Conjugate heat transfer analysis for the effect of the eccentricity of hydrophobic dot arrays on pool boiling

Patterned wettability causes pinning of the contact line, which is the area responsible for the heat flux transition. A new parameter, “eccentricity,” which governs the contact line shape and length, can be used to control the shape of the bubbles. Initially, we placed four hydrophobic dots on a surface. When a high input heat flux was applied, the bubbles merged and the contact line pinned onto the hydrophobic dots, thus preserving the relatively long dumbbell-shaped contact line. Additionally, the heat transfer coefficient was found to be high at high eccentricity values because of the separation of the merging timing and the generation of metastable contact lines. Next, we placed 36 dots on the surface. The merging and pinning behavior and heat transfer coefficient revealed two stages of transition by the heat flux. From a low to intermediate heat flux, a high eccentricity became effective because the merging and pinning location moved from a marginal area to the entire surface. From the intermediate to high heat flux, large bubbles formed through the simultaneous merging of all the nucleated bubbles, and the eccentricity had almost no influence on the merging or pinning. Therefore, the pinning count minus the number of times the lines merged comprised the relevant data required to analyze the heat transfer coefficient variation with heat flux.