Measurements of thermal accommodation coefficients.

Abstract

A previously-developed experimental facility has been used to determine gas-surface thermal accommodation coefficients from the pressure dependence of the heat flux between parallel plates of similar material but different surface finish. Heat flux between the plates is inferred from measurements of temperature drop between the plate surface and an adjacent temperaturecontrolled water bath. Thermal accommodation measurements were determined from the pressure dependence of the heat flux for a fixed plate separation. Measurements of argon and nitrogen in contact with standard machined (lathed) or polished 304 stainless steel plates are indistinguishable within experimental uncertainty. Thus, the accommodation coefficient of 304 stainless steel with nitrogen and argon is estimated to be 0.80 and 0.87 , respectively, independent of the surface roughness within the range likely to be encountered in engineering practice. Measurements of the accommodation of helium showed a slight variation with 304 stainless steel surface roughness: 0.36 for a standard machine finish and 0.40 for a polished finish. Planned tests with carbon-nanotube-coated plates will be performed when 304 stainless-steel blanks have been successfully coated.0.02 ± 0.02 ± 0.02 ± 0.02 ± 4

A Comprehensive Cold Gas Performance Study of the Pocket Rocket Radiofrequency Electrothermal Microthruster

“…In general, α T is not the same as α u for each gas species. α T is measured experimentally [48][49][50][51][52][53] using a variety of techniques often involving two walls held at different temperatures. While α T is roughly constant for each gas across different surface materials and roughnesses, it appears to decrease as the temperature difference between the two walls increases [54].…”

“…While α T is roughly constant for each gas across different surface materials and roughnesses, it appears to decrease as the temperature difference between the two walls increases [54]. However, due to the lack of extensive studies [55] on this behavior, the mean value from Vargaftik [48], Porodnov and Kulev [49], Song and Yovanovich [50], Rader et al [51], Ganta et al [52], and Trott et al [53] is used for each gas in the simulations.…”

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“…Not much is known for our nozzle surface (polished stainless steel or more recently polished ruby). We chose a perpendicular accommodation coefficient of 0.4 and a tangential accommodation coefficient of 0.4 [26][27][28][29] in the simulations to simulate helium. These coefficients determine the boundary layer thickness in the flow (between the flowing gas and the stationary nozzle surface).…”

A large-stroke planar MEMS-based stage with integrated feedback

“…The thermal accommodation coefficient between a gas and a solid is dependent on, for instance, the material, the surface roughness, and the diameter of the gas molecules. Typical values between between 0.8 and 0.9 are reported for oxygen and nitrogen [107]. The heat transfer in the free-molecule region between parallel plates is described by Kennard [64] and later by Corruccini [24],…”