Penetrant size parameter

For many years, molecular orientation and crystallinity have been observed to improve the barrier properties of polymers (1-3). In extreme cases, drawing of semicrystalline polymers has been shown to reduce permeability by as much as two orders of magnitude. A crude understanding of the dependence of the transport parameters on penetrant size and chain packing can be... 

Figure 5. Correlation between penetrant diameter d used in the model of Pace and Datyner and size parameter used in the theory of Vrentas and Duda.

The 4>s versus if plot has the same shape as that of (pi versus ij for a flat plate but is shifted by a factor of 3 on the same log-log plot, if Equations 2.60 and 2.63 are used as basis. Aris (29,38] has shown that, for a first-order reaction in various particle geometries, the plots between the Thiele modulus q> and the isothermal internal effectiveness factor ij become identical at high and low values of

size parameter in the Thiele modulus is defined on a common basis. The characteristic size parameter L is, therefore, defined as the ratio of the particle volume to the external surface area available for reactant penetration, which enables its use for any arbitrary particle shape ... 

Fig. 17. Overall (integrated) penetration as a function of collector particle cut-size and characteristics and inlet particle parameters for collectors that foUow...

FIG. 14-106 Overall integrated penetration as a function of particle-size distribution and collector parameters. (Calvett, Yung, and Leung, NTIS Puhl. PB-248050, 1975.)... 

The models described in the following use only one parameter for the cleaning efficiency, which is thus a simplification that must be kept in mind when using these models. This works quite well as long as the efficiency value is the smallest one—e.g., the efficiency for the most penetrating particle size or the efficiency for the most penetrating gas concentration. 

The standard unit normally used for measuring dust particles is the micron (pm one-thousandth of a millimeter). The smallest particle visible to the unaided eye is between 50 and 100 pm and the most dangerous sizes are between 0.2 and 5 pm. Particles larger than this are usually unable to penetrate the lung defenses and smaller ones settle out too slowly. Some dusts can be both toxic and fibrous (e.g. asbestos) and are therefore harmful even outside these parameters. It may therefore be assumed that dusts which are visible (i.e. between 50 and 100 pm), are quite safe. However, this is not the case, as dust clouds never consist solely of particles of one size. Analysis would show percentages of all sizes, and it is for this reason that special care is needed in measuring dust clouds and concentrations. 

From 8 to 30 pounds [or 120 leaves, if foliage (4)] of the field sample are used penetration samples are dissected or otherwise suitably treated so as to afford several pounds of the desired anatomical portion of the field sample. [The size of the field sample and its method of collection vary tremendously for different materials—e.g., olives vs. alfalfa hay. These two parameters are under statistical investigation, but the paucity of reliable and sufficiently extensive data precludes formal publication of field sampling and processing techniques for materials other than leaves 4). A manual of processing procedure (5) has been mimeographed for guidance of personnel, based upon empirical observations as data are accumulated, it will be revised and expanded periodically. ]... 

An aerosol size distribution can, therefore, be described in terms of the count median diameter, d, and the geometric standard deviation, a These parameters were obtained from experimental data using a diffusion battery method (Busigin et al., 1980). A diffusion battery is an assembly of a number of cylindrical or rectangular channels. The relative penetration of aerosols through different sizes of diffusion batteries at specified flow rates allows the aerosol size distribution to be calculated. 

Gas within a bubble essentially remains in the bubble, but recirculates internally, and penetrates slightly into the emulsion to form a transitional cloud region around the bubble all parameters involved are functions of the size of bubble (Davidson and Harrison, 1963). 

The correlation (or lack of correlation) of other physiochemical characteristics has not yet been established. For instance, are all surfactants irritants Can one classify severity by the size of the molecule Can octanol water partition coefficients predict irritation potential does a propensity to partition out of the ocular fluid mean that a compound presents more of an irritation hazard than one which is more water soluble Theoretically, these data should reflect the ability of a compound to penetrate the eye and cause an irreversible lesion. However, until definitive data are available, physical and chemical parameters will probably have limited utility in an overall assessment of irritation. 

In a bulk silica matrix that differs from the silica nanomatrix regarding only the matrix size but has a similar network structure of silica, several kinetic parameters have been studied and the results demonstrated a diffusion controlled mechanism for penetration of other species into the silica matrix [89-93]. When the silica is used as a catalyst matrix in the liquid phase, slow diffusion of reactants to the catalytic sites within the silica rendered the reaction diffusion controlled [90]. It was also reported that the reduction rate of encapsulated ferricytochrome by sodium dithionite decreased in a bulk silica matrix by an order of magnitude compared to its original reaction rate in a homogeneous solution [89], In gas-phase reactions in the silica matrix, diffusion limitations were observed occasionally [93],... 

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