Pores volume fraction

It is important to realize that all static phases will contribute to retention and, as a result, a number of different distribution coefficients will control the retention of the solute. Nevertheless, the situation can be simplified to some extent. The static interstitial volume (Vi(s)) and the pore volume fraction (Vp(i)) will contain mobile... 

The presence of the pores adds two parameters - the pore volume fraction and the pore radius. The predicted Rp Increases as the pore radius decreases suggesting a preference tor small pore packings. However, for a small pore radius of 1.0 pm a single value of the separation factor corresponds to two values of the particle diameter (13). Such double-valued behavior Is of course undesirable In an analytic technique. 

In the model described in this work every effort has been made to ensure that it embodies physically meaningful parameters. It is inevitcible, however, that some simplistic idealizations of the physical processes involved in GPC must be made in order to arrive at a system of equations which lends itself to mathematical solution. The parameters considered are, the axial dispersion, interstitial volume fraction, flow rate, gel particle size, column length, intra-particle diffusivity, accessible pore volume fraction and mass transfer between the bulk solution eind the gel particles. 

Here Cp is the accessible pore volume fraction of the gel which is a fijnction of the pore size distribution as well as the size of a polymer molecule. The value of p is given by Equation 3 ... 

Fig. 7. Schematic representation of four procedures commonly used to sample a field in stereo-logical analysis. These procedures have been used to study the porous structure of collagen-GAG matrices [74] and yield values for average pore diameter, pore volume fraction and other features. In this illustration, a phase A (cross-hatched) is embedded in a continuous phase B (white background). A Random point count B systematic point count C areal analysis D lineal analysis. (Reprinted from [64] with permission).

Knowing that 1 mg/cm2 of product water is a threshold, how much water can be stored at maximum within each component of the fuel cell, and how much can be removed to the outside For the cathode catalyst layer (CCL) with typical thickness of 10 p,m and 50% pore volume fraction, the CCL water storage capacity is approximately 0.5 mg/cm2. A 30- un-thick membrane can store 1.5 mg/cm2 of water, but its actual water storage capacity depends on the initial water content, A., and therefore is proportional to (ks.where A.sa, denotes the water content of a fully hydrated membrane. The escape of water into the GDL is unlikely due to the very low vapor pressure at cold-start temperatures (Pv>sa, = 40 Pa at —30°C). For reference, the GDL with 300 pm thickness and 50% porosity would store about 15 mg/cm2 of water, if it could be fully utilized. This capacity is too large to be used for cold start. From this simple estimation we can conclude that the CCL water storage capacity alone is not sufficient for successful cold start and that a successful strategy is to store water in the membrane. 

According to the porosity data of Uchida et al. [102] the matrix of carbon grains (20-40 nm) forms an agglomerated structure with a bimodal psd. Primary pores (micropores, 5-40 nm) exist within agglomerates, between the carbon grains. Larger, secondary pores (macropores, 40-200 nm) form the pore spaces between agglomerates. The relation between the relative pore volume fractions of the two pore types depends on the contents of PFSI and PTFE. Due to their molecular size these components are not able to penetrate micropores. They affect only the macropore volume. The experimental study revealed that an increased PFSI content leads to a decrease of the macropore volume fraction. The opposite effect was found for PTFE. 

Internal or intraparticle porosity, Fraction of the column volume contained inside the particles. Also called the fractional pore volume. Fraction occupied by the stagnant mobile phase. 

The A/m ratio may be estimated based on some inherent properties of the adsorbent its density p, porosity e, and the shape and size of the pores. The porosity is pores volume fraction of the total adsorbent particle volume, e = Vp/V. If the pores are assumed to be cylindrical, with diameter d and length L, then the pore surface area per unit pore volume is... 

Composite Materials. Many solid foods can be considered as solid matrixes, interspersed with a continuous liquid phase. Transport through such a material may be greatly hindered. Flow of the liquid through the matrix under the influence of a pressure gradient is proportional to a material constant called permeability, which is about proportional to pore diameter squared and pore volume fraction. 

In addition to the fibrillar morphology of the fibre cell wall, the fibres are characterized by capillaries, voids, and interstices providing the cellulose fibres a highly porous character. The pore size ranged from 5 up to 30 nm and the pore volume fraction attained 1-3% for cotton and wood pulp. However, the total pore volume and pore size distribution are very sensitive to pretreatments. Mercerization leads to a decrease in pore diameter and an enhancement of micropore surface, while enzyme treatments enlarge the existing pores [4]. 

Table III. Invariant and Pore Volume Fraction in Cellulose Samples...

Figure 16.9. Calculated sintering time to 99.5% relative density with various liquid and pore volume fractions for compacts containing initial pores with a log normal distribution from one to 30 times larger than the initial grain size.

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