Annular chamber

Because indirect-heat calciners frequently require close-fitting gas seals, it is customaiy to support aU parts on a selFcontained frame, for sizes up to approximately 2 m in diameter. The furnace can employ elec tric heating elements or oil and/or gas burners as the heat source for the process. The hardware would be zoned down the length of the furnace to match the heat requirements of the process. Process control is normaUy by shell temperature, measured by thermocouples or radiation pyrometers. When a special gas atmosphere must be maintained inside the cyhnder, positive rotaiy gas se s, with one or more pressurized and purged annular chambers, are employed. The diaphragm-type seal ABB Raymond (Bartlett-Snow TM) is suitable for pressures up to 5 cm of water, with no detectable leakage. 

In each run, the annular chamber of the dryer is first filled with a certain amount of dry PVC powder and then the hot airflows I and II are turned on to preheat the system. When the temperature of the material inside the dryer achieves the required value, the screw feeder is turned on and the experimental operation begins. About one hour later, when operation of the system achieves stable conditions, sampling is started and, at the same time, the dry- and wet-bobble temperatures at the inlet and the outlet of the dryer, the flow rates of Hot air I and II, and the rotary speed of the screw feeder are recorded. 

Figure 6.16 Profile of moisture content of material in the annular chamber. m0, m s l O 25.47,...

A set of data on the variation of moisture content of the product with the feed rate under typical operating conditions is given in Fig. 6.21. In critical cases the moisture content may be above the value specified and in more serious cases the material in the annular chamber may completely loss its ability to flow, the system is blocked out, and finally the operation is destroyed. 

In the equipment shown in Fig. 6.14 two possible options for the product discharge were considered. It is reasonable that researchers would want to employ the scheme of overflow through the upper outlet. If such a scheme was feasible, the control of the material level in the annular chamber, which has an important effect on the stable operation of the device, would become very easy and convenient. 

Figure 5. Micrographs showing cross-sections of denuded vascular segntemls perfused with blood fixMn a control donor (A) and fix>m a patient whose platelets are deficient in GPVI (B). Perfusions were perfonned using the annular chamber at a shear rate of800s for 10 minutes. Aggregate formation is almost absent when blood samples om a GPVI-deficient patioit are perfused...

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