A Study on the Flows of Dilute Polymer Solutions : 4th Report, On the Velocity Measurement by a Pitot Tube Method

Abstract

Flow visualization, measurements of velocity fields etc. are utilized to determine flow behaviours of dilute polymer solutions. However except in the case such as using a doppler anemometer, it is expected that the influence of insertion of probes such as a pitot tube on the measurement is comparatively large. In this report, a problem of determination of a flow velocity by a pitot tube method is discussed analytically and experimentally. Velocity measurements in a turbulent pipe flow of dilute polymer solutions show that the flow rate determined from apparent velocities, which are obtained with a customary method assuming fully developed stresses, is less than the true value ( 〓of the order of 10%), but the resultant velocity profile corrected by the analysis of the flow field around a pitot tube is in fairly good agreement with that by other methods and the disagreement of the flow rate is improved. These results show the necessity of the pitot tube coefficient caused from viscoelastic behaviour of dilute polymer solutions.