Particulate solids porosity

The bulk density of particulate solids increases by compaction. Dilation, mentioned earlier, occurs only in the presence of a free surface, which allows for a loosening of the packing arrangements of the particles. The increase in density, or decrease in porosity, seems to follow an exponential relationship with the applied pressure (38,39)... 

Mg is the mass of the bridge building material and Mp the mass of the agglomerate building particulate solids, pg and Pp are the densities of the respective solid materials, 1 - s is the relative volume of the particulate solids building the agglomerate, e is the specific void volume (porosity) of the agglomerate, and is the fraction of voids in the... 

The mechanism of densification of particulate solids (Fig. 6.6) includes, as a first step, a forced rearrangement of particles requiring little pressure followed by a steep pressure rise causing brittle particles to break and malleable ones to deform plastically. During the entire process, porosity decreases so that fluids which originally occupied the pore space of the bulk feed must be able to escape and the initial elastic deformation must have sufficient time to either cause breakage or convert into plastic deformation (see also Section 8.1). These requirements limit the speed of densification and, therefore, the production capacity. 

If the mechanism of densification is considered (refer to the sketches in the upper part of Fig. 8.1), it becomes clear that the pores in the feed for a pressure agglomeration process of any kind must not be filled completely (saturated) with a liquid. An example of such a material would be a normal filter cake, i.e. one that has not been blown dry or otherwise further dewatered. Since liquids are incompressible, the pressing force would increase quickly and mechanical dewatering would have to occur, which further reduces the speed of densification. It would also require an effective separation of solids and liquid during the densification process this is a task which, so far, has not been solved satisfactorily. Therefore, with increasing pressure applied to the particulate solids, which typically results in higher densification or lower porosity, the moisture content of the feed must diminish. In high-pressure a lomeration the feed must be essentially dry ... 

Pneumatic conveying is a common method for transportation of particulate solids within or between processing plants. Particles are mobilized commonly using air and transported inside pipes or ducts. To attain a consistent flow of particles, particle mobilization and fluid pressure drop should be understood in detail. Stationary particles and excessive pressure drop could halt the flow. Figure 7.35 shows a study by Kuang et al. [84] on particle-gas behavior in a horizontal pipe with a view to investigate particle porosity and velocity distribution as well as gas pressure drop. 

Finally, a number of useful definitions of quantities directly or indirectly involved in the study of the surface area and porosity of both particulate and massive solids are given in Table 1.6. 

The small particles are reported to be very harmful for human health [98]. To remove particulate emissions from diesel engines, diesel particulate filters (DPF) are used. Filter systems can be metallic and ceramic with a large number of parallel channels. In applications to passenger cars, only ceramic filters are used. The channels in the filter are alternatively open and closed. Consequently, the exhaust gas is forced to flow through the porous walls of the honeycomb structure. The solid particles are deposited in the pores. Depending on the porosity of the filter material, these filters can attain filtration efficiencies up to 97%. The soot deposits in the particulate filter induce a steady rise in flow resistance. For this reason, the particulate filter must be regenerated at certain intervals, which can be achieved in the passive or active process [46]. 

The difference between IGC and conventional analytical gas-solid chromatography is the adsorption of a known adsorptive mobile phase (vapour) on an unknown adsorbent stationary phase (solid state sample). Depending on experiment setup, IGC can be used at finite or infinite dilution concentrations of the adsorptive mobile phase. The latter method is excellent for the determination of surface energetics and heat of sorption of particulate materials [3]. With IGC at finite dilution, it is possible to measure sorption isotherms for the determination of surface area and porosity [4], The benefits of using dynamic techniques are faster equilibrium times at ambient temperatures. 

Common membrane processes include ultrafiltration (UF), reverse osmosis (RO), electro dialysis (ED), and electro dialysis reversal (EDR). These processes (with the exception of UF) remove most ions RO and UF systems also provide efficient removal of nonionized organics and particulates. Because UF membrane porosity is too large for ion rejection, the UF process is used to remove contaminants, such as oil and grease, and suspended solids. 

The amount of liquid added to the dry particulate matter also influences pellet shape. As shown by Bhrany et a critical moisture exists for each material which depends on particle size and distribution, porosity and surface roughness, or, more generally, the specific surface of the powder, and the wettability of the solid(s) by the liquid. It can be determined experimentally according to proposals of Hainesand Jimeniz and increases with decreasing particle size (see also Section 3.2.3 and Figure 59). 

Mass and heat transfer during fermentation are very important but hard to describe. For mycelial microbes such as T. reesei, the increase in biomass is contributed by tip extension and branching and mycehal pellets are formed. The size, porosity and density of the particulate soHd substrate will change after consumption. The mechanism of the interaction between microbes and solid substrate is not yet fully understood. Therefore, various simplification assumptions must be made to represent the sohd-state fermentation processes. 

Colomer, M.T., and Anderson, M.A. 2001. High porosity silica xerogels prepared by a particulate sol-gel route Pore structure and proton conductivity. Journal of Non-Crystalline Solids 290, 93-104. 

The sol-gel method is widely used to obtain oxide layers on the walls of microchannels. This method is advantageous because a large variety of compositions can be produced, and porosity and surface texture can be tailored. The sol-gel method is also used for the preparation of particulate porous catalytic supports [155,201,202], The colloidal metal oxide sols can be prepared by various methods such as reactions of metal salts with water or by hydrolysis and polycondensation of metal alkoxides. The latter is the most versatile procedure and has been investigated extensively. Often the sol contains varying concentrations of solid particles, and the procedure is no longer a sol-gel but rather a hybrid method, with the coating medium being a mixture between a sol and a suspension (Table 3). 

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