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Transformice codes for points 20191/10/2023 To this end, extensive TFM and DPM simulations were performed to assess the drag coefficients that consider the effect of granular temperature or solid concentration fluctuation, using the experimental and DNS data of Tang et al., 2016a, Luo et al., 2016 and Müller et al. Therefore, it is interesting to see how much improvement can be achieved when those drag coefficients are used. Meanwhile, recent direct numerical simulations (DNS) have concluded that there is a need to consider the effect of the fluctuation of state variables on the interphase drag force, which results in an increase of the effective interphase drag force. Highly-resolved simulations using two-fluid model (TFM) and discrete particle method (DPM) have indicated that the true interphase drag force of gas-solid system was underestimated by currently available drag correlations. This study can serve as a basis for challenging future particle stress and solids-solids drag models. Simulation results reproduced all of the four instabilities and demonstrated that frictional particle stress and solids-solids drag are needed to capture critical qualitative flow features. Herein, we applied multi-fluid modeling (MFM) that treats the gas phase and two separate granular phases as fully interpenetrating continua to simulate these instabilities and compared them with newly conducted experiments. The high packing fraction and bi-disperse nature of these flows allow for new challenges to continuum models. Recently, a family of gravitational instabilities was found between two types of grains, including a Rayleigh-Taylor analog, a granular bubble rising, a granular droplet splitting and particle segregation. Previous studies have demonstrated that continuum modeling can capture some hydrodynamic instability analogs in monodisperse granular materials. Predicting granular flow using continuum approaches is fundamental to advance granular physics and industrial applications. ![]() Pressure and temperature have less effects on the flow structures than fluid velocity and un-fluidized bed height in both SCWFB and HGSFB. Flow structures in SCWFB are similar to those in HGSFB. Compared with CGSFB, SCWFB has lower minimum fluidization velocities, smaller bubble and slug sizes, more bubble and slug numbers, higher bed expansions and slug onset heights, and more uniform gas-solid interactions. The results show that, the drag forces of particulate phase are around 0.4 times particulate phase weights in SCWFB. Bubble (or slug) and particle dynamics, fluid velocities, and bed expansions are investigated. Some recommendations, including the use of novel drag laws and frictional solids stress models in TFM as well as the consideration of particle size distribution that may improve the prediction performance, are provided.Ī comparative study of flow characteristics in three-dimensional supercritical water fluidized beds (SCWFB, 440-560 ℃, 22-26 MPa), cold gas-solid fluidized beds (CGSFB, 20 ℃, 0.1 MPa), and high-pressure and high-temperature gas-solid fluidized beds (HGSFB, 440-560 ℃, 22-26 MPa) was conducted via two-fluid model simulations across different fluid velocities, un-fluidized bed heights, pressures and temperatures. Changing drag laws does not have a significant effect on results, and significant quantitative differences are observed in moving from CFD-DEM to TFM simulations, yet neither provides predictions which are definitively better across a wide range of metrics. However, simulations tend to predict bubble shapes which are taller and narrower with larger wake angles than those observed experimentally. The comparison shows that simulations capture bubble rise velocity and particle velocity data surrounding bubbles fairly well. This comparison allows for quantitative assessment of the accuracy of simulations for deterministic behavior of a single bubble as compared to statistical comparisons of chaotic free bubbling behavior as conducted in several prior studies. ![]() Predictions for bubble and particle dynamics surrounding a single bubble injected into an incipiently cylindrical fluidized bed from CFD-DEM and TFM simulations using different drag laws were compared with prior MRI results.
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