Capillarity conductivity

The atomic structure of a heterogeneous catalyst determines its chemical and phase properties, but texture determines a wide range of additional features that dictate such characteristics as adsorption and capillarity, permeability, mechanical strength, heat and electrical conductivity, etc. For example, the apparent catalytic activity,. of a grain, taking into account diffusion of reagents, depends on the interrelation between the rates of reaction and diffusion, and the latter is determined by a porous structure. 

Two kinds of conductivity detector are distinguished contact detectors and contactless detectors. Both types were originally developed for isotachophoresis in 0.2-0.5-mm-inner diameter (i.d.) PTFE tubes. Contactless detectors are based on the measurement of high-frequency cell resistance and, as such, inversely proportional to the conductivity. The advantage is that electrodes do not make contact with the buffer solution and are, therefore, outside the electric field. As these types of detectors are difficult to miniaturize down to the usual 50-75-jU.m capillar inner diameter, their actual application in capillary electrophoresis (CE) is limited. 

The moisture flux due to capillarity can be expressed in terms of the product of a liquid conductivity parameter and moisture gradient. In this case, the governing equation has, in fact, the same form as the diffusion equation. 

To calculate unsaturated hydraulic conductivity A"(p) we have to take into consideration the spontaneous filling (snap-off) of the slit and the central pore for imbibition and the spontaneous redistribution of liquid for drainage. These aspects are extensively discussed in Film Adsorption on Rat Surfaces and in Slit-Shaped Pores and Capillarity and Pore Shape . The unsaturated conductivity before slit filling is given as ... 

The saltpan in the basin of Fig. 11.1 exemplifies a more common occurrence of soil salinity. Soils in low-lying areas, even in arid regions, may have high water tables. Water from groundwater tables within a few meters of the surface can move by capillarity to the soil surface, where it evaporates and leaves behind its salts. Figure 11.2 shows an example of salt distribution above a water table 90 cm below the soil surface. The soil salinity concentration is expressed as electrical conductivity, the common method of measurement. 

The electrical resistivity of water-saturated sediments depends on the resistivity of its solid and fluid constituents. However, as the sediment grains are poor conductors an electrical current mainly propagates in the pore fluid. The dominant transport mechanism is an electrolytic conduction by ions and molecules with an excess or deficiency of electrons. Hence, current propagation in water-saturated sediments actually transports material through the pore space, so that the resistivity depends on both the conductivity of the pore water and the micro structure of the sediment. The conductivity of pore water varies with its salinity, and mobility and concentration of dissolved ions and molecules. The microstructure of the sediment is controlled by the amount and distribution of pore space and its capillarity and tortuosity. Thus, the electrical resistivity cannot be considered as a bulk parameter which strictly only depends on the relative amount of solid and fluid components, but as shown below, it can be used to derive porosity and wet bulk density as bulk parameters after calibration to a typical sediment composition of a local sedimentation environment. 

If the subgrade is less permeable a perched water table may develop at the lower boundary of the unbound layers, which will facilitate lateral water movement. Therefore, initial water content, hydraulic conductivity and capillarity of the subgrade are significant for the rate of lateral intrusion. 

In the next paper, Vinckier et aL [279] fitted the viscosity and the first normal stress difference of the model PIB/PDMS emulsions to Eq. (2.18). A reasonable description of the rheological behavior was obtained for the diluted and semi-diluted concentrations with the viscosity ratios A = 1.5—4. The experiments were carefiilly conducted within the range of the capillarity numbers (k < Kcr) and ... 

Various other methods have been described for the determination of thermal conductivity. Capillarity has been used to measure the thermal conductivity of LDPE, HOPE and PP at various temperatures and pressures [30]. A transient plane source technique has been applied in a study of the dependence of the effective thermal conductivity and thermal diffusivity of polymer composites [31]. 

Jacquin, C. H. Legait, B. Influence of Capillarity and Viscosity During Spontaneous Imbibition in Porous Media and Capillaries, Phy. Chem. Hydro. 1984,5,307-319. Jirsak, O. Gok, T. Ozipek, B. Pau, N. Comparing Dynamic and Static Methods for Measuring Thermal Conductive Properties of Textiles, Textile Res. J. 1998, 68(1), 47-56. 

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