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Orifice flowmeter manufacturers' selection, market demand, and future development analysis of differential pressure meters and other products
The differential pressure flowmeter is a meter that measures the flow rate based on the differential pressure generated by the flow detection element installed in the pipeline, the known fluid conditions, and the geometry of the detection element and the pipeline. It is a kind of measuring instrument used to measure flow in the early days. The differential pressure flowmeter consists of three parts: (1) a throttling device that converts the flow rate of the measured liquid into a differential pressure signal; (2) a signal pipeline that transmits a differential pressure signal; (3) a measurement of the differential pressure value Differential pressure meter or differential pressure transmitter and display instrument. Differential pressure flowmeters are usually classified by the type of test piece, such as orifice plate flowmeter, venturi flowmeter, and averaging tube flowmeter.
Selection and use of differential pressure flowmeters in chemical installations Note: Differential pressure flowmeters have large pressure losses and a narrow measurement range, generally 3: 1 or 4: 1. The repeatability of the measurement and the maximum degree of flow The calculation is of medium level. The installation of differential pressure flowmeter should include three parts: throttling device, differential pressure induced pressure conduit, and differential pressure gauge. When measuring fluid flow, in order to prevent gas from entering the liquid and existing in the impulse tube and to prevent precipitation of liquid in the liquid, a differential pressure gauge should be installed under the throttle device. To prevent liquid dirt or If dust enters the pressure guiding tube, the differential pressure gauge should be installed above the throttling device. When measuring water vapor, the height of the condensate column in the two pressure-inducing pipes should be equal to prevent high temperature steam from directly contacting the differential pressure gauge. The material of the pressure differential pressure guiding catheter should be determined according to the properties and parameters of the measured medium. Its inner diameter is not less than 6mm, and the length is preferably within 16mm. The differential pressure impulse conduit should be laid vertically or obliquely, and the inclination should not be less than 1:12. For fluids with high viscosity, the inclination should be more increased. When the length of the differential pressure induced pressure conduit exceeds 30m, the pressure guiding tube should be tilted in sections, and the collector (or exhaust valve) and the settler (or blowdown valve) should be installed at the highest and lowest points. ). Anti-freeze protection should be added to the pressure differential pressure guide tube in the severe cold area, and at the same time to prevent overheating, otherwise the vaporization of fluid in the pressure differential pressure guide tube will generate false differential pressure.
6 Rotameter
Rotor flowmeter is a low-medium *** degree instrument, which is a kind of variable area flowmeter. Rotary flowmeter is a volume flow meter which measures the float in a vertical conical tube as the flow rate changes and changes the flow area between them. Generally divided into glass and metal rotor flowmeters, as intuitive flow instructions or on-site indicator instruments that do not require high degrees of measurement, rotor flowmeters are widely used in the chemical industry.
Rotary flowmeter is suitable for flow measurement of medium and small diameter fluids and fluids with low Reynolds number. Rotary flowmeters have low pressure loss and a wide flow range, which is generally 10: 1, the lowest is 5: 1, and the highest is 25: 1. When selecting and using, it should be noted that the main measurement object of the rotor flowmeter is a single-phase liquid or gas. Particles in the liquid or droplets in the gas are generally not applicable. The glass tube rotor flowmeter should be selected with a transparent protective cover. Once the glass cone tube ruptures, it can stop the fluid from splashing forward for emergency treatment. When used for gas, guide bars or ribbed instruments should be selected to avoid accidental operation of the float to break the cone tube.
7 Thermal mass flowmeter
7.1 Application areas
Thermal mass flowmeter is a meter that uses the heat transfer principle, that is, the heat exchange relationship between the fluid in flow and the heat source (the object heated in the fluid or the heating body outside the measuring tube) to measure the flow. Thermal mass flow meters are currently mainly used for measuring gases. Thermal (gas) mass flowmeter It is suitable for the measurement of a single gas and a fixed proportion of multiple component gases. typical application:
(1) Gas flow measurement in industrial pipelines;
(2) Air flow measurement in the gas process;
(3) Flue gas flow measurement from the chimney;
(4) Measurement of waterfall gas flow in water treatment;
(5) Measurement of gas flow in the production process of cement, cigarettes and glass factories; measurement of compressed air flow;
(6) Flow measurement of natural gas, coal gas, liquefied gas, flare gas, hydrogen and other gases;
(7) Gas flow measurement in steel plants.
7.2 Classification
There are two main types of thermal flow meters:
(1) A heat-distributed flow meter that uses the heat transfer effect of a flowing fluid to change the temperature distribution of the measuring tube wall temperature distribution.
(2) A thermal mass flow meter using the King's law of heat dissipation (cooling) effect.
7.3 Selection
When selecting and using, it should be noted that compared with other flowmeters, thermal mass flowmeters have a medium measurement of *** degrees, which is suitable for measurement in the low flow rate range. Because of its long response time, it is not suitable for pulsating flow measurement when measuring gas. Fluid temperature change does not affect mass flow, but the temperature change is too large, and the change in specific heat capacity will cause the range change; thermal mass flowmeters can only be used to measure clean single-phase fluids; gas or liquid, gas models cannot be used for liquids ,vice versa. For hot distributed gas, it must be dry gas and must not contain moisture. The flow sensor of most thermal mass flow meters in installation can be installed in any posture (horizontal, vertical or inclined), and its performance is not affected by the installation posture. Generally, there is no requirement for the length of the upstream and downstream straight pipe sections in the thermal distribution. Tube immersion flow sensors and plug-in meters require a certain length of front straight pipe section.
8 Application and Development Trends of Several Flow Meters
8.1 Coriolis mass flow meters (CMF) have developed more than 30 series abroad. The technical focus of each series development lies in the design innovation of the flow detection and measurement tube structure; improve the zero point stability of the instrument and the performance of the instrument; Increase the measuring tube deflection and improve the sensitivity; improve the measuring tube stress distribution, reduce fatigue damage, and strengthen the ability to resist vibration and interference.
8.2 Electromagnetic Flowmeter (EMF)
Since entering the industrial application in the early 1950s, the field of use has been expanding. Since the late 1980s, it has accounted for 16% to 20% of the sales of flow meters in various countries. China has developed rapidly in recent years, with sales estimated at 6,500 to 7,500 in 1994. China has produced the largest ENF with a diameter of 2 ~ 6m, and has equipment capacity of 3m.
8.3 Vortex Flowmeter
It entered industrial applications in the late 1960s, and has accounted for 4% ~ 6% of the sales of flow meters in various countries since the late 1980s. Worldwide sales in 1992 were estimated to be 3.548 million units, while domestic products were estimated to be 8,000 to 9,000 units during the same period.
8.4 Thermal mass flowmeter
(1) When a flowmeter instrument has made a breakthrough in a certain technology, an adapted and improved instrument will be developed, which makes rapid development in this field. Thermal mass flowmeters were mainly thermally distributed in the past and were used for small gas flow measurement. They are mostly used in the semiconductor industry, heat treatment furnaces, analytical instruments such as hydrogen, oxygen, ammonia and other flow measurement and control, as well as the leakage measurement during valve manufacturing. Wait. In recent years, the application of intrusive and plug-in thermal flowmeters with heat dissipation effects and large and medium-sized pipes in environmental protection and process industries have developed rapidly. Detection rods composed of multiple sets of detection elements in radial segments are mostly inserted into HVAC (heating, ventilation, and air conditioning) engineering large and medium-sized pipes; they are also used to monitor the SO2 and NOX of the air intake and flue gas discharge of large boilers. Total emissions. Thermal gas mass flow meters have been applied to all aspects of production and life in our life today, of course, the main use is in industry. Among them, it has the role of high and new technology, and of course, it cannot be separated from the development of industry itself. But in these developments, how to make better use of the advantages of thermal gas mass flow meters to better play its role and solve the existence The deficiency is the focus of future development.
(2) Although the micro-liquid mass thermal flowmeter has a history of more than 20 years, its industrial application has not developed rapidly until recent years. Several manufacturers have now produced various models of thermal distributed thermal flowmeters. market. At present, it is mainly used in chemical, petrochemical, food and other process industry experimental devices. For example: constant flow ratio control in chemical liquid ratio system, liquid flow measurement and control during liquefied gas injection.
(3) The thermal gas mass flow meter has the characteristics of convenient use, easy control and installation, and does not require excessive pipelines, and can be used normally even in special occasions. Can also take into account environmental protection and energy saving and high standards of control. In the future, the development trend of thermal gas flow meters is still focused on technological improvements while retaining the advantages while strengthening quality monitoring. Of course, the existing shortcomings must be improved to avoid them as much as possible. With the development of the overall economy, it will work with other automation devices to help industrial production with more perfect and precise control and play its due role. It can be seen that with the maturity of technology and the strong support of the country, the development trend of thermal gas mass flow meters will be very good. I believe that as long as we can seize the opportunity in such a good situation, we will certainly realize it. Great value.
8.5 Verabar Flowmeter
It adopts an engineering structure design that fully conforms to the aerodynamic principle, and is a sensor element that has achieved unparalleled levels of accuracy, efficiency and reliability.
9 concluding remarks
Most flow meters require suitable measurement media and working conditions to rely on them to play the correct role. Flow meters with advantages but no disadvantages do not exist today. Reasonable selection of meters is crucial for field engineers and managers. In summary, to properly and effectively select and use flow measurement methods and instruments in chemical plants, you must be familiar with the two aspects of flow instruments and production process fluid characteristics. At the same time, economic factors must be considered, and five aspects must be summarized. Factors, namely performance requirements, fluid characteristics, installation requirements, environmental conditions and costs. In short, no measurement method or flow meter can adapt to various fluids and flow conditions. Different measurement methods and structures require different measurement operations, methods of use, and conditions of use. Each type has its own advantages and disadvantages. Therefore, based on a comprehensive comparison of various measurement methods and instrument characteristics, the best type that is suitable for production requirements, is reliable, economical and durable.
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