The influences of gas–liquid interfacial properties on interfacial shear stress for vertical annular flow

Abstract

The knowledge of the interfacial shear stress is not only essential for estimating the pressure drop but also is fundamental for modeling two-phase flow phenomena. Most annular flow interfacial shear stress models in the open literature are formulated based upon the sand-roughness model, which diverge from reality to some extent because of the mobility of gas–liquid interface. In view of this, a prediction model of gas–liquid interfacial shear stress for vertical annular flow has been proposed, which takes the interfacial characteristics into account, i.e. the local disturbance wave shapes obtained through processing the time trace of liquid film thickness that is measured using high-speed videos and extracted by the Matlab code in previous work. What is more, the influence of the entrainment–deposition process and formation of gas eddy caused by the disturbance wave height when the gas core moves through the disturbance wave and subsequently encounters an abrupt expansion on the interfacial shear stress are incorporated into the model. The results predicted by the current model show that the interfacial shear stress has an increasing trend for the increase of both gas and liquid superficial velocities, and the non-dimensional pressure drop originating from the interfacial shear stress is in the form of cfs=33.6Reg-0.91Ref0.30. The maximum loss of momentum due to entrainment–deposition of droplets and gas eddy can account for approximately 14.5% of the pressure gradient in the current work conditions. In addition, treating the entrainment–deposition and eddy as an indirect factor of the interfacial shear stress caused by the disturbance wave, the non-dimensional pressure drop is in the form of cfs=0.0325+0.01×ln(δ++0.05).