The Experts below are selected from a list of 24357 Experts worldwide ranked by ideXlab platform
Jesse Zhu - One of the best experts on this subject based on the ideXlab platform.
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numerical and experimental studies on the flow multiplicity phenomenon for gas solids two phase flows in cfb risers
Powder Technology, 2011Co-Authors: B Peng, Jesse Zhu, C ZhangAbstract:The flow multiplicity phenomenon in circulating fluidized bed (CFB) risers, i.e. under the same superficial gas velocity and solids circulation rate, the CFB risers may sometimes exhibit multiple flow structures, was numerically and experimentally investigated in this study. To investigate the flow multiplicity phenomenon, the experiments of gas–solids two-phase flows in a 2-D CFB riser with different flow profiles at the inlet of the CFB riser were conducted. Specially designed gas inlet distributors with add-ons are used to generate different flow profiles at the inlet of the CFB rise. The CFD model using Eulerian–Eulerian approach with k–e turbulence model for each phase was employed to numerically analyze the flow multiplicity phenomenon. It is experimentally and numerically proved that for gas–solids two-phase flows, the flow profiles in the Fully-Developed Region are dominated by the flow profiles at the inlet. The solids concentration profile is closely coupled with the velocity profile, and the inlet solids concentration and velocity profiles can largely influence the Fully-Developed solids concentration and velocity profiles.
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friction between gas solid flow and circulating fluidized bed downer wall
Chemical Engineering Journal, 2008Co-Authors: Hui Zhang, Jesse ZhuAbstract:Abstract Friction between co-current downflow gas–solid flow and column wall was investigated by measuring apparent and actual solids concentrations in a circulating fluidized bed (CFB) downer. A new model to predict pressure drops due to friction between the gas–solid suspension in the Fully Developed zone and the downer wall was Developed. The results show that the friction between the gas–solid suspension and the downer wall causes a significant deviation of the apparent solids concentrations from the actual ones, especially for those operating conditions with higher superficial gas velocities and solids circulation rates. When the superficial gas velocity is greater than 8 m/s, the actual solids concentrations in the Fully Developed Region of the downer can be up to two to three times of the apparent values. Particle diameters have different influences on the frictional pressure drops under different superficial gas velocity. After the frictional pressure drop is considered, the predicted actual solids concentrations by the proposed model agree well with the experimental values.
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Solids concentration in the Fully Developed Region of circulating fluidized bed downers
Powder Technology, 2008Co-Authors: Hui Zhang, Jesse ZhuAbstract:Abstract To investigate solids concentration in the Fully Developed Region of co-current downward gas–solid flow, actual solids concentrations were measured in a circulating fluidized bed (CFB) downer with 9.3 m in height and 0.1 m in diameter using a fiber optical probe. The results obtained from this work and in the literature show that the average solids concentration in the Fully Developed Region of the CFB downers is not only a function of the corresponding terminal solids concentration, but the operating conditions and particle properties also have influences on the average solids concentration in the Fully Developed Region of the CFB downers. Particle diameter and density affect the solids concentrations differently under different operating conditions. Downer diameters almost have no influence on the solids concentrations. By taking into account the effects of operating conditions, particle properties and downer diameters, an empirical correlation to predict the solids concentrations in the Fully Developed Region of CFB downers is proposed. The predictions of the correlation are in good agreement with the experimental data of this work and in the literature.
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friction between gas solid suspension and circulating fluidized bed downers
2007Co-Authors: Hui Zhang, Jesse ZhuAbstract:Friction between co-current downflow gas-solid suspension and the column wall was investigated. A new model to predict pressure drops due to friction between the gassolid suspension in the Fully Developed section and the downer wall was Developed. The results show that the friction between the gas-solids suspension and the downer wall causes a significant deviation of the apparent solids concentrations from the actual ones, especially for those operating conditions with higher superficial gas velocities and solids circulation rates. When the superficial gas velocity is greater than 8 m/s, the actual solids concentrations in the Fully Developed Region of the downer can be up to 2~3 times of the apparent values. After the frictional pressure drop is considered, the predicted actual solids concentrations by the proposed model agree well with the experimental values.
Hui Zhang - One of the best experts on this subject based on the ideXlab platform.
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friction between gas solid flow and circulating fluidized bed downer wall
Chemical Engineering Journal, 2008Co-Authors: Hui Zhang, Jesse ZhuAbstract:Abstract Friction between co-current downflow gas–solid flow and column wall was investigated by measuring apparent and actual solids concentrations in a circulating fluidized bed (CFB) downer. A new model to predict pressure drops due to friction between the gas–solid suspension in the Fully Developed zone and the downer wall was Developed. The results show that the friction between the gas–solid suspension and the downer wall causes a significant deviation of the apparent solids concentrations from the actual ones, especially for those operating conditions with higher superficial gas velocities and solids circulation rates. When the superficial gas velocity is greater than 8 m/s, the actual solids concentrations in the Fully Developed Region of the downer can be up to two to three times of the apparent values. Particle diameters have different influences on the frictional pressure drops under different superficial gas velocity. After the frictional pressure drop is considered, the predicted actual solids concentrations by the proposed model agree well with the experimental values.
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Solids concentration in the Fully Developed Region of circulating fluidized bed downers
Powder Technology, 2008Co-Authors: Hui Zhang, Jesse ZhuAbstract:Abstract To investigate solids concentration in the Fully Developed Region of co-current downward gas–solid flow, actual solids concentrations were measured in a circulating fluidized bed (CFB) downer with 9.3 m in height and 0.1 m in diameter using a fiber optical probe. The results obtained from this work and in the literature show that the average solids concentration in the Fully Developed Region of the CFB downers is not only a function of the corresponding terminal solids concentration, but the operating conditions and particle properties also have influences on the average solids concentration in the Fully Developed Region of the CFB downers. Particle diameter and density affect the solids concentrations differently under different operating conditions. Downer diameters almost have no influence on the solids concentrations. By taking into account the effects of operating conditions, particle properties and downer diameters, an empirical correlation to predict the solids concentrations in the Fully Developed Region of CFB downers is proposed. The predictions of the correlation are in good agreement with the experimental data of this work and in the literature.
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friction between gas solid suspension and circulating fluidized bed downers
2007Co-Authors: Hui Zhang, Jesse ZhuAbstract:Friction between co-current downflow gas-solid suspension and the column wall was investigated. A new model to predict pressure drops due to friction between the gassolid suspension in the Fully Developed section and the downer wall was Developed. The results show that the friction between the gas-solids suspension and the downer wall causes a significant deviation of the apparent solids concentrations from the actual ones, especially for those operating conditions with higher superficial gas velocities and solids circulation rates. When the superficial gas velocity is greater than 8 m/s, the actual solids concentrations in the Fully Developed Region of the downer can be up to 2~3 times of the apparent values. After the frictional pressure drop is considered, the predicted actual solids concentrations by the proposed model agree well with the experimental values.
Hui Zhao - One of the best experts on this subject based on the ideXlab platform.
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modeling the axial hydrodynamics of gas solid counter current downers
Particuology, 2020Co-Authors: Juanbo Liu, Xinhua Liu, Zhixin Zhang, Hui ZhaoAbstract:Abstract Gas–solid counter-current downer reactors, in which particles move downward in an upward gas flow, can achieve high solid concentration for high heat and/or mass transfer rates. However, the particles may reverse their direction or even be carried out of the reactor as the gas flow rate increases. This is closely related to “flooding” in counter-current flows. The energy minimization multiscale (EMMS) model well describes multiscale heterogeneity in gas–solid cocurrent upward flows. It is further Developed to simulate gas–solid counter-current downward flows because similar heterogeneity can also be found in downers. The model characterizes well the axial hydrodynamics and predicts an inflexional voidage variation with superficial gas velocity in the Fully Developed Region. This is supported by a simulation based on computational fluid dynamics and the discrete element method. The flooding predicted by the model agrees better with experiment than previous models.
Kamel Hooman - One of the best experts on this subject based on the ideXlab platform.
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heat and fluid flow in entrance Region of a channel with staggered baffles
Energy Conversion and Management, 2006Co-Authors: S S Mousavi, Kamel HoomanAbstract:Laminar fluid flow and heat transfer in the entrance Region of a two dimensional horizontal channel with isothermal walls and with staggered baffles is investigated numerically. The computations are based on the finite volume method, and the SIMPLER algorithm has been implemented. Data for heat and fluid flow as well as pressure drop are presented for Reynolds numbers ranging from 50 to 500 and baffle heights between 0 and 0.75. It was observed that increasing the two parameters (blockage ratio and Reynolds number) will increase the Nusselt number, as expected. The results are reported for the thermal entrance Region with 16 baffles. This relatively large number of baffles allowed us to think of working media other than air and water (to them most attention has been paid up to now) so that the Prandtl number may vary from 0.35 to 10. While most of the work available in the literature showed the effects of Reynolds number on the hydrodynamic development of flow, it was concluded that not only the Reynolds number but also the Prandtl number affects the precise location of the periodically Fully Developed Region similar to the case of the smooth channel. It is not surprising when one observes that most of the previous works are concentrated on low Prandtl number cases, say those of water and air while this paper considers different working media like oils.
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viscous dissipation effects on thermally developing forced convection in a porous medium circular duct with isothermal wall
International Communications in Heat and Mass Transfer, 2004Co-Authors: A A Ranjbarkani, Kamel HoomanAbstract:A numerical study is reported to investigate the thermal development of forced convection in a circular tube filled by a saturated porous medium, with uniform wall temperature, and with the effects of viscous dissipation included. A theoretical analysis is also presented to find expressions for the temperature profile and the Nusselt number for the Fully Developed Region. The Brinkman model is employed. It is seen that while the developing Nusselt number is significantly dependent on the Brinkman number, the Fully Developed Nusselt number is independent of the Brinkman number, but both the developing and the Fully Developed Nusselt numbers, depend on the Darcy number.
Wilko Rohlfs - One of the best experts on this subject based on the ideXlab platform.
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entrance length effects on graetz number scaling in laminar duct flows with periodic obstructions transport number correlations for spacer filled membrane channel flows
International Journal of Heat and Mass Transfer, 2016Co-Authors: Wilko Rohlfs, John H LienhardAbstract:Abstract Self-similarity and scaling laws are powerful tools in engineering and thus useful for the design of apparatus. This self-similarity is well understood for the heat and mass transfer in laminar empty channel flows, including the Fully Developed Region as well as inlet length effects in the developing Region (Graetz problem). In this study, we examine the validity of the scaling behavior arising from the Graetz solution for channel flows disturbed by periodic obstructions. Simulation results show that entrance length effects and scaling laws do not change due to the presence of obstructions if the flow field remains steady in time and the dimensionless inlet length is given by X T / D h ≈ C inl . · Re · Pr , where C inl . ≈ 0.01 for the local and C inl . ≈ 0.03 for the average Nusselt number. The Nusselt number in the inlet Region for an internal flow scales by Nu = ( Re · Pr ) 1 / 3 , similar to the empty channel flow (Shah and London, 1978). If the analogy between heat and mass transfer holds, same conclusions and relations are valid for the Sherwood number, Sh ∝ ( Re · Sc ) 1 / 3 , where Sc denotes the Schmidt number. In the Fully Developed Region, the Nusselt number depends slightly on the Reynolds and Prandtl numbers owing to the loss in self-similarity of the velocity field (contrary to the empty channel flow). The limit of the classical self-similarity is the onset of temporal oscillations (instability) in the flow field. Beyond this limit, the length of the thermal entrance Region is strongly reduced. Furthermore, a strong dependency of the Nusselt number in the Fully Developed Region on the Prandtl number is found.
