A Study of Fluctuation and Expansion Ratios for Gas-Solid Fluidized Columns

The fluctuation and expansion ratios have been studied for cylindrical gas-solid fluidized columns by using air as fluidizing medium and Paracetamol as the bed material. The variables were the column diameter (0.0762, 0.15, and 0.18 m), static bed height (0.05, 0.07, and 0.09 m), and air velocity to several times of minimum fluidization velocity. The results showed that both the fluctuation and expansion ratios had a direct relation with air velocity and an inverse one with column diameter and static bed height. A good agreement was between the experimental results and the calculated values by using the correlation equations from the literature.

Fluidization and Spouting of Fine Particles: A Comparison

The fluidization characteristics of fine particles have been studied in both the fluidized bed and spouted bed. The effect of different system parameters (viz. static bed height, particle size, particle density and superficial velocity of the fluidizing medium, rotational speed of stirrer, and spout diameter) on the fluidization characteristics such as bed expansion/fluctuation ratios, bed pressure drop, minimum fluidizing/spouting velocity, and fluidization index of fine particles (around 60 micron particle size) have been analyzed. A stirrer/rod promoter has been used in the bed to improve the bed fluidity for fluidization process and spout diameter has been varied for spouted bed. Mathematical expressions for these bed dynamics have been developed on the basis of dimensionless analysis. Finally calculated values of these bed dynamics are compared with the experimentally observed values thereby indicating the successful applications of these developed correlations over a wide range of parameters.

Numerical Study of the Influence of Horizontal Tube Banks on the Hydrodynamics of a Dense Gas-Solid Bubbling Fluidized Bed

Numerical study of the influence of tube-bank on the hydrodynamics of a freely bubbling fluidized bed is relatively less reported in the literature. In this paper, results obtained from CFD study of a two dimensional gas-solid fluidized beds with horizontal tube-bank are compared with the published experimental data (Hull et. al., 1999). A 2-D bed, 1 m high and 0.2 m wide with tubes of diameter 0.026 m was taken for the calculations. Two different tube arrangements of staggered and inline pitch with center-to-center distance of 0.05 m were considered. Air was used as the fluidizing medium and ballotini glass (diameter: 230 mm and density: 2723 kg/m3) was the fluidized material. Air velocities used were 0.15 m/s and 0.187 m/s. The Eulerian-Eularian Two-Fluid CFD model was employed for modeling the momentum equations for both the gas and the solid phase with kinetic theory modification for the solid phase to account for the inter-particle interactions. Hydrodynamic features, such as, bubble size and bubble rise velocity and their variation with height within and outside the tube bank showed good agreement with the data of Hull et al.(1999)

Leakage of solids through the perforated distributor

Experiments were conducted to explore the effect of free area, orifice diameter and grid thickness on the rate of backflow of particles (leakage, weeping) through the multi-orifice distributor. Air was used as a fluidizing medium. Two sieved fractions of glass beads and ash particles of different shape and density were employed in the experiments. The measured rates of backflow were fitted by an empirical correlation with an accuracy of ±30%.