科研之友
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摘要
Inhibiting the Leidenfrost effect has drawn extensiveattentiondue to its detrimental impact on heat dissipation in high-temperatureindustrial applications. Although hierarchical structures have improvedthe Leidenfrost point to over 1000 & DEG;C, the current performanceof single-scale structures remains inadequate. Herein, we presenta facile high-temperature treatment method to fabricate superhydrophilicnickel foams that demonstrate ultrafast droplet permeation withintens of milliseconds, elevating the Leidenfrost point above 500 & DEG;C.Theoretical analysis based on the pressure balance suggests that theseremarkable features arise from the superhydrophilic property, highporosity, and large pore diameter of nickel foams that promote capillarywicking and vapor evacuation. Compared to solid nickel surfaces witha Leidenfrost temperature of approximately 235 & DEG;C, nickel foams nucleate boiling at high superheat, triggering an order of magnitudehigher heat flux. The effects of the pore diameter and surface temperatureon droplet permeation behaviors and heat transfer characteristicsare also elucidated. The results indicate that droplet permeationis dominated by inertial and capillary forces at low and high superheat,respectively, and moderate pore diameters are more conducive to facilitatingdroplet permeation. Furthermore, our heat transfer model reveals thatpore diameter plays a negligible role in the heat flux at high surfacetemperatures due to the trade-off between effective thermal conductivityand specific surface area. This work provides a new strategy to addressthe Leidenfrost effect by metal foams, which may promise great potentialin steel forging and nuclear reactor safety.
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单位清华大学
