Local heat-transfer characteristic of a micro droplet impacting onto a heated surface under depressurized environment

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K14166
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: Fluid engineering
• Research Institution: Japan Aerospace EXploration Agency
• Principal Investigator: Hatakenaka Ryuta 国立研究開発法人宇宙航空研究開発機構, 研究開発部門, 研究開発員 (80725333)
• Co-Investigator(Kenkyū-buntansha): 田川 義之 東京農工大学, 工学(系)研究科(研究院), 准教授 (70700011)
• Research Collaborator: Fujita Yuta ; Tran Tuan ; Breitenbach Jan ; Roisman Ilia V. ; Tropea Cameron ; Harth Kirsten ; Lohse Detlef
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 液滴 / ライデンフロスト / 減圧環境 / 真空環境 / 熱電対 / 気泡成長 / 全反射法

Outline of Final Research Achievements

For the development of spray cooling device for space use, single drop impacting onto a heated surface under depressurized environment has been studied. Two characteristic drop behaviors of depressurized environments are newly identified. A theoretical model for the mechanism of one of those has been proposed, whose validity is confirmed by direct observation of growing bubble between the drop and surface. In addition, existing theoretical models for the splash threshold are confirmed not to be directly applicable to micro-sized droplet, which is commonly used for spray cooling. Finally, an elemental prototyping of a fast-response thermocouple array aiming to measurement of local heat flux distributions at the heated surface during drop impact has been conducted, which has successfully demonstrated its feasibility.

Free Research Field

宇宙工学、伝熱工学、流体工学

Academic Significance and Societal Importance of the Research Achievements

減圧環境下に特有の液滴挙動が新たに識別され、その発生メカニズムにおける気泡成長特性の重要性が示されたことは、減圧環境下における液滴挙動を予測するために重要な知見である。また、過去に提案された各種物理モデルを大きく異なる液滴径に適用できるかを検証できないことが多いため、本研究で得られたマイクロ液滴の実験的知見は貴重である。また、相変化を伴う冷却技術の研究では蒸発/沸騰に伴う局所的・過渡的な熱流束を適切に評価することが極めて重要であり、本研究で開発を進めた高速応答熱電対アレイを適用できれば新たな学術的な成果が期待できる。