Operation of Ultrasonic Flow Meters in the Water Industry under Conditions Deviating from Calibration

Abstract: In the case of different calibration conditions, the operation information of ultrasonic flowmeters in the water industry is provided by excellent flowmeter and flowmeter manufacturers and quotation manufacturers. 1. Abstract At present, the calibration of ultrasonic flowmeters for natural gas metering is carried out on the flow calibration device as much as possible. Since almost all of these installations use natural gas to flow through the pipeline, it is usually not possible to change parameters that affect the speed of sound, eg. More flowmeter manufacturers select models and price quotations. You are welcome to inquire. The following is the operation article details of ultrasonic flowmeters in the water industry under different calibration conditions. 1. Abstract At present, the calibration of ultrasonic flowmeters for natural gas metering is carried out on the flow calibration device as much as possible. Since almost all of these installations use natural gas flowing through the pipeline, it is usually not possible to change parameters that affect the speed of sound, such as temperature, pressure, gas composition. When using an ultrasonic flowmeter, can calibration still work if these parameters differ from the values ​​under calibration? In order to quantitatively characterize the effect of changes in these parameters on the calibration of ultrasonic flowmeters, a series of carefully controlled calibration experiments were performed. The first experiment involved calibrating a 200mm (8inch) and a 300mm (12inch) ultrasonic flowmeter in the high pressure loop of the Southwest Research Institute (SwRI) using a natural gas medium with a pressure of 2.8MPa (400psi). As an additional reference, 200mm and 300mm turbine flow meters are also used in the circuit. Then the fluid medium was changed to nitrogen, and the sound velocity changed by 16%, which was equivalent to the pressure of natural gas 4.6MPa (677psi). To further test the effect of pressure on the calibration of an ultrasonic flowmeter, a series of statistical sound velocity measurements were performed on a 300mm bore flowmeter using nitrogen gas at pressures ranging from 1.4MPa (200psi) to 7MPa (1000psi). Measured values ​​indicate that the change in sound velocity over this pressure range is within 0.03% of the calculated value. In addition, further experiments were carried out on changes in the speed of sound caused by changes in temperature and fluid medium. Calibration experiments were performed with natural gas at 21°C (70°F) and 10°C (50°F) and with nitrogen at 21°C (70°F) and 32°C (90°F). For each series of calibrations, the average calibration curve is compared to obtain the effect of changes on the calibration. The calibration of an ultrasonic flowmeter is unresponsive to changes in sound velocity, temperature, and pressure, provided the desired device and flowmeter reproducibility is met. When the fluid medium used for calibration was changed from natural gas to nitrogen, the small change observed was due to the different equations of state used for the two gases. These test results demonstrate that if the calibration procedure of the ultrasonic flowmeter is feasible under one set of conditions, it can also be used under other conditions, including the use of different gaseous media. 2. Introduction The principle of the ultrasonic flowmeter for natural gas measurement used in related transactions is to measure the ultrasonic propagation time of the gas. When the ultrasonic wave is in the same direction as the fluid flow, the propagation time is shorter than that when the flow is countercurrent. The travel time difference between the two states is used to calculate the average velocity of gas flow. The actual volume flow can be expressed by the following formula: where K = meter coefficient of the flowmeter, △T = travel time difference, T1 = travel time in forward flow, T2 = travel time in reverse flow, because only the flow meter is included in this flow equation The physical structure size and propagation time of , which is independent of the speed of sound (SOS) in a flowing gas. Therefore, it can be assumed that the determination of the gas flow rate is independent of the factors that affect the speed of sound in the gas, such as temperature, pressure and gas composition. If this assumption is incorrect, the validity of the calibration of the ultrasonic flowmeter under conditions other than field operating conditions is worth considering. First, the measurement of gas velocity in an ultrasonic flowmeter is independent of sound velocity, but there may be some secondary effects for the following reasons. Acoustic resistance changes the coupling of the signal to the gas; changes in Reynolds number. The Reynolds number is proportional to a specific gravity (SG) to viscosity ratio; the wavelength (WL) of the signal varies with gas composition. It would be interesting to note these parameters in different media. The following tables are for standard conditions. Note that for a given pipe size and flow rate, the Reynolds number is almost constant. Table 1 Gas properties When changing from natural gas to air or nitrogen, many gas properties change, such as speed of sound, specific gravity and viscosity. However, since they also vary with temperature and pressure, ultrasonic flowmeters have a conceivable overlap in gas properties over a range of operating conditions, suggesting that deviations from standard conditions are less critical. 3. Research Objectives The research objectives described in this paper are to determine the effects of temperature, pressure, and fluid medium changes on gas ultrasonic flowmeters. In addition to verifying ultrasonic flowmeter technology, the program also supports the calibration of these natural gas flowmeters with nitrogen or air. Now,There are only two sets of equipment available in North America for calibrating ultrasonic flowmeters larger than 200mm outside the flow range. The installation of these flowmeters is growing at a rate of more than 10% per year. In the future, calibration equipment will become very limited. These calibration devices may require recalibration after less than a few years of use. If the calibration of ultrasonic flowmeters is limited to natural gas installations, the possibility of building new installations is limited by location and cost. However, if it can be demonstrated that calibration with other media is equivalent, the possibility of building a new device is greatly increased. Calibrating a natural gas flowmeter with air is not just for ultrasonic flowmeters. Almost all turbine flow meters and residential gas meters used for natural gas metering can be calibrated with air.

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