The effect of surfactant additives on the flow characteristics such as the gas-liquid interfacial structure, flow pattern transition and liquid lump velocity was investigated in the vertical upward gas-liquid two-phase flow. Experimental studies were conducted by using the surfactant CTAC acted as a DRA(Drag Reducing Agent). The effect of CTAC on flow pattern was confirmed for the slug and churn flows. The intermittence and local flow reversal of liquid film in both slug and churn flows were inhibited by fine bubbles formed in the liquid phase. The slug flow region for high liquid flow rate and low gas flow rate conditions was replaced by the bubble flow, and most of the churn flow regions were changed into the annular flow. The liquid flow structure was also affected by CTAC. βW and βB decreased for the condition of 0.2≤jG≤10m/s. Pw decreased for the churn/annular flow region, which corresponded to the decrease in the frequency of interfacial waves and disappearance of flow reversal. The velocities for both liquid lump and liquid film increased for the annular flow, which was closely related to the increase in the frictional pressure gradient.
