The orifice flow meter is a throttling device and is a differential pressure sensing element that measures flow.Equipped with differential pressure transmitter and realistic, recording, integrating and adjusting instruments, it can be used to measure, calculate and control the instantaneous flow rate and cumulative flow rate of liquid, steam and gas.
The throttling device has the advantages of simple structure, convenient installation, reliable use, low price, convenient maintenance and wide selection range (the measuring pipe diameter of the standard throttling device can be from 50 mm to 1200 mm, and the diameter of the non-standard throttling device can be as small as 6mm, as large as 3000mm; the measuring temperature can be as high as 555°C; the pressure can reach 42MPa), and the standard throttling device also has the advantages of no need for separate calibration, etc.It is the most widely used and most mature product in flow meter, so it is widely used in electric power, chemical industry, metallurgy, petroleum, textile, military and other fields.
The throttling device is composed of a throttle part, a pressure taking device(including pressure taps, pressure pipes and valves, etc.) and matching flanges, sometimes including straight pipe sections that meet the standards.The standard throttle device has standard orifice, standard nozzle and standard Venturi tube. Standard orifice plates are angled (ring chamber or borehole) to take pressure, flange to take pressure, diameter to take pressure; Standard nozzles are divided into nozzles and long-diameter nozzles according to their forms; standard Venturi pipes are divided into Venturi nozzles and Venturi pipes according to their forms (roughly cast or machined or rolled plates). Non-standard throttling devices include small aperture plate, 1/4 round orifice plate, round orifice plate,circular orifice plate, eccentric orifice plate, double orifice plate, concealed orifice plate, conical inlet orifice plate, etc. Other forms of throttle devices include pitot tube, uniform speed pipe, wedge, cone and so on.
When using a standard throttling device, the nature and state of the fluid must meet the following conditions:
(1) The fluid must be filled with pipes and throttling devices and flow continuously through the pipe;
(2) The fluid flow does not change or change very slowly over time;
(3) Fluid does not intersect through throttling parts;
(4) The fluid must be Newtonian fluid, ie physically and thermodynamically homogeneous, single-phase, or can be considered single-phase, including mixed gases, solutions and dispersive particles less than o. 1 m colloid.Solid particles having a uniform dispersion of not more than 2% (mass component) in the gas, or bubbles having a uniform dispersion of not more than 5% (volume component) in the liquid may also be regarded as a single-phase fluid, but the density thereof shall be an average density;
(5) Before the fluid flows through the throttling parts, the flow of fluid is an irrotational flow parallel to the axis of the pipeline.
Standard throttling devices are not suitable for flow measurement of moving and critical flows. The throttling device artificially causes throttling in the pipeline in which the medium flows. When the measured medium flows through the throttling device, a partial contraction occurs, the stream is concentrated, the flow rate is increased, the static pressure is lowered, and then the upstream and downstream of the throttle part are a static pressure difference is generated on both sides. This static pressure difference has a certain function relationship with the flow rate. The larger the flow rate, the larger the static pressure difference generated. Therefore, the flow rate can be measured by measuring the differential pressure.
The orifice flow meter is different from other flow meters in that the orifice flow meter is based on the parameter to design drawings and is finally processed. It is only necessary to select the orifice material according to the measurement medium.