Drag reduction effect of nanobubble mixture flows through micro-orifices and capillaries

Much research on microbubbles and their drag reduction effect has been reported. However, few studies have focused on nanobubbles, which have sub-micrometer size. Mixtures of surfactants and polymers are known to reduce drag, but their use is limited because of environmental concerns. In this research, nanobubble mixtures for water and glycerol were passed through several sizes of micro-orifices and capillaries, and the resultant pressure drops, as compared with water and glycerol, were evaluated. For a small orifice (⩽50 μm) and capillary (⩽70 μm), the experimentally observed pressure drop was less than that for water. This phenomenon is considered in terms of interface behavior and attributed to the electrical interaction between an electric double layer and nanobubbles. The results of the present research suggest that the addition of nanobubbles to a liquid results in excellent drag reduction.