Sintered nozzles

A 2 IB. Braun airlift fermenter with a working volume of about 2000 ml was used. Sterile air is sparged through a sintered plate located near the bottom of the central concentric tube. There was no mechanical stirring only the air nozzle was forced through the centred tube and the flow directed to the annulus tube side. Aeration causes circulation of media the flow is gentle without serious shear forces. The temperature is maintained at 26 °C. 

A schematic diagram of the experimental apparatus is shown in Fig. 1. A rotating fluidized bed composes of a plenum chamber and a porous cylindrical air distributor (ID400xD100mm) made of stainless sintered mesh with 20(xm openings [2-3]. The horizontal cylinder (air distributor) rotates around its axis of symmetry inside the plenum chamber. There is a stationary cylindrical filter (ID140xD100mm, 20(o.m openings) inside the air distributor to retain elutriated fine particle. A binary spray nozzle moimted on the metal filter sprays binder mist into the particle bed. A pulse air-jet nozzle is also placed inside the filter, which cleans up the filter surface in order to prevent clogging. 

In electrostatic atomization, an electrical potential is applied between a liquid to be atomized and an electrode placed in the spray at a certain distance from liquid discharge nozzle. As a result of the mutual repulsion of like charges accumulated on the liquid surface, the surface becomes unstable and disrupts when the pressure due to the electrostatic forces exceeds the surface tension forces of the liquid. Droplets will be generated continuously if the electrical potential is maintained above a critical value consistent with liquid flow rate. Both DC and AC systems have been employed to provide high electrical potentials for generating fine droplets. Many configurations of electrode have been developed, such as hypodermic needles, sintered bronze filters, and cones. 

A plasma spray can therefore be used to apply sintered coatings to substrates which would normally be adversely affected by the sintering temperature of the coating. However, the powders carried by the plasma are exposed to greater thermal stress than the substrate, and some experimenting with specific powders is usually necessary to define the best application conditions. Where molybdenum disulphide in a metal, resin or ceramic binder is applied by this technique, the optimum conditions will usually be different for the two materials. This difficulty has been overcome by the use of two separate entry ports into the nozzle for the two components. The use of this technique has even been applied to molybdenum disulphide in a polyethylene binder. 

The foundry technology does not admit the manufacture of dimensionally precise products of complex shapes. For this reason, sintered basalt technology has been developed for the manufacture of nozzles, drawing dies, dies for auger brick machines, etc., where the materials exhibit a resistance to abrasion still higher than that of cast basalt. The fused basalt powder is mixed with a plasticiser and pressed the pressings are sintered in an electric tunnel kiln at 1120 to 1140 C. 

Spherical fuel particles are produced by the wet chemical sol-gel process" " , which consists of spraying an aqueous solution or a hydrosol of salts of the fissile and/or fertile materials through nozzles into spherical droplets. Homogeneous mixed oxides are prepared by coprecipitation. The droplets are gelled by either internal precipitation or dehydration, then washed and aged, and heat treated to dry and sinter to produce high density spherical particles (Fig. 9) . 

The target quantity of the gassing process is the absorption rate in the gas/liquid (G/L) system. It is directly proportional to the interfacial area between the gas phase and the liquid phase. The limiting factor is the diffusion of the dissolved gas through the liquid-side of the boundary layer, which can only be affected by its thickness to a limited extent. A substantial intensification of mass transfer is only possible by increasing the G/L interfacial area gas sparging by means of stirrers, nozzles, sintered or perforated plates etc. should therefore effect a dispersion of the gas into fine bubbles. 

Sintered glass or ceramic plates and perforated metal plates are classical gas spargers (dispersers) for bubble columns. Static mixers and nozzles became available with the emergence of biological waste water purification. They all realize gas... 

In the spray calciner, liquid waste is pumped to a nozzle at the top of the calciner where it is atomized by pressurized air, producing droplets with diameters less than 70 irni that are dried and calcined in-fli t in the 700 C-wall-temperature spray chamber. Sintered stainless steel dust filters collect a portion of the powder with a mean diameter of 10 fjm. They are periodically cleaned by a reverse pulse of air. Calcine from the spray chambers and filters drops directly into the melting canister. Frit is fed to the cone of the calciner. 

Silicon Nitride, Si3N4 mw 140.31 grey-white amorph powd mp 1900 (sublimes) d 3.44g/cc. Sol in HF acid. Prepn is by reaction of powd Si and nitrogen in an electric furnace (Refs 1, 37 and 38). Si nitride is used as an ablative material in rocket nozzles (Ref 37) the material fabricated by a reaction sintering process is used in radome applications (Ref 24) and a current usage in expls involves those containing electrically conductive compds. For these compns the patent of Harris and Martin (Ref 33) suggests that the incorporation of 5—20% of the nitride raises the electrical power dissipation threshold of the expl compn and improves its resistance to radiofrequency hazards... 

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