Spontaneous net flow generation using passive artificial cilia in the nucleate boiling region

The occurrence of spontaneous net flows in nature is fascinating. Here, we report spontaneous net flow generation using passive artificial cilia consisting of directional fabric in the nucleate boiling regime. Surprisingly, by placing simple ordinary flocking rayon fibers at an angle of approximately 18 degrees on a base cloth on the circular wall in a container as the artificial cilia, we observed the circular flow of the angular velocity of up to ∼2 rad/s (the average velocity of up to ∼34 mm/s) in the nucleate boiling regime. Moreover, by the observation of a high-speed camera (960 fps), we found that the bubbles rise obliquely at a high velocity of about 80–180 mm/s, which drives the net flow. Our findings should contribute to a better understanding of spontaneous flows in nature and should be applied to utilize unused heat, such as factory waste heat effectively.