Mixtures of surfactants and polymers are known to reduce drag, but their use is limited because of environmental concerns. In this study, surfactant/nanobubble mixtures were passed through several sizes of micro-orifices, and the resultant pressure drops, as compared with water and only surfactant solution, were evaluated. For anionic surfactant/nanobubble mixtures, the experimentally observed pressure drop was less than that for water. However, it was found that the pressure drop was greater than that for only anionic surfactant solution. In the case of non-ionic and cationic surfactants, the experimental results of mixed nanobubble liquids were less than those for water and only surfactant solution. This phenomenon is considered in terms of interface behavior and attributed to the electrical interaction between an electric double layer and nanobubbles.
