热工讲义

标准节流装置流量计算公式

Flux calculating formula of standard throttling device qm 质量流量： mass flow qv体积流量： volume flow Ｃ：流出系数，因取压方式和节流件不同而异； Outflow coefficient，varying with the taking pressure methods and throttle components； β：直径比，β＝d / D； Diameter ratio D：管道内径（mm）；Pipe inner diameter ρ：流体密度（kg/m3）fluid density d：节流孔的直径（mm）； Diameter of the throttling orifice ΔP：压差（Pa）；Differential pressure ε：可膨胀性系数，对不可压缩的液体ε为1，对可压缩的流体ε小1，因节流件不同， 用不同的计算公式。 Expandable coefficient，ε is 1for incompressible liquid，ε is less than 1 for the compressible fluid，different calculating formulas for different throttle components.
浮子式流量计： Float flowmeter




金属管浮子流量计为变面积式流量计，当被测介质向上流经管子时，浮子受力向 上移动，当浮子所受升力与浮子重力达到平衡时，浮子稳定在一个固定位置。此 时浮子与锥管间的流通环隙面积保持一定。环隙面积与浮子的上升高度成比例， 浮子的位置与流量的大小成比例。浮子移动时，以磁耦合的形式传递到外部指示 器，指示器的指针跟随浮子移动显示流量的变化。 电远传型是在指针现场指示流量的同时再通过传感器及放大电路，把被测介质的 流量通过位移信号转换成4～20mA的标准信号。适用于小口径和低流速介质流量 测量 如转机的冷却水流量. Metal tube float flowmeter is area-changing type flowmeter. When the measured medium flows upward through the tubes, the floater moves up because of the force. When the lift force and gravity of the floater are balanced, the floater will be stable in a fixed position. At this time, the flowing annulus gap area between the floater and conical tube keeps certain. Annulus area is proportional to the ascending height of the floater, while the position of floater is proportional to the magnitude of the flow. When the floater moves, the pointer of the floater is transferred to external indicator in the form of magnetic coupling. The pointer of the indicator displays the changes of flow following the movement of the pointer. When electrical remote transferring type flowmeter indicates the flow in pointer field, it also converts the flow of measured medium through displacement signal into 4 to 20mA standard signal. It is applied to measure the flow of minor caliber and low velocity medium, such as the cooling water flow of rotation machines.





差压式流量计通常由能将流体流量转换成差压信号的节流装置及测量差压并显示 流量的差压计组成．安装在流通管道中的节流装置也称“一次装置”，它包括节 流件、取压装置和前后直管段．显示装置也称“二次装置”，它包括差压信号管 路和测量中所需的仪表． Differential pressure flowmeter usually consists of throttling device and differential pressure meter. The throttling device can convert the flow rate of fluid into differential pressure signal while the differential pressure meter measures differential pressure and displays the flow. The throttling device installed in the circulation pipe is also called the “primary device”, which includes throttling components, taking pressure device and the before-and-after straight pipes. Display devices are also known as “secondary devices”, including the differential pressure signal pipes and the instruments necessary for measurement. 标准节流件的基本形式 The basic forms of standard throttling element a: 标准孔板（见图a） c: 文丘里管（见图c） b: 标准喷嘴（见图b） d: 文丘里喷嘴（见图d） a: Standard orifice plate（see Figure 1 a） c: Venturitube (see Figure 1 c) b: Standard nozzle (see Figure 1 b) d: Venturi nozzle (see Figure 1 d)
流量测量 Flow Measurement


Biblioteka Baidu

测量流体流量的仪表统称为流量计。流量计按结构原理可分为容积式流量计、 叶轮式流量计、 差压式流量计 、变面积式流量计、 电磁式流量计、超声波 流量计等，下面介绍几种常见流量计。flash\容积式流量计.swf flash\转子式 流量计.swf flash\涡轮流量计.swf The meters measuring liquid flow are called flowmeter. According to the structural principle, the flowmeters can be divided into volumetric flowmeter, impeller flowmeter, differential pressure flowmeter, variable area flowmeter, electromagnetic flowmeter and ultrasonic flowmeter. Several common flowmeters are introduced as following. 差压式流量计 Differential pressure flowmeters 当充满管道的流体流经节流装置时，将产生局部收缩，流速增加，于是在节 流装置前后产生一个静压力差，该压力差与流量存在着一定的函数关系，流 量越大，压力差就越大。通过导压管将差压信号传递给差压变送器，转换成 4～20mA.DC标准信号，经流量显示仪，便显示出管道内的瞬时和累积流量。 When the fluid filled in pipe flows through the throttling device, the shrinkage will occur in part areas and the flow speed will increase. So a static pressure difference appears before and after the throttling device. The pressure difference has a certain functional relation with flow. The greater the flow is, the greater the pressure difference is. The differential pressure signal is transmitted to the differential pressure transmitter through pressure sampling pipes and is converted into DC standard signals from 4 to 20mA. The instantaneous flow and accumulative flow inside the pipe are displayed on the flow indicator.


差压流量计的显示仪表 Display instruments of throttling flowmeter 节流装置节流后所得的差压，需要经过差压计来测量，目前工业上采用的差压计 主要有膜片式差压变送器和双波纹管差压计等。测得差压值后还需经过上述流量 公式计算校正，送进显示仪表显示后，才能得到需要的流量测量值。目前常用的 方法是在DCS的组态中进行修正。 The differential pressure after throttling needs to be measured by differential pressure meter. At present, the differential pressure meters applied in industry mainly include diaphragm-type differential pressure transmitter and dual-bellow differential pressure meter and so on. The measured differential pressure values need calculating and modifying through the above flow formula, sent into the display meter to display, then the needed measurement value of flow is obtained. Now the commonly used method is to modify it in DCS configuration.