Flow rate dipleg, fluidized

For fine Geldart Group C powders that defluidize slowly, it has been shown experimentally that solids continued to be transported through the downcomer even when the fluidizing gas to the dipleg was turned off. The particulate solids move in the dense phase. This operation will be designated self-flow (Kwauk, 1974a). Under this condition, the total gas rate is zero ... 

For practical gas and solids rates, this is possible for very fine powders, for which the terminal velocity ut is small. What happens in self-flow is that the dropping solids fed to the dipleg carry and pump down the surrounding gas, and this compressed gas carries, in turn, the solids up the spout. This is also possible for fine powders, which do not have a sharp incipient fluidization velocity, thus preventing quick defluidization. Self-flow therefore occurs in the band marked in Fig. 13 in the vicinity of e = 1. 

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