Permeability of porous solids

The darcy is a unit for expressing the permeability of porous solids, not area. 

Note—the centigrade temperature scale is obsolete. The unit, degree centigrade, is only approximately equal to the degree Celsius The darcy is a unit for measuring permeability of porous solids This is sometimes called the moment of section or area moment of inertia of a plane section about a specified axis... 

Millington, R.J. and Quirk, J.M. 1961. Permeability of porous solids. Transactions of the... 

MODEL STUDY OF THE COMBINED EFFECT OF BETEROPOROSITY OP MACROSCOPIC HETEROGENEITY GAS RELATIVE PERMEABILITY OF POROUS SOLIDS... 

In previous work [1-4] it was shown that the relative permeability of porous solids is an important source of information about their pore structure. For the simulation of the pore structure, a network model has been employed, consisting of a regular array of nodes joined together by cylindrical capillaries of randomly varying radius r. The model is completely characterized by the capillary radius probability distribution f(r) and the connectivity of the network, nrji, given by the number of capillaries meeting at each node. 

N.K.Kanellopoulos, J.H.Pet.ropoulos and D.Nicholson,Effect of Fore Structure and Macroscopic Non-homogeneity on the Relative Gas permeability of Porous Solids, J.Chem.Soc., Faraday Trans. 1, 81 (1985) 1183... 

This paper reports an investigation of the effects of porous solid structures on their electrical behaviour at different frequencies (from 100 Hz to 100 kHz). For that, we study different parameters such as formation resistivity factor, cementation factor, chargeability, resistivity index and saturation exponent. Different porous solid structures are quantified from the petrographic image analysis and Hg-injection technique. Then, by using different models we obtain the permeability prediction from the electrical behaviour and structure parameters. 

Two models were tested to predict the permeability from the electrical behaviour and microstructure parameters of porous solids. 

Chargeability factor M depends on the brine/gas saturation of porous solids. Figure 3 gives the relationship between the chargeability and brine saturation for two samples. We noted that the M decreases hardly with the decrease of the brine saturation. The presence of vugs and karsts pore types (sample 9-LS8) seems to speed up the decrease of the M Chargeability factor M can be explained by a multi-linear model composed of different structures parameters such as the formation resistivity factor, water porosity, Hg-specific surface area and water permeability, e.g.. Fig. 5. 

Carman-Kozeny equation Asemi-empirical relationship irsed to determine the pressure drop through a packed bed of solids and permeability of porous media as ... 

In the diaphragm-cell process, a solid cathode (iron) is used where hydrogen is evolved [reaction (15.4)]. Porous asbestos diaphragms are used to prevent mixing of the catholyte and anolyte, but owing to the finite permeability of these diaphragms, the alkaline solution that is produced near the cathode stiU contains important levels of chloride ions as an impurity. 

The functions of porous electrodes in fuel cells are 1) to provide a surface site where gas/liquid ionization or de-ionization reactions can take place, 2) to conduct ions away from or into the three-phase interface once they are formed (so an electrode must be made of materials that have good electrical conductance), and 3) to provide a physical barrier that separates the bulk gas phase and the electrolyte. A corollary of Item 1 is that, in order to increase the rates of reactions, the electrode material should be catalytic as well as conductive, porous rather than solid. The catalytic function of electrodes is more important in lower temperature fuel cells and less so in high-temperature fuel cells because ionization reaction rates increase with temperature. It is also a corollary that the porous electrodes must be permeable to both electrolyte and gases, but not such that the media can be easily "flooded" by the electrolyte or "dried" by the gases in a one-sided manner (see latter part of next section). 

Suzuki, F., K. Onozato and Y. Kurokawa. 1987. Gas permeability of a porous alumina membrane prepared by the sol-gel process. J. Non-Cryst. Solids 94 160-62. 

Both ends of a number of parallel membrane tubes or porous solid tubes lined with permeable membranes are connected Lo common header rooms. One ofthe two headers serves as the entrance of the feed, while the other header serves as the outlet for the retentate. The permeate is collected in the shell enclosing the tube bundle. 

Another approach to radiation loss reduction might be the alteration of the salt water surface in some manner to lower its emissivity for thermal radiation. If a transparent thin liquid film or porous solid film of low thermal emissivity, permeable to water vapor, could be floated on the salt water, solar energy could continue to be absorbed on the basin bottom, water would vaporize, but thermal radiation loss would be reduced. Whether materials with these properties can be found and successfully utilized remains to be seen. 

Preparation of test specimens from solid samples invariably requires a portion of the sample to be cut out, for example, from the middle of the original roll or sheet of material. Freshly cut edges are notoriously high emissions sources and failure to adequately seal these and exclude them from the test is a major potential source of error. (Another advantage of emission test cells versus conventional chambers is that they automatically exclude any potential edge effects in most cases.) Similarly, surface emissions testing requires the rear surface of the material (the surface that will not be exposed once the product is installed in a building) to be sealed and excluded from the test. This is always a consideration for emission test chambers but can be an issue for both cells and chambers in the case of porous or permeable materials. 

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