The difference between homogeneous and bubbling fluidization behaviors has been studied for the past 70 years, where several researchers have reported on the influence of interparticle forces in fluidization. Although...The difference between homogeneous and bubbling fluidization behaviors has been studied for the past 70 years, where several researchers have reported on the influence of interparticle forces in fluidization. Although interparticle forces such as van der Waals forces are evident in a real system, these forces are not the determinant in homogeneous fluidization, which can be simulated without any interparticle forces. In our previous study, the difference in fundamental mechanisms of the two fluidization states was analytically determined with a dimensionless gravity term, comprising the Reynolds number, Archimedes number, and density ratio. Nevertheless, some researchers insist that interparticle forces are dominant and a hydrodynamic force is not dominant. In this study, a dimensional analysis was applied to obtain a dominant parameter for distinguishing two fluidizations. Furthermore, some parameters were examined by comparing the experimental data in previous studies. The results indicated that hydrodynamic force is the dominant factor and the dimensionless gravity term is the dominant parameter in differentiating the two fluidized states.展开更多
Gas-solid separation fluidized beds are important for coal cleaning through the removal of ash-forming impurities.Homogeneous fluidization is considered as an ideal separation method because it results in fewer pressu...Gas-solid separation fluidized beds are important for coal cleaning through the removal of ash-forming impurities.Homogeneous fluidization is considered as an ideal separation method because it results in fewer pressure fluctuations and smaller bubbles.And Geldart C ultrafine powder could further intensify the fluidization stability of Geldart A particles.Thus,the present work provides a breakthrough in the density adjustment method in the gas-solid separation field,namely,combining Geldart A magnetite particles and Geldart C fine coal particles as a novel dense medium.The results showed that the addition of ultrafine coal effectively increased the overall expansion of the dense phase by the adhesion of the coal particles on the surfaces of the magnetite particles.To comprehensively understand the difference in the dense phase expansion ratio between the Geldart B/D and Geldart A particles,the flow regime was investigated to determine the transition point of homogeneous expansion using various dense media.The propagation velocities of the shock and continuity waves were analyzed using the theory of elastic systems.A quantitative criterion is proposed to identify the transition point.Based on the error analysis,the available data in the literature and the present work gave an overall in 5×10^(−5) error range compared to the prediction data.Overall,this research provides a comprehensive understanding of homogeneous fluidization characteristics using a novel dense medium and a reliable quantitative transition criterion of the flow regime for Geldart B/D and Geldart A particles in a gas-solid separation fluidized bed.展开更多
Hydrodynamic characteristics of fluidization in a conical or tapered bed differ from those in a columnar bed because the superficial velocity in the bed varies in the axial direction. Fixed and fluidized regions could...Hydrodynamic characteristics of fluidization in a conical or tapered bed differ from those in a columnar bed because the superficial velocity in the bed varies in the axial direction. Fixed and fluidized regions could coexist and sharp variations in pressure drop could occur, thereby giving rise to a noticeable pressure drop-flow rate hysteresis loop under incipient fluidization conditions. To explore these unique properties, several experiments were carried out using homogeneous, well-mixed, ternary mixtures with three dif- ferent particle sizes at varying composition in gas-solid conical fluidized beds with varying cone angles. The hydrodynamic characteristics determined include the minimum fluidization velocity, bed fluctuation, and bed expansion ratios. The dependence of these quantities on average particle diameter, mass fraction of the fines in the mixture, initial static bed height, and cone angle is discussed. Based on dimensional analysis and factorial design, correlations are developed using the system parameters, i.e. geometry of the bed （cone angle）, particle diameter, initial static bed height, density of the solid, and superficial velocity of the fluidizing medium. Experimental values of minimum fluidization velocity, bed fluctuation, and bed expansion ratios were found to agree well with the developed correlations.展开更多
文摘The difference between homogeneous and bubbling fluidization behaviors has been studied for the past 70 years, where several researchers have reported on the influence of interparticle forces in fluidization. Although interparticle forces such as van der Waals forces are evident in a real system, these forces are not the determinant in homogeneous fluidization, which can be simulated without any interparticle forces. In our previous study, the difference in fundamental mechanisms of the two fluidization states was analytically determined with a dimensionless gravity term, comprising the Reynolds number, Archimedes number, and density ratio. Nevertheless, some researchers insist that interparticle forces are dominant and a hydrodynamic force is not dominant. In this study, a dimensional analysis was applied to obtain a dominant parameter for distinguishing two fluidizations. Furthermore, some parameters were examined by comparing the experimental data in previous studies. The results indicated that hydrodynamic force is the dominant factor and the dimensionless gravity term is the dominant parameter in differentiating the two fluidized states.
基金supported by China National Funds for Distinguished Young Scientists(52125403)Natural Science Foundation of Jiangsu Province(BK20200651)+1 种基金National Natural Science Foundation of China(52104276,52261135540,52220105008)International Postdoctoral Exchange Fellowship Program(PC2021086).
文摘Gas-solid separation fluidized beds are important for coal cleaning through the removal of ash-forming impurities.Homogeneous fluidization is considered as an ideal separation method because it results in fewer pressure fluctuations and smaller bubbles.And Geldart C ultrafine powder could further intensify the fluidization stability of Geldart A particles.Thus,the present work provides a breakthrough in the density adjustment method in the gas-solid separation field,namely,combining Geldart A magnetite particles and Geldart C fine coal particles as a novel dense medium.The results showed that the addition of ultrafine coal effectively increased the overall expansion of the dense phase by the adhesion of the coal particles on the surfaces of the magnetite particles.To comprehensively understand the difference in the dense phase expansion ratio between the Geldart B/D and Geldart A particles,the flow regime was investigated to determine the transition point of homogeneous expansion using various dense media.The propagation velocities of the shock and continuity waves were analyzed using the theory of elastic systems.A quantitative criterion is proposed to identify the transition point.Based on the error analysis,the available data in the literature and the present work gave an overall in 5×10^(−5) error range compared to the prediction data.Overall,this research provides a comprehensive understanding of homogeneous fluidization characteristics using a novel dense medium and a reliable quantitative transition criterion of the flow regime for Geldart B/D and Geldart A particles in a gas-solid separation fluidized bed.
文摘Hydrodynamic characteristics of fluidization in a conical or tapered bed differ from those in a columnar bed because the superficial velocity in the bed varies in the axial direction. Fixed and fluidized regions could coexist and sharp variations in pressure drop could occur, thereby giving rise to a noticeable pressure drop-flow rate hysteresis loop under incipient fluidization conditions. To explore these unique properties, several experiments were carried out using homogeneous, well-mixed, ternary mixtures with three dif- ferent particle sizes at varying composition in gas-solid conical fluidized beds with varying cone angles. The hydrodynamic characteristics determined include the minimum fluidization velocity, bed fluctuation, and bed expansion ratios. The dependence of these quantities on average particle diameter, mass fraction of the fines in the mixture, initial static bed height, and cone angle is discussed. Based on dimensional analysis and factorial design, correlations are developed using the system parameters, i.e. geometry of the bed （cone angle）, particle diameter, initial static bed height, density of the solid, and superficial velocity of the fluidizing medium. Experimental values of minimum fluidization velocity, bed fluctuation, and bed expansion ratios were found to agree well with the developed correlations.
