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Investigation of non-equilibrium boundary conditions considering sliding friction for micro/nano flows

Ashwani Assam (Institute Post-Doctoral Fellow, Indian Institute of Technology Palakkad, Kerala, India)
Nikhil Kalkote (Indian Institute of Technology Hyderabad, Hyderabad, India)
Nishanth Dongari (Department Mechanical and Aerospace, Indian Institute of Technology Hyderabad, Hyderabad, India)
Vinayak Eswaran (Department of Mechanical Engineering, Indian Institute of Technology Hyderabad, Hyderabad, India)

International Journal of Numerical Methods for Heat & Fluid Flow

ISSN: 0961-5539

Article publication date: 5 August 2019

Abstract

Purpose

Accurate prediction of temperature and heat is crucial for the design of various nano/micro devices in engineering. Recently, investigation has been carried out for calculating the heat flux of gas flow using the concept of sliding friction because of the slip velocity at the surface. The purpose of this study is to exetend the concept of sliding friction for various types of nano/micro flows.

Design/methodology/approach

A new type of Smoluchowski temperature jump considering the viscous heat generation (sliding friction) has recently been proposed (Le and Vu, 2016b) as an alternative jump condition for the prediction of the surface gas temperature at solid interfaces for high-speed non-equilibrium gas flows. This paper investigated the proposed jump condition for the nano/microflows which has not been done earlier using four cases: 90° bend microchannel pressure-driven flow, nanochannel backward facing step with a pressure-driven flow, nanoscale flat plate and NACA 0012 micro-airfoil. The results are compared with the available direct simulation Monte Carlo results. Also, this paper has demonstrated low-speed preconditioned density-based algorithm for the rarefied gas flows. The algorithm captured even very low Mach numbers of 2.12 × 10−5.

Findings

Based on this study, this paper concludes that the effect of inclusion of sliding friction in improving the thermodynamic prediction is case-dependent. It is shown that its performance depends not only on the slip velocity at the surface but also on the mean free path of the gas molecule and the shear stress at the surface. A pressure jump condition was used along with the new temperature jump condition and it has been found to often improve the prediction of surface flow properties significantly.

Originality/value

This paper extends the concept of using sliding friction at the wall for micro/nano flows. The pressure jump condition was used which has been generally ignored by researchers and has been found to often improve the prediction of surface flow properties. Different flow properties have been studied at the wall apart from only temperature and heat flux, which was not done earlier.

Keywords

Acknowledgements

The authors Ashwani Assam and Nikhil Kalkote would like to acknowledge the fellowship assistance provided by the Department of Higher Education, Ministry of Human Resource Development, Government of India. The authors would like to acknowledge Dr Amaresh Dalal, Department of Mechanical Engineering, IIT Guwahati, for providing the unstructured solver framework Anupravaha-2 over which the current compressible flow solver was developed.

Disclosure statement: The authors declare that they have no conflicting interests.

Citation

Assam, A., Kalkote, N., Dongari, N. and Eswaran, V. (2019), "Investigation of non-equilibrium boundary conditions considering sliding friction for micro/nano flows", International Journal of Numerical Methods for Heat & Fluid Flow, Vol. 29 No. 8, pp. 2501-2523. https://doi.org/10.1108/HFF-04-2018-0170

Publisher

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Emerald Publishing Limited

Copyright © 2019, Emerald Publishing Limited