0 Preface Recirculating water is widely used as a cooling medium for chillers in petrochemical enterprises. Its transmission pipes generally have large diameters, which are usually 600 to 1000 mm or even over 1000 mm. In the past, a variety of flowmeters have been used to measure, such as electromagnetic flowmeters, turbine flowmeters, vortex flowmeters, etc. However, due to the large amount of impurities in the circulating water, the sensors are often covered or entangled in the actual application, affecting normal use. As a result, accurate traffic data cannot be provided. With most companies’ understanding of energy metering updates and increasing demand, stable and accurate measurement of circulating water flow in some large-caliber or straight-line segments has become an urgent problem to be solved. In recent years, with the continuous development and maturity of multi-channel ultrasonic flowmeter technology, ultrasonic flowmeters are easy to install, have a small amount of maintenance, have a wide measurement range, and are suitable for more complex pipe structures and flow distribution. Solve the technical difficulties of large-caliber circulating water flow measurement. 1 Large-diameter circulating water pipeline metering characteristics Due to the larger diameter of the circulating water pipeline and the large flow, a slight deviation in the operation of the instrument will bring about a large measurement error. In order to obtain accurate flow data, it is necessary to meet the following requirements in the measurement process: 1 Low pressure loss. Because the energy loss is proportional to the product of pressure loss and flow, if the pressure loss is too large, the fluid will lose a great deal of kinetic energy in the long-term operation of the flowmeter, resulting in energy waste. In order to accurately measure large-diameter pipes, the pressure loss during the measurement must be sufficiently small. 2 can achieve online maintenance. Because large-diameter pipe installations are relatively humid and difficult to stop flow maintenance, it is generally difficult to arrange bypass for installing flowmeters. Even if bypass and valves are installed, it is difficult to open and close, and it is difficult to ensure the tightness of valves. Therefore, the selected measurement is used. The meter should be small in maintenance and easy to maintain. 3 affected by debris in the medium. Because the medium in the circulating water pipeline contains many impurities, the pipeline often contains mud, oil, debris, etc., and attention should be paid to mechanical strength and impurities in the water to the measuring elements such as pollution, entanglement, and covering. Therefore, no measuring instruments that have no movable mechanical parts or sensors that are not easily affected should be used. 4 can achieve online calibration. Large diameter pipelines, large flow, there are many troubles and difficulties in calibration, so can only be online calibration during operation. 2 Problems with other types of flow meter applications Large-caliber circulating water meters generally have the following types: ultrasonic flowmeters, electromagnetic flowmeters, vortex flowmeters, and differential pressure flowmeters. The main problems of various flowmeters are as follows. 2.1 Electromagnetic flowmeter Electromagnetic flowmeter uses electromagnetic induction principle to measure the average flow rate of conductive liquid in the conduit, and further obtain the volumetric flow rate of the liquid. It has a small pressure loss, is not affected by the temperature, pressure, viscosity, etc. of the liquid to be measured, can measure impurities containing liquids, wide range, large diameter, sensitive reaction, the requirements of straight pipe sections before and after, corrosion resistance, long life and other significant advantages Therefore, it is widely used in circulating water metering. However, there are still some problems in the actual work: 1 The measurement error is affected by the external electromagnetic field. Therefore, special attention should be paid when installing to avoid severe vibration and strong AC and DC magnetic fields. 2 Influenced by the flow velocity distribution, the flow signal is proportional to the average flow velocity when the flow velocity axis is symmetrically distributed. Due to the influence of the flow velocity distribution and eddy current, the upstream straight section of the flowmeter should have a certain length, generally 5D. 3 The electrode surface is easily contaminated. When measuring a fluid with deposited deposits, the surface of the electrode will be contaminated, often causing zero drift. Therefore, during use, attention should be paid to periodic cleaning of the electrode. 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Application of Ultrasonic Flowmeter in Large Diameter Water Pipes