Abstract
The effects of surfactant additives on the pressure drop and the gas-liquid interfacial structure are experimentally investigated in horizontal two-phase flow. The surfactant used in the experiment is n-Hexadecyltrimethylammonium Chloride mixed with a counter-ion sodium salicylate, and is called CTAC hereafter. Simultaneous measurements of liquid holdup and differential pressures are conducted for two test tubes with inner diameters of 13.5mm and 5.0mm. The slug flow regime is affected by the addition of CTAC. The CTAC acts as a foaming agent, and many fine bubbles are suspended in the liquid phase, which leads to the reduction in the average liquid holdup for liquid slug region. The intermittent flow with CTAC additive is called "foam-slug flow" in the present study. The drag reduction is observed in the foam-slug flow regime, and is achieved up to 30%. The drag reduction range is correlated with friction velocity, and the upper limit of friction velocity for drag reduction range is found to be 0.1m/s in both test tubes. In annular flow, an increase in frictional pressure gradient is observed. This is due to the increase in wall shear stress caused by the decrease in the liquid holdup.
