期刊
CHEMICAL ENGINEERING JOURNAL
卷 372, 期 -, 页码 1134-1153出版社
ELSEVIER SCIENCE SA
DOI: 10.1016/j.cej.2019.04.159
关键词
Fluidized bed; Gas-solid flow; Vacuum; Bubble dynamics; Reduced pressure; CFD
资金
- German Federal Ministry of Science and Education (BMBF) within the Unternehmen Region project WIGRATEC+ [O3WKCI5A, O3WKCI5B]
Fluidized beds operated under partial vacuum offer a promising alternative to the expensive freeze-drying technique for processing thermo-sensitive materials in the food and pharmaceutical industries. However, the hydrodynamics of vacuum fluidized beds has not been extensively investigated. In this paper, we apply a two-fluid Eulerian model to investigate the influence of sub-atmospheric pressure on the hydrodynamic characteristics in two-dimensional fluidized beds. The simulations are compared with experiments performed in a batch vacuum fluidized bed plant. A parametric study of the effect of pressure on bed hydrodynamics is performed for two fluidization conditions: (1) constant excess velocity and (2) three times the minimum fluidization velocity. The pressure is varied in the range 1000 mbar-100 mbar with fluidized particles belonging to Geldart group D. A detailed investigation is carried out on porosity distribution, bed expansion, bypass ratio, and bubble characteristics. At low pressure, the porosity distribution is non-homogeneous with increased bubble activity near walls. A decrease in bed porosity and bubble splitting is observed as the operating pressure is reduced. The simulation results are also compared with semi-empirical correlations developed for atmospheric pressure conditions. The applicability of these correlations at sub-atmospheric pressures is, thus, evaluated.
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