# Micro & Nano Flows for Engineering

The* micro & nano flows* group is a research partnership between the Universities of Warwick and Edinburgh, and Daresbury Laboratory. We investigate gas and liquid flows at the micro and nano scale (where conventional analysis and classical fluid dynamics cannot be applied) using a range of simulation techniques: molecular dynamics, extended hydrodynamics, stochastic modelling, and hybrid multiscaling. Our aim is to predict and understand these flows by developing methods that combine modelling accuracy with computational efficiency.

Targeted applications all depend on the behaviour of interfaces that divide phases, and include: radical cancer treatments that exploit nano-bubble cavitation; the cooling of high-power electronics through evaporative nano-menisci; nanowire membranes for separating oil and water, e.g. for oil spills; and smart nano-structured surfaces for drag reduction and anti-fouling, with applications to low-emissions aerospace, automotive and marine transport.

## EPSRC Programme Grant in Nano-Engineered Flow Technologies

Our work is supported by a number of funding sources (see below), including a 5-year EPSRC Programme Grant (2016-2020). This Programme aims to underpin future UK innovation in nano-structured and smart interfaces by delivering a simulation-for-design capability for nano-engineered flow technologies, as well as a better scientific understanding of the critical interfacial fluid dynamics.

We will produce software that a) resolves interfaces down to the molecular scale, and b) spans the scales relevant to the engineering application. As accurate molecular/particle methods are computationally unfeasible at engineering scales, and efficient but conventional fluids models do not capture the important molecular physics, this is a formidable multiscale problem in both time and space. The software we develop will have embedded intelligence that decides dynamically on the correct simulation tools needed at each interface location, for every phase combination, and matches these tools to appropriate computational platforms for maximum efficiency.

This work is strongly supported by nine external partners (see below).

## Current Funding

- “Nano-Engineered Flow Technologies: Simulation for Design across Scale and Phase” EPSRC Programme Grant EP/N016602/1 01/16-12/20 (£3.4M)
- “The First Open-Source Software for Non-Continuum Flows in Engineering” EPSRC grants: EP/K038427/1 K038621/1 K038664/1 07/13-06/17 (£0.9M)
- “Multiscale Simulation of Interfacial Dynamics for Breakthrough Nano/Micro-Flow Engineering Applications” ARCHER Leadership Project 11/15-10/17 (£60k in supercomputer computational resource)
- “Skating on Thin Nanofilms: How Liquid Drops Impact Solids” Leverhulme Research Project Grant 08/16-08/19 (£146k funding a 3-year PDRA)

## Partnerships

- Airbus Group Ltd
- AkzoNobel
- Bell Labs
- European Space Agency
- Jaguar Land Rover
- Oxford Biomedical Engineering (BUBBL)
- TotalSim Ltd
- Waters Corporation

# Latest news and blogs

Prof. David R Emerson,Daresbury LaboratoryArnau Miro from the Universitat Politècnica de Catalunya won a HPC Europa-2 grant for a 13-week visit to the Daresbury group. Arnau will be working on advanced meshing and code coupling strategies and starts his visit mid-January.

Dr James Sprittles,University of WarwickDr Shiwani Singh has joined the Micro and Nano Flows team at Warwick, where she will be based in the Maths Institute. She will be looking into multiscale modelling of viscoelastic flows over the next couple of years.

Dr James Sprittles,University of WarwickWarwick welcomes Vinay Gupta who has started a 2-year Commonwealth Rutherford Fellowship in the Mathematics Institute. Vinay's background is in exploiting moment methods to describe gas mixtures and granular gases.

Dr Laura Cooper,Research Fellow, University of WarwickThis week I attended the BAMC in St Andrews. I have given a talk as part of the “Multiscale Analysis of Porous Media” mini-symposium. I spoke about modelling and upscaling multiphase flow in porous media and the session also included talks on upscaling the poro-elastic properties of soil, the growth of potatoes and using image-based modelling to investigate plant-fertiliser interaction.

There are a wide range of topics were presented and discussed at BAMC, which has combined with the UK Magnetohydrodynamics Meeting this year. In my own work I am modelling phenomena at the millimetre and micrometre scale, but I have had the opportunity to attend interesting talks that aim to model much larger scales, such as the formation of the Milky Way and waves in oceans. Mathematical biology was also a popular topic. There were presentations and posters on the more familiar topics of drop impacts and optimisation.

I have attended talks on the history of mathematics and have learnt that 19

^{th}Century mathematicians could be really mean to each other! Even going as far as writing whole books to explain just how wrong they thought the other person was. Luckily, most of the attendees here did not share this attitude and were friendly.

Jesse Pritchard ,PhD Student, University of WarwickTake a look at this video on the Weissenberg effect.

When stress is applied to a fluid, a certain amount of strain, or deformation, is observed. In particular, for a Newtonian fluid, viscous stresses that arise from the flow are linearly proportional to the local rate of deformation over time. It is determined from this that for Newtonian fluids (such as water and oil), the viscosity of the fluid does not depend on the applied stress. So when a rotational stress is applied (as in the video) at the bottom of a Newtonian fluid, below an air-liquid interface, the resulting flow is dominated by inertial and gravity-effects which causes the fluid to flow down toward the source of the stress and radially outward. For pseudoplastics (such as grease), a type of Non-Newtonian fluid where the viscosity decreases as the applied stress increases, applying the same rotational stress will decrease viscosity near the source, which causes inertia and gravity to no longer dominate the flow, causing the fluid to flow upward and bulge at the air interface.

A fun instance of this effect is known as 'rod-climbing'. Rotating a rod inserted into a pseudoplastic causes the polymer chains that make up the fluid to congregate around the regions of highest stress and orient themselves in the direction of shearing, meaning that chains closer to the rod (where stress is highest) are stretched less than those chains further away, and so occupy 'lower states of energy'. The chains' desire to reach these regions of low energy creates an inward normal force and so the fluid goes in the only direction is can - UP THE ROD.

Shiwani Singh,Research Fellow, University of Warwick

Only upto 40% of the original oil in place could be extracted from the oil reservoir using water flooding, the so-called primary recovery method . A large portion of oil is left behind as immobile ganglia. The enhanced oil recovery (EOR) techniques, the secondary recovery methods, are hence needed to extract the remaining oil. Polymer flooding is one such technique. In this EOR techniques, the injected water is supplemented with the long chain polymers which makes the injected water an visco-elastic fluid with a tunable viscosity. The primary purpose of adding polymer is to increase the viscosity of the flood water so that he mobility of injected water becomes less then that of oil which maximize the sweep efficiency, creating a smooth flood font without viscous fingering. This EOR technique has been successfully used to effectively recover the remaining oil from the reservoir, up to 30% of the original oil in place.