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| 2. |
- Farzaneh, Meisam, 1982, et al.
(author)
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A novel multigrid technique for lagrangian modeling of fuel mixing in fluidized beds
- 2011
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In: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 66:22, s. 5628-5637
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Journal article (peer-reviewed)abstract
- This paper presents a novel Lagrangian approach to model fuel mixing in gas-solid fluidized beds. In the mixing process, fuel particles are considerably larger than the inert bed material and therefore, the present work proposes three grids to account for the difference in size between the fuel particles and inert solids. The information between the grids is exchanged using an algorithm presented in the paper. A statistical method has been developed to analyse the distribution of the fuel particles in the bed. The results for the preferential positions, velocity vectors and horizontal dispersion coefficients are compared with experimental data in a bed applying simplified scaling relationships for different operating conditions. The effects of initial bed height and inlet gas velocity on the fuel mixing are investigated.It is found that the proposed Lagrangian modeling can capture the complex pattern of the movement of the fuel particles, in spite of the large difference in diameter between inert and fuel particles.
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| 3. |
- Farzaneh, Meisam, 1982, et al.
(author)
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A Study of Fuel Particle Movement in Fluidized Beds
- 2013
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 52:16, s. 5791-5805
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Journal article (peer-reviewed)abstract
- Lagrangian simulations are performed to investigate the process of fuel mixing in fluidized-bed energy converters. The computations are carried out for a narrow (0.4 m) and a wide (1.2 m) bed. Movement of a limited number of large and light particles in a bulk of heavy and small particles is studied using a multigrid technique proposed by Farzaneh et al. Preferential positions and the dispersion coefficient of the fuel particles are obtained under different operating conditions. In addition, detailed information on the motion of the fuel particles in the form of upward and downward velocity is obtained. Furthermore, in an attempt to investigate the effect of the inlet boundary conditions on the process of fuel mixing, two boundary conditions are employed: a uniform velocity profile at the air distributor and a non-uniform velocity profile obtained by including the air supply system in the computational domain.It is observed that the numerical simulations which include the air supply system in the computational domain, improve the prediction of the hydrodynamic behavior of the bed. However, regarding the averaged movement pattern of the fuel particles, the effect of the boundary condition employed is not significant in the 0.4 m bed. As for the wide 1.2 m bed, the simulation results differ substantially from the experiments when the uniform velocity profile is employed as inlet boundary condition. Including the plenum in the simulations considerably improves the results, but they are still not in a perfect agreement with the experiments.
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| 4. |
- Farzaneh, Meisam, 1982, et al.
(author)
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Eulerian-Eulerian-Lagrangian Simulation of Fuel Mixing in Fluidized beds
- 2013
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In: 8th International Conference on Multiphase Flow ICMF 2013, Jeju, Korea, May 26 - 31, 2013.
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Conference paper (peer-reviewed)abstract
- In this paper, we combine Eulerian-Lagrangian and Eulerian-Eulerian frameworks to track a limited number of fuel particles in a bulk of inert particles in a gas-solid fluidized bed. The gas and the inert phase are treated as interpenetrating continua and resolved within the Eulerian-Eulerian framework, whereas the fuel particles are regarded as a discrete phase. In the method, the forces acting on a fuel particle are calculated by using the velocity and pressure fields of the mixture of the inert solid particles and gas.. To validate the numerical method, the results are compared with experimental data in the form of preferential positions, velocity vectors and dispersion coefficient of the fuel particles. The effects of a number of operating parameters (e.g. the fluidization velocity and the amount of bed material) on the mentioned properties of the fuel particles are studied. In addition, to accurately formulate the inlet boundary condition the air supply system is included in the computational domain. It is observed that the proposed numerical technique is able to correctly capture the behaviour of fuel particles in fluidized beds.
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| 5. |
- Farzaneh, Meisam, 1982, et al.
(author)
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Simulation of Fuel Mixing in Fluidized Beds using a Combined Tracking Technique
- 2013
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In: Fluidization XIV, 2013, Noordwijkerhout, The Netherlands.
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Conference paper (peer-reviewed)abstract
- This paper presents an Eulerian-Eulerian-Lagrangian (E-E-L) numerical method to track a limited number of fuel particles in a bulk of inert particles in a gas-solid fluidized bed. The gas and the inert phases are treated as the interpenetrating continua and resolved within the Eulerian-Eulerian framework, whereas the fuel particles are regarded as a discrete phase. To validate the numerical method, the results are compared with experimental data in the form of preferential positions, velocity vectors and the dispersion coefficient of the fuel particles. It is observed that the proposed numerical technique is able to capture the behavior of fuel particles in fluidized beds.
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| 6. |
- Farzaneh, Meisam, 1982, et al.
(author)
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The crucial role of frictional stress models for simulation of bubbling fluidized beds
- 2015
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In: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 270:Part A, s. 68-82
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Journal article (peer-reviewed)abstract
- In this paper we combine Eulerian-Lagrangian and Eulerian-Eulerian frameworks to simulate the behavior of a limited number of fuel particles in a bulk of inert particles in a bubbling gas-solid fluidized bed. The gas and the inert phase are treated as interpenetrating continua and resolved within the Eulerian-Eulerian framework, whereas the fuel particles are regarded as a discrete phase. The forces acting on a fuel particle are calculated by using the velocity and pressure fields of the inert solid and gas phases. We assume that the hydrodynamics of the bed are predominantly governed by the motion of the inert solid and gas phases. Therefore, emphasis in this work is on a correct description of the stress tensor of the inert particulate phase and, in particular, on the modeling of frictional stresses, which is of primary importance for continuum simulations of bubbling fluidized beds. Performance of two of the traditionally used frictional stress theories (Schaeffer [12] and Srivastava and Sundaresan [13]) and of the one more recently proposed (Jop et al. [18]) is investigated and the corresponding results are compared with experimental findings in the form of position and velocity of the fuel particles. In addition, preferential positions, the dispersion coefficient, and the average cycle time of the fuel particles motion are obtained by the simulations and compared with experiments. It is observed that the results of the visco-plastic model proposed by Jop et al. [18] are in good agreement with the experiments for prediction of the bed hydrodynamics and the movement of the fuel particles. The other two models underestimate the frictional stresses in the inert solid phase, leading to erroneous predictions of the stress tensor of the inert particulate phase and thus of the entire system.
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| 7. |
- Olsson, Jens, et al.
(author)
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Experimental evaluation of the lateral mixing of fuel in a fluidized bed with cross-flow of solids - influence of tube banks
- 2014
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In: 11th International Conference on Fluidized Bed Technology, CFB 2014; Beijing; China; 14 May 2014 through 17 May 2014. ; , s. 119-124
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Conference paper (peer-reviewed)abstract
- This work investigates the lateral fuel mixing in fluidized beds with a crossflow of solids by means of experiments in a fluid-dynamically downscaled unit of the Chalmers indirect biomass gasifier. Fuel lateral mixing is expressed as the combined effect of fuel dispersion and drag from the solids cross flow, and the work evaluates quantitatively these two effects at two different fluidization velocities. In addition, the work investigates the influence of a bank of horizontal tubes. It is found that there is a significant increase in both lateral fuel dispersion and drag of the fuel particles with fluidization velocity. Furthermore, the two mechanisms for lateral fuel mixing are drastically lowered by the insertion of the tube bank.
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| 8. |
- Sasic, Srdjan, 1968, et al.
(author)
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Characterization of fluid dynamics of fluidized beds by analysis of pressure fluctuations
- 2007
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In: Progress in Energy and Combustion Science. ; :33, s. 453-496
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Journal article (peer-reviewed)abstract
- This paper reviews procedures for investigating the fluid-dynamic behavior of gas–solid fluidized beds using pressuresignals as obtained from modeling or experiments. The procedures studied are applicable to all types of fluidized-bedreactor. Models generating pressure data in such systems are presented with respect to complexity and amount ofinformation provided. There is a discussion on how a calculated pressure can be compared to a measured signal in order tocreate a reliable representation of the fluid dynamics of the system. The type of information resulting from various ways ofmeasuring the pressure in fluidized beds is discussed, as well as the use of absolute versus differential pressure probes. Timeseries analysis is reviewed; it can be applied to modeled and measured pressure signals in time, frequency, time–frequencyand state space. Also, recommendations are provided on the use of the methods of analysis examined. The sources ofpressure fluctuations, propagation features and the nature of pressure waves in fluidized beds are discussed. Finally,examples from the literature are presented, illustrating the outcome of the procedures discussed.
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| 9. |
- Sasic, Srdjan, 1968, et al.
(author)
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Dynamics of gas-solid fluidized beds - inclusion of the air supply system
- 2004
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In: Fluidization XI, Engineering Conferences International, Ischia (Naples), Italy, May 9 -14, 2004.
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Conference paper (peer-reviewed)abstract
- The dynamic behavior of a fluidized bed system consisting of a bed, an air plenum, tubes and a fan is studied. A mathematical model that expresses the response of a fluidized bed to damping and disturbances is investigated. Experiments are performed in two units under non-circulating conditions. Simulations with the model are compared to experiments and the applicability of the model to various cases is discussed. Reasons for disagreement are analyzed.
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| 10. |
- Sasic, Srdjan, 1968, et al.
(author)
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Dynamics of gas-solid fluidized beds through pressure fluctuations: A brief examination of methods of analysis
- 2011
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In: International conference on circulating fluidized beds and fluidized bed technology - CFB10.
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Conference paper (peer-reviewed)abstract
- This paper revisits and critically examines a number of methods used for analysis of in-bed pressure signals recorded in gas-solid fluidized beds. The goal is to obtain information on the time scales of dominant phenomena present in the pressure time series of four fluidization regimes. It is demonstrated that the average cycle time represents an effective alternative to spectral analysis. In addition, we give evidence that the average cycle time yields equivalent information as some of the advanced methods of non-linear analysis (e.g. the Kolmogorov entropy). Finally, by using wavelets and wavelet packets, we show how to obtain an accurate time localization of the different frequency components present in the pressure signal.
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