Domains of Applicability, Transition Evidence and Validation Requirements for the Ergun and Wen-Yu Drag Correlations in Bubbling Fluidized -Bed Roasters

This paper defines the dense and dilute domains represented by the Ergun and Wen-Yu drag correlations and examines the consequences of combining them through the classical Gidaspow switch in a bubbling fluidized-bed roaster. Its specific contribution is a reactor-resolved interpretive and validation framework that separates global fluidization-regime identification from local drag-closure selection and maps the resulting dense, dilute, and switching regions within the roaster. The review is extended with published particle-resolved data, a standard cold-flow benchmark, an original reactor-zone schematic, and quantitative sensitivity calculations. Published lattice-Boltzmann results indicate that an intermediate solids-fraction interval is not adequately represented by either limiting correlation, confirming that the conventional gas-volume-fraction threshold is a numerical selection rule rather than a physical phase boundary. For an illustrative 500 micrometer quartz-air case, the classical switch produces a 7.5% one-sided change in the interphase momentum-exchange coefficient at the threshold, whereas Ergun- and Wen-Yu-based estimates of minimum fluidization velocity differ by 4.4%. These values are calculation examples and do not constitute experimental validation. The paper concludes with a validation matrix and a consistency warning for studies whose reference CFD model uses Syamlal-O'Brien rather than Gidaspow.