The behavior of drops impacting on a gas-liquid interface restricted by surrounding walls is studied using a high-speed video camera. The droplet diameter used in this experiment was 2.64. mm with impact Weber number of between 5 and 630. The highly purified water held by glass tubes of various inner diameters (6. mm, 8. mm, 12. mm, 17. mm and 26. mm) is used as the restricted target liquid. A special phenomenon of bubble entrapment is observed in our experiments. It is found that the bubble formation is not only dependent on the impact velocity of the drop, but also the distance from the surrounding walls to impact point. Moreover, because of the restricted effect of surrounding walls, the critical velocity for the occurrence of canopy bubble decreases sharply with the reduction of the tube size. Decreasing the inner diameter of tube also makes the drop bounce higher than that on a broad liquid surface with the same Weber number.
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