Annular tangential flow concentric

Fig. 5 Schematic diagram of tangential generalized annular Couette flow, (a) Geometry for concentric cylinder model (b) typical velocity profiles under varying flow conditions.

The SDF, like the RTD functions, can be calculated from the velocity distribution in the system that is, a certain flow pattern determines both functions. The reverse, however, does not necessarily apply. The calculation of the SDF requires a complete description of the flow pattern, whereas RTD functions often can be calculated from a less than complete flow pattern. For example, the RTD of axial annular flow between two rotating concentric cylinders (helical flow) of a Newtonian fluid depends only on the axial velocity, whereas the SDF depends on both the axial and the tangential velocity... 

This standard test method specifies the use of a small-scale apparatus to assess the noncombustibility behavior of budding construction materials under the test conditions. The standard test apparatus consists of two concentric, vertical refractory tubes, 76-mm and 102-mm (3 and 4-in.) in inside diameter and 210 to 250-mm (8.5-10-in.) in length. Electric heating coils outside the larger tube are used to apply heat. A controlled flow of air is admitted tangentially near the top of the annular space between the tubes and passes to the bottom of the inner tube. The top of the inner tube is covered. Temperatures are measured by thermocouples at the center (1) between the two concentric tubes, (2) close to specimen location, and (3) sample surface. 

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