Development of empirical relationships for surface accommodation coefficients through investigation of nano-poiseuille f
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RESEARCH PAPER
Development of empirical relationships for surface accommodation coefficients through investigation of nano‑poiseuille flows using molecular dynamics method Kishore K. Kammara1 · Rakesh Kumar1 Received: 8 January 2020 / Accepted: 27 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this work, we have studied the effects of macroscopic (temperature of gas and wall atoms; velocity of gas near the wall) and microscopic properties (energy well-depth parameter, 𝜖 , used in Lennard–Jones potential to describe gas–surface interaction strength) on both energy accommodation coefficients (EAC) and tangential momentum accommodation coefficient (TMAC) using molecular dynamics approach. The effect of aforementioned properties is studied through classical force-driven nano-Poiseuille flow using argon gas and platinum walls. Parameters like temperature of wall, external force acting on gas atoms, and energy well depth ( 𝜖 ) between gas and surface are varied systematically to study the effects of these parameters on accommodation coefficients. Empirical relationship between the accommodation coefficients (TMAC and EAC) and the above-mentioned properties is obtained by performing non-linear regression analysis.
1 Introduction Knudsen number, defined as the ratio of average mean free path of gas molecules to characteristic length, provides a measure of the degree of rarefaction in the flow filed. Flow fields can be characterized based on the global Knudsen number, viz., continuum flow field ( Kn < 0.001 ), slip flow field ( 0.001 < Kn < 0.1 ), transitional flow field ( 0.1 < Kn < 10 ), and free-molecular flow field ( Kn > 10 ). As the focus of the modern industries is increasing in the fields such as micro/nanoscale flows, nano-drug delivery systems, high-altitude outer space vehicles, and vacuum technologies, the study of rarefied flow fields has become more and more relevant. The aforementioned applications fall in the category where the Knudsen number is typically higher than 0.1. For such higher Knudsen number flows (either in outer space conditions or in nano/micro-confinement flows), the applicability of continuum approximations, especially near the surface, becomes questionable (Travis et al. 1997) and requires the need for more suitable models to address the flow physics close to the surfaces and beyond. * Rakesh Kumar [email protected] 1
Department of Aerospace Engineering, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India
Such behavior is observed due to increased surface dominant effects on fluid flows. In this regard, many particle-based models have emerged to provide better insights into the gas behavior near the surfaces. One of the well-known methods, direct simulation Monte Carlo (DSMC), has been well demonstrated in its capability in modeling many practical flow problems accurately (Nedea et al. 2005; Gu et al. 2010; Yamamoto et al. 2006). In DSMC approach, flow physics near a surface is modeled using various gas–surface interaction mode
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