The exchange of energy between a platinum surface and gas molecules

Abstract

R ecent experim ents by R oberts* have shown, not only th a t the accommoda tio n coefficients of helium and neon atom s impinging on a clean heated tungsten surface are extraordinarily low, b u t also th a t these values increase with time after cleaning th e surface. To explain this increase he suggests the gradual form ation of adsorbed films on th e surface of th e tungsten due to residual im purities in th e gas. The prim ary object in starting the investigations to be described in this paper was to gain some inform ation as to the nature of these films, th e existence of which has also been postulated by Blodgett and L angm uir.f F o r this purpose experim ents have been carried out in which th e emission of energy from electrically heated wires of platinum, a metal relatively resistant to contam ination, has been investigated under varied conditions. ApparatusA pure platinum wire about 20 cm long and 0 • 025 mm diameter was silversoldered to platinum leads of 0*4 m m diam eter and mounted loosely in a vertical glass tu b e of approxim ately 5 cm diameter. The wire was connected, b y double leads, to a Thom son bridge, by means of which the resistance could be determ ined and also controlled by suitable adjustm ent of the current. The potential drop along th e wire was measured by means of a Siemens and H alske potentiom eter. The m ean tem perature of, and the heat developed in, th e wire could th u s be determined.The tu b e containing th e wire was connected by glass tubing of 1*5 cnl bore to a flask of about 10 litres and to a pipette system which has been described by K nudsen, % by means of which small qua * ' P roc. R o y . S o c

The Influence of Gas–Wall and Gas–Gas Interactions on the Accommodation Coefficients for Rarefied Gases: A Molecular Dynamics Study

“…Considering that in the performed MD simulation the surface is assumed to be atomistically smooth and clean, it can be inferred that MD results for E/MACs at the first place should be compared with experimental results on very clean and pure solid surface. Herein, assuming that clean Au surface has a similar behavior as clean Platinum and Tungsten surfaces, it is seen that the obtained results for EAC of Au-He using pair potential based on both FH mixing rule and ab-initio computations are similar to the values reported in [36] and [38] for He on clean Pt and Tungsten surface, respectively.…”

“…To elucidate the possible reason behind the observed mismatch, it is noteworthy to mention that the surface roughness and the type of premeasurement treatment employed to clean the surface under investigation have significant impacts on obtained experimental results for E/MACs. For instance, for He-Pt pair at room temperature Mann [36] reported EAC = 0.03. For the same combination, in another experimental study [37] the measured EAC at 303 K was 0.238.…”

Influence of gas-surface interaction models on predicted performance of a micro-resistojet

“…From previous research, the accommodation coefficient for argon impacting a platinum surface ranges from 0.71 9 to 0.9 U at T w = 300 K. At the FMMR operating temperature of T w = 600 K, the accommodation coefficient ranges from 0.5 10 to 0.63. n There is no available data for the accommodation coefficients of argon colliding with a silicon surface which is required to estimate the energy losses on the expansion walls.…”

Gas-surface interactions using accommodation coefficients for a dilute and a dense gas in a micro- or nanochannel: Heat flux predictions using combined molecular dynamics and Monte Carlo techniques

“…We compute the accommodation coefficients from the MD simulations and we compare them with the accommodation coefficients obtained from the energy [17] and with the experimental results [26,27].…”

“…These parameters are used to getting the temperature profiles and heat fluxes of the impinging and reflected molecules, both for an argon and for a xenon gas on a platinum surface. From the temperature profiles in the channel the accommodation coefficients α are computed and compared with the values obtained by Yamamoto [17] and by experimental results [26,27] (see Table XII). We see that these values compare very well with the ones from Yamamoto's model, but even better with the experimental values.…”