Available online at www.sciencedirect.com Chemical Engineering and Processing 47 (2008) 793–798 Local shear stress measurements with microelectrodes in turbulent flow of drag reducing surfactant solutions M.S. Boutoudj a , A. Ouibrahim a , F. Barbeu b , C. Deslouis c,∗ , S. Martemianov b a LEMM, University Boumerd` es, 35 000 Boumerd` es, Alg´ erie b LET UMR N6608, ESIP, 40 Av. duRecteur Pineau 86022 Poitiers C´ edex, France c UPR 15 CNRS, “Interfaces et Syst` emes Electrochimiques”, University P. et M. Curie, 4 place Jussieu, 75252 Paris C´ edex 05, France Received 20 January 2006; received in revised form 15 January 2007; accepted 15 January 2007 Available online 30 January 2007 Abstract The local wall shear stress, in turbulent flow of drag reducing and corrosion inhibiting surfactant solutions, was measured from polarographic mass transfer experiments using microelectrodes. A good agreement was observed between these values and those obtained by pressure drop measurements in a rectangular channel of high aspect ratio (10:1). Irreversible degradation was not observed in these systems at variance with polymer solutions. © 2007 Elsevier B.V. All rights reserved. Keywords: Drag reduction; Microelectrodes; Shear stress; Surfactant; Viscoelastic 1. Introduction It is known since the 1960s that some surfactants show this unique property to reduce the drag (skin friction) between a fluid and a solid wall [1]. For example, quaternary ammonium compounds with long aliphatic chains when associated with an appropriate counter-ion can achieve significant reduction of the skin friction in turbulent flow due to their ability to form thread- like micelles [2]. This is why it has already been suggested by Schmitt [3] that such compounds could be profitably used to mitigate hydrodynamically induced corrosion processes such as erosion corrosion. It was also recently suggested that drag reducing soluble polymers could have a beneficial action on corrosion of pipes for mass transport controlled process (anodic or cathodic) but the dramatic sensitivity of such compounds to irreversible mechanical degradation is pointless with respect to practical applications [4]. On the other hand, chemical compounds among the differ- ent families of organic inhibitors, surfactants, and namely those having nitrogen in their formula, possess the ability to strongly adsorb on solid surfaces, and for this reason are known for a long ∗ Corresponding author. Tel.: +33 1 44 27 41 48; fax: +33 1 44 27 40 74. E-mail address: cld@ccr.jussieu.fr (C. Deslouis). time to be effective in the protection against metallic corrosion [5]. Therefore, in view of the application to erosion–corrosion, quaternary ammonium compounds can be very relevant to cor- rosion inhibition due to this synergistic action. However, it must be borne in mind that this is a physical adsorption, with a weak bonding energy, and the adsorption may cease and the surfac- tants can be swept off in the presence of high wall shear stresses [6]. The use of electrochemical techniques for hydrodynamic diagnostics namely with microelectrodes as friction sensors is well established for Newtonian fluids [7] and also for drag reducing polymer solutions [8]. This work is intended to extend this ability to measure local friction to surfactant solutions for which both the rheological characteristics and the adsorption phenomena might induce deviations with respect to the mass flux–friction relationship which characterizes these sensors. The knowledge of both processes of adsorption and of mass transfer which is needed to calculate the skin friction can be deduced from electrochemical measurements. In this work we focused more specifically our investigation on quaternary ammonium compounds and tried, in terms of local shear stress (in the range of 100 m), to correlate mass transfer data from electrochemical sensors to friction data determined from measurements, here also performed, of the pressure drop at given flow rate. 0255-2701/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cep.2007.01.029