Molecular-dynamics simulations of thermal accommodation of helium gas on a nanoparticle

Thermal accommodation of inert He gas atoms colliding on a nanometer-sized Ar or N2 particle was analyzed using molecular dynamics simulations. The instantaneous values of apparent thermal accommodation coefficient (αth) showed a distribution close to the normal distribution but with a longer tail toward lower values. The mean and standard deviation of αth for Ar particle were about 0.39 and 0.54, respectively, and 0.44 and 0.56 for a N2 particle. Those values were almost independent of gas temperature or pressure, with less than 10% variation over a three- or four-fold variation of the gas conditions. The thermal accommodation coefficient per collision (α0), which was calculated from the apparent αth and the average number of collisions on the particle surface, was about 0.18 on the Ar particle and 0.20 on the N2 particle, both of which are in good agreement with theoretical predictions based on single interactions between free molecules.