Zheqing Huang

This work pursues an integrated filtered reaction rate (FRR) model that incorporates intraparticle diffusion effectiveness factor ( η _I ) into a framework combining reaction kinetics regime (KR) and external mass transfer regime (EMTR) via fine‐grid two‐fluid model (TFM) simulations. Simulation results indicate that the modified Damköhler number remains a reliable criterion for distinguishing between KR and EMTR. Within the KR, the FRR model that neglects η _I overestimates the mesoscale effectiveness factor ( η _Δ ) when η _I < 0.5, though these effects become negligible at η _I >0.5. This overestimation is attributed to the increase in the Damköhler number with decreasing η _I , which subsequently results in a lower η _Δ . Accordingly, an integrated FRR model incorporating η _I is proposed. Coarse‐grid TFM simulations demonstrate that the FRR model without intraparticle diffusion yields only modest improvements, whereas the version integrated with intraparticle diffusion achieves substantially better agreement with the filtered fine‐grid TFM results.

The accuracy of the drag model is critical for achieving reliable simulations of bubble column hydrodynamics. This study develops a drag model for bubble columns with comprehensive applicability across homogeneous and heterogeneous flow regimes by integrating direct numerical simulation with experimental data. Systematic direct numerical simulation of gas-liquid flows at various inlet velocities informs the original model's development. The Reynolds number is incorporated in addition to the gas holdup to account for the different flow regimes, which distinguishes it from traditional models that rely solely on gas holdup. Implemented within a two-fluid model framework, the proposed drag model for bubble swarms is validated through posterior analysis. Results demonstrate its unique capability to accurately capture bubble swarm drag characteristics across all regimes, from homogeneous to heterogeneous.

This work pursues a generalized filtered reaction rate (FRR) model for reactive gas–solid flows via fine‐grid two‐fluid model (TFM) simulations. The power‐law kinetic with various reaction orders ( n ) is considered. It is well known that the solid‐catalyzed reaction rate is bounded by the kinetic regime (KR) and external mass transfer‐controlled regime (EMTR). It is found that the FRR model maintains excellent predictive performance both for n > 1 in two different regimes and n < 1 in the KR. However, an underprediction is observed at n < 1 within the EMTR. Thus, a modified formula for the FRR model in the EMTR is proposed. Then a generalized FRR model is derived. The assessment for the model is performed via a priori analysis and a filtered TFM simulation. The priori analysis and filtered TFM simulations quantitatively demonstrate that the model exhibits robust predictive capability.

In many applications, the chemical reaction changes the number of moles of the gas phase and hence affects the gas–solid flow structures and the reaction behavior. This study analyzes the effect of such non-equimolar reaction on the meso-scale reaction rate model. Based on the filter technique and the fine-grid simulation data, a meso-scale reaction rate model is proposed by correcting the model established by Huang et al. (AIChE, 2021, 67 (5)) in which only equimolar reaction is involved. The Reynolds number calculated by the filtered gas–solid slip velocity is found to be an important marker in the correction factor. The effectiveness of the new model is demonstrated by prior tests and also posteriori tests in fluidized beds.

This work pursues the closure for the effective reaction rate based on fine‐grid two‐fluid model (TFM) simulations in reactive gas‐solid flows. It is found that the mesoscale mechanism in the solid‐catalyzed reaction is constrained by the kinetic regime (KR) and the external mass transfer‐controlled regimes (EMTR). Thus, a filtered reaction rate model η_subgrid considered two different regimes is proposed. The mesoscale effectiveness factor proposed in previous work is adopted in KR. A filtered interphase mass transfer model Q_M, which is constructed by analogy to the interphase heat transfer model, is used in EMTR. η_subgrid shows a good predictability in two regimes via a priori test. The fidelity of η_subgrid is also assessed via a filtered TFM simulation. The results indicate that the simulations incorporating corrections for the drag force and reaction rate yield better agreement with the fine‐grid simulations for both mass fraction and reaction rate profiles.

In this study, flow and heat transfers in bidisperse gas–solid systems were numerically investigated using the computational fluid dynamics–discrete element method (CFD–DEM). Three different models to close the gas–solid heat transfer coefficient for each species of bidisperse systems were compared in the simulations. The effect of the particle diameter ratio and particle number ratio between large and small particles on the particle mean temperature and temperature distribution of each species were systematically investigated. The simulation results show that differences in the particle mean temperature and temperature distribution profiles exist among the three heat transfer models at a higher particle number ratio. The differences between the effects of three heat transfer models on heat transfer properties in bidisperse systems with particle diameter ratios of up to 4 are marginal when the particle number ratio between small and large particles is 1.

The filtered reaction rate for the coarse‐grid simulations of reactive gas–solid flows can be obtained via a correction to its microscopic reaction rate. The correction term is defined as the mesoscale effectiveness factor η_Δ, which is the ratio of the reaction rate obtained from the fine‐grid simulations to that obtained from the coarse‐grid simulations. The considered reaction is an isothermal, solid‐catalyzed surface reaction with a power law reaction rate model. The simulation results show that the mean η_Δ is almost invariant with the reaction orders at the same Damköhler number. A closure correlation for the mean η_Δ is formulated. However, the standard deviation of η_Δ is found to be quite large. A presumed probability density function model is proposed to capture the fluctuating properties of η_Δ. The predictability of the closure correlations are evaluated via performing the filtered two fluid model simulations in circulating fluidized beds of ozone decomposition.

Heat Transfer Studies of Arrays of Prolate Particles in Gas-Solid Flows: Numerical study of forced convection heat transfer from arrays of prolate particles is performed using the second-order Immersed Boundary-Lattice Boltzmann Method (IB-LBM). Prolate particle is studied with aspect ratio of 2.5 with solid volume fraction variation from 0.1 to 0.3. For each solid volume fraction, arrays of prolate particles are generated and simulations have been performed to calculate Nusselt number for four different Hermans orientation factors and various Reynolds numbers. From the simulation results, it has been observed that, for any specific value of Hermans orientation factor, Nusselt number increases with the increase of the Reynolds number and solid volume fraction. More importantly, it is found that the effect of orientations on Nusselt number is significant. Nusselt number correlation is developed for ellipsoidal particles as function of Reynolds number, Prandtl number, solid volume fraction, and orientation factors. This correlation is valid for and .