Thermal transpiration flow is a thermally driven flow from a cold part toward a hot part using a temperature gradient along a wall under a high Knudsen number condition. Many studies have used this type of flow as a pump for microtechnology. The flows adopted in these studies were, in most cases, in the slip or transitional regime. Accordingly, in this research, thermal transpiration flow through a two-dimensional channel with nanoscale clearance in the height direction was studied using the molecular dynamics method. The solid atoms composing the channel walls were explicitly considered. The center part of the nanochannel was controlled as a hot reservoir, whereas both ends of the nanochannel were kept cold. The temperatures of the channel wall atoms were also controlled based on their positions by linearly interpolating the temperature between the hot and cold reservoirs. Two Knudsen number conditions were adopted by changing the width of the computational cell. To study the mean velocity distribution inside the nanochannel, these simulations were performed for 10 ns. We successfully obtained a mean velocity distribution inside the nanochannel, showing the thermal transpiration flow in the vicinity of the channel wall using the pressure-driven counterflow at the center in the height direction even under the dense gas condition. The velocity profile across the nanochannel in the height direction indicated that thermal transpiration flow was induced in the adsorption layer of gas molecules on the channel wall under the dense gas condition.
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