Permeability, packed bed

From the standpoint of the user, reproducible averages are desirable. For example, the pack -bed permeability depends on the square of the particle size. Therefore a 10% shift in the average particle size would result in a 20% change in column backpressure. Such a large difference is unacceptable. Figure 4.3 shows the particle size distribution of several batches of Symmetry silica. One can see that today s sizing techniques can give quite reproducible results. 

Filtration is the concentration of solids (or clarification of liquor) from slurry by fluid flow through a permeable medium. This normally takes the form of a membrane, filter leaf or packed bed, which restricts the particles, more than the fluid (Figure 4.4). 

The fastest HPLC separations are achieved using the maximum available pressure drop. Using reduced variables, Equation 9.6 illustrates a linear relationship between retention time and mobile phase viscosity for packed columns and fixed values of AP (pressure drop), Areq (required efficiency for a given separation) and (a constant that describes the permeability of the packed bed) [4]... 

Researchers at Lehigh University have investigated the ability of ground tire rubber to sorb organic compounds such as benzene, toluene, ethylbenzene, and xylene (BTEX) to determine the feasibility of using the rubber as the sorbent media in reactive permeable barrier systems. Thus far, no field-scale work has been performed on this technology. Both batch and packed-bed column tests have been conducted. All information is from the researchers and has not been independently verified. 

Apatite, a natural calcium fluoride phosphate, can adsorb low to moderate levels of dissolved metals from soils, groundwater, and waste streams. Metals naturally chemically bind to the apatite, forming extremely stable phosphate phases of metal-substituted apatite minerals. This natural process is used by UFA Ventures, Inc., and is called phosphate-induced metals stabilization (PIMS). The PIMS material can by used in a packed bed, mixed with the contaminated media, or used as a permeable barrier. The material may be left in place, disposed of, or reused. It requires no further treatment or stabilization. Research is currently being conducted on using apatite to remediate soil and groundwater contaminated with heavy metals, and the technology may also be applicable to radionuclides. The technology is not yet commercially available. 

The use of hydrothermally formed retaining frits in capillary columns packed with stationary phase particles is an accepted limitation in CEC. The introduction of the frit to hold the packed bed is vital, yet introduces problems such as EOF and flow non-uniformities, compromised frit permeability [87], capillary fragility, increased likelihood of bubble formation [88] and a thermally induced modified frit surface chemistry which can detrimentally alter the chromatography [23]. Practical aspects to be considered include the appreciable effort and skill of the analyst who is required to repeatably manufacture capillaries of a particular phase and redevelop the fritting and packing methodology for each different stationary phase type. 

In CEC, the EOF depends on the column packing structure and pore size of the packing material [51,111-116]. In a packed bed, there are many interconnected channels between particles, which leads to a porous packed structure. The porosity of the packed bed dictates the permeability through the column. The average channel size between particles in a CEC column can be estimated if the packed bed is assumed a... 

The last ten years have witnessed a number of extensive field tests of underground coal gasification (UCG) in the United States and Europe. Model development is essential to the proper understanding of these test results and to the planning of future experiments. This report will focus upon the steady-state "permeation" or "packed bed" model of in situ gasification (forward combustion mode). In this useful but idealistic model the coal bed is assumed to be uniformly permeable to reactant and product gases. 

If flow is the dominant mechanism bringing a velocity bias to an end, then S will be the average length of the channel having a consistently higher or lower than average permeability, ultimately responsible for that bias. Channel lengths, like other distances in the packed bed, are scaled to particle diameter dp. Thus the S value based on a flow mechanism is proportional to... 

Weiland [42] used a similar idea but based on the Blaine permeability method. An automatic weigher produced a packed bed of powder, of known voidage, in a standard cell. Air was drawn through the bed by the passage of water from one reservoir to another. After a certain volume of air had passed through the bed, measured by a certain volume of water flowing, the time required was converted to an electrical proportionality... 

Coke deposits arc not limited to the catalysts. The membranes, in the case of packed bed catalysts, arc also subject to the adverse effects of carbonaceous deposits leading to possible reduction in the membrane permeability. Catalytic membranes such as Pd-based... 

Packed beds, 117-119 fiiction factor, 117 permeability, 117 porosity, 177... 

In the less turbulent flow through the straight channel of a monolith, momentum transfer from the fluid to the wall is less effective and in the case of two-phase, countercurrent annular flow, momentum transfer between gas and liquid will also be less than in the interstitial channels of a packed bed. The lower rates of momentum transfer, which is the reason for the higher permeability of monoliths, should in principle improve the possibility for achieving countercurrent flow of gas and liquid at realistic velocities. 

Complete model, including heat and mass transfer differential balances in the packed bed. Constant hydrogen permeability across the membrane. 

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