Axial and Radial Investigation of Hydrodynamics in a Bubble Column; Influence of Fluids Flow Rates and Sparger Type
Résumé
A detailed investigation of local hydrodynamics in a pilot plant bubble columnhas been performed using various techniques, exploring both axial and radial vari-ations of the gas hold-up, bubble average diameter and frequency, surface area. Awide range of operating conditions has been explored up to large gas and liquidflow rates, with two sparger types. Two main complementary techniques wereused: a quasi local measurement of gas hold-up via series of differential pressuresensors to get the axial variation and a double optic probe giving radial variationsof gad hold-up, bubble average size and frequency and surface area.According to axial evolutions, three zones, where radial evolutions have been de-tailed, have been separated: at the bottom the gas injection zone, the large centralregion or column bulk and the disengagement zone at the column top. It wasfound that significant axial and radial variations of the two phase flow character-istics do exist even in the so called homogeneous regime. The normalized profilesof bubble frequency appear sparger and gas velocity independent contrary to bub-ble diameter, gas hold-up and interfacial area normalized profiles. In any casebubbles are larger in the sparger zone than elsewhere.The main result of this work is the very strong effect of liquid flow on bubble col-umn hydrodynamics at low gas flow rate. First the flow regime map observed inbatch mode is dramatically modified with a drastic reduction of the homogeneousregime region, up to a complete heterogeneous regime in the working conditions(uG>0.02 m/s). On the contrary, liquid flow has limited effects at very high gasflow rates.A large data bank is provided to be used for example in detailed comparison with CFD calculations.
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