脉动热管实验台的搭建及可视化实验研究

介绍了脉动热管可视化实验台的搭建,通过此实验台可以定量研究工质种类、充注量、管道特性、倾斜角度、加热功率、冷却能力等参数对脉动热管传热性能的影响,并能实现整个管道工质流型变化的可视化,通过可视化实验观察到,脉动热管从启动到稳定运行的过程,工质的流型会经历泡状流、弹状流、塞状流到搅拌流的变化.     

Characterization of slug flows in horizontal piping by signal analysis from a capacitive probe

The slug flow is a common occurrence in gas–liquid piping flows. Usually it is an undesirable flow regime since the existence of long lumps of liquid slug moving at high speed is unfavorable to gas–liquid transportation, so that considerable effort has been devoted to study its hydrodynamic characteristics. In this work, a capacitive probe was used for dynamic measurements in the horizontal air–water slug flows, for several flow rates. The acquired signals were representative of the effective liquid layer thickness near every cross sectional area of the flow, instead of merely the holdup or void fraction in a finite volume of the flow. This was possible because probe had a thin sensing electrode that minimizes the axial length effect on the measurements. Tests were performed in a 34 mm i.d. acrylic pipe, 5 m long; in which slug flows as well as stratified-smooth and stratified-wavy flows were generated. Signal analysis techniques were applied for flow regime identification and toward characterization of these two-phase flows: Power Spectrum Density (PSD) from Fourier Transform and Probability Density Function (PDF) from Statistical Analysis. Therefore, PSD and PDF graphs were taken as signatures of each flow under test and a correlation was calculated for each PSD and PDF set of data, which showed to be a robust parameter for correct flow regime identification.     

Neutralizing the effect of the angle variations on the drop detachment in automatic GMAW system

Two forces play the main role on the drop detachment in gas metal arc welding process: the electromagnetic and gravitational forces. Since in an automatic pipeline system, the welding angle varies from 0° to 180° in each pass, the total force will vary, so the drop detaching will not remain invariable during the welding time. In the previous works Doodman Tipi (Int J Adv Manu Technol 50:137?C147, 2010 [1]), Doodman Tipi (Int J Adv Manu Technol 50:149?C161, 2010 [2]), the angle variation effects on the metal transfer was studied on both transfer modes (free flight and short circuit). In this paper, the effect of the input parameters on the drop detaching is studied. Also, a welding current pattern is presented in order to neutralize the effect of the angle variation around the pipe. Furthermore, suitable patterns for other parameters (arc voltage, travel speed, and electrode speed) are introduced to keep constant the molten electrode volume, heat input, voltage to current relation, and energy density. This would guarantee stabilization of the other welding specifications. Finally, several experimental and simulation examples illustrate to achieve the regular detachment using the presented method, and results are compared with the un-neutralized case.     

仿生液压管路双向流固耦合机理及脉动吸收研究

高速高压化导致液压泵口流量压力脉动加剧,其振动控制尤为重要。借鉴“猎豹心脏出口血管能耐受高压高频血液脉动”的生物学机理和结构,提出一种具有3层结构的仿生管路,其外层为钢管,中层为硅橡胶,内层涂有减摩材料。针对仿生管路的中层,考虑硅胶材料非线性,对比分析国内外已有的硅胶材料数学模型后,选用Mooney-Rivlin模型描述硅胶材料,其模型参数由拉伸实验确定;然后,结合硅胶材料模型,对液压管路流固耦合14-方程进行修正;最后,采用ANSYS Workbench软件分别对不同管路长度和硅胶层厚度的仿生管路进行双向流固耦合仿真。数值分析结果表明,随着管路长度和硅胶层厚度的增加,仿生管路对流量脉动吸收效果不断增强。     

Measurements of translational slug velocity and slug length using an image processing technique

Slug flow is a common flow regime that occurs in various industries, such as oil, gas, and power generation industries. In this study, the mean slug translational velocity and slug liquid length were measured using Phantom 9.2 software and an image processing analysis technique. The adopted image processing technique involved the analysis of video frames recorded from a high-speed camera (Phantom 9.2) in a horizontal transparent pipe using a combination of the approximate median method and blob analysis, along with an additional morphological process for detecting and segregating individual slugs. The experimental data were obtained from a designed two-phase flow test section, in which sets of superficial water and air velocities were selected to generate numerous slug flows. A good agreement with a maximum deviation of 6.7% between the estimated slug parameters from the adopted technique and the Phantom cine view controller software was achieved. Additionally, the developed technique provided precise results with a high processing speed of 10 frames per second.     

Identification of gas-liquid two-phase flow patterns in a horizontal pipe based on ultrasonic echoes and RBF neural network

This paper proposes a novel flow pattern identification method using ultrasonic echo signals within the pipe wall. A two-dimensional acoustic pressure numerical model is established to investigate the ultrasonic pulse transmission behavior between the wall-gas and wall-liquid interface. Experiments were also carried out at a horizontal air-water two-phase flow loop to measure the ultrasonic echo pulse signals of stratified flow, slug flow, and annular flow. It is interesting to find that the attenuation of the ultrasonic pulse at the wall-liquid interface is faster than the attenuation at the wall-gas interface. An RBF neural network is constructed for online flow pattern identification. The normalized envelop area and the area ratios of the echo spectrum are selected as the input parameters. The results show that the stratified flow, slug flow, and annular flow can be identified with an accuracy of 94.0%.     

气力输送过程分支管路阻力特性的研究

在水平T型分支管道中,用压缩空气对平均粒径为0.25 mm的砂石进行气力输送试验。试验结果表明,在发送压力保持不变的情况下,输送气速和分支管路流量控制阀开度差值的变化,对分支管各自的阻力特性和相互间的压差有显著影响。当输送气速下降时,两分支管相互间的压差减小,各分支管的单位长度压差在开始时逐渐减小,但当气速下降到一定程度后,单位长度压差转而增大。当分支管流量控制阀开度差值由小变大时,两分支管各自的压差曲线逐渐远离,且两分支管相互间的压差逐渐增大。     

气固两相管道输送分支流动阻力特性的研究

在水平T型分支管道中用压缩宅气对平均粒径为0．5mm砂石进行了气力输送试验,对气固两相分支管道输送的阻力性能进行了研究。试验结果表明,在发送压力基本保持不变的情况下,当输送气速下降时各分支管的单位长度压差在开始时逐渐减小;但当气速下降到一定程度后,单位长度压差下降趋势减缓,其中局部阻力相对较大的分支管路则开始增大。当分支管流量控制阀开度差值由小变大时,两分支管各自的压差曲线逐渐远离,局部阻力较大的分支管路的临界速度增大。     

Numerical simulation,validation, and analysis of two-phase slug flow in large horizontal pipes

Multiphase flow, especially two-phase gas-liquid flow, is of great importance for a variety of applications and industrial processes, for example in the nuclear, chemical, or oil and gas industries. In this contribution, we present simulation results for gas-liquid slug flow in large horizontal pipes. Six test cases with different oil, water, and gas flow rates are considered, which cover a wide range of different slug flows. The numerical predictions are validated by comparison with experimental data obtained from video observations. The relative error of the mean liquid level between experiment and simulation is less than 12.3% for all but one test cases. Furthermore, a frequency analysis is performed. The single-sided amplitude spectrum as well as the smoothed power spectral density are calculated. For both, experimental and simulation data, one observes an increase of the dominant frequencies if the ratio of liquid and gas superficial velocity is increased.     

粉煤灰管道气力输送特性的研究

对浓相粉煤灰气力输送系统三维流场进行了数值模拟,给出了流场特性,分析了颗粒对气相的影响,描述了颗粒沉降的具体过程。研究表明单位长度压力损失与速度平方、体积浓度成正比,而与管道长度无关;颗粒直径越大,压力损失就越小;颗粒的沉降与运动速度、颗粒直径和管道长度有关。     

定子偏斜角对正脉冲器压力信号的影响

为了提高随钻正脉冲测井仪的信号强度,需要对定子偏斜角角度及偏斜特性进行优化。依据计算流体力学的方法建立了不同的定子偏斜角数值计算模型,分析了偏斜角对旋转阀压力信号幅值和速度场分布规律的影响,并通过试验验证了优化结果的合理性。结果表明:定子流域特性对信号强度有很大影响,压力信号幅值随定子偏斜角的减小而减小;单边偏斜比双边偏斜的压力信号强度大。     

重油在分叉管内合流的数值研究

采用数值模拟方法对高粘性流体在不同夹角的分叉管合流的流动、换热进行研究,分析了不同夹角分叉管内合流的流动特性,讨论了分叉管夹角的大小对分叉管合流的流动、换热充分发展前的管道长度和压力损失的影响。     

Optical method for flow patterns discrimination,slug and pig detection in horizontal gas liquid pipe

An optical method including infrared ray and laser was developed to discriminate flow pattern, and detect liquid slug and pig in horizontal gas–liquid pipe. Based on the principle that infrared ray attenuates differently during penetrating gas and liquid, the infrared ray method was developed to discriminate flow pattern and detect liquid slug. In experiment, infrared ray was emitted on one side of the transparent pipe, and detected on the other side. Simultaneously, a signal of output voltage that is proportional to the intensity of infrared ray detected was generated and recorded. A series of experiments in horizontal air/water loop were carried out to generate bubble, stratified smooth, wavy and intermittent flow, and the output voltages under the four flow patterns were analyzed. The flow patterns can be discriminated by characteristics of output voltage. Meanwhile, the velocity and frequency of liquid slug were measured by this method, and the results were consistent with that calculated by formulas. However, infrared ray is easily affected by interface between gas and liquid, a laser method was explored to detect pig. The laser method is similar to infrared ray, a laser beam was emitted and detected and then a signal of output voltage was recorded. The results from pigging experiments show that the laser method could correctly detect the passing of a pig. The combined use of infrared ray and laser method could rightly detect pig and pigging slug during pigging operation.     

Magnetic field effect on fluid flow characteristics in a pipe for laminar flow

The influence of a magnetic field on the skin friction factor of steady fully-developed laminar flow through a pipe was studied experimentally. A mathematical model was introduced and a finite difference scheme used to solve the governing equations in terms of vorticity-stream function. The model predictions agree favourably with experimental results. It is observed that the pressure drop varies in proportion to the square of the product of the magnetic field and the sine of the magnetic field angle. Also, the pressure drop is proportional to the flow rate. This situation is similar to what applies in the absence of a magnetic field. It is found that a transverse magnetic field changes the axial velocity profile from the parabolic to a relatively flat shape. At first, the radial velocity rises more rapidly and then gradually decreases along the pipe until falling to zero. A numerical correlation can be written for the considerable distance required for the new axial velocity profile to establish. Owing to the changes taking place in the axial velocity profile, it exhibits a higher skin friction factor. The new axial velocity profile asymptotically approaches its limit as the Hartmann number becomes large.     

Uncertainty analysis for multiphase flow: A case study for horizontal air-water flow experiments

This work describes the procedure used to define the measurement uncertainties of horizontal two-phase air-water flow experiments conducted to determine influences due to pipe diameter on pressure gradient on such flows. These experiments were performed with 4 different pipe diameters, always using the same test section length, therefore varying the length-to-diameter (L/D) ratio. Several parameters were measured, such as volumetric/mass flow rate, pressures, temperatures and pressure drop; other parameters were calculated, such as the superficial velocities of each fluid, as well as their corresponding properties. The main parameters studied were the flow patterns for different velocity configurations and the two-phase pressure drop to be used for model improvement, thus the importance of uncertainties analysis. The sources of uncertainty were defined, detailed, systematically studied and quantified. Also, the reproducibility capacity of the experimental setups were analysed through the uncertainty analysis and proving them to be able for future similar studies. The flow maps with their uncertainties could help understand the thresholds for each defined flow pattern region, and the plots of two-phase pressure drop variation with diameter confirmed the homogeneous model as a possible approach to calculate pressure drop if the uncertainties are considered.     

钻柱内连续波信号传输模型与幅频特性研究

借鉴电力线路信号传递的研究方式,利用阻抗和传递系数来描述钻柱对连续压力波动的影响,建立了连续波动在钻柱中的传递矩阵以及压力和流量沿钻柱分布情况的数学模型,并分析了钻柱倾角对波动信号的影响。通过对模型的仿真,得出了在井下连续波信号传递过程中钻柱内压力波呈驻波分布的结论;在分析不同特征阻抗对信号传递的影响的基础上,研究了钻柱内不同频率信号的衰减情况,绘制了钻柱内信号传递的幅频特性曲线,说明随着频率的升高,钻柱内信号呈波动性衰减,通过分析钻柱长度和通信频率之间的关系,说明了按照钻柱两端波动幅值比选择通信频率的方法;并通过地面模拟实验,证明了不同频率信号在相同钻柱内的信号传递情况符合仿真分析。     

柱塞倾角对球面配流副轴向斜柱塞泵流体特性的影响

运用CFD技术对球面配流副轴向斜柱塞泵的单柱塞腔内压力脉动、输出流量脉动以及配流盘对缸体作用力矩等重要性能进行研究,分析柱塞倾角与上述流体特性的关系,得到柱塞倾角对柱塞泵流体特性的影响规律。     

Calculating the reliability of a straight line segment of a gas pipeline under crack-like defects

In the framework of the random number theory, a mathematical model describing gas pipeline nonfailure reliability according to crack growth resistance criterion when the crack resistance of the pipe steel, the operation pressure of the cargo gas, the diameter and wall thickness of the pipe, the Poisson ratio, the linear expansion coefficient of the pipe metal, the Young modulus, and the temperature drop through the wall are all distributed according to the normal distribution law, has been obtained. The permissible value of the mathematical expectation of the longitudinal crack length has been found under which the standard reliability and safe operation of a defect segment of a gas pipeline is guaranteed.     

Slug frequency in high viscosity oil-gas two-phase flow: Experiment and prediction

The number of slug units that traverses a particular point at a given time within a defined pipe cross-section is known as slug frequency. The behaviour of this critical parameter for two-phase flow in high viscosity oils is significantly different from those of conventional oils (of less than 1 Pa s). In this experimental investigation, new data on slugging frequency in high viscosity oil-gas flow are reported. Scaled experiments were carried out using a mixture of air and mineral oil in a 17 m long horizontal pipe of 0.0762 m ID. A high-speed Gamma Densitometer of frequency of 250 Hz was used for data acquisition over a time interval of 30 s. For the range of flow conditions investigated, increase in oil viscosity was observed to strongly influence the slug frequency. Comparison of the present data with prediction models available in the literature revealed discrepancies. A new correlation incorporating the effect of viscosity on slug frequency has been proposed for horizontal flow. The proposed correlation will improve the prediction of slug frequency in high viscosity oils.     

旋风分离器排气管缩口半径优化的数值模拟

利用FLUENT中的RSM模型和DPM模型对不同排气管底口半径r的缩口式旋风分离器进行了内部流场的数值模拟。对结果的时均图进行分析,得到随着收缩半径r的减小,排气管入口面积在减小,轴向速度及切向速度均增加,速度的增加可使靠近中心的颗粒获得更大的离心力,因此被捕集的颗粒数增多。当半径r与排气管半径R比值为1~0.9时,分离效率提高不大,压降变化也较小,比值为0.8~0.5时,分离效率提高很多,同时能量损失也较大,在半径r逐渐减小的过程中,旋风分离器分离效率增加,压降增加。综合考虑,当r/R为0.6~0.5左右时,分离效率约为97%~98%,此时压降也较合理。