在流体中心，流体颗粒具有最大的速度.
6
2. Basic Terms
• Thus, the average rate of flow is used in flow calculations.
• 因Th此e，un在its流o量f v计el算oc时ity采ar用e n流o体rm的all平y f均ee速t p率er.
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.
4
速度是对2一.个B物a体s速ic率和T方e向rm的测s量.
• Velocity (速度) is a measure of speed and direction of an object.
• When related to fluids it is the rate of flow of
second (fps), feet per minute (fpm), meters per second (mps), and so on. •速P度re的v单iou位s通ly,常th为e英p尺re每ss秒ur(efpss)a，ss英oc尺ia每te分d 钟with (fpflmu)id，米flo每w秒w(merpes)，de等fin等ed. as static, impact (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.
7
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.
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).
3
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.
Байду номын сангаас
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)
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.
8
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).
2
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.
这一单元讨论流量测量和仪器仪表所使用的基本术 流 语体与流公量 式的. 测量在工业应用中是非常重要的. 某些 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.
applications
• Flow measurements using differential pressure measuring devices and their characteristics
1
1. Introduction
• This unit discusses the basic terms and fomulas used in flow measurements and instrumentation (仪器仪表).
the velocity of the liquid particles is virtually
zero;
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
，流体粒子的速度实质上为零；
5
2. Basic Terms
• in the center of the flow the liquid particles will have the maximum velocity.
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