Gas–solid cyclone separators are widely utilized in many industrial applications and usually involve complex multi-physics of gas–solid flow and heat transfer. In recent years, there has been a progressive interest in the application of computational fluid dynamics (CFD) to understand the gas–solid flow behavior of cyclones and predict their performance. In this paper, a review of the existing CFD studies of cyclone separators, operating in a wide range of solids loadings and at ambient and elevated temperatures, is presented. In the first part, a brief background on the important performance parameters of cyclones, namely pressure drop and separation efficiency, as well as how they are affected by the solids loading and operating temperature, is described. This is followed by a summary of the existing CFD simulation studies of cyclones at ambient temperature, with an emphasis on the high mass loading of particles, and at elevated temperatures. The capabilities as well as the challenges and limitations of the existing CFD approaches in predicting the performance of cyclones operating in such conditions are evaluated. Finally, an outlook on the prospects of CFD simulation of cyclone separators is provided.

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Multiscale 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.

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