Impact of Pitot tube calibration on the uncertainty of water flow rate measurement

[摘要] Water utility companies often use Cole type Pitot tubes to map velocity profiles and thus measure flow rate. Frequent monitoring and measurement of flow rate is an important step in identifying leaks and other types of losses. In Brazil losses as high as 42% are common and in some places even higher values are found. When using Cole type Pitot tubes to measure the flow rate, the uncertainty of the calibration coefficient (Cd) is a major component of the overall flow rate measurement uncertainty. A common practice is to employ the usual value Cd= 0.869, in use since Cole proposed his Pitot tube in 1896. Analysis of 414 calibrations of Cole type Pitot tubes show that Cdvaries considerably and values as high 0.020 for the expanded uncertainty are common. Combined with other uncertainty sources, the overall velocity measurement uncertainty is 0.02, increasing flowrate measurement uncertainty by 1.5% which, for the Sao Paulo metropolitan area (Brazil) corresponds to 3.5 × 107m3/year.

[发布机构] Instituto de Pesquisas Tecnologicas Do Estado de Sao Paulo - IPT, Av. Prof. Almeida Prado, 532, São Paulo; SP, 05508-901, Brazil^1

[效力级别] 力学 [学科分类] 力学，机械学

[关键词] Calibration coefficients;Common practices;Flow rate measurements;Measurement uncertainty;Metropolitan area;Monitoring and measurements;Uncertainty sources;Velocity profiles