Numerical simulation of flow regions in red mud separation thickener's feedwell by analysis of residence-time distribution

The residence-time distribution （RTD） and the compartment model were applied to characterizing the flow regions in red mud separation thickener’s feedwells. Combined with the experimental work, validated mathematical model as well as three-dimensional computational fluid dynamics （CFD） model was established to analyze the flow regions of feedwells on an industrial scale. The concept of RTD, although a well-known method for the characterization of mixing behavior in conventional mixers and reactors, is still a novel measure for the characterization of mixing in feedwells. Numerical simulation results show that the inlet feed rate and the aspect ratio of feedwells are the most critical parameters which affect the RTD of feedwell. Further simulation experiments were then carried out. Under the optimal operation conditions, the volume fraction of dead zone can reduce by10.8% and an increasement of mixing flow volume fraction by 6.5% is also observed. There is an optimum feed inlet rate depending on the feedwell design. The CFD model in conjunction with the RTD analysis then can be used as an effective tool in the design, evaluation and optimization of thickener feedwell in the red mud separation.

^(234)Th-derived particulate organic carbon export flux in the western Arctic Ocean

To evaluate the particle dynamics and estimate the POC (particulate organic carbon) export flux from the euphotic zone in the western Arctic Ocean,234 Th238 U disequilibrium was applied during the second Chinese National Arctic Research Expedition (July 15-September 26,2003).The POC export fluxes are estimated from the measured profiles of the 234 Th/238 U activity ratios and the POC/PTh ratios.The average residence times of the particulate and dissolved 234 Th in the euphotic zone are 33 d and 121 d,and their average export fluxes are 480 dpm/m 2 d and 760 dpm/m 2 d,respectively.The scavenging and removal processes of particle reactive elements are active in the upper layer of the Chukchi Sea.The average residence time of 234 Th increases from shelf to basin,while the export fluxes of 234 Th decrease.The estimated POC export fluxes from the euphotic zone vary from 2.1 to 20.3 mmol/m 2 d,indicating that the western Arctic Ocean is an important carbon sink in summer due to efficient biological pump.

Mean Residence Time of CO2 Molecules in Flexible ZIF-8 Cages Explored by Molecular Dynamics Simulations

The adsorption sites and diffusion mechanism of CO2 molecules in the flexible Zn（MeIM）2 （MeIM=2-methylimidazole） （ZIF-8） have been investigated by grand canonical Monte Carlo and molecular dynamics simulations. A reasonable time correlation function is for the first time constructed to explore the mean residence time of CO2 molecules in the ZIF-8 cages, suggesting that C02 molecules can remain in the same cage for up to several tens of picoseconds. Furthermore, we find that the mean residence time almost linearly increases with the increasing pressure （or loading） at 273 and 298 K.

The Resident Time Distribution of Injected Dispersed Drops in Stirred Extraction Columns

A resident time model is proposed to evaluate the performance of agitated extraction columns. In this model, the resident time of dispersed drops is simulated with the discrete phase modeling, where the continuous phase and the dispersed phase （drops） are described by the single-phase Navier-Stokes （turbulence） model and Lagrangian model, respectively. The interaction of dispersed phase and continuous phase is neglected for the low concentration of drop in the cases studied. The statistical parameters of drops （the average resident time and standard deviation） under different operation conditions are computed for four columns. The relation of the above statistical parameters with the performance of columns is discussed and the criterions for an optimal compartment are outlined. Our results indicate that the resident time model is useful to evaluate the performance and optimize the design of extraction columns.

Hydrodynamics of Liquid Flow in the Model of Theoretical Stage with Perfect Displacement

For the cyclic process of mass transfer in tray columns there are considered the hydrodynamic models of liquid flow during steam supply and during overflow of liquid from tray to tray. During steam supply, the hydrodynamic model is determined as perfect displacement model, and during liquid overflow, it is described as cell model. There were received the characteristics of liquid flow as follows： average residence time of liquid, degree of dispersion around the mean on the tray, number of perfect mixing cells depending on multiplication factor of exchange of liquid delay. In Y-X coordinates there is depicted a work line and theoretical stage of perfect displacement model. There were considered the conditions of mutual transfer of theoretical stage and theoretical stage with perfect displacement. The advantages of the mass transfer cyclic process to the stationary one arc stated.

光谱法结合分子对接研究普罗帕酮与牛血清白蛋白的相互作用

综合运用圆二色谱、停留-动力学、荧光、同步荧光、三维荧光、等温量热滴定法(ITC)等技术并结合分子对接进行表征牛血清白蛋白(BSA)与普罗帕酮的结合热力学及结合动力学参数。研究结果表明,BSA对普罗帕酮结合特异,在291K,298K,310K二者的亲和常数分别是2.612×105,2.879×105,6.793×105mol^-1,结合位点数n约为1。同步荧光光谱及三维荧光光谱表明,普罗帕酮与BSA结合后,荧光光谱发生蓝移,揭示BSA结合药物分子后高级构象发生变化。BSA结合普罗帕酮的停留-动力学反应符合三级指数方程曲线,快反应在约0.03 s完成结合,结合速率常数k1=0.097!0.02 s^-1,k2=1.058!0.18 s^-1,k3=31.410!1.18 s^-1。进一步通过分子对接显示普罗帕酮结合在蛋白的I域的IB疏水性口袋中,有12个氨基酸残基参与配体结合,其中Tyr160与Phe13各提供1个氢键参与配体结合,而带电氨基酸Glu125,Lys136,Arg185紧紧把配体束缚在结合口袋中。研究工作将有助于在分子水平上更为详细了解普罗帕酮与BSA的相互作用,并为进一步了解普罗帕酮在生物体内的作用提供理论基础。