The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
Jam Hans Kuipers - One of the best experts on this subject based on the ideXlab platform.
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coarse grid simulation of Bed Expansion characteristics of industrial scale gas solid bubbling fluidized Beds
Chemical Engineering Science, 2010Co-Authors: Junwu Wang, Van Der Ma Martin Hoef, Jam Hans KuipersAbstract:Two-fluid modeling of the hydrodynamics of industrial-scale gas-fluidized Beds proves a long-standing challenge for both engineers and scientists. In this study, we suggest a simple method to modify currently available drag correlations to allow for the effect of unresolved sub-grid scale structures, by assuming that the particles inside each computational cell are presented in the form of a two-phase structure. This method would thus make it possible to simulate the hydrodynamics of industrial-scale bubbling fluidized Beds of Geldart B and D particles with a coarse computational mesh. It is shown that with the proposed modification of the drag force correlation, the experimentally measured Bed Expansion characteristics of industrial-scale bubbling fluidized Beds can be reasonably predicted at acceptable computational cost. Also the simulation result for the macroscopic solid circulation pattern is in qualitative agreement with the experimental data.
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Coarse grid simulation of Bed Expansion characteristics of industrial-scale gas–solid bubbling fluidized Beds
Chemical Engineering Science, 2010Co-Authors: Junwu Wang, Van Der Ma Martin Hoef, Jam Hans KuipersAbstract:Two-fluid modeling of the hydrodynamics of industrial-scale gas-fluidized Beds proves a long-standing challenge for both engineers and scientists. In this study, we suggest a simple method to modify currently available drag correlations to allow for the effect of unresolved sub-grid scale structures, by assuming that the particles inside each computational cell are presented in the form of a two-phase structure. This method would thus make it possible to simulate the hydrodynamics of industrial-scale bubbling fluidized Beds of Geldart B and D particles with a coarse computational mesh. It is shown that with the proposed modification of the drag force correlation, the experimentally measured Bed Expansion characteristics of industrial-scale bubbling fluidized Beds can be reasonably predicted at acceptable computational cost. Also the simulation result for the macroscopic solid circulation pattern is in qualitative agreement with the experimental data.
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why the two fluid model fails to predict the Bed Expansion characteristics of geldart a particles in gas fluidized Beds a tentative answer
Chemical Engineering Science, 2009Co-Authors: Junwu Wang, Van Der Ma Martin Hoef, Jam Hans KuipersAbstract:It is well known that two-fluid models (TFMs) can successfully predict the hydrodynamics of Geldart B and D particles. However, up to now, TFM have failed to accurately describe the hydrodynamics of Geldart A particles inside bubbling gas-fluidized Beds: Researchers have reported that Bed Expansions are over-predicted by as much as 70%. In this work we show—for the first time—that TFM can predict the correct Bed Expansion, without any artificial modifications, provided that a sufficiently fine grid size and small time step is used. This suggests that the previously reported failure of TFM is mainly due to the lack of scale resolution, and that from a modeling point of view there is no fundamental difference between Geldart A particles and Geldart B and D particles.
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digital image analysis measurements of Bed Expansion and segregation dynamics in dense gas fluidized Beds
Powder Technology, 2003Co-Authors: Mjv Goldschmidt, J M Link, S Mellema, Jam Hans KuipersAbstract:One of the most crucial steps in the development of fundamental hydrodynamic models is the validation of these models with accurate, detailed experimental data. Therefore a whole-field, non-intrusive digital image analysis technique has been developed which enables measurement of Bed Expansion and segregation dynamics of coloured particles in dense gas-fluidised Beds. The development, calibration and accuracy of the technique are discussed in detail. The image analysis technique traces bubbles and voidage waves accurately, whereas the mixture composition in a fluidised Bed could be determined within 10%. Experiments have been carried out with 1.5 and 2.5 mm coloured glass beads, for which particle?particle and particle?wall collision parameters were accurately known. They were performed in pseudo two-dimensional laboratory scale fluidised Beds with a simple rectangular geometry and well-defined gas inflow conditions. An extensive set of results obtained with both mono-disperse systems and binary mixtures, suitable for validation of fundamental hydrodynamic models, is presented.
Mingyan Liu - One of the best experts on this subject based on the ideXlab platform.
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Hydrodynamic behavior of liquid–solid micro-fluidized Beds determined from Bed Expansion
Particuology, 2018Co-Authors: Mingyan LiuAbstract:Abstract The Bed-Expansion characteristics of liquid–solid micro-fluidized Beds were experimentally studied. Bed columns with inner diameters of 0.8, 1.45, and 2.3 mm were fabricated based on capillaries. Five particle sizes in a range of 22–58 μm were investigated. Bed-Expansion curves were plotted using visually recorded Bed-Expansion heights. The Bed Expansion and initial fluidization behavior were compared with predictions for conventional-scale Beds. Evident differences are reflected in lower Expansion ratios and higher minimum fluidization velocities for micro-fluidized Beds. These were attributed to the increase in the internal surface area of the particle Beds and specific surface area of wall contact. The wall effect for micro-fluidized Beds at higher particle/Bed diameter ratios caused higher local voidage and an increase in Expansion ratio. Correlations for the exponent and proportional coefficient in the Richardson–Zaki equation for micro-fluidized Beds were proposed. The minimum fluidization velocities were correlated using a modification of the Ergun equation.
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hydrodynamic behavior of liquid solid micro fluidized Beds determined from Bed Expansion
Particuology, 2017Co-Authors: Mingyan LiuAbstract:Abstract The Bed-Expansion characteristics of liquid–solid micro-fluidized Beds were experimentally studied. Bed columns with inner diameters of 0.8, 1.45, and 2.3 mm were fabricated based on capillaries. Five particle sizes in a range of 22–58 μm were investigated. Bed-Expansion curves were plotted using visually recorded Bed-Expansion heights. The Bed Expansion and initial fluidization behavior were compared with predictions for conventional-scale Beds. Evident differences are reflected in lower Expansion ratios and higher minimum fluidization velocities for micro-fluidized Beds. These were attributed to the increase in the internal surface area of the particle Beds and specific surface area of wall contact. The wall effect for micro-fluidized Beds at higher particle/Bed diameter ratios caused higher local voidage and an increase in Expansion ratio. Correlations for the exponent and proportional coefficient in the Richardson–Zaki equation for micro-fluidized Beds were proposed. The minimum fluidization velocities were correlated using a modification of the Ergun equation.
K. Krishnaiah - One of the best experts on this subject based on the ideXlab platform.
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voidage characteristics and prediction of Bed Expansion in liquid solid inverse fluidized Bed
Chemical Engineering Science, 2005Co-Authors: T. Renganathan, K. KrishnaiahAbstract:Abstract Studies on voidage fluctuations, axial voidage profile and Bed Expansion are carried out by measuring the local void fraction using particles of wide ranging characteristics in liquid–solid inverse fluidized Bed. The quality of fluidization is elucidated by the local voidage fluctuations. The RMS voidage fluctuation depicts a maximum with respect to average Bed void fraction and increases with increase in Archimedes number. The fluidization quality has been quantified using average normalized RMS voidage fluctuation in terms of Transition number. The axial void fraction is almost uniform throughout the Bed except for particles with size distribution. All the literature and present experimental data on Bed Expansion are unified in terms of Richardson and Zaki equation using experimental terminal velocities. A new correlation is proposed for predicting the wall effect corrected experimental terminal velocities, as a substitute for standard drag equation. The Bed Expansion data are also predicted using the drift flux model.
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Voidage characteristics and prediction of Bed Expansion in liquid–solid inverse fluidized Bed
Chemical Engineering Science, 2005Co-Authors: T. Renganathan, K. KrishnaiahAbstract:Abstract Studies on voidage fluctuations, axial voidage profile and Bed Expansion are carried out by measuring the local void fraction using particles of wide ranging characteristics in liquid–solid inverse fluidized Bed. The quality of fluidization is elucidated by the local voidage fluctuations. The RMS voidage fluctuation depicts a maximum with respect to average Bed void fraction and increases with increase in Archimedes number. The fluidization quality has been quantified using average normalized RMS voidage fluctuation in terms of Transition number. The axial void fraction is almost uniform throughout the Bed except for particles with size distribution. All the literature and present experimental data on Bed Expansion are unified in terms of Richardson and Zaki equation using experimental terminal velocities. A new correlation is proposed for predicting the wall effect corrected experimental terminal velocities, as a substitute for standard drag equation. The Bed Expansion data are also predicted using the drift flux model.
K.c. Biswal - One of the best experts on this subject based on the ideXlab platform.
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experimental studies and empirical models for the prediction of Bed Expansion in gas solid tapered fluidized Beds
Chemical Engineering and Processing, 2010Co-Authors: D C Sau, Swati Mohanty, K.c. BiswalAbstract:Studies in the Expansion behaviour of tapered fluidized Bed systems are important for specifying the height of the Bed. Data have been obtained on the expanded heights of tapered fluidized Beds and Bed Expansion ratios for spherical and non-spherical particles have been calculated. Based on dimensional analysis, models have been developed as a function of geometry of tapered Bed, static Bed height, particle diameter, density of solid and gas and superficial velocity of the fluidizing medium. The data used to derive the models cover a wide range of operating conditions, with varying fluidization velocities. Effects of static Bed height, particle diameter, density, tapered angle and superficial gas velocity over minimum fluidization velocity on Bed Expansion ratios have been investigated experimentally. A comparison has been made between the calculated values of Bed Expansion ratios using proposed models and the experimental data. It has been seen that calculated values by models agree well with the experimental values. Models have also been compared with literature data of conventional Bed and found its applicability at higher gas velocities with good accuracy.
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Experimental studies and empirical models for the prediction of Bed Expansion in gas–solid tapered fluidized Beds
Chemical Engineering and Processing: Process Intensification, 2010Co-Authors: D C Sau, Swati Mohanty, K.c. BiswalAbstract:Studies in the Expansion behaviour of tapered fluidized Bed systems are important for specifying the height of the Bed. Data have been obtained on the expanded heights of tapered fluidized Beds and Bed Expansion ratios for spherical and non-spherical particles have been calculated. Based on dimensional analysis, models have been developed as a function of geometry of tapered Bed, static Bed height, particle diameter, density of solid and gas and superficial velocity of the fluidizing medium. The data used to derive the models cover a wide range of operating conditions, with varying fluidization velocities. Effects of static Bed height, particle diameter, density, tapered angle and superficial gas velocity over minimum fluidization velocity on Bed Expansion ratios have been investigated experimentally. A comparison has been made between the calculated values of Bed Expansion ratios using proposed models and the experimental data. It has been seen that calculated values by models agree well with the experimental values. Models have also been compared with literature data of conventional Bed and found its applicability at higher gas velocities with good accuracy.
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Bed Expansion Behaviour of Cylindrical Particles in a Three-phase Fluidized Bed
2008Co-Authors: Hara Mohan Jena, G K Roy, K.c. BiswalAbstract:The Bed Expansion profile of a co-current three-phase fluidized Bed with an antenna type air sparger have been studied using liquid as the continuous phase and gas as the discontinuous phase. Air, water and ceramic raschig rings of equivalent diameter 0.006864 m are used as the gas, liquid and solid phases respectively. The experiments have been carried out in a 0.1 m internal diameter, 1.88 m height vertical Perspex column. The expanded Bed height in the fluidized Bed regime has been measured visually. Correlations for Bed voidage have been developed. The developed correlation for Bed voidage can be used for the sizing of such systems. The Bed voidage is a strong function of both the liquid velocity and gas velocity. The experimental values have been compared with those predicted by the correlations and have been found to agree well.
Junwu Wang - One of the best experts on this subject based on the ideXlab platform.
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coarse grid simulation of Bed Expansion characteristics of industrial scale gas solid bubbling fluidized Beds
Chemical Engineering Science, 2010Co-Authors: Junwu Wang, Van Der Ma Martin Hoef, Jam Hans KuipersAbstract:Two-fluid modeling of the hydrodynamics of industrial-scale gas-fluidized Beds proves a long-standing challenge for both engineers and scientists. In this study, we suggest a simple method to modify currently available drag correlations to allow for the effect of unresolved sub-grid scale structures, by assuming that the particles inside each computational cell are presented in the form of a two-phase structure. This method would thus make it possible to simulate the hydrodynamics of industrial-scale bubbling fluidized Beds of Geldart B and D particles with a coarse computational mesh. It is shown that with the proposed modification of the drag force correlation, the experimentally measured Bed Expansion characteristics of industrial-scale bubbling fluidized Beds can be reasonably predicted at acceptable computational cost. Also the simulation result for the macroscopic solid circulation pattern is in qualitative agreement with the experimental data.
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Coarse grid simulation of Bed Expansion characteristics of industrial-scale gas–solid bubbling fluidized Beds
Chemical Engineering Science, 2010Co-Authors: Junwu Wang, Van Der Ma Martin Hoef, Jam Hans KuipersAbstract:Two-fluid modeling of the hydrodynamics of industrial-scale gas-fluidized Beds proves a long-standing challenge for both engineers and scientists. In this study, we suggest a simple method to modify currently available drag correlations to allow for the effect of unresolved sub-grid scale structures, by assuming that the particles inside each computational cell are presented in the form of a two-phase structure. This method would thus make it possible to simulate the hydrodynamics of industrial-scale bubbling fluidized Beds of Geldart B and D particles with a coarse computational mesh. It is shown that with the proposed modification of the drag force correlation, the experimentally measured Bed Expansion characteristics of industrial-scale bubbling fluidized Beds can be reasonably predicted at acceptable computational cost. Also the simulation result for the macroscopic solid circulation pattern is in qualitative agreement with the experimental data.
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why the two fluid model fails to predict the Bed Expansion characteristics of geldart a particles in gas fluidized Beds a tentative answer
Chemical Engineering Science, 2009Co-Authors: Junwu Wang, Van Der Ma Martin Hoef, Jam Hans KuipersAbstract:It is well known that two-fluid models (TFMs) can successfully predict the hydrodynamics of Geldart B and D particles. However, up to now, TFM have failed to accurately describe the hydrodynamics of Geldart A particles inside bubbling gas-fluidized Beds: Researchers have reported that Bed Expansions are over-predicted by as much as 70%. In this work we show—for the first time—that TFM can predict the correct Bed Expansion, without any artificial modifications, provided that a sufficiently fine grid size and small time step is used. This suggests that the previously reported failure of TFM is mainly due to the lack of scale resolution, and that from a modeling point of view there is no fundamental difference between Geldart A particles and Geldart B and D particles.