Energy exchange between gas and graphite surface from molecular dynamics simulations

Unraveling the microscopic mechanism of energy exchange between gas molecules and solid surfaces is crucial for the thermal protection design of high-speed vehicles. Here, the effects of the incident gas temperature, gas molecular mass, interfacial interaction strength, and surface vacancy defects on energy exchange at the interface between argon gas molecules and a graphite surface are systematically investigated with molecular dynamics simulations. It is found that the energy accommodation coefficient (EAC) shows an initial slight rise followed by a declining trend with increasing incident gas temperature. By enhancing the interfacial interaction strength between gas molecules and a graphite surface, it is shown that the EAC rapidly increases toward unity because the adsorption rate and interaction time are significantly boosted as the interaction strength grows. Our calculations further reveal that at a constant simulation temperature, the adsorption rate increases monotonically with incident gas molecular mass, while the energy transfer efficiency between gas molecules and a graphite surface follows a rise-then-fall trend. This leads to an initial sharp increase in EAC with growing incident gas molecular mass, followed by a marginal decrease. The simulations also demonstrate that the vacancy defects on the graphite surface decrease the adsorption rate. However, the prolonged interaction time between gas molecules and graphite promotes a more thorough interfacial energy exchange, ultimately resulting in a monotonic increase in EAC with higher vacancy concentration.