An experimental investigation on the characteristics of heat pipes with annular type composite wick structure

Hierarchical Superspreading Structures for Ultrafast Droplet Transport and Bubble Management

Integrated with multi-scale structure and surface chemical composition, superspreading micro-nano porous materials have made breakthroughs in the fields of bubble adhesion resistance and fluid transport. The pressing problems associated with superspreading materials are their inherent defects such as system compatibility issues, capillary limitation, or loss of modified hydrophilic groups. Here, leveraging the spontaneous agglomeration of inorganic particles and the optimization of the micro-nano structure, the ingeniously designed SiC─SiO2-based superspreading micro-nano structures have excellent droplet spreading (6.5 ms) and extremely high capillary performance parameter of K/Reff = 2.08, thus forming a scalable, efficient and cost-effective structure. The combination of superhydrophilicity (water contact angle, WCA = 0°) and capillary effect can significantly eliminate the local pinning effect, promote the advancement of the three-phase contact line (TCL), and form a stable and efficient superspreading water flow. Furthermore, the superspreading micro-nano structures exhibit the fastest evolution of bubble growth with an extremely fast growth-desorption cycle (<20 ms) and the smallest bubble stripping size (139.9 µm). The system provides insights into the experimental and theoretical applications of two-phase (liquid, vapor) flow, and can be further extended to other more complex liquid transport functional systems for the development of intelligent superspreading structural materials.

Superspreading Surface with Hierarchical Porous Structure for Highly Efficient Vapor-Liquid Phase Change Heat Dissipation

Superspreading surfaces with excellent water transport efficiency are highly desirable for addressing thermal failures through the liquid-vapor phase change of water in electronics thermal management applications. However, the trade-off between capillary pressure and viscous resistance in traditional superspreading surfaces with micro/ nanostructures poses a longstanding challenge in the development of superspreading surfaces with high cooling efficiency in confined spaces. Herein, a heat-treated hierarchical porous enhanced superspreading surface (HTHP) for highly efficient electronic cooling is proposed. Compared with the single porous structures in nanograss, nanosheets, and copper foam, HTHP with hierarchical honeycomb pores effectively resolves the trade-off effect by introducing large vertical through-pores to reduce viscous resistance, and connected small pores to provide sufficient capillary pressure synergistically. HTHP exhibits excellent capillary performance in both horizontal spreading and vertical rising. Despite a thickness of only 0.33 mm, the as-prepared ultrathin vapor chamber (UTVC) fabricated to exploit the superior capillary performance of HTHP achieved effective heat dissipation with outstanding thermal conductivity (12 121 Wm-1K-1), and low thermal resistance (0.1 KW-1) at a power of 5 W. This regulation strategy based on hierarchical honeycomb porous structures is expected to promote the development of high-performance superspreading surfaces with a wide range of applications in thermal management.