Rarefied gas flows in complex microfluidic 3D-structures fabricated via additive manufacturing

Abstract

In this work, two-photon-polymerization (TPP) is introduced as a method for manufacturing three-dimensional devices for rarefied gas flow applications. The novel 3D manufacturing capabilities of TPP are demonstrated by the fabrication of a microfluidic structure that consists of a circular micro-tube with a varying radius (tapered channel). The micro-tube has interesting features, such as a conical structure with one order of magnitude difference between minimum and maximum radii, that is $14\mu m$ and $215\mu m$, respectively, and a very high aspect ratio, that is defined as the length over the minimum radius, of 72.3. To our knowledge, this is the first time that such a geometrical configuration has been successfully tested for rarefied gas flow applications. It supports the suitability of the presented fabrication method for further 3D new-generation applications in the field. The geometrical characteristics of the device were measured by $\mu$-tomography and subsequently analyzed allowing the assessment of the geometrical precision of the fabrication method. From a fluid dynamics perspective, the device was tested by imposing pressure-driven gas flows in the converging and diverging directions of the structure for a wide range of rarefaction. The flow parameters linked to the structure, such as mass flow rates and conductances, were obtained experimentally using the constant volume technique. The experimental results were compared to numerical simulations obtained via Computational Fluid Dynamics solving the Navier–Stokes equation in the slip and hydrodynamic flow regimes. The experimental vs. numerical comparison showed good agreement within geometrical uncertainty.