The application of the throttle device
Throttling device is one of the categories of differential pressure type flowmeter, is suitable for the measurement of gas, liquid and steam flowmeter, application range is wide, including six kinds of throttling device is commonly used in industry (circular orifice, standard orifice, nozzle flowmeter, V cone flowmeter, venturi tube, balance meter). Flowmeter throttle device in more than 100 years continuously perfecting and developing, gradually formed the international standard, SIKE measurement and control technology co., LTD., the manufacturer the design, manufacture and use of the product conforms to the international standard ISO5167 and the provisions of the national standard GB/T2624.
Throttling device is widely used in various industry, how to selection of the throttle device of flow at different operating conditions of accurate and stable measurement is very important. When the fluid flows through the tube when the throttle device of tube, velocity will visit local contraction in throttling device so that the flow velocity increases, the static pressure is reduced, so the production of the static pressure difference before and after the throttle device. Works according to Bernoulli and two fluid continuity equation, the fluid density is constant, can be deduced through the throttle device is proportional to the square root of the fluid flow and the differential equation. Therefore, when the throttle device and the measured medium, in the form of physical parameter is determined, by differential pressure measured by the value of fluid flow can be calculated.
When the state of the nature of the fluid and choose the throttle device must meet the requirements: must be filled with fluid tube, and must be continuous flow; Fluid through the throttle device does not occur, the velocity stability; Before fluid flow through the throttle device, the flow rate must be balanced to the pipe axis, there can be no rotating flow.
Measurement of fluid flow through the pipe type medium, must consider the flow state and flow distribution, because the flow of the medium in the pipe can be divided into two kinds of laminar and turbulent and laminar flow state is limited to small flow rate when rendering, when flow larger can produce turbulent flow, the velocity distribution in the pipe and two state is different, the throttling with sticky, so through the pipe is in contact with the wall part adhesive lining, frictional resistance is big, so, even in a unified pipeline interface, the pipe fluid flows through the location of the different velocity caused by different velocity, namely the more close to the tube wall of the fluid, the velocity is, the slower the flow through the central part of the pipeline of the medium, the velocity is the fastest. So when installing a throttling device, the velocity distribution is under the certain condition of the straight pipe is applicable, especially in the fast speed of turbulent situation, through the long enough competent to medium section will appear, so when installing a throttling device piping, inevitably in the pipe installed on the valve and the elbow, and so on the velocity distribution in the downstream piping is chaos, such as: in the bent pipe will produce secondary flow, the flow of its downstream to produce bias current; Space double bend flow will produce cyclone. So, when the flow rate measurement, if you don't adjust the velocity distribution in the pipe is not accurate measurement. Adjust the velocity distribution, the method of upstream side is generally in the throttle device installed fully long straight section. Such as not enough long straight section, to live after the bent pipe and valve throttling device installed upstream side rectifier device. However, due to loss of rectifying it can produce certain resistance, low pressure piping in industrial, don't usually don't use.
Continuity equation (conservation of mass) and the Bernoulli equation (energy conservation) : mass flow rate value kg/s. M3 / s volume flow value; Expansion coefficient; Diameter ratio; Orifice diameter m; Pipe diameter m; The throttle device before fluid density kg/m3; The pressure difference between the before and after Pa throttling devices.
Measured by formula can be obtained, the throttle device differential pressure value, and then measured the mass flow rate and volume of fluid flow. For incompressible fluids, density is a constant value, for compressible fluids, density are greatly influenced by pressure and temperature, therefore in the medium flow rate, to fully consider the cultured compensation effect on the flow parameters.
First of all, on the safe and reliable to ensure the reliable measurement, measuring instrument in normal production or failure cases do not affect the safety of production system. Therefore, generally preferred to choose standard throttling device.
The throttling device is a long history and mature technology perfect flow meter. It has a simple structure, convenient installation, reliable operation, low cost, energy saving, maintenance free design processing standardization, etc. It also determines the throttle device is the most widely used industrial field flow meter, features suitable for large flow measurement. Pressure loss of the determination of this type of meter is larger, the precision is not high, the medium to be measured is more sensitive, belong to the universal instruments. Throttling device development early, therefore, but as other forms of flow meter in perfecting and development, the requirement of industrial development of flowmeter is increasing, the throttle device in industrial measurement of bai gradually advanced, high precision, convenient replaced other flowmeters.