Measurement of Gas-Surface Accommodation

Trott, Wayne M.; Rader, Daniel J.; Castañeda, Jaime N.; Torczynski, J. R.; Gallis, Michail A.

doi:10.1063/1.3076551

Cited by 23 publications

(21 citation statements)

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“…However, the differences are more than what would be expected based on the comparisons of molecular and FEM gas simulations. An accommodation coefficient of 0.3 would represent the high-power profile well and the low-power profile marginally, but this value is much lower than expected (Saxena and Joshi, 1989;Trott et al, 2009). …”

mentioning

confidence: 65%

“…In their compilation, Saxena and Joshi (1989) present values measured by many experimenters for a wide variety of solid-gas combinations. Table 4.3 contains their most relevant data, as well as some more recent values from Trott et al (2009) and Arkilic et al (2001). The glass values are included because a bare silicon surface exposed to air quickly develops a thin layer of "native oxide" (i.e., silicon dioxide, or glass).…”

Section: Thermal Accommodation Coefficientmentioning

confidence: 99%

“…A value of 1.0 produces the maximum gas heat transfer possible, a value of 0.0 produces the minimum gas heat transfer possible (namely, zero), and the intermediate value of 0.3 is a low value compared to measurements (Saxena and Joshi, 1989;Trott et al, 2009). …”

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confidence: 93%

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Validation of thermal models for a prototypical MEMS thermal actuator.

Gallis¹,

Torczynski²,

Piekos³

et al. 2008

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This report documents technical work performed to complete the ASC Level 2 Milestone 2841: validation of thermal models for a prototypical MEMS thermal actuator. This effort requires completion of the following task: the comparison between calculated and measured temperature profiles of a heated stationary microbeam in air. Such heated microbeams are prototypical structures in virtually all electrically driven microscale thermal actuators. This task is divided into four major subtasks. (1) Perform validation experiments on prototypical heated stationary microbeams in which material properties such as thermal conductivity and electrical resistivity are measured if not known and temperature profiles along the beams are measured as a function of electrical power and gas pressure. (2) Develop a noncontinuum gas-phase heat-transfer model for typical MEMS situations including effects such as temperature discontinuities at gas-solid interfaces across which heat is flowing, and incorporate this model into the ASC FEM heat-conduction code Calore to enable it to simulate these effects with good accuracy. (3) Develop a noncontinuum solid-phase heat transfer model for typical MEMS situations including an effective thermal conductivity that depends on device geometry and grain size, and incorporate this model into the FEM heat-conduction code Calore to enable it to simulate these effects with good accuracy. (4) Perform combined gas-solid heat-transfer simulations using Calore with these models for the experimentally investigated devices, and compare simulation and experimental temperature profiles to assess model accuracy. These subtasks have been completed successfully, thereby completing the milestone task. Model and experimental temperature profiles are found to be in reasonable agreement for all cases examined. Modest systematic differences appear to be related to uncertainties in the geometric dimensions of the test structures and in the thermal conductivity of the polycrystalline silicon test structures, as well as uncontrolled nonuniform changes in this quantity over time and during operation. 4 ACKNOWLEDGMENTSThe authors gratefully acknowledge the careful technical reviews of this report by Michael J. Shaw and Sean P. Kearney and the thorough programmatic reviews of this project by

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confidence: 65%

Section: Thermal Accommodation Coefficientmentioning

confidence: 99%

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Validation of thermal models for a prototypical MEMS thermal actuator.

Gallis¹,

Torczynski²,

Piekos³

et al. 2008

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“…The flow conditions, given in Table I, are for the Mach 15.6 nitrogen flow experiments performed by Holden et al [14]. The surface accommodation of nitrogen on the stainless steel surface is taken to be 0.87, as suggested by Trott et al [15]. Nitrogen is simulated using the VSS collision model with Bird's suggested parameters [1].…”

Section: Flow Over a 25-55 • Biconicmentioning

confidence: 99%

Effect of collision‐partner selection schemes on the accuracy and efficiency of the direct simulation Monte Carlo method

Gallis

Torczynski

2010

Numerical Methods in Fluids

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SUMMARYThe effect of the collision-partner selection scheme on the accuracy and the efficiency of the Direct Simulation Monte Carlo method is investigated. Several schemes that reduce the mean collision separation, including the fixed sub-cell scheme, the transient adaptive sub-cell scheme, and the virtual sub-cell scheme, are evaluated. Additionally, a new scheme is proposed that limits the population from which collision partners are selected based on the distance traveled by a simulator and performs near-neighbor collisions using this population. These collision-partner selection schemes are assessed for Fourier flow (heat conduction between parallel plates) and a standard hypersonic benchmark problem (Mach 15.6 nitrogen flow over a 25-55 • biconic). The new limited-selection near-neighbor scheme has superior performance compared to the other schemes for both flows and reduces both the spatial and temporal discretization errors relative to random-selection and nearest-neighbor collision-partner selection schemes.

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“…[3][4][5] The two coaxial cylinders' configuration has been extensively studied during the last decades both experimentally and theoretically. This configuration has been considered for the investigation of so-called "high Knudsen number flows" when the mean free path of the gas molecules is considerably larger than the radius of internal cylinder.…”

Section: Introductionmentioning

confidence: 99%

Investigation on heat transfer between two coaxial cylinders for measurement of thermal accommodation coefficient

et al. 2012

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Heat transfer through a rarefied gas confined between two coaxial cylinders with high radius ratio Heat transfer in a gas mixture between two parallel plates: Finite-difference analysis of the Boltzmann equation AIP Conf.The heat flux between two coaxial cylinders was measured in the range from the free molecular to the early transitional flow regimes for extraction of the thermal accommodation coefficient using an approximate relation on the pressure dependence of the heat flux. The experimental coaxial cylinders' geometry has been traditionally implemented for the measurement of the thermal accommodation coefficient using the low-pressure method; however, the actual experimental setup was characterized by large temperature difference and large cylinders' radius ratio. Compared to the original low-pressure method, much higher pressure range was applied. In order to verify assumptions in the accommodation coefficient extraction, the heat flux under measurement conditions was simulated numerically by the nonlinear S-model kinetic equation. Very good agreement was found between the measured and the simulated heat flux. The proposed procedure of the thermal accommodation coefficient extraction was discussed in detail and verified. The temperature dependence of the thermal accommodation coefficient was also found. C 2012 American Institute of Physics.

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Measurement of Gas-Surface Accommodation

Cited by 23 publications

References 0 publications

Validation of thermal models for a prototypical MEMS thermal actuator.

Validation of thermal models for a prototypical MEMS thermal actuator.

Effect of collision‐partner selection schemes on the accuracy and efficiency of the direct simulation Monte Carlo method

Investigation on heat transfer between two coaxial cylinders for measurement of thermal accommodation coefficient

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