Reappearance of azimuthal waves in turbulent Taylor-Couette flow at large aspect ratio

Velocity field data were acquired for Taylor-Couette flow in the annular gap between an inner rotating cylinder and a stationary concentric outer cylinder using particle image velocimetry (PIV) in a meridional plane of the annulus. Data were acquired for several rotational Reynolds numbers with the ratio of the rotational and critical Reynolds numbers ranging from 6 to 200, corresponding to flow states ranging from laminar wavy Taylor vortex flow to turbulent Taylor vortex flow. Spatial correlations of velocity fluctuations were found to exhibit a sharp decrease as R, the ratio of Reynolds number to the critical Reynolds number, increases from 16, indicating the disappearance of azimuthal waves and the onset of turbulence, reaching a minimum at R=18. However, correlation lengths subsequently increase with increasing R, displaying a secondary peak from 20?R?38, suggesting the reappearance of azimuthal waves. The reemergence of azimuthal waves was confirmed through other methods including analysis of the axial velocity. At still higher Reynolds numbers, correlation lengths decay once again. The magnitude and Reynolds number associated with the secondary peak in the fluctuation velocity correlations were found to be dependent on the location of the basis point used in the calculations. Specifically, correlation lengths were longest near the outer cylinder in the inflow boundary and near the inner cylinder in the outflow boundary. This was shown to be due to the spatial dependence of Reynolds stresses in turbulent Taylor-Couette flow.     

Simulation of Jet Drying of a Moist Cylinder at Low Reynolds Number

A numerical analysis of the process of jet drying of a moist cylinder was conducted. The drying jet was a laminar 2D jet stationed at three different distances (D/H = 0.22, 0.25, and 0.33) from the moist cylinder to investigate the jet effectiveness on heat and mass transfer. The diameter of the object and initial jet height were fixed in all cases. Temperature and mass distributions were obtained inside the object for different jet velocities. A finite volume method was used to solve the governing equations for momentum and energy with a commercial code. Calculations were performed for three different Reynolds numbers, namely, Re = 100, 200, and 300. It was found that heat and mass transfer increased with decreasing the distance, D/H, between the jet and the cylinder. In addition, increasing Reynolds number showed a positive effect on heat and mass transfer. Locally, jet drying was found to be most effective near the stagnation point on the leading side of the cylinder.     

非定常绕流主动控制的数值分析

为抑制圆体后尾流区涡脱落,降低流动阻力;在主圆柱体后方以上下对称方式各设置一旋转小圆柱体,以此实现对流场的控制。采用数值模拟方法,对采用此控制策略下的二维非稳态圆柱绕流尾流流动特性进行了分析研究;考察了Re=200时,附属小圆柱旋转速度α及旋转方向对主圆柱尾流流动特性的影响。数值模拟结果表明:当上部小圆柱顺时针旋转、下部小圆柱逆时针旋转时,可以抑制涡脱落并降低流动阻力;当α=2.4时即可实现对主圆柱体尾流区涡脱落的抑制效果;同时阻力系数和升力系数得到较大幅度降低,圆柱绕流的尾流流动特性被完全改变,有效控制了尾流区的不稳定性;而当上部小圆柱逆时针旋转、下部小圆柱顺时针旋转时,会导致尾流涡量增强,阻力及升力系数增大。     

Reaction and characterization of crosslinking hyperbranched poly(amine-ester) with succine anhydride

Basing on hydroxyl terminated hyperbranched poly(amine-ester)s (HPAEs), the cross-linking reactions and preparation of ester-crosslinked HPAE films were investigated using succine anhydride (SA) as crosslink reagent. It was proved that the cross-linking reaction between HPAE and SA followed a two-step mechanism. This mechanism provides an efficient route to prepare HPAE/SA cross-linked films, in which, the precursor films were prepared by casting HPAE/SA solution at a lower temperature, and then curing the films at a higher temperature. By varying SA content, the solid HPAE/SA films with different cross-linking degrees were prepared successfully. The highest tensile strength of the cross-linked film could reach 59.60 MPa. With all water contact angle smaller than 74.3°, the crosslinked films demonstrated good hydrophilic properties. __________ Translated from Journal of East University of Science and Technology (Natural Science Edition), 2006, 32(10): 1,164–1,168 [译自: 华东理工大学学报 (自然科学版)]     

Residence time distribution analysis from a continuous couette flow device around critical taylor number

This paper presents an experimental study of residence time distribution (RTD) analysis by pulse response technique in a continuous Couette flow device with rotating inner cylinder and stationary outer cylinder. Two kinds of experimental tests using pulses of tracer dye solution and particles resulting from a fast precipitation were performed in the region near the critical Taylor number characterizing boundary between laminar and laminar vortex flow. For most experiments performed in laminar and laminar vortex flow regime around the critical Taylor number over the ranges 0 < T_a < 120 and 0 < R_e < 5.5 the normalized response can be described by a dispersion model. The results of the critical Taylor number as characterized by the minimum dispersion number appear consistent with both theoretical predictions and other empirical observations.     

High-expression of recombinant human concensus interferon-α by Pichia pastoris

The present work focused on the high expression of recombinant human consensus interferon-α (cIFN) by Pichia pastoris. The cycle of glycerol feeding, the strategy of methanol feeding and the optimum pH for protein induction were studied. The optimized strategies were a 4-h glycerol-feeding period, induction pH being kept at 5.0 and methanol concentration being kept under 5 g/L. The maximum dry cell weight, cIFN production and bioactivity obtained were 168, 1.24 g/L and 5.4 × 10⁷ U/mL, respectively. __________ Translated from Journal of East China University of Science and Technology (Natural Science Edition), 2007, 33(2): 172–176 [译自: 华东理工大学学报 (自然科学版)]     

Self-ignition and special features of flow in a planar vortex chamber

Regular self-ignition of hydrogen and kerosene was registered upon their mixing with oxygen-enriched air in a straight-flow vortex, chamber of planar-radial geometry. These fuel components were injected into the chamber from tanks with room temperature and pressure 4–10 MPa. The velocity, pressure, and temperature fields in the chamber were studied using experimental methods and numerical modeling on the basis of full Navier-Stokes equations. The measurment and calculation showed that a region of elevated temperatures appears in an unsteady vortex flow. The calculation was performed for Reynolds number up to 5·10³ and revealed an increase in temperature with increase in Reynolds number. Nevertheless, both the calculated and measured temperatures were lower than the known self-ignition temperatures. The nature of the ignition, observed remains unclear. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 6, pp. 26–41, November–December 1999.     

CFD simulation of Taylor–Couette flow in scraped surface heat exchanger

The flow between two concentric cylinders which is termed as Taylor–Couette flow has been studied in scraped surface heat exchanger with and without blades. Shear rate in annular flow with and without blades was measured by Dumont et al. (2000a) using electrochemical method and determined the onset of Taylor vortices at specific Taylor number in both cases for Newtonian flow. CFD simulations have been carried out to determine the transition zone from laminar Couette flow to Taylor vortex flow using the same geometry for which Dumont et al. (2000a) had carried out the experiments. The Reynolds stress model (RSM) and k–? model are used for Taylor vortex flow (Ta > 300) to characterize the flow pattern in annular flow and SSHE respectively. The aim of the present work is to analyze the effect of rotating scraper on the existing flow patterns in simple annular flow using CFD simulations.     

A NUMERICAL SOLUTION OF THE FLOW AROUND A SPHERE IN A CIRCULAR CYLINDER

A numerical solution of the Navier-Stokes equations is presented for Poiseuille flow around an axially placed, fixed sphere in a circular cylinder. Streamlines and isovorticity lines are calculated from the governing equations for the strearnfunction and the vorticity. Isobars are calculated from a Poisson equation, derived from the Navier-Stokes equations. The pressure and vorticity distribution on the surface of the sphere, the additional pressure drop and the drag coefficients are presented. Solutions are obtained for Reynolds numbers up to 150 (based on cylinder diameter and mean velocity). The wall effects are examined by comparison with results of previous investigations for an unbounded flow around a sphere.     

A NUMERICAL SOLUTION OF THE FLOW AROUND A SPHERE IN A CIRCULAR CYLINDER

A numerical solution of the Navier-Stokes equations is presented for Poiseuille flow around an axially placed, fixed sphere in a circular cylinder. Streamlines and isovorticity lines are calculated from the governing equations for the strearnfunction and the vorticity. Isobars are calculated from a Poisson equation, derived from the Navier-Stokes equations. The pressure and vorticity distribution on the surface of the sphere, the additional pressure drop and the drag coefficients are presented. Solutions are obtained for Reynolds numbers up to 150 (based on cylinder diameter and mean velocity). The wall effects are examined by comparison with results of previous investigations for an unbounded flow around a sphere.     

Experimental studies on the influence of porosity on membrane absorption process

Eight kinds of flat membranes with different micro-structures were chosen to carry out the membrane absorption experiments with CO₂ and de-ionized water or 0.1 mol·L⁻¹ NaOH solution as the experimental system. According to experimental results, the membrane pores shape (stretched pore and cylinder pore) and membrane thickness do not affect the membrane absorption process, and the membrane porosity has only little influence on membrane absorption process for slow mass transfer system. However, the influence of porosity on the membrane absorption process became visible for fast mass transfer system. Moreover, the mass transfer behavior near the membrane surface on liquid side was studied. The results show that the influence of membrane porosity on mass transfer relates to flow condition, absorption system and distance between micro-pores, etc. __________ Translated from Journal of Chemical Engineering of Chinese Universities, 2007, 21(1): 14–19 [译自: 高校化学工程学报]     

Axial symmetric flow model for a flat bottom hydrocyclone

Experiments with laser Doppler velocimetry show that, for flat bottom hydrocyclones, the axial velocity field is a function of the radius and a linear function of the axial co-ordinate, while the tangential velocity is a function of the radial co-ordinate only. Based on these results, a physical model is presented, where the flow field is divided in two zones. Zone I corresponds to the feed inlet, which occurs through a ring in the upper portion of the cylinder, the length of which depends on the length of the vortex finder tube. Zone II includes the rest of the cylinder. The axial symmetric solution of Reynolds equations for the isotropic turbulent flow leads to two sets of field equations, one for each zone in the hydrocyclone. In zone II, where experimental data were determined, simulation compares favourably with the flow pattern determined experimentally for water in a 100-mm flat bottom hydrocyclone.     

Solubility of CO2 in solid-state PET measured by pressure-decay method

The solubility of CO₂ in solid-state PET was measured using a pressure-decay method. In order to calculate the solubility of CO₂ in the amorphous region of PET, the crystallinity of solid state PET dissolved in CO₂ at different pressures and temperatures was measured by differential scanning calorimetry (DSC). The solubility increases with increasing pressure and it follows a linear relationship and obeys Henry’s law when the pressure is below 8 MPa. The effect of temperature on solubility is weak and the solubilities at different temperatures are almost the same under low pressures. At higher pressure, the solubility decreases with an increase in temperature. The solubility of CO₂ in the amorphous region of PET at 373.15 K, 398.15 K and 423.15 K was correlated with the Sanchez-Lacombe equation of state with a maximal correlation error of 6.69%. __________ Translated from Journal of East China University of Technology (Natural Science Edition), 2007, 33(4): 445–449 [译自: 华东理工大学学报(自然科学版)]     

Numerical simulation of two-dimensional spouted bed with draft plates by discrete element method

A discrete element method (DEM)-computational fluid dynamics (CFD) two-way coupling method was employed to simulate the hydrodynamics in a two-dimensional spouted bed with draft plates. The motion of particles was modeled by the DEM and the gas flow was modeled by the Navier-Stokes equation. The interactions between gas and particles were considered using a twoway coupling method. The motion of particles in the spouted bed with complex geometry was solved by combining DEM and boundary element method (BEM). The minimal spouted velocity was obtained by the BEMDEM-CFD simulation and the variation of the flow pattern in the bed with different superficial gas velocity was studied. The relationship between the pressure drop of the spouted bed and the superficial gas velocity was achieved from the simulations. The radial profile of the averaged vertical velocities of particles and the profile of the averaged void fraction in the spout and the annulus were statistically analyzed. The flow characteristics of the gas-solid system in the two-dimensional spouted bed were clearly described by the simulation results. __________ Translated from Chemical Engineering (China), 2007, 35(6): 24–28 [译自: 化学工程]     

Effects of Co2+ on the erythromycin biosynthesis

Erythromycin biosynthesis is a highly complicated process, which involves both primary metabolism and secondary metabolism. The specific activities of the key enzymes related to glucose metabolism such as hexose kinase (HK), glucose-6-phosphate dehydrogenase (6-PDH), phosphofructokinase (PFK), and isocitrate dehydrogenase (ICD), were determined in Saccharopolyspora erythraea. The specific activities of the enzymes involved in secondary metabolism, such as methylmalonyl-coenzyme A mutase (MCM) and methylmalonyl-coenzyme A transcarboxylase (MCT), were detected as well. Some organic acids contained in fermentation broth were also analyzed. The results show that Co²⁺ is able to increase erythromycin biosynthesis. It maybe due to Co²⁺ improving the specific activities of methylmalonyl-coenzyme A mutase and methylmalonyl-coenzyme A transcarboxylase. Meanwhile, it also enhances the flux of the glucose metabolism pathway. Translated from Journal of East China University of Science and Technology (Natural Science Edition), 2006, 32(11): 1 280–1 284 [译自: 华东理工大学学报 (自然科学版)]     

Characterization of Taylor vortex flow in a short liquid column

We present a study on Taylor vortex flow in the annulus between a rotating inner cylinder and a stationary outer cylinder, featured with a wide gap (radius ratio is 0.613) and a short column (aspect ratio is 5.17). A particle image velocimetry (PIV) system was used to determine the position, shape, and velocity distribution of the vortices, by which the flow was also confirmed to lie in the nonwavy Taylor vortex regime for all operating conditions explored in this study. Our results suggest that end boundary effects are important, in which the vortex number decreases with decreasing column length. For a system with an aspect ratio of 5.17, six vortices appear in the gap with their position, size, and shape varying at different Reynolds numbers. The fluid velocities show an asymmetric feature with respect to the vortex centers, while the maximum axial and radial velocities increase almost linearly with the increasing reduced Reynolds number (Re ? Re_c). In addition, computational fluid dynamics study was employed under the same conditions, and its results agree well with the PIV measurements. Overall, this study provides a quantitative understanding of the formation of Taylor vortices in a constrained space. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Synthesis and characterization of 2,5-bis[4-(2-arylvinyl) phenyl]-1,3,4-oxadiazoles with two-photon fluorescence properties

Four novel 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles that exhibit strong two-photon absorption and enhanced two-photon excited fluorescence were designed and synthesized based on “push-core-pull-core-push” molecules built from embedding electron-transporting 1,3,4-oxadiazole in aromatic conjugated system through Wittig-Horner reaction. Their chemical structures were determined to show trans-vinylene character according to infrared (IR) and ¹H nuclear magnetic resonance (NMR) spectra. A very effective energy transfer from the excited units to the π-conjugated bridging unit can enhance the two-photon absorption and two-photon fluorescence. __________ Translated from Journal of Southeast University (Natural Science Edition), 2006, 36(5): 795–798 [译自: 东南大学学报 (自然科学版)]     

Synthesis and thermosensitive behavior of dextran graft copolymers containing poly(N-vinylcaprolactam) side chains

New graft copolymers were synthesized by grafting N-vinylcaprolactam onto dextran. Their composition and structure were investigated by elemental analyses, infrared spectra and thermogravimetric analyses. By optical transmittance measurements, it was found that the aqueous solutions of these graft copolymers showed a temperature-dependent transmittance change due to the introduction of thermosensitive poly(N-vinylcaprolactam) graft chains. Moreover, the lower critical solution temperature (LCST) of the graft copolymer in aqueous solution was dependent on its grafting extent and concentration. The LCST value was found to increase with the increase of the grafting extent and decrease with the increase of the copolymer concentration. With these stimuli-response properties, such polysaccharide derivative may hold potential applications in biomedicine and biotechnology. Translated from Acta Scientiarum Naturalium Universitatis Sunyatseni, 2006, 45(1): 50–52 [译自: 中山大学学报 (自然科学版)]     

Electrochemical analysis of Taylor vortices

Steady Taylor vortices in the annular gap between coaxial cylinders were studied using the electrodiffusion method. The cylinders had an aspect ratio of 17.7 and a radius ratio of 0.5. The inner cylinder was driven with a stepping motor. The Reynolds number was in the range (113, 880). Two three-segment circular probes were imbedded with a horizontal shift of 5 mm in the wall of the outer fixed cylinder. The vortexes were swept along the probes by a slow upwards axial motion of the electrolyte solution. The axial distribution of the axial and azimuthal components of the wall shear rate was obtained and fitted by sixth-order Fourier series. The torque was calculated from the azimuthal component. The vortex ascending velocity and vortex height were evaluated from the correlation and autocorrelation functions of the measured current.     

不同流量条件下导叶式旋流器内部流动的数值模拟

应用Fluent软件和雷诺应力模型(RSM)对导叶式旋流器内部三维强旋湍流流动进行了数值模拟,考察了不同入口流量对旋流器内速度场的影响。研究结果表明,旋流器内径向速度远小于切向速度和轴向速度,锥段的切向速度明显小于柱段的切向速度;随着流量的增加,各向速度均增加,最大切向速度的分布直径并不随流量的变化而改变,且最大切向速度位于准自由涡与准强制涡的分界处。通过计算还发现,在旋流器圆柱段存在循环流和短路流,锥段的上行区域均小于柱段,而且截面越靠底流口,上行区域越小。