Computation of Rarefied Gas Flows in Nano/micro Devices using an Indigeneous Developed Computational Fluid Dynamics Solver

Assam, A and Kalkote, Nikhil Narayan and Dongari, Nishanth and Eswaran, Vinayak (2017) Computation of Rarefied Gas Flows in Nano/micro Devices using an Indigeneous Developed Computational Fluid Dynamics Solver. In: Proceedings of the International Conference on Nanotechnology, Ideas, Innovations & Initiatives (ICN:3I),, 6-8 December 2017, IIT Roorkee, India.

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Abstract

Gaseous Nano/micro Electronic Mechanical Systems (NEMS/MEMS) are used for measurement and control in the atomic level. Numerical simulation of such system is important for understanding the gas flow behaviour in such devices. Non-equilibrium effects such as small characteristic length, rarefaction and gas-surface interactions characterize such flow behaviour. The Knudsen number, Kn, ratio of the molecular mean free path, λ, to the characteristic length of the geometry, l is used to characterize the translational non-equilibrium of a rarefied gas flow in nano/micro devices. For high gas density with small Kn (Kn≤0.001) the conventional Navier-Stokes (NS) equations are applicable. When the gas density becomes small, the mean free path of gas becomes large and the non-equilibrium effects appear in the flow with fewer collisions between molecules. The conventional NavierStokes equation with velocity slip and temperature jump conditions can be used to simulate the slip-flow regime 0.001≤ Kn ≤ 0.1. The only other method for such flows, direct simulation Monte Carlo (DSMC), is computationally quite expensive, especially for three-dimensional flows. In this work we demonstrate the functionality of our all-speed three-dimensional indigenously developed unstructured grid cell-based finite-volume computational fluid dynamics (CFD) solver for MEMS/NEMS devices. The solver is well validated for relatively high gas density flows corresponding to small Kn (Kn≤0.001). The mean-flow in NS equation is solved using low-speed preconditioning with ROE flux in a density based solver. The time-stepping has been done implicitly using the LU-SGS scheme. The Maxwell velocity slip and Smoluchowski temperature jump boundary condition is used at the wall. The Sutherland Law of viscosity is used for the gases considered in this study, i.e. nitrogen and argon. In the final paper, we will present the results for gaseous flow in (NEMS/MEMS) devices such as pressure driven micro/nano channel and cavity. Three cases will be considered (a) pressure driven 90-degree bent microchannel, (b) lid-driven micro-cavity and (c) pressure driven backward facing step nanochannel. The results will be compared with available experimental, DSMC and other CFD data.

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