Abstract - Recently the importance of spouted bed technology has significantly increased in the context of drying processes as well as granulation, agglomeration or coating processes。 Par- ticulate systems concerning very fine or non spherical particles that are difficult to fluidize, of- ten cannot be treated in conventional fluidized beds。 In contrast to those fluidized beds, the spouted bed technology with its specific flow structure offers the opportunity of stable fluidiza- tion under controlled conditions。 Within this work the fluid dynamics of a novel spouted bed with two adjustable gas inlets is investigated。 By analysis of gas fluctuation spectra by means of a fast Fourier transformation algorithm, different operation regimes are identified and depicted graphically。 Furthermore, continuum CFD-modeling of the granular solid phase motion by means of an Euler/Euler approach and comparisons with experimental obtained velocity vector fields by means of particle image velocimetry (PIV) measurements will be presented in this work。79606

INTRODUCTION

In food, pharmaceutical and chemical industry, fine and polydisperse solids are treated and produced, re- spectively。 Analogous to conventional fluidized beds, spouted beds are well known for their good mixing of the solid phase and also for their intensive heat and mass transfer characteristics between the fluid phase (gas) and the solid phase yielding nearly isothermal conditions。 The special flow structure of a spouted bed is characterized by a simple apparatus construction。 Like the fluidized bed technology, the spouted bed tech- nology can be applied for mixing of particpulate systems, for heat and mass transfer processes, e。g。 cooling, drying (Kmiec et al。 (1994)), calcination, combustion, gasification as well as for complex multiphase proc- esses like spray granulation (Hatano et al。 (2004)), agglomeration (Jacob et al。 (2005)), particle layering and coating (Kfuri and Freitas (2005)) and also for chemical reactions。 The elementary differences of spouted beds in comparison to conventional fluidized beds are:

•a gradual decrease of the gas velocity over the apparatus height, enabling the treatment of poly-disperse particle systems at different pneumatic operating ranges,

•a sufficient high gas velocity in the bottom part of the apparatus, that allows the treatment of materials where an extended contact with the gas distributor is unallowable,

•high possible gas inlet temperatures。 Particles are located in the jet zone for only a short period of time, whereby a high degree of thermal efficiency and high evaporation rates are realized。 Also temperature sensitive materials can be treated gently due to much lower gas temperatures outside the jet zone。

Knowledge of the stable fluid dynamic operation range of the spouted bed, which is smaller compared with conventional fluidized beds, is of importance for operating the apparatus。 In the recent literature, the pneu- matic operation range is depicted with the aid of different diagrams, e。g。 P = f(velocity) (Markovski and Kaminski (1983), Olazar et al。 (1992)), Ho = f(velocity) (Olazar et al。 (1992)), velocity = f(diameter) (Čati- pović et al。 (1978)) or by Re-G-Ar-diagrams (Mitev (1979), Piskova (2002))。 The pneumatic operation ranges of spouted beds are usually characterized in a quantitative manner by analysis of measured gas phase pressure fluctuations and fast Fourier analysis (FFT) on these spectra。 Based on the FFT analysis the pneu- matic stable operation range will be identified and depicted in a dimensionless Re-G-Ar-diagram similar to the work of Mitev (1979)。

Another aspect of this work is modeling the pneumatic behavior of the spouting process with the commer- cial software package FLUENT 6。2。 The aim of the investigations is to predict the pressure drop of the void apparatus as well as the solid phase motion by means of a continuum Euler/Euler approach。 In this approach both the fluid phase and the granular solid phase are considered as fully interpenetrating continua。 The re- sults obtained by CFD modeling, e。g。 solid phase velocity vector fields, are compared with experimental re- sults provided by particle image velocimetry (PIV)。