Evaluation of passive cooling driven by self-propelled drops

2022 Fiscal Year Final Research Report

• Project/Area Number: 19K21926
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 19:Fluid engineering, thermal engineering, and related fields
• Research Institution: Hirosaki University
• Principal Investigator: Shirota Minori 弘前大学, 理工学研究科, 教授 (40423537)
• Project Period (FY): 2019-06-28 – 2023-03-31
• Keywords: 液滴 / 沸騰 / 自己推進 / 冷却 / 登坂

Outline of Final Research Achievements

We conducted experimental investigations on the drop propulsion characteristics on a composite wettability ratchet that combines superhydrophobic and superhydrophilic regions. The results showed that as the drop size decreases, the acceleration increases. Additionally, we found that the maximum acceleration and the maximum uphill angle occur at a ratchet temperature of 150 ℃. The model predictions and experimental findings were generally consistent, revealing that drops can climb due to the propulsive force generated by nucleate boiling, surpassing the pinning force and gravity. We also discovered the importance of an asymmetric wetting property on the heating surface for drop propulsion through nucleate boiling. In the hybrid wettability ratchet, we revealed that the propulsive force is generated by the internal flow induced by the expansion and contraction of bubbles formed in the superhydrophilic region.

Free Research Field

流体工学

Academic Significance and Societal Importance of the Research Achievements

本研究で開発した複合濡れ性を加熱面へ付与することで，加熱面が飽和温度以上になると液滴を自動的に推進させることが可能となる。推進する液滴の最新登坂角度は75°であり，ほぼ垂直な壁面であっても液滴を輸送可能である。また，液滴は沸騰を伴いながら推進するため，液滴が進行する加熱面から短時間で熱を奪うことが可能となる。これらの特徴は，新しいパッシブ冷却技術の開発を導く。このパッシブ冷却技術は，センサーやアクチュエーターを必要としないため，電源を喪失したような緊急時であっても，加熱による機器の暴走や過剰な発熱を抑制することができ，工学的意義は大きい。