不同压实度下红层泥岩路堤沉降研究

压实系数是控制路堤填筑的关键性指标。本文通过分析不同压实系数下的强度特点以及通过离心试验和有限元对不同压实系数路堤沉降的模拟,得到粘聚力c值和摩擦角φ与不同压实系数的关系以及不同压实系数下路堤沉降的特点,为路堤填筑提供了重要的依据。     

压气机超速制造时弹塑性接触的数值模拟

“叶轮超速工艺“是叶轮制造中的一种重要方法.以某柴油机涡轮增压器的压气机为例,采用有限元参数二次规划法结合多重子结构技术分析模拟超速预加载制造时叶轮、轴套与轴之间接触应力的相应分布规律.针对不同的超速转速进行了大量计算,获得了超速转速与接触应力;超速转速与压气机内孔最大残余变形量;超速转速与轴套壁厚之间的关系.结果表明本文所采用的分析方法是可行的,弹塑性接触分析结果可作为叶轮设计及加工工艺的参考.     

叶片与蜗舌相对位置对离心泵性能数值模拟精度影响的研究

本文选择RANS方程和RNG k-ε湍流模型,采用有限体积法,在假定流动定常的前提下对离心泵中叶片与蜗舌不同相对位置时的流场进行数值模拟,总结分析了各性能参数的计算误差在不同的相对位置时的变化规律.通过叶片与蜗舌不同相对位置时对各性能参数计算误差的均方差进行比较,认为存在一个合适的相对位置使得对各性能参数的总体预测精度保持最高,为数值方法分析离心泵的性能提供了指导.     

On the separation of a suspension in a tube centrifuge: critical comments on theoretical models and experimental verifications

Summary We consider the batch centrifugal separation of a suspension of heavy particles in a cylindrical tube which rotates about an axis perpendicular to the axis of the tube. The theoretical analysis by means of a kinematic approximation covers two models: (1) the one-dimensional, which assumes that the particles settle along lines parallel to the sidewalls of the tube and sediment on the outer wall, and (2) the two-dimensional, which assumes that the particles settle along the centrifugal-field lines and sediment on both sidewalls and outer wall. A comparison shows that both models produce similarly simple formulas for the motion of the interface and the volume fraction as functions of time. However, the two-dimensional model is recommended for use because its results and insights are more reliable from both mathematical and physical considerations, and provide a more acceptable interpretation to recent experimental data, [5]. The author wishes to thank Prof. W. Schneider for stimulating discussions on the subject. The research was partially supported by the the Technion Fund V.P.R Fund – New York Metropolitan Research Fund.     

透平机械离心压缩机和离心泵叶轮动力分析的三维旋转循环对称CN群算法

以离心压缩机叶轮为例,建立三维有限元模型,采用循环对称CN群算法计算了它的动力特性,详细讨论离心力作用下叶轮的应力状态,分析与轴连接的不同方式对叶轮应力的影响。应用循环对称算法能大大减少建模与计算的工作量,有很好的实用价值。计算结果表明,离心压缩机叶轮在旋转中,叶轮外缘应力比较高,轮盖上的应力较轮盘上的应力大,叶片根部容易产生应力集中,应采用适当的园角避免应力集中,过盈配合的叶轮内孔处应力比较大,需要确定合理的过盈量,既要保证叶轮不松动也要保证叶轮内孔处的强度条件。     

Solid Particle Distribution in Centrifugal Impeller Contactors

The recently developed centrifugal impeller is examined to investigate the solid–liquid mixing in a mechanically agitated contactor. Using the sample withdrawal method, the effects of impeller geometrical parameters, impeller rotational speed (200–700 rpm), solid particle size (500–1100 µm), and solid loading (2–10 vol%) on the degree of homogeneity are studied. The axial and the radial solid concentration profiles and the minimum impeller speed for the complete homogenization are also determined. In comparison with a widely used propeller impeller, considerably higher homogeneity values in lower impeller speeds are obtained (90% homogeneity against 16% homogeneity at 200 rpm at the same conditions). Having also lower power consumption makes this a superior impeller in solid–liquid mixing processes especially in shear-sensitive systems.      

Salting-out gradients in centrifugal partition chromatography for the isolation of chlorogenic acids from green coffee beans

In addition to sample solubility constraints, the use of polarity gradients in normal-phase centrifugal partition chromatography (CPC) for the purification of complex mixtures is also limited by the instability of biphasic systems as a consequence of dramatic changes in the settling times along the gradient, leading in many cases to column bleeding when working under maximum efficiency conditions. In this paper an electrostriction approach is proposed as a strategy in reversed-phase CPC to fractionate intermediate polarity extracts in a single run by bringing its components into the “sweet spot” in a controlled fashion through a stepwise reduction of salt concentration in the aqueous mobile phase. The salting-out gradient method was successfully tested with the separation of the major chlorogenic acids (CGAs, hydroxycinnamoylquinic acids) present in green coffee beans (5-caffeoylquinic acid (5-CQA), 5-feruloylquinic acid (5-FQA) and 3,5-dicaffeoylquinic acid (3,5-diCQA)) using ethyl acetate-hexane as the stationary phase and an ionic gradient of LiCl (5.0, 2.5 and 0.1 M) as the mobile phase in one case and (NH₄)₂SO₄/KNO₃ (3.0 and 1.5 M/1.5 M) in another. Regioisomers of each chlorogenic acid obtained by base-catalyzed isomerisation were also separated by CPC using isocratic elution. The best resolution for both FQAs and diCQAs was achieved with a chloroform–n-butanol–0.01 M pH 2.5 phosphate buffer (84:16:100; v/v) system, while CQAs were best isolated using chloroform–n-butanol–0.01 M pH 2.5 phosphate buffer/5.0 M LiCl (82:18:100; v/v).     

Influence of cell packing by centrifugation on 40-MHz ultrasound backscatter

High-frequency ultrasound (HFUS) signals backscattered from RBL-2H3 cell pellets prepared under different centrifugal forces were analyzed to investigate the packing effect of cell aggregates. The measurements were performed in a pulse-echo setup with a 40-MHz transducer. The changes of ultrasound signals from cell pellet in backscattered power, statistical parameter, and pellet thickness were monitored after centrifugation at between 100g and 1600g. Experimental results showed that the HFUS backscattered power from cell pellets was inversely proportional to centrifugal force and increased to a plateau within 1-2 h after centrifugation. The initial thickness of cell pellets decreased with higher centrifugal force, but the changes in thickness and time that took to reach a plateau increased at higher centrifugal force. The envelope statistics of backscattered signals with Nakagami distribution indicates that the centrifugal force and elapsed time after centrifugation affected the backscattering characteristics. The present study suggests that centrifugal force and data acquisition time after cell pellet formation should be considered in in vitro cell packing method with centrifugation to emulate the tissue in vivo.     

The flow simulation of a low-specific-speed high-speed centrifugal pump

In this paper a general three-dimensional simulation of turbulent fluid flow is presented to predict velocity and pressure fields for a centrifugal pump. A commercial CFD code was used to solve the governing equations of the flow field. In order to study the most suitable turbulence model, three known turbulence models of standard k–ε, RNG and RSM were applied. The complex flow configuration required us to use around 5,800,000 cells, and 12 computational nodes (processors) for parallel computing. Simulation results in the form of characteristic curves were compared with available experimental data, and an acceptable agreement was obtained. Additionally, effect of number of blades on the efficiency of pump was studied. The number of blades was changed from 5 to 7. The results show that the impeller with 7 blades has the highest head coefficient. Finally, it was observed also that the position of blades with respect to the tongue of volute has great effect on the start of the separation. Thus, to analyze the effect of blade number on the characteristics of the pump, the position of blade and tongue should be similar to each other. Investigations of this kind may help to reduce the required experimental work for the development and design of such devices.     

Effects of the pump-circuit acoustic coupling on the blade-passing frequency perturbations

Centrifugal pumps are a source of pressure and flow rate perturbations in hydraulic pumping systems. In particular, a significant excitation is usually induced at the blade-passing frequency and harmonics as a consequence of the fluid-dynamic interaction between the rotor and the stator. The magnitude of this excitation is very dependent on the internal geometry of the pump and on its point of operation, but it depends also on the acoustic response of the hydraulic network to the perturbations. The induced and transmitted perturbations can be either amplified or reduced depending on the pump-circuit acoustic coupling, and thus they can lead to excessive levels of noise and vibration under certain conditions. The purpose of the present investigation is the theoretical and experimental characterization of the perturbations induced in a laboratory pumping system, as a function of the acoustic impedance of the pipelines. For different points of operation, the blade-passing frequency impedance is changed by varying the speed of rotation and, additionally, by modifying a closed side branch of the hydraulic system (that is, in the absence of net flow through it). For the theoretical calculations an acoustic model, based on matrix formulation, is applied to obtain the influence of different acoustic impedances of the suction side on the pressure fluctuations at the pump. Test measurements with a fast-response piezoelectric pressure transducer situated at the tongue region of the pump under the same system configurations confirm the significant effect of the pump-circuit acoustic coupling on the pressure perturbations.