Problem Vent Flow

The heaters are fed from hot-water flow and return mains, and to ensure uniform distribution of the heating medium, adequate connections to each row or bank of tubes or sections are necessary. To reduce air-locking problems, venting of the heater flow connections should be arranged. Parallel and counterflow are common arrangements with water coils. Counterflow is preferred, as this gives the highest possible mean temperamre difference. 

Flow maldistribution problems in condensers may be severe and should not be underestimated [146], Most problems with flow maldistribution in condensers, though, can be resolved through good venting and condensate drainage [2],... 

It is possible to make simplified calculations to determine approximate interior pressure conditions by assuming uniform vent flow and essentially working the problem in steps over discrete time intervals. The purpose of the present paper, however, is to set up exact thermodynamic and flow equations. A critical parameter in the results arises in connection with the net effect of the four processes mentioned above. After the thermodynamic formulation, the magnitude of these effects will be discussed. 

The design of the extruder screw is very critical to the proper functioning of the vented extruder. One of the main problems that vented extruders are plagued with is vent flow. This is a situation where not only the volatiles are escaping through the vent port, but also some amount of polymer. Thus, the extruder screw has to be designed in such a way that there will be no positive pressure in the polymer under the vent port (extraction section). This has led to the development of the two-stage... 

A potential problem for rotary valve usage is that they tend to pull material preferentially from the upside of the valve, which can affect the mass flow pattern. Another problem is that once soHd drops from the vane, the air or gas that replaces it is often pumped back up into the bin. In addition, air can leak around the valve rotor. Such air flows can decrease the soflds flow rates and/or cause flooding problems. A vertical section shown in Figure 13 can alleviate the preferential flow problem because the flow channel expands in this area, usually opening up to the full outlet. To rectify the countercurrent air flow problem, a vent line helps to take the air away to a dust collector or at least back into the top of the bin. 

Industrial, centrifugal elevators usually operate at speeds of about 75 m /min, and handle free-flowing, fine and loose materials having lump sizes of <50 mm. Sticky material can be a problem. Fine fluidizing materials often require perforations in the bottom of the buckets to vent entrapped air. Centrifugal elevator capacities range up to 370 m /h for a single row of buckets, and up to 1400 m /h for multiple rows of buckets. The buckets can be mounted on a belt or chain. 

Flammable or toxic vapors can be piped to a flare after separation of liquid is obtained. An important design problem in flare use is the very high vent rate experienced for a relatively short time, if an existing flare is used. Also back-pressure effects on the liquid separator vessel must be considered, especially if choked flow of vapor occurs downstream of the separator. 

The extruder would operate for several hours to days at steady state, and then for no apparent reason It would flow surge for several hours. After a period of time, the extruder would return to a steady-state operation and would remain there until the cycle repeated. Problem diagnosis was impossible without transient process data. Moreover, molten resin would frequently flow out the vent, especially during times of unsteady-state operation. 

For example, if a two-stage vented extruder has a screw that was designed for resins with an Mi range of 2 to 20 dg/min, and plant personnel are asked to manufacture a resin with an MI of 100 dg/min, the extruder may not process the resin acceptably. For this case and flood feeding, the extruder is likely to have resin flowing into the vent because the first stage can deliver more resin than the second stage can pump. One practical solution to this problem is to operate the slide valve in a partially open manner such that it controls the rate of the extrusion process. This will allow the extruder to operate at a lower specific rate and allow operation without the flow of resin into the vent. 

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