Study on condensation invalid mechanism of superhydrophobic structure in gravity heat pipes

In order to study the effect of superhydrophobic structure failure on condensation heat transfer and flow in gravity heat pipe, superhydrophobic surfaces with three diameters (D = 10 mu m, 15 mu m, 20 mu m), three heights (H = 19 mu m, 22 mu m, 25 mu m), three angles (alpha = 75 degrees, 82.5 degrees, 90 degrees) and two spacings (S = 50 mu m, 70 mu m) were established by means of simulation. The results showed that when the angle of the superhydrophobic structure is 90 degrees, although the superhydrophobic structure fails, the contact angle hysteresis of the liquid film is small, the liquid film renewal cycle can reach 0.108 s at the fastest, and the average temperature of the wall surface is 4.2 % higher than that of the ordinary surface. When the liquid film is pinned to the surface, the temperature is positively correlated with the diameter. When the liquid film renewal period is short, the temperature is negatively correlated with the diameter and height of the structure, and the highest temperature is 284.477 K. When the spacing is 70 mu m, there are two droplets in opposite directions between the columns, which is beneficial for droplets to be pulled out of the superhydrophobic structure columns, showing the wetting state of Cassie, and effectively correcting the occurrence of superhydrophobic failure. The research results provide a reference for the application of superhydrophobic structure in heat pipes.

Automated summary

This study establishes superhydrophobic surfaces with different diameters, heights, angles, and spacings through simulations and examines their effects on condensation heat transfer and flow in gravity heat pipes. The results show that superhydrophobic structures can still maintain a small contact angle hysteresis and a short liquid film renewal period under certain conditions, leading to higher wall surface temperatures compared to ordinary surfaces. The fixation of the liquid film and factors such as the diameter and height of the superhydrophobic structures also affect the temperature.