Open porosity, definition

In resin-coated, impregnated, or laminated nonwoven composites, a small portion of the pores is not accessible (ie, not connected to the fabric surface), and the definition of porosity in above equation gives the so-called total porosity of the fabric. Thus, the open porosity (or effective porosity) is defined as the ratio of accessible pore volume to total fabric volume, which is a part of the total porosity of the fabric. 

To evaluate the average pore length, it is necessary to recognize that the porosity sp will represent not only the volumetric void fraction but also at any cross section the fraction of the area occupied by the pore openings. If the average open area associated with each pore is assumed to be 7cr2, the definition of the porosity indicates that... 

Most solids of high surface area are to some extent porous. The texture of such materials is defined by the detailed geometry of the void and pore space. Porosity, , is a concept related to texture and refers to the pore space in a material. An open pore is a cavity or channel communicating with the surface of a particle, as opposed to a closed pore. Void is the space or interstice between particles. In the context of adsorption and fluid penetration powder porosity is the ratio of the volume of voids plus the volume of open pores to the total volume occupied by the powder. Similarly, particle porosity is the ratio of the volume of open pores to the total volume of the particle. It should be noted that these definitions place the emphasis on the accessibility of pore space to the adsorptive. 

Areal Porosity and Tortuosity. Areal porosity or areosity, Ap, is defined as the effective areal ratio of the open pore cross-section to the bulk space. A more strict definition of areosity was introduced by Ruth and Suman (56). However, the areosity as defined by them is not a property of the porous medium only but a property of both the porous medium and the transport strength of the fluid such as the flow strength and electric current strength. The areal porosity is undoubtedly a very useful quantity for a bundled or ensemble passage model because it represents the ratio of the total passage cross-sectional area to the total cross-sectional area of the porous medium at a given planar section. 

The areal porosity has been invariably considered to be equivalent to the porosity, e, of the medium (I, 31, 33). This is by and large due to the success and popularity of the straight bundle passage models and nonconnecting constricted passage models, in which the ratio of the total open pore area to the total cross-sectional area for the direction under consideration has to be equivalent to the (volume) porosity of the porous medium. However, as it is expected from the difference in the definitions, it is no surprise that Dullien and Mahta (57) found their measured (areal) porosity is significantly different from the measured (volume) porosity with a different technique for the same porous medium sample. 

Mesoporosity is defined as that porosity which has an entrance dimension >2nm and <50 nm. Such a definition is based around the way that nitrogen is adsorbed into porosity. The filling of the porosity, >2 <50 nm, is called capillary condensation. Adsorption occurs initially on the pore walls with the result that the pore is not only a narrower pore, but also it behaves as a narrower pore with a higher adsorption potential well in the center (Figure 4.2). This process continues with increasing relative pressure within pores of increasing diameter until the 50 nm limit (or thereabouts) is reached when the entrance dimension of the pore (gap between the pore walls) is so large that the porosity behaves as an open surface. 

Considering the contributions of open and closed pores to the total sample volume, two types of density of a porous sample specimen can be defined. The bulk density, /Obuik, takes contributions both from open and closed pores into account. The apparent density, Papp, considers only the contribution of closed porosity. The definitions of these densities are ... 

The input parameters of the model are stated in the Chapter 2 (the definition of the area geometry, hydraulic conductivity and porosity of rocks and fissures zones, fissures openings, substances sorption parameters, diffusion coefficient, released volumes of substances in time). These parameters are analyzed (in the view of the model sensitivity and supposing the same calculated mesh but different input parameters—e.g. those of hydraulic conductivity or porosity) in the Chapter 4. 

The preceding definitions are centered on lattice sites a fraction of sites are randomly assigned as pores. The definitions can also be based on lattice bonds by allowing the probability p to determine the fraction of open bonds in the lattice. Open pores then exist at sites which are connected by open bonds. Bond percolation and site percolation are two distinct methods of describing the lattice each leads to quantitative predictions of material properties. Since the site percolation description corresponds more naturally to the porous materials-for example. In site percolation, the lattice probability p is exactly equal to the material porosity-it is used for the remainder of this discussion. The results which are described in the sections that follow could, however, be based on a bond percolation description. 

Sonic logs. The sonic log provides in situ measurement of the speed of sound in the formation over the scale of the sonde. It can only be used in open, uncased holes. The measurement is useful in seismic processing, it can be used to infer porosity but not that accurately and can be used to identify the rock type since the sound speed is a definite characteristic of each type of rock. Further detail can be found in [45, 138]. 

These refractory products are heterogenous materials whose composition broadly consists of one or more minerals making up the refractory medittm as such, with or without additives which provide or reinforce specific properties, whose cohesion is ensured, before or during the installation of refractory hnings, by an appropriate binder. Added to these different constituents is an additional phase constituted by porosity (open or closed) of the product which greatly contributes to fixing the properties of the material. This design definition can be considered as universal with the exception of electrofused refractories (see section 10.2.4). 

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