A collaborative investigation of two-fluid mixing in a swirl micro-mixer was carried out by the Shanghai Jiao Tong University and the Tokyo Denki University. Pure water and a mixture of glycerol and water were separat...A collaborative investigation of two-fluid mixing in a swirl micro-mixer was carried out by the Shanghai Jiao Tong University and the Tokyo Denki University. Pure water and a mixture of glycerol and water were separately injected into branch channels and they were subsequently mixed in the central chamber. The two-fluid flow pattern was numerically modeled, in which the dependence of the mixture viscosity and density on the mass fraction of glycerol in the mixing fluid was carefully taken into consideration. The mixing performance of the two fluids was evaluated by varying the Reynolds numbers and the mass fractions of glycerol in water. The mixing process was extensively analyzed using streamline maps and contour plotting distributions of pressure and glycerol concentration. The numerical results show that the acceptable uniformity of mixing at Re = 0.1 is primarily attributed to the time-consuming molecular diffusion, whereas the cost-effective mixing at Re 〉 500 was obtained because of the generation of the swirling flow. The increasing mass fraction of glycerol in water was found to attenuate the mixing performance. The preliminary microscopic visualization of the two-fluid mixing at Re=1300 demonstrated the consistence with the numerical results.展开更多
Because of potential high energy densities,microfluidic fuel cells can serve as micro-scale power sources.Because microfluidic fuel cells typically operate in the co-laminar flow regime to enable a membrane-less desig...Because of potential high energy densities,microfluidic fuel cells can serve as micro-scale power sources.Because microfluidic fuel cells typically operate in the co-laminar flow regime to enable a membrane-less design,they generally suffer from severe mass transfer limitations with respect to diffusion transport.To address this issue,a novel channel design that integrates slanted groove micro-mixers on the side walls of the channel is proposed.Numerical modeling on the design of groove micro-mixers and grooveless design demonstrates a mass transfer enhancement that has a 115%higher limiting current density and well-controlled convective mixing between the oxidant and the fuel streams with the use of slanted groove micro-mixers.Moreover,the growth of the thickness of the depletion boundary layer is found to be terminated within approximately 2 mm from the channel entrance,which is distinct from the constantly growing pattern in the grooveless design.In addition,a simplified mass transfer model capable of modeling the mass transfer prFocess with the presence of the transverse secondary flow is developed.Further,a dimensionless correlation is derived to analyze the effects of the design parameters on the limiting current density.The present theoretical study paves the way towards an optimal design of a microfluidic fuel cell integrating groove micro-mixers.展开更多
Mixing problems are most likely encountered and sometimes can be severe in scaling-up projects. Micro-mixing is an important aspect for fast or quasi-instantaneous reactions. Poor micro-mixing might produce more undes...Mixing problems are most likely encountered and sometimes can be severe in scaling-up projects. Micro-mixing is an important aspect for fast or quasi-instantaneous reactions. Poor micro-mixing might produce more undesired by-products, leading to higher purification costs. This paper gives an extensive review and analysis of micro-mixing studies in single- and multi phase stirred tanks. The relevant experiment techniques, micro-mixing models and nurherical approaches are critically reviewed and analyzed with remarks and perspectives. The reported studies on two-phase micro-mixing experiments and on the impact of the presence of the dispersed phases on turbulence have been limited to a narrow range of conditions. More importantly, disparities widely exist among different reports. Both Lagrangian and Eulerian models are based on oversimplified assumptions, which may lead to uncertainties or even unrealistic results. A heuristic model, which is from the perspective of CFD （computational fluid dynamics） and can cover the whole spectrum of scales and also focus on every subrocess, is desired in the future.展开更多
The coupled CFD-E-model for multiphase micro-mixing was developed,and used to predict the micro-mixing effects on the parallel competing chemical reactions in semi-batch gas–liquid and solid–liquid stirred tanks.Bas...The coupled CFD-E-model for multiphase micro-mixing was developed,and used to predict the micro-mixing effects on the parallel competing chemical reactions in semi-batch gas–liquid and solid–liquid stirred tanks.Based on the multiphase macro-flow field,the key parameters of the micro-mixing E-model were obtained with solving the Reynolds-averaged transport equations of mixture fraction and its variance at low computational costs.Compared with experimental data,the multiphase numerical method shows the satisfactory predicting ability.For the gas–liquid system,the segregated reaction zone is mainly near the feed point,and shrinks to the exit of feed-pipe when the feed position is closer to the impeller.Besides,surface feed requires more time to completely exhaust the added H+solution than that of impeller region feed at the same operating condition.For the solid–liquid system,when the solid suspension cloud is formed at high solid holdups,the flow velocity in the clear liquid layer above the cloud is notably reduced and the reactions proceed slowly in this almost stagnant zone.Therefore,the segregation index in this case is larger than that in the dilute solid–liquid system.展开更多
为探索纸质被动式农药微混合器的主要参数对农药混合效果的影响规律和增强农药混合的机理,选取Y型、Z型和方波型3种结构的纸质被动式农药微混合器,试验研究了每种微混合器不同参数条件对混合性能的影响,选出最优参数,再将最优参数下的3...为探索纸质被动式农药微混合器的主要参数对农药混合效果的影响规律和增强农药混合的机理,选取Y型、Z型和方波型3种结构的纸质被动式农药微混合器,试验研究了每种微混合器不同参数条件对混合性能的影响,选出最优参数,再将最优参数下的3种微混合器的混合性能进行对比。试验结果表明,Y型微混合器的最优参数为:入口速度0.010 m L/min、入口角30°,Z型微混合器的最优参数为:入口速度0.010 m L/min、峰间距3 mm、转角30°,方波型微混合器的最优参数为:入口速度0.010 m L/min、波高2 mm、波宽5 mm;在各自的最优参数条件下,Y型微混合器出口处混合强度为0.622 7,Z型微混合器出口处混合强度为0.690 2,方波型微混合器出口处混合强度为0.732 6,方波型微混合器混合性能最好;纸质被动式农药微混合器通道内部存在纸纤维,可以提供流体流动的动力,也可以加剧分子间的扩散作用,同时也在一定程度上限制了对流作用。展开更多
文摘A collaborative investigation of two-fluid mixing in a swirl micro-mixer was carried out by the Shanghai Jiao Tong University and the Tokyo Denki University. Pure water and a mixture of glycerol and water were separately injected into branch channels and they were subsequently mixed in the central chamber. The two-fluid flow pattern was numerically modeled, in which the dependence of the mixture viscosity and density on the mass fraction of glycerol in the mixing fluid was carefully taken into consideration. The mixing performance of the two fluids was evaluated by varying the Reynolds numbers and the mass fractions of glycerol in water. The mixing process was extensively analyzed using streamline maps and contour plotting distributions of pressure and glycerol concentration. The numerical results show that the acceptable uniformity of mixing at Re = 0.1 is primarily attributed to the time-consuming molecular diffusion, whereas the cost-effective mixing at Re 〉 500 was obtained because of the generation of the swirling flow. The increasing mass fraction of glycerol in water was found to attenuate the mixing performance. The preliminary microscopic visualization of the two-fluid mixing at Re=1300 demonstrated the consistence with the numerical results.
基金supported by the National Natural Science Foundation of China(No.51606164).
文摘Because of potential high energy densities,microfluidic fuel cells can serve as micro-scale power sources.Because microfluidic fuel cells typically operate in the co-laminar flow regime to enable a membrane-less design,they generally suffer from severe mass transfer limitations with respect to diffusion transport.To address this issue,a novel channel design that integrates slanted groove micro-mixers on the side walls of the channel is proposed.Numerical modeling on the design of groove micro-mixers and grooveless design demonstrates a mass transfer enhancement that has a 115%higher limiting current density and well-controlled convective mixing between the oxidant and the fuel streams with the use of slanted groove micro-mixers.Moreover,the growth of the thickness of the depletion boundary layer is found to be terminated within approximately 2 mm from the channel entrance,which is distinct from the constantly growing pattern in the grooveless design.In addition,a simplified mass transfer model capable of modeling the mass transfer prFocess with the presence of the transverse secondary flow is developed.Further,a dimensionless correlation is derived to analyze the effects of the design parameters on the limiting current density.The present theoretical study paves the way towards an optimal design of a microfluidic fuel cell integrating groove micro-mixers.
基金Supported by the State Key Development Program for Basic Research of China (2010CB630904)the National Natural Science Fund for Distinguished Young Scholars (21025627)+2 种基金the National Natural Science Foundation of China (21106154,20990224)the National High Technology Research and Development Program of China (2011AA060704)the Beijing Natural Science Foundation (2112038) and Jiangsu Province Project (BY2009133)
文摘Mixing problems are most likely encountered and sometimes can be severe in scaling-up projects. Micro-mixing is an important aspect for fast or quasi-instantaneous reactions. Poor micro-mixing might produce more undesired by-products, leading to higher purification costs. This paper gives an extensive review and analysis of micro-mixing studies in single- and multi phase stirred tanks. The relevant experiment techniques, micro-mixing models and nurherical approaches are critically reviewed and analyzed with remarks and perspectives. The reported studies on two-phase micro-mixing experiments and on the impact of the presence of the dispersed phases on turbulence have been limited to a narrow range of conditions. More importantly, disparities widely exist among different reports. Both Lagrangian and Eulerian models are based on oversimplified assumptions, which may lead to uncertainties or even unrealistic results. A heuristic model, which is from the perspective of CFD （computational fluid dynamics） and can cover the whole spectrum of scales and also focus on every subrocess, is desired in the future.
基金supported by the National Key Research and Development Program(2016YFB0301702)the National Natural Science Foundation of China(21808221,21776282,21938009)+3 种基金Major Research Plan of NSFC(91934301)the Key Research Program of Frontier Sciences,CAS(QYZDJ-SSW-JSC030)the Key Research Program of Nanjing IPE Institute of Green Manufacturing Industry(No.E0010719)the Youth Innovation Promotion Association CAS。
文摘The coupled CFD-E-model for multiphase micro-mixing was developed,and used to predict the micro-mixing effects on the parallel competing chemical reactions in semi-batch gas–liquid and solid–liquid stirred tanks.Based on the multiphase macro-flow field,the key parameters of the micro-mixing E-model were obtained with solving the Reynolds-averaged transport equations of mixture fraction and its variance at low computational costs.Compared with experimental data,the multiphase numerical method shows the satisfactory predicting ability.For the gas–liquid system,the segregated reaction zone is mainly near the feed point,and shrinks to the exit of feed-pipe when the feed position is closer to the impeller.Besides,surface feed requires more time to completely exhaust the added H+solution than that of impeller region feed at the same operating condition.For the solid–liquid system,when the solid suspension cloud is formed at high solid holdups,the flow velocity in the clear liquid layer above the cloud is notably reduced and the reactions proceed slowly in this almost stagnant zone.Therefore,the segregation index in this case is larger than that in the dilute solid–liquid system.
文摘为探索纸质被动式农药微混合器的主要参数对农药混合效果的影响规律和增强农药混合的机理,选取Y型、Z型和方波型3种结构的纸质被动式农药微混合器,试验研究了每种微混合器不同参数条件对混合性能的影响,选出最优参数,再将最优参数下的3种微混合器的混合性能进行对比。试验结果表明,Y型微混合器的最优参数为:入口速度0.010 m L/min、入口角30°,Z型微混合器的最优参数为:入口速度0.010 m L/min、峰间距3 mm、转角30°,方波型微混合器的最优参数为:入口速度0.010 m L/min、波高2 mm、波宽5 mm;在各自的最优参数条件下,Y型微混合器出口处混合强度为0.622 7,Z型微混合器出口处混合强度为0.690 2,方波型微混合器出口处混合强度为0.732 6,方波型微混合器混合性能最好;纸质被动式农药微混合器通道内部存在纸纤维,可以提供流体流动的动力,也可以加剧分子间的扩散作用,同时也在一定程度上限制了对流作用。
