On the thermally-driven gas flow through divergent micro/nanochannels

Abstract

A detailed study on thermally driven flows through divergent micro/nanochannels is presented. Rarefied gas flow behavior and thermal mass flow rate were investigated with different divergence angles ranging between 0[Formula: see text] and 7[Formula: see text] at two aspect ratios ([Formula: see text]) using particle-based direct simulation Monte-Carlo (DSMC) method. We compare our DSMC solutions for normalized thermal mass flow rate with the numerical solution of the Boltzmann–Krook–Walender (BKW) model and Bhatnagar–Gross–Krook (BGK) model and asymptotic theory over a wide range of Knudsen number in the transition regime. The flow field properties including Mach number, pressure, overall temperature and magnitude of shear stress are examined in detail. Based on our analysis, we observed an approximately constant velocity and pressure distribution at a microchannel with a small opening angle. Our results also demonstrate that the heat lines from weakly nonlinear form of Sone constitutive law and DSMC show good agreement at low Knudsen numbers. Moreover, we show that the effect of divergence angle is influential in increasing normalized thermal mass flow rate at early transition regime.

Knudsen pumps: a review

“…The mass flow rate always decreases with the increase of channel inclination 134 . Note that this conclusion contradicts later research 135 , because the connection channels of the models are not considered in the latter. In fact, the connection channels influence the flow field patterns and mass flow rate in microchannels 194 .…”

“…The channels for all the KPs discussed above can be regarded as rectangular structures. The compression ratios achieved with other forms of micro-channel configurations proposed recently 94,116,[121][122][123][124][125][126][127][128][129][130][131][132][133][134][135] have already been reported in the corresponding numerical studies. Table 1 records the maximum compression ratios of different varieties of KPs in simulation studies.…”

“…This is because the addition of connection channels will affect the inlet and outlet conditions at the two ends of micro-channels. In addition, increasing the aspect ratio can also increase the mass flow rate 135 . In particular, for a large Kn, the aspect ratio has more influence on the mass flow rate than the divergence angle 135 .…”

“…In addition, increasing the aspect ratio can also increase the mass flow rate 135 . In particular, for a large Kn, the aspect ratio has more influence on the mass flow rate than the divergence angle 135 . Therefore, it may be said that if the gases are in the free-molecular limit (Kn ~50), the maximum flow rate will be attained.…”

Fluid flow and heat transfer in microchannel heat sinks: Modelling review and recent progress

“…Their results found that the effect of the heat flux gradient on the direction of net heat flux increases with the increase of divergence angle. Mozaffari et al [95] applied the DSMC method to simulate the thermal creep flow in the microchannel, and analyzed the Mach number, pressure and other parameters in the channel under different Knudsen numbers. Their results concluded that the gas flow was mainly affected by the wall temperature gradient, viscous forces and regional expansion effect.…”