Porous wall

Fibers spun by this method may be isotropic or asymmetric, with dense or porous walls, depending on the dope composition. An isotropic porous membrane results from spinning solutions at the point of incipient gelation. The dope mixture comprises a polymer, a solvent, and a nonsolvent, which are spun into an evaporative column. Because of the rapid evaporation of the solvent component, the spinning dope solidifies almost immediately upon emergence from the spinneret in contact with the gas phase. The amount of time between the solution s exit from the spinneret and its entrance into the coagulation bath has been found to be a critical variable. Asymmetric fibers result from an inherently more compatible solvent/nonsolvent composition, ie, a composition containing lower nonsolvent concentrations. The nature of the exterior skin (dense or porous) of the fiber is also controlled by the dope composition. 

In 1981, a novel flotation device known as the air-sparged hydrocyclone, shown in Figure 3, was developed (16). In this equipment, a thin film and swid flotation is accompHshed in a centrifugal field, where air sparges through a porous wall. Because of the enhanced hydrodynamic condition, separation of fine hydrophobic particles can be readily accompHshed. Also, retention times can be reduced to a matter of seconds. Thus, this device provides up to 200 times the throughput of conventional flotation cells at similar yields and product quaHties. 

Fig. 3. Air-sparged hydrocyclone, where A represents the tangential feed that estabHshes swid flow B, the area of small bubbles formed by high shear at the porous wall and C, the outlet for the (D) hydrophilic particles rejected by the swid flow. The (B) hydrophobic particles are in the axial froth flow.

Transpiration Cooling Cooling by this method requires the coolant flow to pass through the porous wall of the blade material. The heat transfer is directly between the coolant and the hot gas. Transpiration cooling is effective at very high temperatures, since it covers the entire blade with coolant flow. This method has been used rarely due to high costs. 

Cooling by this method requires the coolant flow to pass through the porous wall of the blade material. The heat transfer is directly between the... 

A hollow-fiber reverse-osmosis module consists of a shell which houses the hollow fibers (Fig. 11.3). The fibers are grouped together in a bundle with one end sealed and the other open to the atmosphere. The open ends of the fibers are potted into Ml epoxy sealing head plate after which the permeate is collected. The pressurized feed solution (denoted by the shell side fluid) flows radially from a central porous tubular distributor. As the feed solution flows around the outer side of the fibers toward the shell perimeter, the permeate solution penetrates through the fiber wall into the bore side by virtue of reverse osmosis. The permeate is collected at the open ends of the fibers. The reject solution is collected at the porous wall of the shell. 

As Cu2+ ions are reduced, the solution at the cathode becomes negatively charged and the solution at the anode begins to develop a positive charge as the additional Zn2+ ions enter the solution. To prevent this charge buildup, which would quickly stop the flow of electrons, the two solutions are in contact through a porous wall ions provided by the electrolyte solutions move between the two compartments and complete the electrical circuit. 

Example of the failure of the cellular structure at the passage from solid walls to porous walls in the detonation of C2H2 + 2.5O2 mixture at 2.6kPa initial pressure. (Reprinted from Radulescu, M.I. and Lee, Combust. Flame, 131,29,2002. With permission.)... 

M.I. Radulescu and J.H.S. Lee, The failure mechanism of gaseous detonations Experiments in porous wall tubes. Combust. Rame, 131, 29-46,2002. 

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]. 

Reactor performance with porous catalyst particles and porous walls that are catalyst coated... 

Careful sealing of the floor-to-wall joints and of the ground floor walls was unsuccessful in reducing pressure-driven flow of radon from the subsoil. This merely diverted the flow of radon up through the internal walls of the dwelling and into upstairs rooms. The problem arose in this old dwelling because it has very porous walls and no damp proof course, thus allowing radon to by-pass the sealed floor. Incorporation of a passive radon barrier into the floor of a modern house with less porous walls is likely to be effective. 

FIG. 17-56 Typical porous wall tube array diesel particulate filter. 

Formation of Porous Wall Hollow Glass Spheres... 

ENCAPSULATION OF PALLADIUM IN POROUS WALL HOLLOW GLASS MICROSPHERES... 

The experimental work involved two parts. The first part was to produce porous wall hollow glass microspheres. The second part was to fill the PWHGMs with palladium. 

Encapsulation of Palladium in Porous Wall Hollow Glass Microspheres... 

The HGMs produced were heat treated at 620 °C for 18 hours before they were leached in 4 molar HC1 solutions at 80 "C for 4 hours. Heat treatment produced phase separation which resulted in a silica-rich phase and a more soluble and interconnected, sodium borate phase. Leaching removed the soluble sodium borate phase of the glass and created porosity through the microsphere walls. The porous wall, hollow glass microspheres, sank to the bottom of the solution. These sinkers were collected, water washed and dried at 100 °C overnight. 

The porous wall hollow glass microspheres were filled with palladium by a soak-and-dry process followed by hydrogen reduction. Saturated solutions of palladium salt were prepared at room... 

Dope Preparation. A porous wall substrate fiber is prepared by the extrusion of a quasi-solution, the principal component of... 

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