The behaviors of single nitrogen gas bubble chains, with diameters of from 0.5 mm to 2.5 mm, in stagnant water were experimentally studied. We developed an innovative acoustic bubble generator, which can precisely control both bubble diameter and generation frequency in an independent manner. We discuss the effects of interactions between bubbles in bubble chains on the behaviors of each bubble quantitatively, comparing to those of single rising bubble. Bubble trajectories and surrounding water flow field generated by the bubble chains were carefully investigated by applying the image processing technique to the high-speed video camera data. We analyzed the experimental data and identified the following two significant physical phenomena. (1) Under the condition of bubble radii kept unchanged, while bubbles passed almost the same path in the current measurement region in the case of low generation frequency, they deviated from this path and scattered about 30 mm from the generator with the increase of bubble generation frequency. (2) With higher bubble generation frequency, characteristic structures of the surrounding flow fields were clearly observed. These flow fields possessed the planer structure which could be spanned by the bubble trajectory direction and vertical axis through bubble generator.

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