Novel Capillary Effect in a Curled Open Capillary Tube

Capillary action in microchannels, a well-established phenomenon, plays a significant role in various applications, such as the extraction of reagents and heat dissipation. However, multilevel microstructures on the inner wall are often required to achieve flexible capillary effect in thin tubes, and their performance is frequently hindered by the presence of bubbles. Modulating capillary behavior by relying on a simple structural design alone remains a challenge. In this study, a curled open capillary tube with a smooth inner wall is proposed and designed, in which the novel stratification in the capillary effect is clearly demonstrated. The capillary height at the geometric center of the tube is governed by the local radius of curvature, while that away from the center is primarily determined by the spacing between adjacent walls. An approximate theoretical model for predicting the maximum capillary height is established and verified experimentally. Furthermore, such a curled capillary tube is utilized to mimic the transport channels within plant leaves, aiming to enhance the rapid transport of nutrients in leaf veins through highly efficient evaporation. The results offer fundamental insights into liquid transport in open capillary tubes and pave the way for their potential applications in microfluidic devices with broader implications for fluid manipulation technologies.