Revised drag calculation method for coarse grid Lagrangian-Eulerian simulation of gas-solid bubbling fluidized bed

In discrete element model (OEM) for simulation of gas-solid fluidized bed, drag force is correlated by use of local parameters which would be excessively smoothed within coarse grid. This work studies the method of calculating drag force for coarse grid OEM simulation of bubbling fluidized bed. The so-called complete circumstance-dependent local porosity (CCLP) model is proposed to correlate drag force taking the local circumstance of particle into account. The resulting circumstance-dependent drag force is employed in two-dimensional OEM simulations of a real small-scale bubbling fluidized system, using coarse grid. The local porosity is shown to be revised to a greater extent at the junctions of the gas-rich and particle-rich regions by the proposed CCLP model, which indicates that the circumstance influences on drag force are highlighted in the dense-dilute transitional regions. The parameter, i.e. the amplification factor, involved in the CCLP model is rationalized by investigating the comprehensive capability of predicting the fluidization features. The bubble size and shape simulated at the optimal parameter are generally consistent with the experimental observations. The simulated fluctuation time scales and amplitudes of solid volume fraction, relative pressure and bed layer height are close to the experimental results. Simulations show that OEM performs well in modeling the time-varying waveforms for the physical quantities in bubbling fluidized bed by use of the revised drag calculation method, which proves the unfamiliar merits of coarse grid simulation in some ways. (C) 2012 Elsevier B.V. All rights reserved.