微沟槽热管充液旋压成形实验研究

对微沟槽热管充液旋压成形工艺进行了研究,通过试验对影响充液旋压成形加工的三种关键性因素进行了研究与分析.结果表明,在影响充液旋压加工沟槽式热管的三种因素中,旋压当量直径和刀具与滚珠间相对位置主要影响热管内微沟槽形状和尺寸大小,如槽深、槽宽和深宽比;刀具与滚珠间相对位置和拉伸速度影响充液旋压加工过程中铜管是否被拉断;拉伸速度对热管表面粗糙度影响很大.     

矩形微流道内流体电动效应研究

由于固-液界面双电层的作用,矩形微流道中的压力驱动流存在电动效应。矩形微流道截面上双电层场和速度场的控制方程分别是二维Poisson-Boltzmann方程和修正Navier-Stokes方程。应用有限控制容积法对控制方程进行了数值求解,并计算了压力梯度与雷诺数之间的关系,模型预测值与试验值之差在5%之内。相同尺寸的微流道中,考虑电动效应的模型预测液体摩擦系数的值大于宏观流体理论中液体摩擦系数的值,且电解质溶液浓度越低,摩擦系数偏离宏观流体理论值越大。     

小直径深孔冷板流道枪钻加工工艺参数研究

小直径深孔冷板流道的加工精度直接影响深孔冷板的散热效率和使用寿命.文中采用正交实验法对深孔流道的枪钻加工工艺进行了研究,通过分析刀具转速、进给量及冷却液流量对深孔流道中心线偏差的影响规律,优化了工艺参数.试验结果表明,小直径深孔冷板流道中心线偏斜≤0.9 mm/m,可满足深孔冷板的精度要求.     

疏水表面微通道交变电场电渗流数值模拟

基于有限元方法,针对具有特定滑移长度的疏水表面微通道,建立了控制方程,对交变电场电渗流进行了数值模拟,分析了电场强度、电场频率、微通道高度和溶液浓度等对电渗流的影响。结果显示,疏水表面和亲水表面微通道交变电场电渗流具有相似的速度分布,疏水表面微通道交变电场电渗流整体速度更大;双电层滑移速度与电场强度成正比,由于边界滑移,疏水表面微通道交变电场电渗流双电层滑移速度随溶液浓度增大先缓慢减小后迅速增大。     

BTA深孔钻喉部结构的数值优化研究

针对深孔切削加工进行时,排屑效率低与钻头喉部易堵屑的问题,对BTA冷却系统冷却液出口断面速度,以及冷却液在钻头喉部的流动过程与特性进行了研究,基于计算流体动力学(CFD)与射流卷吸效应,提出了一种新型的BTA深孔钻头喉部结构。对加工时的压强和流量参数进行了分析后,修订了有限元冷却液模型的湍流强度和耗散速率,在此基础上进行了两种钻头喉部结构的排屑能力对比试验,测量了冷却液系统的冷却液出口断面流出平均速度。研究结果表明:实验时,新型喉部结构的直径38 mm BTA深孔钻头所组成的冷却系统,其冷却液出口断面流出的平均速度提高12.6%;同时,冷却液系统整体的排屑能力也得到了提高。     

微通道内交变电场电渗流有限元分析

基于有限元方法,以粘性不可压缩流体N-S方程和双电层P-B方程为基础,建立交变电场驱动微通道电渗流模型,并进行数值模拟,分析溶液浓度、电场强度和微通道高度对电渗流的影响。结果表明,微通道内双电层滑移速度与电场强度成正比,受微通道高度影响较小,随溶液浓度的增大非线性减小。同时,微通道高度和溶液浓度的增加使双电层相对厚度减小,交变电场电渗流瞬时速度的波峰更加尖锐。该结论为微通道内交变电场电渗流精确控制提供了理论参考。     

深海矿石输送设备输送特性研究

为研究深海矿石输送设备输送特性,运用计算流体力学理论和Fluent软件对设备内固液两相流进行三维仿真,研究喷射速度、泵水速度、喷射高度和颗粒粒径对出料质量流量和出口处颗粒平均速度的影响规律。研究结果表明:随喷射速度的增加,出料质量流量先增大后减小,存在最佳喷射速度,出口处矿石平均速度基本呈线性增加;随泵水速度增加,出口处矿石颗粒平均速度大致呈直线上升,出料质量流量变化不大;随喷射高度增加,出料质量流量先上升后下降,在喷射高度为500 mm时最大,而出口处矿石平均速度基本不受影响;随颗粒粒径的增大,出料质量流量先急剧增大,当粒径超过15 mm时缓慢上升,最后缓慢下降,出口处颗粒平均速度基本不受粒径的影响。     

内射流对离心泵进口流场及压力脉动影响

为探究内射流对离心泵进口流场及压力脉动的影响,本文以一台有内射流循环回路的模型泵为研究对象,采用数值方法对泵全流道进行定常和非定常计算。结果表明:无内射流时泵性能模拟与实验值基本吻合,设计点扬程误差在1%以内;有内射流时泵扬程略有下降,效率最大下降1.8%。内射流流量与射流孔轴向平均速度随流量增加而减小。内射流对泵进口流场影响显著,其存在使得进口段轴向速度、压力、涡量及湍流强度均发生变化。小流量时内射流对进口流场的影响范围更大。距射流孔越远,轴向速度梯度越小。进口段内射流流场呈周期性变化,压力脉动频谱图中存在的低频信号f=9.13 Hz为内射流轴向速度场周期变化频率。     

粗糙表面上微织构对流量因子的影响

为研究混合润滑条件下粗糙表面上微织构对流量因子的影响,在不同表面纹理方向的高斯随机粗糙表面的基础上,建立不同织构参数的几何模型,通过数值求解雷诺方程,研究织构的面密度及深宽比对压力流量因子、剪切流量因子的影响。结果表明:压力流量因子和剪切流量因子随着表面织构面密度和深宽比的增大而增大,且随着深宽比的增加,压力流量因子增大的幅度逐渐减小;在各向同性、横向纹理及纵向纹理表面下,表面织构的面密度和深宽比对压力流量因子和剪切流量因子的影响大致相同。     

层流流量计设计参数的选择与确定

对于给定最大体积流量和最大压差时,涉及层流流量计的设计参数有：最大平均流速Ｗｍｍａｘ、流量计的直径ｄｍ、层流流道的当量直径ｄｉ、层流流道的长度１和层流流道的数目ｎ,这５个未知数可用所选择的限定条件、流体力学阻力的方程和几何条件组成的方程组求出,从而为层流流量计的具体设计与研制打下坚实的基础。     

Quantitative multiphase flow characterisation using an Earth's field NMR flow meter

We present a novel nuclear magnetic resonance (NMR) multiphase flow metering system with the ability to interpret the flow regime and quantify both the liquid volumetric flowrate and holdup for gas-liquid flows. The flow measurement apparatus consists of a pre-polarising permanent magnet upstream of an Earth's field radio frequency NMR detection coil. In this work, the system is applied to measure the free induction decay (FID) NMR signal of gas-liquid flows at a range of flow rates in both the stratified and slug flow regimes. Tikhonov regularisation is applied to fit a model equation to the acquired FID signal in order to determine the relevant liquid velocity probability distribution. Signal interpretation applied to the individual NMR scans allows monitoring of both the liquid velocity and holdup with time. The NMR estimate of the liquid holdup is comparable to video analysis of the flowing stream through a transparent pipe section. The accuracy of the NMR metering system is successfully validated against an independent in-line rotameter measurement of the liquid volumetric flowrate during multiphase flow. Finally, analysis of the temporal variation in measured liquid flowrate is shown to clearly distinguish the stratified and slug flow regimes.     

An instrumentation system for multi-parameter measurements of gas-solid two-phase flow based on Capacitance-Electrostatic sensor

In this paper, an instrumentation system for the measurements of local solid volumetric concentration, local solid velocity, local solid mass flowrate and solid mass flowrate in gas-solid two-phase flow system is developed. It is based on a new type of a Capacitance-Electrostatic sensor (CES). The CES sensor is mainly composed of a capacitance electrode array and two electrostatic electrode arrays. The optimum design of the sensor is achieved by finite element method. The capacitance electrode array is employed to detect the solid distribution over the cross-section of the pipe, and the local solid volumetric concentration measurement is further derived. The electrostatic electrode arrays are used to measure the local solid velocities in conjunction with cross-correlation method. From the local solid velocity and local volumetric concentration, the solid mass flowrate and the local solid mass flowrate can be achieved. The developed system for the local solid volumetric concentration measurement is verified through analogue simulation experiments and static experiments. Finally, the system is employed to measure the local solid volumetric concentration, local solid velocity, local solid mass flowrate and solid mass flowrate on a belt conveyor. The experimental results show that the measurement error of the local solid volumetric concentration measurement results are less than 10.43% for solid local volumetric concentration ranging from 0.02 to 0.56, the standard deviations of the local solid velocity measurement results are less than 0.42 for solid velocity ranging from 3.5 m/s to 15.0 m/s, and the relative error of the solid mass flowrate is within −19.6% to +14.9% for solid mass flowrate ranging from 0.006 kg/s to 0.103 kg/s, indicating that the system is capable of achieving multi-parameters measurement in gas-solid two-phase flow system.     

毛细管电渗流微泵的流型及驱动

采用二维纳维一斯托克方程、拉普拉斯方程、泊松-玻尔兹曼方程表述电渗流微泵的计算模型,讨论了电渗流在各种工况下的流型,分析了双电层(EDL)厚度、外加垂直电势、Zeta电势、背压以及管径对电渗流(EOF)驱动时间的影响。仿真结果表明:影响驱动时间的主要是管径,其他因素可以忽略;无载驱动与反向驱动时间是毫秒级,有载驱动时间是在微秒级。通过改变外加垂直电势或Zeta电势的极性,可以实现双向驱动。     

Air velocity and flow measurement using a Pitot tube

The accurate measurement of both air velocity and volumetric airflow can be accomplished using a Pitot tube, a differential pressure transducer, and a computer system which includes the necessary hardware and software to convert the raw transducer signals into the proper engineering units. The incorporation of sensors to measure the air temperature, barometric pressure, and relative humidity can further increase the accuracy of the velocity and flow measurements. The Pitot tube measures air velocity directly by means of a pressure transducer which generates an electrical signal which is proportional to the difference between the pressure generated by the total pressure and the still air (static pressure). The volumetric flow is then calculated by measuring the average velocity of an air stream passing through a passage of a known diameter. When measuring volumetric flow, the ‘passage of a known diameter’ must be designed to reduce air turbulence as the air mass flows over the Pitot tube. Also, the placement of the pitot tube in the passage will influence how accurately the measured flow tracks the actual flow through the passage. Calibrating the measurement system in a wind tunnel can further increase the accuracy of the velocity and the flow measurements. This objective of this paper is to provide the field engineer with single, concise source of information on flow measurement using a Pitot tube.     

矩形进料体高宽比对旋流器流场和分离性能影响的数值模拟

横截面为矩形的进料体比圆形的分离性能更好,但是一直没有找出矩形进料体合适的高宽比.本文采用数值分析法研究了矩形进料体的高宽比对直径为75 mm旋流器分离性能的影响,将数值结果与Hsieh经典试验结果进行了对比,发现两者有良好的一致性,验证了该方法的有效性.探究了进料体不同高宽比下的压力场、速度场、湍流场和分离效率.结果...     

几何尺寸对矩形微通道液体流动和传热性能的影响

基于连续介质方法数值研究液体在不同几何结构微通道中的流动和传热性能。在相同热边界条件下,通过比较水力直径、通道长度和宽高比等几何参数对液体微流动的影响,得到各参数对泊肃叶数(Po)和努塞尔数(Nu)的影响关系。研究发现,截面宽高比越大,Po数越小,且雷诺数对泊肃叶数基本无影响;雷诺数(Re)小于500情况下,水力直径小于0.545 mm时,Po数随水力直径减小而减小,水力直径大于0.545 mm时,水力直径变化对Po数基本无影响;Po数不随通道长度变化而变化,但略受流动雷诺数影响;在Re=20～1 800时,Nu数正比于水力直径和宽高比,但是通道长度对Nu数的作用受流动Re数的影响;在通道材料和流动介质相同的条件下,Nu数和Re数之间的关系受通道几何参数的影响,并且拟合得到其关系式。     

High GVF and low pressure gas–liquid two-phase flow measurement based on dual-cone flowmeter

Parameter measurement of gas–liquid two-phase flows with a high gas volume fraction (GVF) has received great attention in the research field of multiphase flow. The cone meter, as a new proposed differential pressure (DP) meter, is increasingly being applied in flowrate measurement of gas–liquid two-phase flow. A dual-parameter measurement method of gas–liquid two-phase flow based on a dual-cone meter is proposed. The two-phase flow is investigated in a horizontal pipeline with high GVF and low pressure, and exists in the form of annular flow. By adding a second cone meter, both gas mass fraction (GMF) and mass flowrate are measured. The pressure drop performances of five different sized cones have been discussed to make a cooperating cone selection and efficiently position the dual-cone in the pipe. Dual-cone flowmeter experiments of 0.45 and 0.65 equivalent diameter ratio combination, and 0.65 and 0.85 equivalent diameter ratio combination are respectively carried out to analyze the linearity of two-phase flow multiplier with Lockhart–Martinelli parameter and obtain the dual-parameter measurement results. The relative experiment error of GMF, gas mass flowrate and total mass flowrate are respectively within ±7%, ±5% and ±10%. The relative error of the liquid phase is within ±10% when the liquid mass fraction is beyond 40%. The experimental results show that it is efficient to utilize this dual-cone method for high GVF and low pressure gas–liquid two-phase flow measurement.     

微流道壁面粗糙度影响的电渗流数值模拟

基于微流控动力学理论,应用有限元分析方法求解二维平板粗糙壁面微流道模型内矩形截面双电层场和速度场的耦合控制方程。从数值模拟角度研究不同矩形粗糙元对称分布微流道内的电渗流流动特性,分析了粗糙度对微流体流动的影响机理。结果表明:由于粗糙元的阻力作用,粗糙壁面流道内流体速度减小,引起的压力突变导致壁面附近速度出现波动。随着粗糙元高度、宽度的增加,电渗流流速相应地降低或升高。     

无掩膜流动刻蚀技术研究

为了实现玻璃材料高深宽比微结构的加工,提出了一种基于微尺度下流体分层流动现象的微流道内无掩膜流动刻蚀方法。通过对玻璃基体材料进行大量的工艺实验,明确了流动参数对于刻蚀成型微结构深宽比、侧壁形状、刻蚀速率的影响。证明了可以通过改变刻蚀剂与隔离剂的流动参数实现对成型微结构形貌的控制。实验结果表明约束流动刻蚀工艺可以在玻璃基体材料上加工出形态复杂、大深宽比的微结构,微结构的形貌取决于微流道中流体的流速。本实验的结果对于微尺度下分层流动的特性研究有一定的参考价值,并可为解决各向同性材料的微结构加工难题提供有效的解决方案。