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Minerva Biotecnologica 2005 December;17(4):203-13

language: English

Powder bed behavior during fluidized bed processing

Depypere F. 1, 2, Pieters J. G. 2, Dewettinck K. 1

1 Food Technology and Engineering, Faculty of Bioscience Engineering, Ghent University-UGent, Ghent, Belgium;
2 Biosystems Engineering, Faculty of Bioscience Engineering, Ghent University-UGent, Ghent, Belgium


In contrast to solids, liquids or gases, the properties and the behavior of powders are more difficult to describe. In the food area, however, powder technology becomes increasingly important as most food ingredients are supplied under powdered form. Originally developed as a drying operation, the fluidized bed is widely used in typical food processing applications such as coating and agglomeration. Therefore, the present paper aims at describing some aspects of the powder bed behavior during fluidized bed processing: a) for both model systems and real food powders, the relevant powder properties with respect to fluidization processes were investigated. This enabled to classify the powders according to the classification of Carr and Geldart and to determine their fluidization potential. b) In addition, one of the most important parameters in the characterization of the fluidized bed is the minimum fluidization velocity. Therefore, this parameter was experimentally determined for the powders under investigation and compared with predictions from existing widely used equations from the literature. The applicability of the well-known equations and a newly proposed correlation was critically reviewed. c) Despite the good mixing qualities attributed to the fluidized bed, it is known that segregation can nevertheless take place due to size and/or density differences between the fluidized particles. So, powder samples were taken from a fluidized bed under operation, in order to investigate whether and to what extent particle segregation, based on a difference in size, occurred during bubbling fluidization in a tapered lab-scale reactor.

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