On the choice of mesoscale drag markers

Abstract

AbstractMultiscale simulations of fluidized beds should account for the effect of sub‐grid structures on drag. How to extract the features of these structures in the form of proper finite quantities, namely markers, has posed great challenges in mesoscale drag modeling. The choice of markers has seldom been investigated in terms of their rationality and adequacy. This article introduces a two‐step scheme that is applied in the classic experimental approach to reflect on the choice of markers. The steady‐state definitional relations of the drag correction factor are deduced from force balance equations, with emphasis on the difference between definitional relations and constitutive relations. A comparison between common drag models obtained from fine‐grid simulations and corresponding definitional relations shows that the challenge in developing a general mesoscale drag model cannot be circumvented by correlating the heterogeneity index or drift velocity with the solid volume fraction, slip velocity, and gas‐phase pressure gradient.