(365a) Flow Regime Maps for Pneumatic Conveying

In previous works we have shown that by defining various threshold velocities in terms of the modified Reynolds number as a function of the modified Archimedes number a Generalized Master-Curve can be plotted. Then, using this curve, the ratio between various threshold velocities can be easily determined. Based on the above, a generalized flow regime diagram for vertical pneumatic conveying and CFB systems was developed. We analyze dozens of experimental and theoretical studies in order to understand the influence of the various parameters including particle and gas properties, pipe diameter and particle concentration. Ee found that the four Geldart classification groups explain the appearance of different fluidization and pneumatic conveying states also. Based on the empirical and theoretical analysis it was shown that the generalized flow regime diagram for vertical systems can be presented by the relationship between the Archimedes and the Reynolds numbers modified by the solid flow rate or the volumetric concentration of circulating solids and the gas void fraction. However, it is much more complicated to develop the flow regime map for horizontal pipes. Based on the threshold velocities analysis, the border line between stationary bed and moving bed can be defined, in the case that the superficial velocity is lower than the saltation velocity.

Figure : Regimes of suspension, stationary bed and moving bed as a function of the particles concentration.

REFERENCES

[1]      H. Kalman and E. Rabinovich, "Analyzing Threshold Velocities for Fluidization and Pneumatic Conveying," Chemical Engineering Science, Vol. 63, pp. 3466-3473, 2008.

[2] E. Rabinovich and H. Kalman, "Flow Regime Diagram for Vertical Pneumatic Conveying and CFB Systems," Powder Technology, Vol. 207, pp. 119-133, 2011.