Choke section

The amount of material extracted from a flooded region by a screw feeder is mainly determined by the screw construction at the outlet end of the infeed region interface. The restraint offered by material in the clearance space between the flight tip and the casing as the screw leaves this region affects whether extra material is carried out by the boundary layer. This section of casing adjacent to the exit point of the screw from the supply hopper is termed the choke section . 

It should be noted that no screw form or length of choke section would prevent the escape of a fully fluidized material. Apart from the essential tip clearance space between the flight and the casing, there is also an unrestricted channel of flow around the helix form of the screw flight. This channel will allow the passage of a fluid-like bulk material, which is invariably under the pressure of a hydrostahc head if the material at the base of the stored contents is in a fluid state. It is quite impressive to witness a fine powder product squirting from any pinhole, crevice, or non-watertight... 

A choke section is then usually formed as part of the covers to restrain overcarry with the screw. This form of construction allows access to inspect the screw and the outlet port by cover removal, but introduces sealing requirements not called for with extended circular sections of casing. Casing thickness is normally not a difficult issue. There is no wear by movement of material on the contact surface, unless the product is fibrous or of such a nature as to scour the clearance layer as it moves along the screw axis. 

Finally, at the muzzle is the short choke section, which is responsible for shaping the shot pattern and helping separate the wad from the shot. Unless a shotgun is very old or is built for a specialized purpose, it will have replaceable, screw-in chokes. This allows you to give your shot pattern a different shape or a different length (called a shot string). 

The end of field life is often determined by the lowest reservoir pressure which can still overcome all the pressure drops described and provide production to the stock tank. As the reservoir pressure approaches this level, the abandonment conditions may be postponed by reducing some of the pressure drops, either by changing the choke and separator pressure drops as mentioned, or by introducing some form of artificial lift mechanism, as discussed in Section 9.7. 

First the core style and material should be selected. This is done in an identical fashion as the single-output filter choke. Either a mopermalloy (MPP) toroid (refer to Section 3.5.5) or a ferrite bobbin core (refer to Section 3.5.2)... 

More windings could be added to the mutually coupled filter choke core, but I highly recommend against this temptation. If the windings are not exact (to the turn), the supply will loose approximately 1 percent in efficiency for each turn in error on each output. Instead, use a mutually coupled filter choke for each complementary set of outputs, and use the output cross-sensing technique described in Section 3.9. 

Designing the output filter choke La) in a forward-mode converter is done first. This simple procedure can be seen in Section 3.5.5. A key design factor is to design the inductor to operate in the continuous current mode. The typical value of peak inductor current is 150 percent of the rated output current. The typical valley (minimum) current is about 50 percent of the rated output current. 

Critical and Subcritical Flow - The maximum vapor flow through a restriction, such as the nozzle or orifice of a pressure relief valve, will occur when conditions are such that the velocity through the smallest cross-sectional flow area equals the speed of sound in that vapor. This condition is referred to as "critical flow" or "choked flow . 

Other incidents due to trapped pressure and clearing chokes are described in Sections 17.1 and 17.2. 

Several other things were wrong. The vent was not heated its location made it difficult to inspect. Most important of all, neither manager, supervisors, nor operators recognized that if the vent choked, the air pressure was sufficient to burst the tank. Nevertheless, if the 6-in. vent had not been blanked, the incident would not have occuiTed (see also Section 12.1). 

As mentioned in Section 1.1.4. bacterial action on river water A choke gccurred m the flexible pipe that drained the roof of a float- an atso, produce metn if tank. It was decidet... 

Another incident in which a pressure vessel was ruptured by compressed air, this time because the vent was choked, is described in Section 2.2 (a). 

Many operators find it hard to grasp the power of compressed air. Section 2.2 (a) describes how the end was blown off a pressure vessel, killing two men, because the vent was choked. Compressed air was being blown into the vessel, to prove that the inlet line was clear. It was estimated that the gauge pressure reached 20 psi (1.3 bar) when the burst occurred. The operators found it hard to believe that a pressure of only twenty pounds could do so much damage. Explosion experts had to be brought in to convince them that a chemical explosion had not occurred. 

Section 10.4.2 lists some items that should be registered for inspection as part of the relief valve register. Section 2.2 (a) described an accident that killed two men. A vent was choked, and the end of the vessel was blown off by compressed air. 

Drain holes in relief valve tailpipes. If they choke, rainwater will accumulate in the tailpipe (see Section 10.4). 

S = cross-sectional area of the choke, fd L = length of choke, ft Vi = volume of the filter bottle, fd T = frequency at cut-off, all greater than eliminated (almost), cycles/sec... 

C = velocity of sound, ft/sec S = cross-sectional area of choke-tube, fti L = choke-tube length, ft... 

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