微溝槽表面上自推進亞努斯液滴之動力學

Abstract

高速、長距離且定向的液滴自推進現象，對於微尺度熱管理與高效熱交換等應用具有重要價值。現有研究多利用萊頓弗洛斯特狀態下所形成的低阻力蒸氣層與週期性結構(如棘齒表面)，實現液滴的自發與高速運動。然而，蒸氣層亦大幅降低了液滴與加熱表面間的熱交換效率，限制其在高效熱傳領域的應用。因此，本研究旨在開發兼具高速自推進與高效熱交換功能之新型週期性表面，以突破現有技術瓶頸。 本論文設計並製備出矽/白金混合V型微溝槽表面(PTVM)，並驗證其可同時產生接觸沸騰與萊頓弗洛斯特現象。此機制使液滴在接觸沸騰區域獲得顯著推力的同時，亦可藉由萊頓弗洛斯特現象有效減少其所受之阻力，進而促使自推進亞努斯液滴於表面上實現高速、定向且長距離之運動。藉由接觸沸騰的發生，液滴於運動過程中能與加熱表面進行高效熱交換，有效改善傳統棘齒表面熱傳效率低落之問題。 本研究結合紅外線與高速攝影技術，量測液滴運動行為及表面溫度分布，並利用ANSYS暫態熱傳系統計算液滴與PTVM間的接觸熱通量。實驗結果顯示，當表面溫度達239 °C時，液滴可達最高瞬時速度0.67 m/s；於255 °C時，液滴與表面間之熱通量可達4.5 MW/m²，展現本設計於提升液滴運動效率與熱傳性能上的雙重優勢。進一步之動力學與理論分析證實，液滴驅動力主要來自不對稱結構引發的非對稱氣泡動量力，理論模型與實驗結果於亞努斯區域呈現良好一致性，確立了主要驅動機制。 本研究不僅突破傳統棘齒表面無法兼顧高速液滴運動與高效熱傳的限制，亦為微尺度熱管理、快速冷卻與智慧液滴操控等應用領域帶來嶄新解決方案，具備重要學術價值與應用潛力。

High-speed, long-distance, and directional self-propelled droplet motion holds great potential for applications in microscale thermal management and efficient heat exchange. Previous studies have primarily utilized the low resistance vapor layer formed under the Leidenfrost state, together with periodic structures such as ratchet surfaces, to achieve spontaneous and rapid droplet motion. However, the presence of the vapor layer also greatly reduces the heat exchange efficiency between the droplet and the heated surface, limiting practical applications in high-performance heat transfer. Therefore, this study aims to develop a novel periodic surface that combines both high-speed self-propulsion and efficient heat exchange, overcoming the limitations of existing techniques. In this work, a silicon/platinum hybrid V-shaped microgroove surface (PTVM) was designed and fabricated. It was demonstrated that this surface can simultaneously induce both contact boiling and the Leidenfrost effect. This mechanism enables the droplet to gain significant propulsion in the contact boiling region while effectively reducing resistance through the Leidenfrost phenomenon, resulting in high-speed, directional, and long-distance motion of self-propelled Janus droplets on the surface. The occurrence of contact boiling further allows efficient heat exchange between the moving droplet and the heated surface, effectively improving the low heat transfer efficiency seen in traditional ratchet surfaces. Infrared thermography and high-speed imaging were used to measure droplet dynamics and surface temperature distribution, while calculations of the contact heat flux between the droplet and the PTVM were performed using the ANSYS Transient Thermal System. Experimental results showed that at a surface temperature of 239 °C, the maximum instantaneous velocity of the droplet reached 0.67 m/s, and at 255 °C, the heat flux between the droplet and the surface reached 4.5 MW/m², demonstrating the dual advantages of the proposed design in enhancing both droplet mobility and heat transfer performance. Further dynamic and theoretical analysis confirmed that the driving force of the droplet mainly originates from asymmetric bubble momentum induced by the structured surface, with the theoretical model and experimental results showing good consistency in the Janus region, thus clarifying the main propulsion mechanism. This study not only overcomes the limitation of conventional ratchet surfaces in simultaneously achieving high-speed droplet motion and efficient heat transfer, but also offers novel solutions for microscale thermal management, rapid cooling, and smart droplet manipulation, demonstrating significant academic value and application potential.