Stacked screening

The determination of the activity size distribution of the ultrafine ions is of particular interest due to their influence on the movement and deposition of Po-218. These ultrafine ions are the result of radiolysis and their rate of formation is a function of radon concentration, the energy associated with the recoil path of Po-218, and the presence of H O vapor and trace gases such as S02 a joint series of experiments utilizing a mobility analyzer, the separate single screen method, and the stacked screen method were conducted to examine the activity size distribution of the ultrafine mode. 

Briquettes must be transported carefliny to avoid breakage. They ate usually dumped into piles in sheds and frequently ate screened to remove smaller broken particles. Hand-stacking significantly improves storage quaHty, and permits mote material to be stored in a limited volume. 

Screening. A 100-g sample of mica is usually used for this test, plus a rack of six Tyler sieves and a pan. The stack of sieves containing the sample is rotated, and after screening, the mica remaining on each screen is weighed and the percentage retained is calculated. A combination of wet and dry screening may also be used to determine particle size distribution of fine mica (<0.147 mm ( — 100 mesh)). 

For non-Newtonian fluids in slow flow, friclion loss across a square-woven or fuU-twill-woven screen can be estimated by considering the screen as a set of parallel tubes, each of diameter equal to the average minimal opening between achacent wires, and length twice the diameter, without entrance effects (Carley and Smith, Polym. Eng. Set., 18, 408-415 [1978]). For screen stacks, the losses of individual screens should be summed. 

Trays may be square or rectangular, with 0.5 to I m" per tray, and may be fabricated from any material compatible with corrosion and temperature conditions. When the trays are stacked in the truck, there should be a clearance of not less than 4 cm between the material in one tray and the bottom of the tray immediately above. When material characteristics and handling permit, the trays should have screen bottoms for additional diying area. Metal trays are preferable to nonmetalhc trays, since they conduct heat more readily. Tray loadings range usually from I to 10 cm deep. 

Ptdp) filtei. s. These filters employ one or more packs of filtermasse (cellulose fibers compressed to a compact cylinder) stacked into a pressure case. The packs are sometimes supported in individual trays which provide drainage channels and sometimes rest on one another with a loose spacer plate between each two packs and with a drainage screen buried in the center of each pack. The liquid being clarified flows under a pressure of 345 kPa (50 psig) or less through the pulp packs and into a drainage manifold. Flow rates are somewhat less than for disk filters, on the order of 20 L/(min-m ) [0.5 gal/ (min-ft")]. Pulp filters are used chiefly to polish beverages. The filtermasse may be washed in special washers and re-formed into new cakes. 

Figure 3.10 Final CAPRAtol screen for the solenoid tolerance stack design...

Figure 3.13 Data screen for solenoid tolerance stack redesign...

SCREEN can not explicitly determine maximum impacts from multiple sources, except for the procedure to handle multiple nearby stacks by merging emissions into a single "representative" stack. The reader is directed to the MPTER (Pierce and Turner, 1980) or ISC (EPA, 1995b) models on EPA s Support Center for Regulatory Air Models (SCRAM) Bulletin Board System (BBS) to model short-term impacts for multiple sources. With the... 

The SCREEN model uses free format to read the numerical input data, with the exception of the exit velocity/flow rate option. The default choice for this input is stack gas exit velocity, which SCREEN will read as free format. However, if the user precedes the input with the characters VF= in columns 1-3, then SCREEN will interpret the input as flow rate in actual cubic feet per minute (ACFM). Alternatively, if the user inputs the characters VM= in columns 1-3, then SCREEN will interpret the... 

In order to obtain results from SCREEN corresponding to the procedures for the simple elevated or flat terrain option, the user should select the full meteorology option, the automated distance array option, and, if applicable for the source, the simple elevated terrain option. The simple elevated terrain option would be used if the terrain rises above the stack base elevation but is less than the height of the physical stack. These, as well as the other options listed in the sidebar, are explained in more detail below. 

If more realistic stack parameters can be determined, then the estimate could alternatively be made with the point source option of SCREEN. In doing so, care should be taken to account for the vertical height of the flame in specifying the release height. Figure 12 shows an example for a flare release. 

The use of the methods of Briggs to estimate plume rise are relied on in the SCREEN model. Stack tip downwash is estimated following Briggs (1973, p.4) for all sources except those employing the Schulman-Scire downwash algorithm. Buoyancy flux for non-flare point sources is calculated from ... 

Inversion Break-up Fumigation - The inversion break-up screening calculations are based on procedures described in the Workbook of Atmospheric Dispersion Estimates (Turner, 1970). The distance to maximum fumigation is based on an estimate of the time required for the mixing layer to develop from the top of the stack to the top of the plume, using ... 

Shoreline Fumigation - For rural sources within 3000 m of a large body of water, maximum shoreline fumigation concentrations can be estimated by SCREEN. A stable onshore flow is assumed with stability class F (A0/AZ = 0.035 K/m) and stack height wind speed of 2.5 m/s. Similar to the inversion break-up fumigation case, the maximum ground-level shoreline fumigation concentration is assumed to occur where the top of the stable... 

Screen oriented, menu driven program that facilitates data editing, data analysis and preparation of reports for stack emissions. 

Normally the filter strueture consists of a stack of plates attached to a hollow shaft which are mounted inside a pressure vessel with eaeh plate eovered with a suitable filter medium. The slurry is fed under pressure into the vessel and the eake, which is retained by the filter medium, forms on the top of eaeh plate whilst the filtrate passes through the hollow shaft further to the proeess. Filter sizes may vary but generally the maximum is 60 m area and designed for a 6 bar operating pressure. Each circular plate in the staek is eonstructed with radial ribs that are welded to the bottom and support a horizontal eoarse mesh screen whieh is eovered with a fmer woven metal screen or filter cloth to retain the cake. The bottom of the plate slopes towards the hollow eentral shaft whieh lets the filtrate flow freely through circumferential holes and further down the shaft to the filtrate outlet. The elearanee between the plates is maintained by speeial spacers... 

During operation the slurry is pumped under pressure into a vessel that is fitted with a stack of vertical leaves that serve as filter elements. Each leaf has a centrally located neck at its bottom which is inserted into a manifold that collects the filtrate. The leaf is constructed with ribs on both sides to allow free flow of filtrate towards the neck and is covered with coarse mesh screens that support the finer woven metal screens or filter cloth that retain the cake. The space between the leaves may... 

Step 5. Cake Discharge - At this point the air pressure is released, the cake outlet is opened and the leaf stack is vibrated to discharge the cake. The cake outlet opening must be interlocked with a pressure sensor to avoid opening under pressure. On some filters the cloth or mesh screen may be backwashed with water after cake discharge to dislodge and remove any cake residue that adhered to the medium. 

The metallic catalyst support can be in form of chips, open-mesh and reinforced wire structures, and staggered layers of metal screens or saddles. In one design, screens woven from metallic wires 0.01 to 0.03 in. diam are placed in a deep stack. In another design, metal foils 0.004 in. thick are perforated and expanded to form a screen, which is then rolled into a cylinder. See Fig. 12. 

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