Wall shear measurements by electrochemical probe for gas‐liquid two‐phase flow in vertical duct

Abstract

For over 40 years, gas-liquid two-phase flows have been very important in the field of industrial sciences as their heat and mass transfer properties, particularly in chemical, oil and nuclear engineering. These flows are usually classified according to the relative configuration of the two phases, mainly by geometrical and visual criteria (bubble, slug, annular flows, etc.). To better understand the transport phenomena in these rather complicated flows, we need more experimental data, among which is the momentum transferred to the wall by the shear stress. Usually this quantity is indirectly obtained from overall measurements (total pressure drop, average void fraction, etc.). In vertical ducts, the pressure loss by friction is small compared with the total pressure drop and the pressure loss by gravity (weight of the fluid column); therefore, a small error concerning these two terms may involve a considerable uncertainty for the friction. This leads to the interest on the direct measurement of the local wall shear stress. The electrochemical technique using probes mounted flush to the wall appeared to be convenient for that purpose.