Impacto da calibração de tubos de pilot na incerteza da medição de vazão de água


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 discharge coefficient (C) is a major component of the overall flow rate measurement uncertainty. A common practice is to employ the usual discharge coefficient (C) of 0.869, in use since the Cole proposed his Pitot tube in 1896. Analysis of 414 calibrations of Cole type Pitot tubes show that C varies considerably and values as high 0.020 for the expanded uncertainty are common. Combined with other uncertainty sources, the overall velocity measurement uncertainty is 0,028, increasing flowrate measurement uncertainty by 1.5% which, for the São Paulo metropolitan area corresponds to 1,5 x 107 m³/year.

BUSCARINI, Icaro de Oliveira; TAIRA, Nilson Massami ; JABARDO, Paulo José Saiz ; NADER, Gilder . Impacto da calibração de tubos de pilot na incerteza da medição de vazão de água. In: SIMPÓSIO INTERNACIONAL DE INICIAÇÃO CIENTÍFICA DA USP, 22., 2014, São Paulo. Trabalho apresentado… 4 p.

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