Basic concepts and terms of valve hydrodynamics-1

Basic concepts and terms of valve hydrodynamics-1

1.1阀门的定义

1.1 definition of valve

用来控制管道内介质的，具有可动的机械产品的总体（ 见GB/T21465-2008 2.1）

The total number of movable mechanical products used to control the medium in the pipeline (see 2.1 of GB / t21465-2008)

阀门是在流体系统中，用来控制流体的方向、压力、流量的装置。

Valve is used to control the direction, pressure and flow of fluid in the fluid system.

阀门是使配管和设备内的介质（液体、气体、粉末）流动或停止、并能控制其流量的装置。

The valve is a device that makes the medium (liquid, gas, powder) in the piping and equipment flow or stop, and can control its flow.

1.2流体力学基本概念与术语

1.2 basic concepts and terms of fluid mechanics

1.2.1.流动——物质在外力（如重力、离心力、压差等）作用下，发生宏观运动。

1.2.1. Flow - macroscopic movement of matter under the action of external forces (such as gravity, centrifugal force, pressure difference, etc.).

1.2.2.流体——能够流动的物质 液体、气体

1.2.2. Fluid - material, liquid and gas that can flow

液体可以发生形变，其形状取决于所盛装的容器的形状，在理想状态下，液体不可压缩。气体可以改变大小，在密闭的容器中气体总是充满容器空间，气体可以压缩。

Liquid can deform, its shape depends on the shape of the container, in an ideal state, the liquid is incompressible. The gas can be changed in size. In a closed container, the gas always fills the container space, and the gas can be compressed.

1.2.3.理想流体与实际流体：流动时没有粘滞性的流体为理想流体，流动时有粘滞性的流体为实际流体。很显然，理想流体并不存在，只是为了研究某些问题的方便而提出的假设。

1.2.3 ideal fluid and actual fluid: the fluid without viscosity in the flow is ideal fluid, and the fluid with viscosity in the flow is actual fluid. Obviously, the ideal fluid does not exist. It is only a hypothesis put forward for the convenience of studying some problems.

1.2.4. 流体力学——研究流体平衡状态规律的科学为流体静力学，研究流体运动力学规律及其应用的科学为流体动力学，综合称流体力学。

1.2.4. Hydrodynamics - Hydrostatics is the science to study the law of fluid equilibrium state, and hydrodynamics is the science to study the law of hydrodynamics and its application, which is called hydrodynamics comprehensively.

1.2.5. 粘度——流体在流动时，在其分子间产生内摩擦的性质，称为流体的粘性。流体的粘性与温度有关，对于液体，温度升高粘度减小，气体温度升高粘度增加。粘性的大小用粘度表示，粘度又分为运动粘度与动力粘度。

1.2.5 viscosity the property of internal friction between molecules of a fluid during its flow, which is called the viscosity of the fluid. The viscosity of the fluid is related to temperature. For the liquid, the viscosity decreases with the increase of temperature, and the viscosity increases with the increase of gas temperature. Viscosity is expressed by viscosity, which is divided into kinematic viscosity and dynamic viscosity.

运动粘度υ单位是m2/S，简称斯。动力粘度η单位是N•s/m2。或Pa.s（帕.秒）

The unit of kinematic viscosity V is m2 / s, which is abbreviated as S. The unit of dynamic viscosity η is n · s / m2. Or Pa.s (Pa.s)

1.2.6.密度与比容

1.2.6. Density and specific volume

单位容积物质的质量称为密度，单位为“千克/米3。常用符号ρ表示。

The mass of the substance per unit volume is called density, and the unit is "kg / m3". It is usually represented by the symbol ρ.

单位质量的物质所占有的容积称为比容，用符号表示单位为“米3/千克(m3/kg)”。 常用符号v表示。

The volume occupied by the substance with unit mass is called specific volume, and the unit is "m3 / kg" (m3 / kg) with symbols. It is usually represented by the symbol v.

显然，ρ=1/v

Obviously, ρ = 1 / V

比重：γ=ρg。国际单位为：N/m3或kN/m3。

Specific gravity: γ = ρ G. International unit: n / m3 or kn / m3.

η=ρυ

ETA = Rho

1.2.7.流动状态：层流和紊流

1.2.7. Flow state: laminar and turbulent

层流：各层之间不相混杂的分层流动叫做层流。

Laminar flow: laminar flow is a kind of stratified flow which is not mixed between different layers.

湍流：流动具有混杂、紊乱的特征时叫做湍流。

Turbulence: turbulence refers to the flow with the characteristics of mixing and disorder.

1.2.8.雷诺数

1.2.8. Reynolds number

英国物理学家雷诺曾作过试验并得到判断流型的计算式，称为雷诺公式：

The British physicist Renault has made experiments and obtained the calculation formula for judging the flow pattern, which is called the Renault formula:

Re=Vd/υ，式中，V为流速，m/s，d为管子直径，m., υ为运动粘度，单位m2/s。因此，雷诺数Re是个无量纲常数，当Re＜2320时为层流，Re＞2320为紊流，所以，Re2320称之为临界雷诺数。

Re = VD / У, where V is the flow rate, M / s, D is the pipe diameter, M., У is the kinematic viscosity, in m2 / s. Therefore, Reynolds number Re is a dimensionless constant. When Re < 2320, it is laminar flow and re > 2320 is turbulent flow. Therefore, re2320 is called critical Reynolds number.

1.2.9.水锤

1.2.9. water hammer

水锤——当管道中介质流速因某种外界原因发生急剧变化时，将引起液体内部压力产生迅速交替升降，这种交替升降的压力作用在管壁、阀门或其它管路元件上好像锤击一样，故称为水击（或水锤）。

Water hammer - when the velocity of the medium in the pipeline changes rapidly due to some external reasons, the internal pressure of the liquid will rise and fall alternately rapidly. The pressure of this alternative rise and fall acts on the pipe wall, valve or other pipeline components as if it were hammering, so it is called water hammer (or water hammer).

1.2.10.汽蚀

1.2.10. Cavitation

汽蚀——由液体中逸出的氧气等活性气体，借助气泡凝结时放出的热量，会对金属起化学腐蚀作用。这种气泡的形成发展和破裂以致材料受到破坏的全部过程，称为汽蚀现象。在泵或阀门压力低处水开始发生汽化时，随着流体流动到高压区域，气泡溃散，产生巨大冲击，破坏金属材料。

Cavitation - the heat released by the active gas such as oxygen escaping from the liquid when condensing with the help of bubbles, will have a chemical corrosion effect on the metal. The whole process of the formation, development and fracture of this kind of bubble that causes the material to be damaged is called cavitation phenomenon. When the water starts to vaporize at the low pressure of pump or valve, as the fluid flows to the high pressure area, the bubble will burst, which will produce a huge impact and destroy the metal materials.

气穴、空化。

Cavitation, cavitation.