自动化专业英语第三版

Viscosity (dynamic viscosity, or absolute viscosity) can be measured in poise (泊) or centipoise (厘泊), whereas kinematic viscosity (运动粘度)(without force) is measured in stokes (沱) or centistokes (厘沱). 动态粘度(或叫绝对粘度)的计量单位是泊或厘泊， 而运动粘度(没有力的单位，即没有牛顿单位)的计 量单位是沱或厘沱 Dynamic or absolute viscosity is used in the Reynolds (雷诺) and flow equations. 动态粘度或绝对粘度用于雷诺数的推导和流体方程 中.
许多液体和气体的成本都是基于管道中测量的流量 ，出于核算的目的，必须精确的测量与控制流体的 速度(流速，流量).
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2. Basic Terms
• This unit will be using terms and definitions from previous units as well as introducing a number of new definitions related to flow and flow rate sensing.
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粘度是描述气体或液体对运动或流动的阻力的一种 2. Basic Terms 特性.
• Viscosity (粘度，粘性) is a property of a gas or liquid that is a measure of its 粘性的液体比如糖浆，其粘度要远大于水，而水的 resistance to 粘度又高于空气 . motion or flow. • A viscous (粘性的) liquid such as syrup (糖 浆) has a much higher viscosity than water and water has a higher viscosity than air. • Syrup, because of its high viscosity, flow very slowly and it is very hard to move an object through it. 由于糖浆的高粘度，它的流动非常缓慢，并很难使 一个物体在其中移动. 10
Lesson 2.3 Flow Measurements
This unit covers the following topics: • Reynolds number ( 雷 诺 数 ) and its application to flow patterns (流型，流动模式) • Formulas (公式) used in flow measurements • Bernoulli equation ( 伯 努 利 方 程 ) and its applications • Flow measurements using differential pressure measuring devices and their characteristics
the liquid. 2000到5000之间，该流型处于中间区域，可以 雷诺数介于 If the Reynolds number for the flow in a pipe is equal to 是层流，湍流或两者的混合，取决于其它因素 . 如果雷诺 数大于 . or less 5000 than，那么该流体是湍流型式 2000 the flow will be laminar.
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1. Introduction
• This unit discusses the basic terms and fomulas used in flow measurements and instrumentation (仪器仪表).
这一单元讨论流量测量和仪器仪表所使用的基本术 流体流量的测量在工业应用中是非常重要的 . 某些 语与公式. 设备和操作的最佳性能需要精确的流速 • The measurement of fluid flow is very important in industrial applications. Optimum performance of some equipement (设备) and operations (操作) require specific flow rates.
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1. Introduction
• The cost of many liquids and gases are based on the measured flow through a pipeline making it necessary to accurately measure and control the rate of flow for accounting purpose.
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2. Basic Terms
• Laminar flow (层流) of a liquid occurs when its average velocity is comparatively low and the fluid particles tend to move smoothly in layers, as shown in Figure 2.3.1(a). The velocity of the particles across the liquid takes a parabolic (抛 物线) shape.
这一单元将使用以前单元的术语和定义，同 时也会引入一些新的关于流体和流速测量的 定义.
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速度是对一个物体速率和方向的测量 2. Basic Terms .
• Velocity ( 速度 ) is a measure of speed and direction of an object. • When related to fluids it is the rate of flow of fluid particles in a pipe. The speed of particles in a fluid flow varies across the flow, i.e., where the fluid is in contact with the constraining (约束) walls (the boundary layer) the velocity of the liquid particles is virtually zero;
在流体中心，流体颗粒具有最大的速度.
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2. Basic Terms
• Thus, the average rate of flow is used in flow calculations. • 因此，在流量计算时采用流体的平均速率 The units of velocity are normally feet per. second (fps), feet per minute (fpm), meters per second (mps), and so on. 速度的单位通常为英尺每秒 (fps) ，英尺每分钟 • Previously, the pressures associated with (fpm) ，米每秒 (mps)，等等 . as static, impact fluid flow were defined (冲击，作用), or dynamic. 以前（章节中），与流体流量相关的压力定义为静 压，全压，或动压.
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Flow patterns (流型，流动型式 ) can be considered to be 1880年， Osborne Reynolds观察到流态可以根据液体的 物理特性预测得到 laminar, turbulent,.or a combination of both. Osborne Reynolds observed in 1880 that the flow 流型(流动型式)可以是层流，湍流，或两者的结合. pattern could be predicted from physical properties of
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Viscosity is a measure of the resistance of a fluid which is being deformed by either shear 粘度描述的是流体流动时内部的阻力，并且可认为是 液体摩擦力的一种测量。 stress (剪应力) or tensile stress (张应力). Viscosity describes a fluid‘s internal 粘度是流体的阻力测量，它是由于剪应力或张应力而形 成的。 resistance to flow and may be thought of as a 对流体问题的研究被认为是流变学，其中包括粘度及其 measure of fluid friction (摩擦力). 相关概念。 The study of flowing matter is known as rheology (流变学), which includes viscosity 动力粘度，也称为绝对粘度，是最常用的概念(典型的 and related concepts. 单位：帕斯卡 .秒，泊，厘泊) Dynamic viscosity, also absolute (viscosity, the 运动粘度是动力粘度与液体密度之比 典型的单位：平方 more usual one (typical units Pa.s, Poise, cP); 米每秒，沱，厘沱 ) Kinematic viscosity is the dynamic viscosity divided by the density 12
当与流体相关时，指的是管道中流体粒子的 流量速度. 流体流动中，粒子的速率各不相 同，比如，当流体与约束壁(边界层)接触时 5 ，流体粒子的速度实质上为零；
2. Basic Terms
• in the center of the flow the liquid particles will have the maximum velocity.
R=VDρ/μ
Where
V=average fluid velocity D=diameter of the pipe ρ=density of the liquid μ=absolute viscosity
雷诺数R是一种派生关系，它结合了液体的密度和粘度 ，流体速率和横截面积的大小，并具有如下形式
The Reynolds number R is a derived (派生) relationship combining the density and viscosity Of a liquid with its velocity of flow and the crosssectional dimensions (大小，尺寸) of the flow and takes the form
层流发生在液体流速相对较低时，流体粒子在各层中倾 向于平滑移动，如图2.3.1(a)所示. 液体中的粒子速度呈 抛物线分布.
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2. Basic Terms
• Turbulent flow (湍流) occurs when the flow velocity is high and the particles no longer flow smoothly in layers and turbulence (紊乱) or a rolling (旋转，滚动) effect occurs. This is shown in Figure 2.3.1(b). Note also the flattening ( 平 均 化 ， 扁 率 ) of the velocity profile (外形，轮廓). 湍流发生在液速较高，在各层中，粒子不再是平滑移动， 而会发生紊乱或旋转动作. 如图2.3.1(a)所示. 同时也要注 意速度分布的扁率.