Method for measuring thermal accommodation coefficients of gases on thin film surfaces using a MEMS sensor structure

Grau, Mario; Völklein, F.; Meier, Andreas; Kunz, Christina; Heidler, Jonas; Woias, Peter

doi:10.1116/1.4948527

Cited by 13 publications

(5 citation statements)

References 17 publications

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“…An ideal assumption α = 1 denotes a perfect thermal accommodation. 18 Actually, α is taken as an empirical value based on a specific case. For silica aerogels, it was taken to be between 0.68 and 1.…”

Section: ■ Introductionmentioning

confidence: 99%

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How Gas–Solid Interaction Matters in Graphene-Doped Silica Aerogels

et al. 2022

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It was interesting to experimentally find that the thermal insulation of silica aerogels was improved by doping graphene sheets with high heat conductivity. The underlying mechanism is investigated in the present work from the perspective of gas−solid interaction using a comprehensive analysis of molecular dynamics (MD) simulations, theoretical modeling, and experimental data. The MD-modeled small pores are demonstrated to effectively represent big pores in silica aerogels because of similar heat conduction physics, because it is found that adsorption does not contribute to gas heat conduction. Meanwhile, based on the experimentally measured density, the porous structures are schematically re-engineered using molecular modeling for the first time. The evaluated pore size distributions numerically present a consistency with available experimental data. Inspired by the visualization of the 3D pore structure, we proposed a graphene/silica/nitrogen model to evaluate the role of graphene in heat conduction: it can not only reduce effective gas collision (impede heat transport) but also enhance the gas−solid coupling effect. The former is dominant because of the high porosity, leading to an improvement in thermal insulation. The competition between them can be the reason for the "trade-off" phenomenon in the graphene doping effect in the available experiment.

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Section: ■ Introductionmentioning

confidence: 99%

“…The most popular method is based on the thermal accommodation coefficient (α). An ideal assumption α = 1 denotes a perfect thermal accommodation . Actually, α is taken as an empirical value based on a specific case.…”

Section: Introductionmentioning

confidence: 99%

How Gas–Solid Interaction Matters in Graphene-Doped Silica Aerogels

et al. 2022

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“…The energy transfer at the gas-surface interface is usually evaluated by the parameter of the thermal accommodation coefficient (TAC) [20], which describes the ensemble behavior of the gas molecules on a solid surface for engineering applications. In typical experimental systems, heat flux is generated from an electrically heated filament to a coaxial cylinder immersed in a bath at a constant temperature [21,22] or between two parallel plates at a controlled temperature [23,24]. Then, the TAC value is calculated using the measured heat flux and temperature distribution, as described by different theoretical models [21,25], such as the low-pressure method (free molecular method) [22,26], the temperature-jump method [27], and the mean free path method [28].…”

Section: Introductionmentioning

confidence: 99%

Thermal Energy Transfer between Helium Gas and Graphene Surface According to Molecular Dynamics Simulations and the Monte Carlo Method

Zhang

Ban

2022

Nanomaterials

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The scattering of gases on solid surfaces plays a vital role in many advanced technologies. In this study, the scattering behavior of helium on graphene surfaces was investigated, including the thermal accommodation coefficient (TAC), outgoing zenith angle of helium, bounce number, and interaction time. First, we performed molecular dynamics simulations to describe the incident angle-resolved behaviors, and showed that the scattering is highly dependent on the zenith angle of incident helium but insensitive to the azimuthal angle. The contribution of the normal velocity component of the incident helium dominated the energy transfer. The nonlinear relationship of the parameters to the zenith angle of the incident helium could be suppressed by increasing the graphene temperature or decreasing the speed of the incident helium. Subsequently, the scattering performance considering all gas molecules in the hemispherical space was evaluated using the Monte Carlo method with angle-resolved results. The result showed that the TAC, its nominal components, and the zenith angle of the scattered helium increased with higher speeds of incident helium and lower temperatures of graphene. This study should provide a fundamental understanding of energy transfer between gas and two-dimensional materials and guidelines to tune the scattering behavior between them.

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“…Here, 𝑇 𝑟 is the temperature of reflected gas molecules, 𝑇 𝑖 and 𝑇 𝑠 are incident molecule and structure temperature, respectively. For every combination of a surface material and gas species, there is a unique α, which depends on a variety of factors such as temperature, surface roughness, density and atomic/molecular weight of the surface and the gas, and even electronic properties of the surface [30][31][32][33][34] . If the thermal accommodation coefficient is larger on the bottom surface of a film, the momentum change of the gas molecules and the corresponding recoil of the structure is larger on the bottom side, resulting in a net lift force (Fig.…”

Section: Introductionmentioning

confidence: 99%

Controlled levitation of nanostructured thin films for sun-powered near-space flight

et al. 2021

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We report light-driven levitation of macroscopic polymer films with nanostructured surface as candidates for long-duration near-space flight. We levitated centimeter-scale disks made of commercial 0.5-micron-thick mylar film coated with carbon nanotubes on one side. When illuminated with light intensity comparable to natural sunlight, the polymer disk heats up and interacts with incident gas molecules differently on the top and bottom sides, producing a net recoil force. We observed the levitation of 6-mm-diameter disks in a vacuum chamber at pressures between 10 and 30 Pa. Moreover, we controlled the flight of the disks using a shaped light field that optically trapped the levitating disks. Our experimentally validated theoretical model predicts that the lift forces can be many times the weight of the films, allowing payloads of up to 10 milligrams for sunlight-powered low-cost microflyers at altitudes of 50 to 100 km.

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Method for measuring thermal accommodation coefficients of gases on thin film surfaces using a MEMS sensor structure

Cited by 13 publications

References 17 publications

How Gas–Solid Interaction Matters in Graphene-Doped Silica Aerogels

How Gas–Solid Interaction Matters in Graphene-Doped Silica Aerogels

Thermal Energy Transfer between Helium Gas and Graphene Surface According to Molecular Dynamics Simulations and the Monte Carlo Method

Controlled levitation of nanostructured thin films for sun-powered near-space flight

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