1、 Turbine flowmeter
Turbine flowmeter The principle is a velocity flowmeter. The fluid first passes through the front guide piece of special structure and accelerates, and the fluid passes through the turbine and produces rotational torque to the turbine. There is a linear relationship between the angular velocity of turbine and the flow rate. The signal detection unit uses the principle of electromagnetic induction to amplify and reshape the induced pulse signal by the preamplifier, and then calculates the instantaneous volume flow rate and cumulative flow rate after temperature and pressure compensation.
Advantages: wide range, easy to install, no interference.
Disadvantages: it is easy to be affected by fluid flow characteristics and medium types; bearing is easy to wear after long-term use, which affects instrument characteristics.
2、 Electromagnetic flowmeter
Electromagnetic flowmeter is based on Faraday's law of electromagnetic induction, which is used to measure conductive medium. It is a new type of flow measurement instrument developed rapidly with the development of electronic technology. Because the detection element is outside the flowmeter pipe, it can be used to measure high pollution and high corrosion medium. With the development of science and technology, the new electrodeless electromagnetic flowmeter has strong resistance to mud noise and can stably measure low conductivity fluid.
Advantages: simple structure, no moving parts, no pressure loss, can measure dirty medium and corrosive medium, sensitive response, can measure flow in both positive and negative directions.
It is difficult to measure the conductivity of liquid and liquid by electromagnetic medium.
Rotameter, also known as rotameter, is a volumetric flow meter in which the float rises and falls with the change of flow rate in the vertical cone tube, and changes the flow area between them to measure. Rotameter is the most widely used flowmeter after differential pressure flowmeter, especially in the field of micro flow measurement.
Advantages: simple structure, suitable for small diameter, low flow rate, low pressure loss, wide range and low requirement for straight pipe section.
Disadvantages: low pressure resistance, fragile glass tube.
4、 Ultrasonic flowmeter
Ultrasonic flowmeter is an instrument that uses the influence of fluid on ultrasonic wave to measure flow. It is a non-contact instrument with the development of integrated circuit technology in 1970s. It is based on the principle that the velocity difference of ultrasonic wave propagating in the fluid is proportional to the flow velocity of the fluid. According to the principle, it can be divided into time difference type, phase difference type, frequency difference type and Doppler ultrasonic flowmeter (suitable for the measurement of two-phase flow). With the development of technology, Instromet introduced artificial intelligence technology into ultrasonic sensor, and realized the real high-precision gas flow measurement. Ultrasonic flowmeter has been developed and popularized rapidly in recent years because of its own advantages. It is especially suitable for the measurement of large diameter pipeline. It is expected that it will be easy to carry, more universal and not affected by the measurement environment in the future.
Advantages: no pressure loss, wide range, up to 400:1.
Disadvantages: it is sensitive to inlet velocity and requires long branch pipe length.
5、 Mass flowmeter
Mass flowmeter can be divided into direct type and indirect type. The direct mass flowmeter uses the principle related to mass flow to measure. The indirect mass flowmeter is to obtain the mass flow rate by multiplying the densitometer and the volumetric flow rate directly. At present, the most widely used direct mass flowmeter is thermal mass flowmeter and Coriolis mass flowmeter.
Thermal mass flowmeter is a kind of instrument that uses heat transfer principle to measure flow rate, that is, heat exchange relationship between fluid and heat source in flow. Its advantages are no moving parts and low pressure loss; its disadvantage is that it is easy to be affected by medium composition, so it is not widely used in natural gas measurement.
Coriolis flowmeter uses the deflection corresponding to the mass flow rate generated in the vibrating fluid tube to measure. It has the advantages of high precision, direct measurement of mass flow rate and density, so that users can not only know the volume of the fluid, but also understand its composition. Its disadvantage is that the pressure loss is large, and it is easily affected by the temperature and pressure of the fluid. Because of its high accuracy, it is a promising mass flowmeter.
6、 Fluid vibration flowmeter
Fluid vibration flowmeter can be divided into vortex type and jet type according to the principle of induced fluid vibration. Vortex type fluid vibration flowmeter includes vortex flowmeter and Precession Vortex flowmeter. Its basic working principle is that the vibration frequency of vortex generated by fluid flowing through a specific pipe is directly proportional to the flow velocity.
Vortex flowmeter has the advantages of low pressure loss, but the disadvantage is that it needs long straight pipe section and is easily affected by pipeline vibration. However, the Precession Vortex flowmeter has higher accuracy, shorter straight pipe section, lower flow lower limit and stronger anti-interference ability, but its disadvantage is high pressure loss.
The principle of the jet flowmeter is based on the phenomenon that the high-speed airflow is attached to the surface at the corner of the object surface. It will flow through the nozzle to form a high-speed jet, so as to produce wall attachment effect on the wall, so it is called jet flowmeter. Because the viscosity of fluid can affect the wall attachment effect, its application is limited. However, because of its role of fluid amplification, it has a greater advantage in small flow measurement.
7、 Orifice flowmeter
Orifice flowmeter is a differential pressure flowmeter. The principle is that when the fluid flows through the orifice plate in the pipeline, the current beam will form a local contraction at the orifice plate, the flow rate will increase, and the static pressure will decrease. A small static pressure difference will be generated before and after the orifice plate. The flow rate can be determined by measuring the differential pressure value. It is a common flowmeter for measuring liquid, gas and steam flow.
Advantages: suitable for large diameter, no movable parts, durable; long service time, the most complete standard; easy to manufacture and cheap.
Disadvantages: narrow measurement range; large pressure loss; measurement accuracy affected by installation conditions and human factors; long straight pipe section before and after.
8、 Nozzle flowmeter
The nozzle flowmeter is designed and manufactured on the basis of Laval nozzle principle in hydrodynamics. When the ratio of nozzle outlet pressure to inlet pressure is equal to 0.528, the gas flow velocity in the nozzle reaches supersonic speed. When the pressure ratio continues to decrease, the gas flow rate remains unchanged.
Advantages: the standard nozzle has a long history, no movable parts, simple and firm structure, stable and reliable, and high degree of standardization.
Disadvantages: complex manufacturing and high unit price.
9、 Venturi flowmeter
Venturi is a standard throttling device, which is a throttling flow sensor developed according to venturi effect. According to the structure, the venturi is divided into general venturi and standard Venturi. The measuring principle is that when the fluid flows through the throttling parts in the pipe, the velocity will shrink at the throat neck of the venturi pipe, which will increase the flow rate and reduce the static pressure, resulting in a pressure difference between the front and the back of the venturi throat. The flow rate is calculated by measuring the pressure difference.
Advantages: small pressure loss, accurate calculation, low energy consumption, simple structure and easy installation.
Disadvantages: only suitable for the measurement of clean gas or liquid; serious wear and tear in long-term use, affecting the measurement accuracy; small range ratio; high price.
10、 Positive displacement flowmeter
Volumetric flowmeter is a kind of flow meter which uses mechanical measuring elements to divide the fluid into a single known volume continuously, and fill and discharge the volume part repeatedly to accumulate and measure the total amount of fluid. It is widely used to measure the flow of petroleum fluid, beverage fluid, gas and water. It is one of the most accurate instruments in flowmeter. According to its measuring elements, volumetric flowmeter can be divided into double rotor flowmeter, elliptical gear flowmeter, rotary piston flowmeter, scraper flowmeter, reciprocating piston flowmeter, liquid seal rotary cylinder flowmeter, disc flowmeter, wet gas flowmeter and membrane gas flowmeter.
Wide range, high measurement accuracy, no influence on the measurement condition of liquid.
Disadvantages: complex structure, large volume; only suitable for clean single-phase fluid; noise and vibration when working; easy to wear.