Experiments on the turbulent shear flow in a turn-around duct(I)—The mean flow characteristics

The Complex turbulent water flow in a strongly curved turn-around duct has been studied. The turn-around duct had an aspect ratio of 10∶1 and the ratio of the channel height to the mean radius was 1.0. Extensive measurements throughout the curved duct including wall static pressures and mean velocities were made using Laser Doppler Velocimeter for a Reynolds number of 210,000 based on the height of the channel and the average velocity. Analytical calculations of the potential flow were made using Green’s function and the Rayleigh-Ritz method. Based on the turbulence mechanism and stability consideration, a simplified physical model for the outer layer near the start, of the turn along the inner convex wall was hypothesized. This physical model leads to a system of non-linear equations represented in orthogonal curvilinear coordinates. These equations were solved numerically using an iteration method. Comparison of the measured data with the calculated values reveals that the present flow shows the characteristics of an inertial dominated, developing curved flow. The outer layer in a quasi-laminar flow was governed by inviscid-rotational motion. The numerical solution for this region was verified by comparing the calculated and measured flow results. Near the turn exit along the inner wall, a large flow reversal was observed. Spanwise measurements showed that the present turn-around duct flow was approximately two-dimensional. The local mean velocity profiles in the turn for different flow rates were similar when normalized by the average velocity.     

Two-fluid non-Newtonian models for blood flow in catheterized arteries — A comparative study

Steady flow of blood through catheterized arteries is studied by assuming the blood as a two-fluid model with the suspension of all the erythrocytes in the core region as a non-Newtonian fluid and the plasma in the peripheral layer as a Newtonian fluid. The non-Newtonian fluid in the core region of the artery is modeled as (i) Casson fluid and (ii) Herschel-Bulkley fluid. The expressions for the shear stress, velocity, flow rate, wall shear stress and flow resistance, obtained by Sankar and Lee (2008a, 2008b) for the two-fluid Casson model and two-fluid Herschel-Bulkley model are used to get the data for comparison. It is noticed that the plug flow velocity, velocity distribution and flow rate for the two-fluid H-B model are considerably higher than that of the two-fluid Casson model for a given set of values of the parameters. Further, it is found that the resistance to flow is significantly lower for the two-fluid H-B model than that of the two-fluid Casson model. Thus, the two-fluid H-B model is more useful than the two-fluid Casson model to analyze the blood flow through catheterized arteries.     

Volume fraction measurement and flow regime recognition in dynamic gas–liquid two phase flow using gamma ray radiation technique

Gas–liquid two phase f low is probably the most important form of multiphase f lows and is found widely in industrial applications, particularly in the oil and petrochemical industry. In this study, in the first instance a gas–liquid two phase f low test loop with both vertical and horizontal test tube was designed and constructed. Different volume fractions and f low regimes were generated using this test loop. The measuring system consists of a ¹³⁷Cs single energy source which emits photons with 662 keV energy and two 1-inch NaI (Tl) scintillation detectors for recording the scattered and transmitted counts. The registered counts in the scattering detector were applied to the Multi-Layer Perceptron neural network as inputs. The output of the network was gas volume fraction which was predicted with the Mean Relative Error percentage of less than 0.9660%. Finally, the predicted volume fraction via neural network and the total count in transmission detector were chosen as inputs for another neural network with f low regime type as output. The f low regimes were identified with mean relative error percentage of less than 7.5%.     

基于Mold flow软件的PC面板CAE分析

通过应用Mold flow/MPI软件,对电脑面板零件的注射成型过程进行了CAE流动模拟分析,显示了CAE技术在模具开发过程中对于最佳浇口位置与浇口数量的确定、流道系统的布置、塑件设计优化、模具一次试模成功率等方面所起到的突出作用.     

SPX’s flow unit sees solid revenue gains

SPX Corp’s Flow Technology division, which includes Bran+Luebbe and Waukesha Cherry Burrell, reported revenues of US$352.2 million for the first quarter of 2003, up 25.9% on 2002’s US$279.7 million.This is a short news story only. Visit www.worldpumps.com for the latest pump industry news.     

基于Mold flow软件的组合型腔模具流动平衡设计

使用Mold flow软件对电器元件外壳组合型腔模具进行了流道平衡分析,结果显示,当分流道的直径分别为Φ4mm和Φ4.3 mm时,塑料熔体能够基本上在同一时刻充满各型腔,实现了塑料熔体的平衡流动,防止了由于流动不平衡而产生的过保压等缺陷。     

Gas–liquid two-phase flowrate measurement in pseudo-slug flow with Venturi

The importance of pseudo-slug flow research is becoming increasingly prominent in the petrochemical field. But the gas–liquid two-phase flowrate measurement in the pseudo-slug flow has not been properly understood and modeled. Based on the differential pressure of Venturi, this study proposes a new pseudo-slug flowrate prediction model. By means of Fast Fourier transform (FFT), the representative frequency range (3.125 Hz < f < 6.25 Hz) is determined. Then, the fourth detail component of the differential pressure after wavelet transform is selected as the flag to distinguish the liquid film region and the pseudo-slug body region. Based on the gas–liquid density ratio, a logarithmic model is established to predict the threshold value. In the liquid film region, the gas–liquid two-phase flow is regarded as wet gas and the flowrate is measured through the over-reading model. In the pseudo-slug body region, the volume gas holdup model is established based on the fluctuation information of the differential pressure. Then the gas–liquid two-phase flowrate can be obtained by solving the Bernoulli equation. Compared to the experiment, the confidence probability of ±10% relative deviation band is 97.78% for the gas, and the confidence probability of ±20% relative deviation band is 95% for the liquid.     

A knowledge-based approach for designing effective grooved chip breakers — 2D and 3D chip flow,chip curl and chip breaking

This paper presents details of a knowledge-based approach for designing effective grooved chip breakers for two- and three-dimensional chip flow, curl and breaking. The design criterion used in formulating this new approach is effective chip breaking at minimum power consumption. This work was aimed at achieving the optimum groove parameters and the best utilisation of groove profile under varying machining conditions. A systematic knowledge-pool was established from a series of well-designed machining experiments which form four knowledge databases (reference database, grooved chip breaker database, natural contact length database and 3D chip flow database). This paper shows how the chip breaker design parameters can be estimated for effective chip breaking at reduced power consumption. The basic tool design strategy presented in the paper also includes some guidelines, for cutting tool designers, highlighting the need for implementing a scientific approach for designing a chip breaker against the current practice of try and see methods.     

Theoretical flow instability of the Kármán boundary layer

The hydrodynamic stability of the Kármán boundary-layer flow due to a rotating disk has been numerically investigated for moving disturbance waves. The disturbed flow over a rotating disk can lead to transition at much lowerRe than that of the well-known Type I instability mode. This early transition is due to the excitation of the Type II instability mode of moving disturbances. Presented are the neutral stability results concerning the two instability modes by solving new linear stability equations reformulated not only by considering whole convective terms but by correcting some errors in the previous stability equations. The reformulated stability equations are slightly different with the previous ones. However, the present neutral stability results are considerably different with the previously known ones. It is found that the flow is always stable for a disturbance whose dimensionless wave numberk is greater than 0.75.     

A review of information flow diagrammatic models for product–service systems

Quality of an assembly of any manufactured product is mainly based on the quality of mating components. Due to random variations in sources such as materials, machines, operators, and measurements, mating components manufactured by even the same process may vary in their dimensions. When mating components are assembled linearly, the resulting assembly tolerance will be the sum of the mating components tolerances. All precision assemblies demand for a closer assembly tolerance. A significant amount of research has already been done to minimize assembly variation using selective assembly, when the dimensions of components follow normal distribution. However, in reality, the dimensions of components produced especially in smaller to medium size batches, invariably have some skewness (non-normality), which makes the methods developed and reported in the literature, often not suitable for practice. In this work, batch selective assembly methodology is proposed for components having non-normal distributions to minimize the assembly tolerance variations. The proposed method which employs a genetic algorithm for obtaining the best combination of mating components is able to achieve minimum variations in assembly tolerances and also maximum number of acceptable assemblies. The proposed algorithm is tested with a set of experimental problem datasets and is found outperforming the other existing methods found in the literature, in producing solutions with minimum assembly variation.     

Flow noise characterization of gas–liquid two-phase flow based on acoustic emission

Flow noise of gas–liquid two-phase flow in horizontal pipeline was detected by using the acoustic emission technique (AE); signals were processed by wavelet transform and chaotic analysis. Conclusions were drawn that stratified flow, annular flow and their transition can be divided clearly through multi-scale energy distribution of flow noise, and that dynamic characteristic of flow pattern transition from stratified flow to annular flow, which is described via correlation dimension, acts in accordance with that of annular flow. The dynamic characteristic of the transition condition has already been consistent with that of the annular flow, but due to the low gas flow rate, the energy of the hydrodynamic noise was not enough to reach the complete annular flow pattern. Results were in accordance with experimental facts. Flow noise reflects the complexity of gas–liquid two-phase flow by means of multi-scale energy distribution and chaotic features. Consequently, flow noise based on acoustic emission is a novel and promising point for researching gas–liquid two-phase flow.     

Evaluation of multi-holed orifice flowmeters under developing flow conditions – An experimental study

This study focuses on multi-holed orifice plates, which have superior flow measuring characteristics as compared to their conventional counterparts. However, literature is scant on quantitative parametric investigations. In this experimental study, the performance of a multi-holed orifice plate is evaluated for variable number of holes (n), equivalent diameter ratio (EDR), compactness ratio (C), plate thickness ratio (s/d) and upstream developing length (L/D) in developing flow regimes for the Reynolds number range of 24,500–55,500 by using Central Composite Design. A total number of 324 experiments were performed. It was found that EDR has the most significant effect on pressure loss coefficient, followed by ‘n’ and ‘C’. Moreover, it was found out that single orifice (SO) and multi-holed orifice (MO) have almost the same pressure losses for the same value of EDR/β. However, flow develops quickly for MOs. Higher values of coefficient of discharge were observed in the case of MOs as compared to the SOs with little effect of upstream disturbances. The effect of developing length is significant on the accuracy of orifice meter. However, when the multi-holed orifice plates are installed at 2D upstream length, the effect of upstream disturbances are diminished. This result provides the flexibility of installation, which means that multi-holed orifices can be installed at 2D. The experimental data is in good agreement with literature. Finally, an optimum orifice plate (5,0.4,0.7) was selected for flow developing region with minimum pressure loss coefficient based upon the experimental results.     

Multi – oil droplet recognition of oil-water two-phase flow based on integrated features

Multi-oil droplet target recognition is one of the applications of machine vision in the measurement of oil-water two-phase flow parameters, which could combine other algorithms to obtain the oil droplet velocity and the water holdup of oil water two-phase flow. Appropriate target representation features can improve the recognition effect of multiple oil droplets. However, due to shooting environment differences and quality differences of oil-water two-phase flow images, existing target representation features do not perform well in low-quality oil-water two-phase flow images. To improve the precision of multi-oil droplet target recognition in oil-water two-phase flow and reduce the miss rate, this paper constructs an integrated feature on the basis of aggregate channel features (ACF). The integrated feature named aggregate channel features with histogram of local gravitational feature（ACFHG） contains the color feature channels reflecting the overall color features of the oil droplet sample, the gradient amplitude channel reflecting the overall gradient of the oil droplet sample image, the gradient direction histogram feature channels reflecting the local gradient of the oil droplet sample image, and the local gravitational feature channels that ensure oil droplet target recognition in low quality photos and photos taken in complex shooting environments. Moreover, the rotation invariance is obtained by taking the oriented gradient histogram of the local gravitational feature to further improve the multi-oil droplet target recognition effect. Experiment results show that the average precision of multi-oil droplet target recognition using the integrated features is 83.38%, which is 9.93% higher than that with using ACF, and the miss rate is 9.13%, which is 57.18% lower than that with using ACF. Compared with other existing target detection methods, the method proposed in this paper still has an advantage in the rate of missed detection.     

Numerical simulation of turbulent flow of hydraulic oil through 90° circular-sectional bend

Oil flow through pipe bends is found in many engineering applications. However, up to now, the studies of oil flow field in the pipe bend appear to be relatively sparse, although the oil flow field and the associated losses of pipe bend are very important in practice. In this paper, the relationships between the turbulent flow of hydraulic oil in a bend and the Reynolds number Re and the curvature ratio ? are studied by using computational fluid dynamics (CFD). A particular emphasis is put on hydraulic oil, which differs from air or water, flowing through 90° circular-sectional bend, with the purpose of determining the turbulent flow characteristics as well as losses. Three turbulence models, namely, RNG k-? model, realizable k-? model, and Reynolds stress model (RSM), are used respectively. The simulation results in the form of contour and vector plots for all the three turbulence models for pipe bends having curvature ratio of ??0.5, and the detailed pressure fields and total pressure losses for different Re and ? for RSM are presented. The RSM can predict the stronger secondary flow in the bend better than other models. As Re increases, the pressure gradient changes rapidly, and the pressure magnitude increases at inner and outer wall of the bend. When ? decreases, two transition points or transition zones of pressure gradient arise at inner wall, meanwhile, the transition point moves towards the inlet at outer wall of the bend. Owing to secondary flow, the total pressure loss factor k increases as the bend tightens, on the contrary, as Re increases, factor k decreases due to higher velocity heads, and the rapid change of pressure gradient on the surface of the bend leads to increasing of friction and separation effects, and magnified swirl intensity of secondary flow. A new mathematical model is proposed for predicting pressure loss in terms of Re and ? in order to provide support to the one-dimensional simulation software. The proposed research provides reference for the analysis of oil flow with higher Re in the large bends.     

2—苯基—3—烷基—7—硝基—1,4—氧硫杂萘—4,4—二氧化物的质谱研究

本文研究了新合成的八种２－苯基－３－烷基－７－硝基－１,４－氧硫杂萘－４,４－二氧化物的电子轰击质谱,对裂解规律进行了探讨     

Concentration and pressure measurements of dense sand and gravel multiphase flows under transient flow conditions in a vertically oriented closed conduit — Assessment of system and sensor performance

The hydraulic transport of sediments in sediment–water multiphase mixtures is an important process in nature and many industrial applications. The flows are characterized by complex transient phenomena, in which the overall system scale and the particle scale are equally important. Experimental research into dense mixture flows is focused on measurement of flowrates, differential pressures and concentrations of the suspended sediments.Concentration measurements are especially challenging in the case of coarse particles (beyond millimeter size scale) flowing in dense mixtures, limiting the range of available sensors for accurately measuring the in-situ solids concentrations. For the investigation of transient processes, a quick sensor response is required, which makes concentration measurement based on mixture conductivity an interesting option.This study is focused on combined concentration and pressure measurements in dense sediment–water mixtures with coarse particles in a vertically oriented closed conduit, using differential pressure sensors over the vertical segments and conductivity probes for measuring the mixture concentration. We experimentally investigated the dispersion process of an initially densely packed batch of sand and gravel by measuring the concentration on different segments of the conduit, resulting in data on mixture wall shear stresses for different sand and gravel mixtures and data of attenuation of concentration gradients in vertical upward and downward flow, in the conduit horizontal top section and in the centrifugal pump.We describe in the detail the sensor calibration and data processing method, giving a best practice for the use of conductivity concentration sensors in dense coarse particle mixtures, and we suggest a novel method for analysis of density wave amplification and attenuation based on concentration measurements in general, which allows for the detailed analysis of transient multiphase flow phenomena at pipe system component level.     

Nanofinishing of flat workpieces using rotational–magnetorheological abrasive flow finishing (R-MRAFF) process

A new finishing process named as “rotational–magnetorheological abrasive flow finishing (R-MRAFF)” has been proposed to enhance the finishing performance of MRAFF process. In this process, a rotation cum reciprocating motion is provided to the polishing medium by a rotating magnetic field and hydraulic unit. By intelligently controlling these two motions, a uniform smooth mirror-like finished surface with improved material removal rate and finishing rate (nanometer per cycle) is achieved for both stainless steel and brass workpieces. From the preliminary experiments, it is found that R-MRAFF process produces better results than MRAFF. Experiments have been planned using design of experiments technique. Analysis of variance is conducted to find out the contribution of each model term affecting percent improvement in surface finish. The optimum finishing conditions are identified from optimization study. The present study shows that the combinations of rotational speed of the magnet and its square term together have the highest contribution to the percentage improvement in surface roughness. Other significant parameters in the order of decreasing percent contribution to the change in surface roughness value are finishing cycles, extrusion pressure, and fluid composition. The best surface finish obtained on stainless steel and brass workpieces with R-MRAFF process are 110 and 50 nm, respectively. From the scanning electron micrographs and atomic force micrographs, it has been observed that the abrasive cutting marks generate cross-hatch pattern on the surface finished by R-MRAFF process.     

Nautilus——鹦鹉螺

第一次接触Nautilus，比第一次听到发烧级音响还要吃惊。竟然有如此的喇叭，也竟然会有如此出色的效果!B＆W不是世界上最贵的喇叭，但绝对是世界上最物超所值的喇叭之一。