Session: 04-24-05: Materials Processing and Characterization V

Paper Number: 165732

Biomimetic Hierarchical Surface for Enhanced Boiling Heat Transfer 

Boiling is a fundamental phase-change phenomenon with critical applications in energy conversion, cooling systems, and thermal management. The performance of boiling heat transfer is primarily characterized by the heat transfer coefficient (HTC) and the critical heat flux (CHF). Enhancing these parameters is essential for improving heat dissipation efficiency; however, traditional approaches are often constrained by surface structure limitations. While surface modifications such as micro- and nano-texturing have been explored to increase nucleation-site density and optimize liquid-vapor interactions within artificial leaf designs, natural leaf designs have yet to be investigated. This study introduces a biomimetic hierarchical surface, inspired by the venous structures of the Ficus religiosa leaf, fabricated using a combination of potassium hydroxide (KOH) wet etching and inductively coupled plasma reactive ion etching (ICP-RIE). The hierarchical design replicates the multi-scale venation structure of natural leaves, which optimizes fluid transport and heat dissipation. By integrating slanted microchannels formed through KOH etching with nanoscale roughness induced by ICP-RIE, this novel surface enhances HTC and CHF compared to conventional smooth surfaces. The biomimetic approach maximizes nucleation site availability while facilitating efficient liquid replenishment and vapor release, preventing the formation of an insulating vapor layer.

To fabricate the biomimetic surfaces, a natural leaf skeleton was used as a template to transfer the hierarchical venation pattern onto silicon wafers. The fabrication process included photolithography, followed by KOH wet etching to create anisotropic microchannels, mimicking natural leaf veins. These microchannels function as capillary pathways, enhancing fluid transport and ensuring continuous liquid replenishment. Next, ICP-RIE was applied to introduce nanoscale roughness in the form of nanocones, further improving surface wettability and nucleation-site density. Pool boiling experiments were conducted using a heated copper block setup equipped with a heat flux meter. Multiple K-type thermocouples were strategically placed to measure the temperature distribution and assess heat transfer performance. Heat flux and HTC values were determined using Fourier’s law, and uncertainty analyses were conducted to ensure measurement accuracy. Additionally, static water contact angle measurements were performed to evaluate wettability characteristics of the hierarchical surface.

Preliminary results indicate that the biomimetic hierarchical surface significantly enhances HTC and CHF. Compared to smooth silicon surfaces, the biomimetic surface demonstrated an HTC improvement of 20% and a CHF enhancement of 35%. These enhancements are attributed to the synergistic effects of micro- and nanoscale surface features, which promote capillary-driven liquid rewetting while minimizing vapor film formation. The hierarchical structures sustain continuous liquid supply to nucleation sites, reducing dry-out regions and improving boiling stability. Additionally, static water contact angle measurements revealed a substantial decrease in contact angle, confirming improved surface wettability. Enhanced hydrophilicity promotes liquid spreading and replenishment, further contributing to superior heat transfer performance. These findings highlight the potential of bioinspired hierarchical surfaces in optimizing boiling efficiency for advanced thermal management applications.

This study demonstrates the effectiveness of bioinspired surface engineering in enhancing boiling heat transfer. By leveraging natural multi-scale venation patterns and integrating them with scalable nanofabrication techniques, the proposed approach offers a cost-effective and highly efficient solution for heat dissipation. The superior performance of the biomimetic surface makes it a strong candidate for high-performance cooling applications, including power electronics, data centers, and thermal energy storage systems. Future research will focus on refining fabrication techniques for large-scale manufacturing and exploring alternative bioinspired designs to further enhance HTC and CHF. Additionally, investigations into different material substrates and surface modifications will be pursued to expand the applicability of this technology across a broader range of thermal management systems.

Presenting Author: Fabian Medina University of Arizona

Presenting Author Biography: Fabian Medina is a Ph.D. student in Mechanical Engineering at the University of Arizona under the advisement of Dr. Qing Hao. His research focuses on micro-nanofabrication for thermal applications, specifically investigating the impact of engineered surfaces on phase-change heat transfer, with an emphasis on boiling experiments. His work aims to advance high-performance cooling technologies for applications in power electronics, data centers, and thermal energy storage systems.

Mr. Medina has published research on biomimetic leaf designs for condensation applications and continues to explore nature-inspired surface structures to enhance thermal performance. His current study examines a natural leaf-inspired design etched onto silicon substrates to assess its influence on boiling performance and real-world thermal management systems.

His research interests include advanced manufacturing techniques, thermal-fluid sciences, and surface engineering for enhanced heat transfer. Through his work, Mr. Medina seeks to bridge the gap between academic research and practical applications in energy-efficient cooling solutions.

Authors:

Fabian Medina University of Arizona