An Experimental Study on Two-Phase Downward Flow of Medium Viscosity Oil and Air

Abstract

Abstract The gas-liquid downward flow is the least studied flow condition, which is critically important in predicting the flow between two platforms in offshore systems and wells for CO2 injection for CCSU applications. These processes require a reliable prediction of pressure drop and phase fraction. This paper focuses on the liquid viscosity effect on downward gas-liquid flow. Flow patterns, pressure drop, and liquid holdup are measured for downward vertical and near-vertical flow. The acquired data are compared with available mechanistic models, and the discrepancies are discussed. The 2-in ID oil/water/gas outdoor facility of The University of Tulsa Fluid Flow Project has been used for this effort. The facility is 22.72 m long and is operated with medium viscosity oil and air. Liquid viscosity is fixed at 40 and 70 cP by controlling the temperature. Superficial liquid and gas velocity ranges are 0.1 – 0.3 m/s and 0.5 – 5 m/s, respectively. The inclination angle is varied between 60 and 90° with a 10° increment. Visual observations and Capacitance Sensor (CS) signals are utilized to determine flow patterns. Facility instrumentation also allows measuring pressure gradient and liquid holdup. Two classic flow patterns observed were: stratified and annular flows. Stratified is further sub-classified as stratified wavy and stratified wavy with a thin film. Annular flow is sub-classified into falling film, liquid slip, and wavy annular. Experimental interfacial shear stress (τI) and wall-liquid shear stress (τWL) were compared to model values. Existing models and commercial simulators show very poor performance in downward flow and need further improvements.