Liquid transport factor

Besides gas and liquid transport in the diffusion media, there is also electronic conduction. Most models neglect this due to the high conductivity of the carbon in the diffusion media, although it can become a limiting factor due to geometry or diffusion-media composition. For those that take it into account. Ohm s law is used... 

Until now we have ignored an important factor. The electric field affects not only the surface charges of the particle, but also the ions in the electrical double layer. The counterions in the double layer move in a direction opposite to the motion of the particle. The liquid transported by them inhibits the particle motion. This effect is called electrophoretic retardation. Therefore the equation is only valid for D [Pg.77]

P. Aptel, J. Cuny, J. Jozefonvicz, G. Morel, J. Neel, Liquid transport through membranes prepared by grafting of polar monomers onto PTFE films. Part II. Some factors determing pervaporation rate and selectivity, J. Appl. Polym. Sci. 18 (1974) 351-364. 

Here cci is the liquid expansion factor fg is the fractional void or free voltune at the glass temperature Tg, B is related to the fractional void voliune required to be in the vicinity of a segment for that segment to make a jump and is an inherent jump frequency factor, which may depend slightly on temperature, but much less so than does f itself. These interpretations are based principally on recent theoretical investigations of mass transport in liquids near their glass transition temperature. Unfortunately, the values for B, fg and cannot usually... 

Increasing the pressure of the gaseous reactant not only increases the amount present in the gas phase but also increases gas/liquid transport and the solubility of the gas in the liquid phase. This, in turn, facilitates liquid/solid transport of this species. All of these factors increase the availability of the gaseous reagent to the catalyst. Fig. 5.11 shows a typical plot for the relationship between hydrogen pressure and the reaction rate at a fixed catalyst quantity and agitation rate.28 At lower values an increase in pressure promotes an increase in rate but above a given value further increases in pressure have little or no effect on the rate. In the... 

The estimation of Rav for characteristic parameter values shows that Rav where Aq = d/Re /" is the internal scale of turbulence. In a turbulent flow, both heat and mass exchange of drops with the gas are intensified, as compared to a quiescent medium. The delivery of substance and heat to or from the drop surface occurs via the mechanisms of turbulent diffusion and heat conductivity. The estimation of characteristic times of both processes, with the use of expressions for transport factors in a turbulent flow, has shown that in our case of small liquid phase volume concentrations, the heat equilibrium is established faster then the concentration equilibrium. In this context, it is possible to neglect the difference of gas and liquid temperatures, and to consider the temperatures of the drops and the gas to be equal. Let us keep all previously made assumptions, and in addition to these, assume that initially all drops have the same radius (21.24). Then the mass-exchange process for the considered drop is described by the same equations as before, in which the molar fluxes of components at the drop surface will be given by the appropriate expressions for diffusion fluxes as applied to particles suspended in a turbulent flow (see Section 16.2). In dimensionless variables (the bottom index 0" denotes a paramenter value at the initial conditions). 

The physical interpretation of the load factors is that a liquid flow should be transported through the interface, and this transport is augmented by the density difference and decreased by the continuous phase viscosity. The liquid load factor accounts for transport of both phases through the interface, while the other two only transport the applicable dispersed phase. Flence, the liquid load factor is in line with the new separator design philosophy proposed by Polderman et al. (12, 15), while the oil and water load factors are in line with the dispersion layer theory developed by Jeelani and Flartland (16-20) (for the corresponding dispersed phase). 

The porosity and pores structure will be of special importance for liquids transport in concrete. These both properties relate directly to w/c ratio and the degree of hydration, because porosity of concrete is affected mainly by cement paste the porosity of aggregate is generally very low. Continuous pores volume is increasing with w/c ratio and decreases with degree of cement hydration. There ate the permeability controlling factor, because the transport of liqitids in concrete composite occurs principally in continuous pores. 

Liquid transport in paper is, as can be understood from the above examples, a complex issue. Imbibition can occur by various mechanisms and is affected by many factors, such as the structure of the fibre network which controls the size of the capillaries and continuity, fibre surface chemistry and morphology, sizing and other chemical treatments of the fibre surfaces. Each practical case must be carefully thought over in order to make fruitful predictions of the absorbency behaviour and a correct analysis of the experimental data. 

Wang and co-workers [68, 69] adopted the liquid coverage model to account for the droplet influence. They treated the droplet covering the GDL surface as a boundary condition for the liquid transport equation in GDLs, that is, the ratio of the liquid-covered surface area to the total area. As the liquid droplet detachment is related to several major factors, such as gas flow rates, wettability, and liquid production rate, the saturation at the surface can be written as a function of them ... 

The requirements for liquid fuels obviously depend strongly on vehicle mileage. For example, if average vehicle fuel efficiency were to increase by a factor of two, demand for liquid fuels would be cut in half. Were that to happen, the fuel efhanol that could be produced just from the residues of these three major crops might satisfy nearly half of fhe worldwide demand for liquid transportation fuels, without the need to plant additional crops dedicated for energy uses. We must not lose sight of the need to work on the demand side of the fuel equation, as well as the supply side. 

This direct proportionality between the rough hard-sphere transport properties and the Enskog coefficients has formed the basis for many correlations of liquid transport properties (Easteal Woolf 1984 Li etal. 1986 Walker etal. 1988 Greiner-Schmid et al 1991 Harris etal 1993). For a successful data fit, with unique values for Vq and the proportionality factors, it is necessary to fit a minimum of two prt rties simultaneously, with the same Vq values. This is exemplified in the case of methane in Chapter 10. It is further shown in Chapter 10 that successful correlation of transport property data for nonspherical molecular liquids can be made, based on the assumption that transport properties for these fluids can also be directly related to the smooth hard-sphere values. 

Modules Eveiy module design used in other membrane operations has been tried in peivaporation. One unique requirement is for low hydraulic resistance on the permeate side, since permeate pressure is veiy low (O.I-I Pa). The rule for near-vacuum operation is the bigger the channel, the better the transport. Another unique need is for neat input. The heat of evaporation comes from the liquid, and intermediate heating is usually necessary. Of course economy is always a factor. Plate-and-frame construc tion was the first to be used in large installations, and it continues to be quite important. Some smaller plants use spiral-wound modules, and some membranes can be made as capiUaiy bundles. The capillaiy device with the feed on... 

For the transport of coarse particles, the relative velocity between the liquid and solids is an important factor determining the hold-up, and hence the in-line concentration of solids. Cloete et a/. 65) who conveyed sand and glass ballotini particles through vertical... 

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