Drag reduction effect for microbubble mixtures flows has been investigated and reported. However, few studies have focused on nanobubble mixtures, which have sub-micron meter size fine bubbles. In the present study, nanobubble mixtures for water and glycerol solution were passed through several sizes of micro-apertures, and the resultant pressure drops, as compared with water and glycerol solution alone, were evaluated. For small apertures, the experimentally measured pressure drop was less than that for water and glycerol alone. This phenomenon is considered in terms of interface behavior and attributed to the electric interaction between an electric double layer and fine bubbles. The results of the present study suggest that the addition of nanobubbles to a liquid results in excellent drag reduction.

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