TP24-03 Characterization of Elliptical Pitot Tube for Water Flow Measurements

In 2018, CTI switched from simplex pitot tubes to an elliptical style pitot tubes for water flow measurements. This change was made to reduce the impact of change in Reynolds number on the calibration coefficient of the pitot tube. In addition, the new design incorporated a one-inch (1”) round body to reduce the vibration of the pitot. In this process, the blockage area of the pitot probe was increased. McHale has performed calibration studies at three different laboratories, (TVA Norris Engineering Laboratory, Alden Research Laboratory, LLC., University of Illinois, Urbana Champaign) and noted changes in the estimated coefficients. These calibrations were performed in different diameter pipes at each of the facilities. The relationship between the calibration coefficients and the Reynold’s Number varied from test to test. When blockage was considered, the variation in the curves was reduced. In addition, a study was performed in a free jet flow and showed the velocity followed a power law fit to the differential pressure. However, the exponent of the power law was 0.45 which is slightly less than the 0.5 that would be expected from Bernoulli’s equation. Based on the variation in the results between laboratories, it is possible that the calibration process may need to be revaluated. At a minimum, if the pitot is not used in the same size pipe as the calibration was made, then blockage must be accounted for in both the calibration and the calculation of the flow.