Sierpinski亲/疏水分形图案表面气泡分布及强化换热研究

The heat dissipation of chip, which releases much more heat from its center than from the marginal area, shows a typical non-uniform distribution feature. Based on this, a non-uniform wetting copper surface with fractal features of three-order Sierpinski carpet was designed, and then the dynamic behaviors of the bubble on the surface with typical hydrophobic/hydrophilic fractal pattern were observed experimentally. The results showed that small bubbles would first nucleate and grow at the preset high-order hydrophobic points, and their distribution presented typical fractal feature, which indicates that the controllable distribution of the initial bubble nucleation sites is achieved. Subsequently, the neighboring bubbles at the hydrophobic points began to merge with each other after overcoming the energy barrier. Directional migration of small bubbles from the high-order hydrophobic region to central low-order region could also be observed simultaneously. A large bubble was finally formed in the central first-order hydrophobic region after bubbles coalescence. Compared with smooth and hydrophobic point array surfaces, the fractal non-uniform wetting surface can reduce the onset boiling temperature effectively, and increase the critical heat flux density of boiling heat transfer. More importantly, the nucleation sites of the bubbles and their moving and merging processes on the fractal pattern surface can be designed and planned in advance, so the distribution of the bubbles can keep consistent with the heat flux on heating surface. Therefore, this non-uniform wetting surface with Sierpinski fractal pattern can further improve the boiling heat transfer performance.