- 4:39 PM

Revisiting the Standard Drag Law for Bubbling, Gas-Fluidized Beds

Josť Leboreiro, Gustavo G. Joseph, and Christine M. Hrenya. Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309-0424

Gidaspow (1994) proposed a drag law, a combination between the Ergun (1952) and the Wen and Yu (1966) correlations, which has been the standard drag law in many works in the literature. The physical reasons for the stitching done by Gidaspow (1994) are not clear, since it presents a discontinuity at a solid volume fraction of 0.2. Benyahia et al. (2006) developed a continuous drag law from the expressions proposed by Hill, Koch, and Ladd from Lattice-Boltzmann simulations. In that work, the authors found significant differences in the computed simulation results of gas-solid fluidized systems between the continuous drag law and a discontinuous version of the Koch and Hill model proposed by Bokkers et al. (2004). Physically, the drag force is a continuous function of both Reynolds number and solid volume fraction, and therefore continuous drag laws are required.

In this study a continuous version of the Gidaspow drag law is proposed to remove the discontinuity in the solid volume fraction. Based on an analysis of the experimental data of Ergun (1952) and Wen and Yu (1966), it is more appropriate to stitch both correlations at a solid volume fraction of 0.55 in a continuous manner. Multi-Phase Particle-in-Cell (MP-PIC) simulations are carried to evaluate the effect that the stitch point and stitch method have on predictions of bubbling, monodisperse gas-solid fluidized beds. A comparison with the Hill, Koch, and Ladd drag model is also presented.