Heat Conduction Characteristic of Rarefied Gas in Nanochannel

Abstract

Nonequilibrium molecular dynamics simulations is applied to investigate the simultaneous effect of rarefaction and wall force field on the heat conduction characteristics of nano-confined rarefied argon gas. The interactive thermal wall model is used to specify the desired temperature on the walls while the Irving-Kirkwood expression is implemented for calculating the heat flux. It is observed that as the temperature differences between the walls increases by lowering the temperature of the cold wall, the number of adsorbed gas atoms on the cold wall increases notably due to the increment in the residence time of the gas atoms. Consequently, the interfacial thermal resistance between the gas and the cold wall reduces which results in a reduction of the temperature jump. Meanwhile, the increase in the temperature of the hot wall leads to a reduction of the residence time of gas atoms in the near-wall region which decreases the number of absorbed gas atoms on the hot wall. This results in an increase in interfacial thermal resistance which leads to a higher temperature jump. It is observed that the bulk, wall force field and interface regions form approximately 10%, 45% and 45% of the total thermal resistance, respectively. Furthermore, unlike the interfacial thermal resistance, the bulk and the wall force field thermal resistance are approximately independent of the implemented temperature difference.

Effect of wall stiffness, mass and potential interaction strength on heat transfer characteristics of nanoscale-confined gas

“…Similarly, forK S ¼ 900er À2 , these density peaks become 5:84kg=m 3 and 6:24kg=m 3 for the hot and cold walls, respectively. It should be considered that as the temperature difference increases, the difference between the density peaks increases [46,49].…”

“…Besides, it should be noted that there is a small kink in the temperature profile near each wall in 0:2nm < y < 0:4nm which can be named as the near-wall layer. The reduction in gas temperature in the near-wall layer occurs due to the strong repulsive force between the wall/gas atoms in the adjacent vicinity of the walls [46,48,49]. Fig.…”

“…This leads to the fact that by changing the temperature differences between the walls, different normalized temperature profiles were obtained in the gas medium along the channel height. Besides, the variation of the corresponding effective thermal conductivity for each case reveals that for calculating the effective thermal conductivity based on this nonequilibrium method, the implemented temperature differences between the channel walls should not exceed 50 K [46].…”

“…Heat transfer characteristics of argon gas confined in 5:4nm channel height have been studied thoroughly [46] by implementing the interactive thermal wall model [47]. The modified Knudsen number, k ¼ ffiffiffi ffi p p =2 À Á Kn, was considered as 10 which corresponds to the onset of the free molecular regime.…”

Thermally induced stress in a nanoconfined gas medium

“…Second, considering the fact that collisions between rarefied gas atoms happen much less often in comparison to the atoms in a dense gas or a liquid, it takes substantially longer time for a rarefied gas to reach its equilibrium. Besides, longer averaging time in the order of several hundred nanoseconds is needed to attain converged macroscopic properties [24][25][26]. Therefore, the molecular simulation of gases was mainly limited to dense systems and small Knudsen numbers (Kn = λ/H,where λ denotes the local gas mean free path and H is the characteristic domain size) [27][28][29][30][31][32][33].…”