Gas flowmeters are a new type of flowmeter developed based on the principle of liquid vibration. They are widely used in the metering of fluids in industries such as petroleum, chemical engineering, metallurgy, and papermaking. This type of flowmeter has no moving parts, featuring strong reliability, high accuracy, and a long service life. It can accurately measure the instantaneous flow and cumulative flow of liquids within a very wide flow range. It is not affected by the temperature, pressure, viscosity, or composition of the medium. At the same time, it is not prone to blockage, jamming, or scaling, can withstand high temperatures and pressures, is safe and explosion-proof, and is suitable for harsh environments. Main characteristics of gas flowmeters: 1. Simple installation and very convenient maintenance. 2. Wide measurement range, with a range ratio of up to 1:10. 3. Relatively small pressure loss, low operating cost, and greater energy-saving significance. 4. Wide application range, capable of measuring the flow of steam, liquids, and gases. 5. The detection sensor does not directly contact the measured medium, with stable performance and a long service life. 6. The output is a pulse signal proportional to the flow, with no zero drift and high accuracy. 7. Simple and robust structure, no moving parts, high reliability, and very reliable long-term operation. 8. Within a certain Reynolds number range, the output signal frequency is not affected by changes in the physical properties and composition of the fluid. The instrument coefficient is only related to the shape and size of the vortex generator. There is no need for compensation when measuring the volumetric flow of the fluid, and generally, there is no need to re-calibrate the instrument coefficient after replacing accessories. Comparative analysis of commonly used gas flowmeters (1) Differential pressure flowmeter Working principle: Calculate the flow based on the differential pressure generated by the throttle installed in the pipeline and the pipeline size. Advantages: Simple structure, low cost, good repeatability, and stable performance. Disadvantages: Large pressure loss, high on-site installation requirements (requiring a long straight pipe section), and moderate accuracy level. Applicable range: All closed pipelines, all one-way fluids, and some multiphase fluids. (2) Critical flowmeter Working principle: When the inlet pressure and outlet pressure reach a certain ratio, that is, the gas flow velocity reaches the speed of sound at the throat of the nozzle, the mass flow of the nozzle is calculated according to empirical formulas. Advantages: Good repeatability, high measurement accuracy, wide rangeability, and not limited by temperature, pressure, etc. Disadvantages: High requirements for gas media, not applicable to complex gases; high noise. Applicable range: Used in laboratories. (3) Ultrasonic flowmeter Working principle: Measure the fluid flow by detecting the effect of fluid flow on ultrasonic pulses. Advantages: No flow obstruction during measurement, no pressure loss. Disadvantages: High requirements for gas cleanliness, low accuracy. Applicable range: Used in occasions that are difficult to measure in laboratories. (4) Rotameter Working principle: Based on the float moving up and down in a vertical conical tube, the corresponding flow area indicates the flow rate. Advantages: Simple structure, small pressure loss, and low price. Disadvantages: Generally can only be installed vertically, easy to damage, and low accuracy. Applicable range: Generally used as an intuitive flow indicator or as an on-site indicator instrument with low measurement accuracy requirements. (5) Vortex flowmeter Working principle: Calculate the fluid flow by detecting the frequency of vortices generated on both sides of the non-streamlined vortex generator. Advantages: High accuracy, applicable to a wide range of fluid types, wide range, and small pressure loss. Disadvantages: Requires a long straight pipe section, not applicable to low Reynolds number measurement. Applicable range: Used for large-diameter pipes and medium to high-speed fluids. (6) Positive displacement flowmeter Working principle: Use mechanical measuring elements to continuously divide the fluid into individual known volumes, and measure the total flow based on the number of such volume divisions. Advantages: High accuracy, no pipeline installation requirements, and wide range. Disadvantages: Complex structure, large volume, high installation and maintenance costs, and requirements on medium types and calibers. Applicable range: Suitable for clean single-phase flows. (7) Laminar flowmeter Working principle: When the gas flow passes through the laminar flow element, the volumetric flow is calculated by the linear relationship between the pressure difference before and after the laminar flow element and the flow. Advantages: Not limited by pressure, can perform high-pressure testing, and applicable to both positive and negative pressures. Disadvantages: The internal structure of the laminar flow element is complex, and the tiny fluid channels are easily blocked by impurities in the fluid. Applicable range: Suitable for small and micro gas flow detection. Article sources: Jiake Flowmeter, Ceshi Instrument (Shanghai) Co., Ltd.