Adsorption, apparent velocity

Before casting Equation 7.1 in dimensionless form, the inclusion of terms to describe adsorption and velocity enhancement of the transported species will be considered. These phenomena are, of course, more appropriate to polymer transport than tracer transport but the form of the equation is very similar. The velocity enhancement referred to concerns the effect of the excluded volume or inaccessible pore volume effect which the polymer shows (Chauveteau, 1982, Dawson and Lantz, 1972) and which is discussed in more detail below. However, the physical observation on polymer transport is that there appears to be a fraction of the pore space—either the very small pores (Dawson and Lantz, 1972) or regions close to the wall of the porous medium (Chauveteau, 1982)—which is inaccessible to polymer transport. This leads to an enhancement of the average velocity of the polymer through the porous medium. When there is both adsorption of transported polymer onto the rock matrix and a fraction of the pore volume is apparently inaccessible to the polymer, Equation 7.1 must be extended to ... 

It is the effective mobility that determines selectivity since the effect of the electroosmotic mobility is equal for all the sample constituents. The effective mobility can be worked out from the apparent mobility if the extent of / eof known. Several methods are applied to determine however, the procedure of applying a neutral marker is commonly used. A marker is a compound that migrates only due to the EOF (neutral). The velocity of a neutral compound represents the velocity of the EOF when no other disturbing processes such as wall adsorption occur. Using the practically obtained migration time of the neutral marker (tgoi) the velocity of the EOF can be calculated ... 

The electronic interaction between benzene and the metal surface may be made up of two effects the polarization of the molecule, which may be concluded from the above-described research, and the shifting of the v electrons to the metal surface to become part of the metal electron gas, which has been hypothesized by Polanyi (77). The first effect has been shown in Fig. 28, the second apparently can be seen from the research (18) illustrated by Fig. 29, in which the change of resistance of a transparent nickel film was studied during the adsorption of benzene molecules. As the temperature of the benzene capsule was 90°K., the evaporation velocity was so low that only a small number of benzene molecules struck the surface in unit time. The resistance therefore diminished only... 

The natural line of inquiry is to study the progress of a given reaction on various catalytic surfaces, to determine the relative numbers of molecules adsorbed on each surface, and to seek a correlation between the heat of activation, using provisionally the apparent value as a sufficiently good approximation to the true value, and the velocity of change referred to equal numbers of adsorbed molecules. Unfortunately, no example has hitherto been found suitable for experimental investigation, in which both the adsorptions and the reaction velocities can be measured. Thus no really valid test can be made. The existence of centres of varying activity would still further complicate the interpretation even of direct measurements of adsorption. 

In this equation, c is the concentration in the fluid phase and q is the quantity in the solid phase. The column porosity e (expressed as phase ratio f = (1 -e)/e) defines the fraction of the fluid phase in the column. Furthermore, u stands for the linear velocity and t and x are the time and space coordinates, respectively. All contributions leading to band-broadening are lumped in a simplifying manner into an apparent dispersion coefficient, D p. In equation (21-2), it is assumed that the two phases are constantly in equilibrium expressed by the adsorption isotherms. Due to the nonlinear character of the isotherm equations, the solution of equation (21-2) requires the use of numeri-... 

Data obtained in fixed-bed reactors and in continuous high-velocity coil-t ype reactors (fluid catalyst) indicate that the catalytic cracking of gas oils is approximately a first-order reaction, but that the apparent order approaches two because of the effect of nonhomogeneity of the feed and because of the increasing dilution of reactant with cracked products as conversion increases at constant total pressure (73). The extent of reaction is determined by the intrinsic activity of the catalyst surface, reaction time at the surface, temperature, and susceptibility of the feed to cracking. Superficial contact time in the reactor is of little consequence. The effective time of reaction is the time spent by oil on the active surface of the catalyst. For a given extent of adsorption, the reaction time should be inversely proportional to weight space velocity and should also be a function of the reactant partial pressure. Results of experiments with... 

The effectiveness of boundary lubrication by PLL(10)-g[2.9]-PEG(2) in aqueous buffer solution is very apparent in relatively low velocity regimes, where lubrication by water alone is practically impossible due to its extremely low pressure-coefficient of viscosity and poor film-forming properties. The relative adsorption behavior of the polymer onto SiO,t and FeO surfaces, as investigated by OWLS ( 120ng/cm for SiO and 60 ng/cm for FeO,t surfaces), seems to explain the relatively less effective lubrication for FeO /FeOx compared with the FeO t/SiO t tribo-pair. In summary, the PLL(10)-g[2.9]-PEG(2) appears to form a protective layer both on silicon oxide and iron oxide surfaces, thus effectively improving load-carrying and boundary lubrication properties of water for a variety of dynamic contact regimes. 

At low crack velocities. Lynch and Trevena proposed that H diffusion is likely to occur however, adsorption was thought to still be the dominant mechanism for embrittlement. This was evidenced by the correlation between the fracture planes, crack propagation directions and fracture surfaces for LME and slow SCC fracture. It was also noted that no evidence of hydride formation was apparent on the fracture surfaces. At low crack velocities, adsorption at external crack tips could be inhibited by film formation, necessitating diffusion to and adsorption at internal cracks. The authors... 

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