Wire screens

Fast catalytic reac tions that must be quenched rapidly are done in contac t with wire screens or thin layers of fine granules. Ammonia in a 10% concentration in air is oxidized by flowthrough a fine gauze catalyst made of 2 to 10% Rh in Pt, 10 to 30 layers, 0.075-mm (0.0030-in) diameter wire. Contact time is 0.0003 s at 750°C (1,382°F) and 7 atm (103 psi) followed by rapid quenching. Methanol is oxidized to formaldehyde in a thin layer of finely divided silver or a multilayer screen, with a contact time of 0.01 s at 450 to 600°C (842 to 1,112°F). 

Permissible corrosion rates are an important factor and differ with equipment. Appreciable corrosion can be permitted for tanks and hnes if anticipated and allowed for in design thickness, but essentially no corrosion can be permitted in fine-mesh wire screens, orfices, and other items in which small changes in dimensions are critical. 

In applications where the filter aid layer is to be formed on open-weave synthetic fabric or wire screens, wider size distributions may have to be... 

Pulp and Paper Technical Association of Canada - Standards of Sulphite Waste Liquor, C-3, Jan. 68. Viscosity of Sulphite Waste Liquor, C-4,Jan. 68. F-2, Nov. 70. Wire Screening, F-3, July 92. Alum Solutions, F-4, Jan. 68, http //WWW. paptac.ca/english/engdatsh.htm. 

The only available test data [44] indicate that the plain flat plate (26-45% free area) has a decided detrimental effect on the allowable flooding conditions of the tower whereas the wire screen, weir-type, and fused Raschig ring designs have very little effect when using Intalox saddles for packing. 

A = Wire Screen, also Weir-Type(Steel)... 

Wire Screen Plate =92% Free Space with 3/8 Squore Openings... 

Simple strainers remove gross materials. These should not normally occur in public supply, but strainers are sometimes fitted to protect sensitive equipment or processes against breaks in the main, etc. The commonest form contains a stainless-steel wedge wire screen and is piped with a bypass so that the screen element can be isolated and removed for cleaning when necessary. If the load on the filter makes this kind of cleaning burdensome a self-flushing filter can be used. These can incorporate strainer elements down to 50 pm. 

In a series of experiments, the radical concentrations are varied by attenuating the light intensity, with wire screens for example. One then makes a plot of 1/[R2 ] versus [R2 ]/lR ]. The result is a straight line with an intercept of 2k,2/kc and a slope of... 

The packing itself may consist of spherical, cylindrical, or randomly shaped pellets, wire screens or gauzes, crushed particles, or a variety of other physical configurations. The particles usually are 0.25 to 1.0 cm in diameter. The structure of the catalyst pellets is such that the internal surface area far exceeds the superficial (external) surface area, so that the contact area is, in principle, independent of pellet size. To make effective use of the internal surface area, one must use a pellet size that minimizes diffusional resistance within the catalyst pellet but that also gives rise to an appropriate pressure drop across the catalyst bed. Some considerations which are important in the handling and use of catalysts for fixed bed operation in industrial situations are discussed in the Catalyst Handbook (1). 

Holub, R.F. and E.O. Knutson, Measurement of 21 Po Diffusion Coefficient Spectra Using Multiple Wire Screens, this volume (1987). 

Measuring Polonium-218 Diffusion-Coefficient Spectra Using Multiple Wire Screens... 

Following Barry, James et al (1972), and Thomas and Hinchliffe (1972) investigated the use of wire screens for collecting 218Po atoms or ions. Experiments were done in the absense of aerosol particles, yielding collection efficiency as a function of screen dimensions and face velocity. Information was developed on the fraction of deposited o-activity that could be counted from the front and back sides of the screens. 

In 1975 there was a new development in the use of wire screens Sinclair and Hoopes (1975) described a diffusion battery (for measuring the particle size of aerosols) made of very fine 635-mesh stainless steel screen. An empirical equation was developed for the collection efficiency. This diffusion battery has become one of the standard techniques in aerosol measurements. Later, Sinclair et al (1978) described a screen diffusion battery configuration suited for measuring the activity - weighted size distribution of radon daughter aerosols. 

Cheng and Yeh (1980) greatly facilitated the use of wire screens by showing that a theory developed for fiber filters also worked for predicting aerosol penetration through 635-mesh wire screens. The equation is ... 

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