The boundary between micro and macro in heat transfer from micro-bodies to gases

2023 Fiscal Year Final Research Report

• Project/Area Number: 21H01263
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 19020:Thermal engineering-related
• Research Institution: National Institute of Technology, Kumamoto College (2022-2023); Kyushu University (2021)
• Principal Investigator: Takamatsu Hiroshi 熊本高等専門学校, 八代・熊本キャンパス, 校長 (20179550)
• Co-Investigator(Kenkyū-buntansha): 藏田 耕作 九州大学, 工学研究院, 教授 (00368870)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 微小伝熱面 / 熱伝達 / 気体希薄性 / 高クヌッセン数 / 自然対流発生限界 / 熱伝導支配

Outline of Final Research Achievements

This study aims directly at designing a microbeam MEMS sensor that measures the thermal conductivity of a fluid by heating a beam-shaped free-standing thin strip in the fluid. Experiments and numerical simulations were conducted to elucidate the effects of gas rarefaction and natural convection on the heat transfer from the sensor to the surrounding fluid. It was revealed that the rarefied gas effect does not appear if the Knudsen number, with the sensor width as the representative dimension, is Kn < 0.033, and that the effect of natural convection is negligibly small if the Rayleigh number, with the sensor length as the representative dimension, is Ra < 10, indicating that heat conduction alone prevails.

Free Research Field

熱工学

Academic Significance and Societal Importance of the Research Achievements

熱伝達に及ぼす気体の希薄性および自然対流の影響を明らかにしたことは，MEMS応用技術の開発という応用の観点で重要である．しかし，それ以上に，これまで伝熱分野であまり想定されていなかったスケールの微小伝熱面から気体への伝熱におけるマクロとミクロの境界，すなわち気体を連続流体として取り扱える範囲がKn < 0.05であり，従来から流体力学的観点からの限界値（0.01）と同じオーダーであることを実験的に明らかにした点の学術的意義が大きい．また，自然対流の影響を無視し，熱伝導のみを仮定してよい限界がRa < 10であることを示した点も学術的に大きな意義がある．