Mesh types

To resolve the problems associated with structured and unstructured grids, these fundamentally different approaches may be combined to generate mesh types which partially posses the properties of both categories. This gives rise to block-structured , overset and hybrid mesh types which under certain conditions may lead to more efficient simulations than the either class of purely structured or unstructured grids. Detailed discussions related to the properties of these classes of computational grid.s can be found in specialized textbooks (e.g, see Liseikin, 1999) and only brief definitions are given here. 

Fig. 4. Configurations of mercury chlorine ceU anodes (a) blade type (b) mnner technology (c) rod type and (d) mesh type.

The woven wire mesh type are formed to control the open space between the wires, thereby limiting the maximum size particle that can pass through. The cartridge is installed in cases or small vessels to facilitate quick replacement, or they can be arranged for backwash by use of proper piping connections. The wire wound units have consistent spaces for uniform particle size filtering. 

The materials of construction are usually stainless steel as well as specific other metals that will draw into wire, or crimp without cracking. The wire mesh types have been fabricated of some plastics such as Teflon , polypropylene, etc. however, the surface must be wettable by the liquid, or the efficiency will be poor, and performance data are needed to complete a good design. 

For structured packings as loadings increase, HETP increases, and is more pronounced for wire-mesh types, and the effect is less for the corrugated sheet packings [90]. 

Chart, 204, 205, 207 Vortex, 190 Water hammer, 98 Wire mesh separators, 246, 247 Calculations, 247-254 Efficiency, 248, 250 Installation, 251-253 k-value for mesh, table, 249 Mesh patterns, 247 Pressure drop, 249, 251 Specifications form, 254 Vapor velocity, 247, 250 Wire mesh types, 248... 

The amount of hardness deposits in steam is a function of entrainment of water, as well as the TDS of the boiler feedwater. A well-designed boiler, then, often is equipped with a mesh-type demister pad to remove entrainment from the produced steam. 

An excimer lamp has dual quartz-tube structure, where a metal electrode is set at the inner side of the inner tube, and a mesh-type metal electrode is placed at the outside of the outer tube as shown in Fig. 5. When we apply ac high voltage between two electrodes, the dielectric barrier discharge ignites between two dielectric materials, and reaches an excimer state instantaneously by the excitation of atoms of a filling gas. Then the excimer light is emitted by the... 

Fig. 24. Composite LEED pattern for the FeCrNi(lll) surface exposed to electrolytes and annealed. Type 1 integral-index beams due to alloy. Type 2 pattern-of-twelve beams due to square CrO mesh. Type 3 beams due to initial growth phase of oxide with (2 x 2) local structure in (11 x 11) domains. Type 4 beams due to Cr203(001) film. The alloy contained Fe (70at.%), Cr (18at.%), and Ni (12at.%). Reprinted from ref. 54.

To investigate the role of heat transfer in OMD and measure the asymptotic temperature difference, Celere and Gostoh [86] used the flat sheet membrane module shown in Figure 19.15. This contains a few flat sheet membranes placed 1 mm apart and supported by mesh-type spacers of 2 mm thickness, leaning against polypropylene walls. One stream (feed) flows between the membranes and other (extractant) flows cocurrently through the spacers. The mass transfer zone of each membrane is 80 mm in breadth and 200 mm in length. 

To illustrate the effect on Prox performance by changing the substrate from a monolith to an SCT, Figure 7.10 shows the conversion versus selectivity for the exact same Pt/y-Al203 formulation. The SCT reactor was a woven mesh type where a number of interlaced wires are woven together to form a screen. The wire diameters were 0.003 in. and made of Inconel. The monolithic reactor was constructed of 400 cells in. 2 with a foil thickness of 0.003 in. and 0.3-in. thick. The material was made from Hastelloy-X, which is a high-temperature metal alloy. The catalyst formulation was identical on both reactors with a nominal loading per piece of 0.5244 g or 178.1 mg/in. 3. 

Electron micrographs are taken on a Zeiss EM IOC apparatus. Copper grids (3.05 mm diameter 200 mesh Type G200-Cu) were from EMS (Aurion, Wageningen, The Netherlands). Uranyl acetate (UCB, Belgium) is used as a negative stain. 

For very complex geometries, meshing can be simplified by subdividing the flow domain into different volumetric zones that can be meshed independently, choosing the best mesh type for that particular zone. The meshes for the different zones then can be combined into one mesh, usually called a multiblock mesh. When combining the meshes for the different zones, the cells and the nodes at the shared faces do not necessarily have to be lined up exactly. Multiblock meshes are called conformal meshes when the nodes at the shared faces do line up, and when they do not line up they are called nonconformal meshes. 

In the spiral wire mesh type, the edges of the wire scrape against the sides of the column. This causes a thin film of liquid to form on the side wall and, in addition, increases the surface area considerably as the wires move across it. The wire is spun so as to throw the vapors back down into the column. If spun the opposite way, it can suck the system dry in a few minutes. The spinning spiral band operates in the same manner. These are expensive columns, but they have a low holdup and a high throughput. 

Typically, an internal demister in the intertray space is about 2 in thick and contains wire mesh. Attention must be paid to correctly specifying the mesh type, size, and materials. In a refinery vacuum column, it is also important to keep the mesh wet (eg, by spraying wash oil above the demister) in order to inhibit coking. AVhen the service has a high plugging tendency, chevrons rather than wire-mesh may be the best demister choice (270). 

Fractions 3 and 4 from the Sephadex column, which contained primarily nonpolar polycyclic aromatic compounds, were combined and then subfractionated on a column of silica gel. The silica (Sigma Chemical Co., 60-200 mesh type I chromatographic grade) gel was activated at 110 C for 1 hr and placed in the column (30 cm X 2 cm I.D.) as a slurry in toluene. Combined Fractions 3 and 4 (200 mg) were placed on the column in 5 ml of toluene and eluted sequentially with 115 mL of toluene (subfraction A), 110 mL of propanol (Subfraction B) and 300 mL of methanol (Subtraction C). When Fractions 3 and 4 were subfractionated separately 1 1 toluene n-propanol (V V) was used in place of propanol. For a filter sample Fractions 1 and 2 were also separated on the silica gel column. 

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