is needed to produce a velocity of 1 cm/s if the surface potential (xjro) is 100 mV. 

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