Advances and Challenges in Computational Research of Micro and Nano Flows

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.This paper presents a collective overview of recent studies regarding the computational modelling of micro- and nano-fluidic systems. The review provides an introduction to atomistic, mesoscale and hybrid methods for simulating micro and nano-flows, as well as discusses recent applications and results from the application of such methods

Hybrid molecular-continuum methods for micro- and nanoscale liquid flows

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.Many flows at microscale and below are characterised by an inherent multiscale nature and accurate numerical modelling of the phenomena involved is the cornerstone for enhancing the applicability of micro and nanofluidics in the industrial environment. This paper presents a hybrid molecular-continuum strategy named as point wise coupling for studying complex micro- and nanoscale flows. In this strategy one performs continuum simulations and uses a molecular solver for computing flow properties. The hybrid methodology utilises a numerical procedure to minimise the cost of the computationally expensive molecular solver. Simulations have been carried out for a slip Poiseuille flow test case. The hybrid results are in good agreement with analytical solutions and pervious molecular simulations.This study is funded by the EPSRC, MoD and AWE through the grant EP/D051940-JGS 607, as well as from the European Commission under the 6th Framework Program (Project: DINAMICS, NMP4-CT-2007-026804)

A New Heterogeneous Multiscale Technique for Microscale Gas Flows

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.We present a new hybrid method for dilute gas flows that heterogeneously couples a continuumfluid description to the direct simulation Monte Carlo (DSMC) method. A continuum-fluid model is applied across the entire domain, while DSMC is applied in spatially-distributed micro regions. Using a field-wise coupling approach, DSMC sub-domains of any size can be placed at any location. The sub-domain arrangement can therefore be adjusted for each problem to capture non-equilibrium behaviour both close to bounding walls and in the bulk. We demonstrate our method on a test case of high-speed micro Couette flow. With large differences in wall velocity, significant viscous heating is present, and so our coupling considers the transfer of both momentum and heat. Our hybrid results are validated against a pure DSMC simulation, and the results show that the method can deal with missing boundary and constitutive information

Computational uncertainty in hybrid atomistic-continuum frameworks

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Over the past decade micro and nanofluidics emerged as vital tools in the ongoing drive towards the development of nano-scale analysis and manufacturing systems. Accurate numerical modelling of the phenomena involved at these scales is ssential in order to speed up the industrial design process for nanotechnology. However a parameter often ignored in hybrid simulations is the uncertainty level introduced in the numerical modelling of phenomena taking place at micro and nanoscales. The main interest of the present study is the propagation of the inherent atomistic fluctuations to the continuum solver in the case of multiscale modelling and hybrid solvers

Thermal Conductivity of Nano-fluids in Nano-channels

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The behaviour of an Argon-copper nano-fluid spatially restricted in a nano-channel is studied by using Molecular Dynamics simulations. Specifically, the channel size and particle loading effects on nanofluids thermal conductivity are investigated. A direct comparison is made between the calculated results and the prediction of classical macroscopic models with the latter under-estimating the computed values by up to 20%. The thermal conductivity enhancement is correlated with the structure of Argon atoms close to the walls of the channel and around the particle, whose solid like nature enables them to propagate heat more efficiently

Multiscale simulation strategies and mesoscale modelling of gas and liquid flows

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.This paper presents a review of multiscale simulation strategies for the modelling of micro- and nanoscale flows. These have been developed in the last two decades in an attempt to bridge the application gap between molecular and continuum simulation methods preventing the simulation of many micro- and nanofluidic devices. The paper is focused on hybrid molecular-continuum methods and reviews different coupling strategies, including geometrical decomposition in conjunction with state- and flux coupling, pointwise coupling, the heterogeneous multiscale method and the equation free approach. The different applications of these methods are briefly discussed

A Laplacian-based algorithm for non-isothermal atomistic-continuum hybrid simulation of micro and nano-flows

We propose a new hybrid algorithm for incompressible micro and nanoflows that applies to non-isothermal steady-state flows and does not require the calculation of the Irving–Kirkwood stress tensor or heat flux vector. The method is validated by simulating the flow in a channel under the effect of a gravity-like force with bounding walls at two different temperatures and velocities. The model shows very accurate results compared to benchmark full MD simulations. In the temperature results, in particular, the contribution of viscous dissipation is correctly evaluated

Transport properties and structure of fluids in hydrophobic/hydrophilic nanochannels

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.When downsizing towards the nanoscale, system dimensions have been found to affect channel flows mainly because of the presence of the walls that interact strongly with fluid particles. Parameters which are not taken into account at the classical theory continuum theory at the macroscale, should be taken into account at the nano or even micro-scale where the surface to volume ratio increases significantly. Such property is the wall/fluid interaction which determines the wetting (hydrophilic behavior) or not (hydrophobic behavior) of a surface. We first investigate the effect of wall/fluid interaction on fluid atom distribution near the wall through the radial distribution function and, next, we calculate the three most important fluid transport properties, i.e., the diffusion coefficient, shear viscosity and thermal conductivity. Transport properties seem to be affected significantly in the channel region adjacent to the wall