Drag forces on nanoparticles in the free-molecule regime: Effect of the particle temperature

In the present paper, we theoretically study the drag force on nanoparticles in the free-molecule regime. It has been widely assumed that the particle temperature is equal to the gas media temperature in the open literature. However, this assumption can be invalid in some real applications. Based on the kinetic theory, we obtain the generalized formulas for the drag force on nanoparticles in the free-molecule regime. It is found that there exists a significant error induced by the assumption of equal temperature between the particle and the surrounding gas. Therefore, it is necessary to consider the effect of the particle temperature in the analysis of the particle transport properties.