Investigation into the anomalous behavior of Pitot tubes in dilute polymer solutions

Abstract

The anomalous behavior of Pitot tubes in the turbluent pipe flow of a dilute polymer solution is investigated and discussed. Pitot tube error is measured using an alternative optical means of local velocity measurement. Unlike previous research in this field a strict control is kept on the state of degradation of the solutions and Pitot tube error is measured directly whilst the tube is under test. Errors which occurred in total head pressure measurement were found to be negative and in some cases were as high as 40%. Factors which influence the Pitot tube accuracy are identified and a dynamical similarity argument is used to express the error as a function of these. Pitot tube error is attributed to the polymer solutions storing energy viscoelastically at the tube tip. A critical review of explanations previously put forward for Pitot error with reference to the results is included in the discussion. The polymer used was polyox WSR-301.

Structural, Viscoelastic, and Electrochemical Characteristics of Self-Assembled Amphiphilic Comblike Copolymers in Aqueous Solutions

“…However, in some specific flow fields, which are characterized by elongational deformations, these fluids may also display anomalous pressure drops versus strain-rate. This has been reported in the past for dilute and semidilute solutions of linear polymers of high molecular weight at the entrance of capillary flows , or for flows displaying a stagnation point . In both cases, it was suggested that the existence of a characteristic time was strongly correlated with a critical value of the shear rate.…”

“…This has been reported in the past for dilute and semidilute solutions of linear polymers of high molecular weight at the entrance of capillary flows 1,2 or for flows displaying a stagnation point. 3 In both cases, it was suggested that the existence of a characteristic time was strongly correlated with a critical value of the shear rate. More precisely, at the onset of transition, the reciprocal of the shear rate scaled as the time needed for the polymer coil to be fully extended (so-called "coil−stretch transition"), 4−6 which corresponded to the Zimm relaxation time.…”

Mass transfer rate and conductivity instabilities in surfactant solutions submitted to a laminar elongational flow

“…On the other hand, in laminar flows, polymer solutions display for orifice and capillary tube as well as for the flow around a Pitot tube probe, anomalous increase or defect pressure drop measurements with respect to Newtonian or purely viscous non Newtonian behavior [6][7][8][9]. These anomalous pressure drop results have been explained as the elastic response of the polymer solutions to the elongational flow existing at the upstream of these geometries.…”

Electrochemical characterization of viscoelastic solutions of supramolecular polymers in phosphonium-based ionic liquids

“…These drag reducing solutions in turbulent flow display correlatively anomalous effects in laminar flows (e.g. Weissenberg effect, anomalous pressure drop/flow rate behavior, entrance flows) as shown for polymer solutions [11][12][13][14] and their drag reducing ability can therefore be studied in well-defined laminar flows.…”