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During the selection process of vortex flowmeters, there are situations where the data provided by the customer is inaccurate, or where the parameters no longer match the actual conditions due to changes in process conditions after selection; all of these factors can affect the proper operation of the vortex flowmeter. To this end, CHANGHUI Instruments provides ten considerations for selecting vortex flowmeters for use as a guide and reference for instrument technicians. http://yunrun.com.cn/upload/202001/18/202001180115047261.png 1. The specifications and types of vortex flowmeters should be selected based on the volumetric flow rate, pressure, temperature, density, and viscosity of the fluid being measured, as well as the flow totalizing instrument used in conjunction with it. The flow range of the selected vortex flow meter should cover the volumetric flow rate of the medium under operating conditions. 2. The flow rate measured by a vortex flow meter refers to the volumetric flow rate under operating conditions. When the mass flow rate under the operating conditions of the medium being tested or the volume flow rate at standard conditions is provided, it must be converted to the volume flow rate under the operating conditions. Similarly, when the density under standard conditions is provided, it must also be converted to the density under operating conditions. The conversion formula is as follows. ①The mass flow rate under operating conditions is converted to the volumetric flow rate under those same conditions using the formula Qv = Qm/ρ (unit: m3/h), where Qv represents the volumetric flow rate under operating conditions (in m3/h) ； Qm is the mass flow rate under operating conditions (kg/h) ； ρ is the density of the medium under operating conditions (kg/m3). ②Conversion of the gas volumetric flow rate under standard conditions to that under operating conditions: In the formula, Qv represents the volumetric flow rate under operating conditions (m3/h) ； QN is the volumetric flow rate of the gas under standard conditions (m3/h) ； t is the temperature in operating condition (°C) ； P is the gauge pressure in operating condition (MPa). ③The density under standard conditions is converted to the gas density under operating conditions as ρ=(ρN×QN)/Qv (unit: m3/h); in this formula, ρ represents the density of the medium under operating conditions (kg/m3) ； Density at standard conditions for ρN (kg/m3) ； QN is the volumetric flow rate of the gas under standard conditions (m3/h) ； Qv is the volumetric flow rate under operating conditions (m3/h). 3. Selection of the nominal pressure for vortex flow meters: ① The nominal pressure of the flow meter must be the same as that of the specialized flange used with it ； ②At the operating temperatures of different fluid media, the operating pressure of vortex flow meters and flanges varies. As shown in Table 1 ； ③To ensure production safety, sufficient attention must be paid when making choices ； ④The operating pressure of the fluid medium must be lower than the maximum shock-free operating pressure listed in Table 1. The maximum shock-free operating pressure for flanged vortex flowmeters (in MPa): http://yunrun.com.cn/upload/202001/18/202001180109378114.png 4. Selection of the diameter for vortex flowmeters: ① Choose based on the fluid pipeline – select a vortex flowmeter with a diameter that corresponds to the inner diameter of the pipeline. If the flow rate range of the medium under test falls within the range specified in Article 5, then the selected flow meter is appropriate. ②Select based on the flow rate range of the medium being measured. Determine the vortex flow meter with the appropriate diameter from the reference flow rate range table provided by the manufacturer, using the maximum flow rate of the medium in question; then determine the minimum flow rate using the method outlined in point 5. If it falls within the flow range of the medium being measured, the selected vortex flow meter is appropriate. ③If the above requirements are not met, another vortex flow meter with a different path should be selected to ensure it meets the flow range of the medium being measured. When vortex flowmeters with both diameters are available, the one with the smaller diameter should be chosen. 5. Determine the flow rate range of the medium under test. ① The maximum flow rate can be taken as the upper limit value in the reference flow rate range table provided by the manufacturer ； ②The general method for determining the minimum flow rate is as follows: a. Calculate the minimum flow rate based on the density ρ of the medium under operating conditions. In the formula, Q0 represents the lower limit value of flow rate given in Table 4 (in m3/h) ； ρ0 is the reference density (liquid ρ0=1000kg/m3 ； Gas ρ0=1.205kg/m3) ； ρ is the density of the medium under operating conditions (kg/m3). b. The minimum flow rate Qvνmin is calculated based on the dynamic viscosity ν of the medium under operation, using the formula Qvνmin=30×D×V. Here, D represents the inner diameter of the vortex flow meter in meters ； ν is the dynamic viscosity at operating conditions (cSt). c. Compare the values of Qvρmin and Qvνmin; the larger value is taken as the minimum flow rate. 6. To ensure the measurement accuracy of the vortex flow meter, it is necessary to have a Reynolds number Re corresponding to the minimum flow rate of the medium being measured of at least 2×104 (for DN≤100 mm) or Re≥4×104 (for DN≥125 mm). Except for liquid media with a high kinematic viscosity, the Reynolds number of most fluids under operating conditions is greater than the values mentioned above. If it is below the above value, its measurement accuracy will decrease, but it will not be lower than ±0.5% of the full-scale value. In the formula: U is the average flow velocity of the fluid in the pipe (m/s) ； D is the inner diameter of the vortex flow meter (m) ； QV is the volumetric flow rate under operating conditions (m3/h) ； ν is the dynamic viscosity at operating conditions (cSt). 7. The pressure loss of the vortex flow meter shall not be greater than the value calculated by the following formula: In this formula, Cd is the drag coefficient of the vortex flow meter, with Cd = 2.4 ； ρ is the density of the medium under operating conditions (kg/m3) ； U is the average flow velocity of the fluid in the pipeline (m/s) ； QV is the volumetric flow rate under operating conditions (m3/h) ； D is the inner diameter of the vortex flow meter (m). 8. When measuring liquids, especially those at high temperatures, cavitation often occurs when the pressure inside the pipeline is low and the flow rate is high, which affects the accuracy of measurement. To prevent cavitation, the minimum pressure inside the pipeline must meet the following requirement: P ≥ 2.7×△P + 1.3×P0. In this formula, △P represents the pressure loss of the vortex flow meter (in Pa) ； P0 is the saturated vapor pressure corresponding to the temperature of the liquid (Pa). 9. The average instrument coefficient value is indicated on the back of the factory calibration certificate for the vortex flowmeter produced by Changhui Instrument Manufacturing Co., Ltd., with the unit being l/m3. It indicates the number of pulses generated per unit volume flow rate passing through the vortex flow meter. 10. Temperature correction of the average instrument coefficient K value: When the operating temperature of the medium being measured is above 100°C, the K value must be corrected. In the formula: represents the corrected instrument coefficient (l/m3) ； Instrument coefficient given for calibration (l/m3) ； t is the operating temperature of the medium under test (°C) ； t0 is the operating temperature of the medium during testing, and it can generally be set at 20°C. Original text: http://yunrun.com.cn/tech/2883.html