Diode characteristics of gas flow through conical nanochannels at atmospheric pressure

Even at atmospheric pressure, non-continuum effects become noticeable in gas flow through nanoscale channels due to their extremely small dimensions. These effects result in diode-like behavior in the gas flow within conical nanochannel. This study combines experimental measurements with theoretical models to investigate the mass flow rate of gas through nanoscale conical channels under varying pressure ratios and channel sizes. The experimental results show that the diode effect becomes more pronounced as the aperture ratio and pressure ratio at the ends of the conical channels increase, in agreement with theoretical predictions. However, experimental measurements consistently yield significantly higher values. The strength of the gas flow diode is evaluated across a broad range of slip coefficients, characteristic dimensions, and pressure ratios. We propose that the diode effect arises from the interaction between discrete molecular effects and continuous flow dynamics, peaking when these two effects are in balance. In contrast, when one effect dominates, as seen in the regimes of free molecular flow or continuum flow, the diode effect diminishes. The gas diode behavior is primarily attributed from the varying scattering of molecules as they collide with the inclined channel walls.