Periodic Fluctuations of Flow and Porosity in Spouted Beds

Abstract

The results of experimental investigations of bed flow hydrodynamics in spouted beds are compared with CFD simulations (Eulerian-Eulerian approach) for two different column geometries. The experimental results of bed porosity and fluctuation frequency of mass flow rate of grain in the fountain region are compared with the corresponding results of simulations. The simulation results confirmed the observations of Muir et al. (1990, Chem. Eng. Comm. 88: 153-171) and Yang and Keairns (1978, AlchE Symp. Ser. No. 176 74: 218) that fluctuations of bed flow in DTSB are caused by particle cluster formation in the loading region at the bottom of column.The solids cross into the jet and cover the column inlet and are carried upward periodically through a draft tube. Subsequent figures obtained from simulations, which show stages of particle cluster formation at the entrance of column, exactly match visual observations. The frequency of fluctuations of grain mass flow rate predicted in simulations (∼5-6 Hz) is in the range of that experimentally determined. The fluctuating inflow of solids results in slug formation and explains the vertical variations of height and porosity of the fountain. NotationGravity acceleration (m/s 2 ) h bed Initial height of bed (m) = I Identity tensor

Numerical simulation of a spouted bed with a draft tube with and without liquid spray

“…The dense region at the top of the fountain as reported in spouted fluidized beds (He et al, 1994) is predicted at low gas velocities and tends to disappear at high gas velocities. Similar experimental observations were reported by Karlsson et al (2006) and Szafran and Kmiec (2007).…”

“…They investigated the effect of the inlet gas velocity on the pressure drop in the draft tube, particle residence time, and voidage distribution along the axis of the draft tube. Szafran and Kmiec (2004) carried out a series of numerical simulations of DTSB; the hydrodynamics of the flow was investigated and numerical results were qualitatively validated with experimental data (see also Szafran et al, 2005; Szafran and Kmiec, 2007). Eulerian–Eulerian multifluid modelling approach was used in both simulations of Marschall and Mleczko and Szafran et al, and numerical results showed fair agreement with the available experimental data.…”

Hydrodynamic simulations of gas–solid spouted bed with a draft tube

“…However, in comparison to conical spouted beds without draft tube, relatively little has been published on spouted beds with draft tube. Flow behavior of particles in a two-dimensional spouted bed dryer with a draft tube was simulated (Szafran and Kmiec, 2007). A heat-and mass-transfer model was added as compiled executable code by means of UDF programming to FLUENT 6.1 in the simulations of spouted bed dryer with a draft tube (Szafran and Kmiec, 2004).…”

Cylindrical‐conical spouted bed dynamics: Laminar and turbulent flow predictions

“…This jet is clearly seen in Figures e–h and d–f. Similar near‐wall‐jet formation of reflected particles was observed in other works …”