Measurement of thermal accommodation coefficients using a simplified system in a concentric sphere shells configuration

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Abstract
For heat transfer in the microscale, the interaction between the gas and the solid surface is characterized by the thermal accommodation coefficient, and is important owing to the large surface-to-volume ratio existing as a consequence of the small size. However, there are few data of the thermal accommodation coefficients on the nonmetal surfaces often employed in microdevices. In this research, a novel simplified system in a spherically symmetric configuration is proposed, achieving a low-cost measurement of the thermal accommodation coefficient for both metal and nonmetal surfaces. Tiny flat-plate samples on a heater are placed at the center of a spherical vacuum chamber, and the conductive heat flux is measured and analyzed under the assumption of a concentric spherical shells geometry based on the low-pressure method. An approximate relation for the heat flux is also employed to measure under the near free-molecular and the transitional flow regimes. The proposed novel measurement system is validated by measurements of the thermal accommodation coefficient on a platinum surface with helium, argon and xenon. The measured heat fluxes as a function of pressure are well fitted by the approximate relation, and the obtained thermal accommodation coefficients agree well with the data in the literature. Finally, the measurement is demonstrated on a nonmetal surface of glass, showing good feasibility of the measurement system.

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