Investigation of rarefied gas flow in microchannels of non-uniform cross section

Abstract

Study of rarefied gas flow in converging and diverging cross sections is crucial to the development of micro-nozzles and micro-thrusters. In other practical cases too, a microchannel may not always be straight and may include diverging and converging sections in the flow path. In this context, isothermal rarefied gas flow in microchannels of longitudinally varying cross section is studied experimentally in this work. The primary objective is to investigate the existence of Knudsen minimum in microchannels of varying cross sections. The effect of geometrical cross section and fluid properties on the Knudsen minimum are also investigated by performing experiments on three divergence angles (4°, 8°, and 12°) and three different gases (argon, nitrogen, and oxygen) to prove the robustness of the result. The Knudsen minimum, which is one of the characteristic features of rarefied flows, is experimentally observed for the first time in a microchannel of varying cross section. The position of the Knudsen minimum (at Kn ≈ 1) is seen to depend only weakly on the divergence angle and fluid properties.

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

“…They showed that the pressure drop, centerline velocity, and wall shear decrease with an increase in divergence angle for their range of study. Hemadri et al 10 studied rare¯ed gas°ow in converging and diverging cross-sections. They observed Knudsen minimum for thē rst time in a microchannel of varying cross-section.…”

Determination of tangential momentum accommodation coefficient and slip coefficients for rarefied gas flow in a microchannel

“…Till recently, there was no clarity on the position and magnitude of Knudsen minimum (or even its existence) for microchannels of non-uniform cross section. Recent measurements by Hemadri et al [27,28] have experimentally established the existence of Knudsen minimum in diverging and converging microchannels. They also noted the position and magnitude of the minimum to be weakly dependent on the geometrical cross section of the microchannel and the molecular weight of the gas species.…”

Free-molecular and near-free-molecular gas flows over backward facing steps

“…Motivated by the overwhelming complexity of channels networks contained in microfluidic chips (Thorsen, Maerkl & Quake 2002), the study of heat and mass transfer phenomena in non-straight channel geometries has become the focus of several works. In the context of rarefied gas flows, these have included, among others, studies on the effects of channels bending (Sharipov & Graur 2012;Liu et al 2018), gradual section expansion (Naris, Tantos & Valougeorgis 2014;Graur et al 2015;Hemadri, Parade & Bhandarkar 2016;Tatsios et al 2017) and geometrical irregularities, including sudden expansion and contraction (Agrawal, Djenidi & Antonia 2005;Gat, Frankel & Weihs 2008;Hong, Zhen & Yang 2008;Varade, Agrawal & Paradeep 2014).…”