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).
- “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)
- Airbus Group Ltd
- Bell Labs
- European Space Agency
- Jaguar Land Rover
- Oxford Biomedical Engineering (BUBBL)
- TotalSim Ltd
- Waters Corporation
Latest news and blogs
Dr Juan C. Padrino, Research Fellow, University of Warwick
MNF will be present in the upcoming 3rd UK InterPore Conference on Porous Media to be held at the University of Warwick, Coventry, UK, on 4 and 5 September 2017. On the afternoon session of 5 September, Juan C. Padrino will give a talk on multiscale modeling of diffusive transport in complex networks.
Dr Benzi John, Senior Computational Scientist, Daresbury Laboratory
Benzi John (PI) and David Emerson (Co-I) have successfully won about 32, 000 KAU (~ £18,000) frunding from EPSRC to run large-scale simulations on ARCHER. The project titled "High fidelity non-equilibrium DSMC flow simulations at scale using SPARTA" will run for 12 months, starting from August 1st 2017. More information here.
Prof. Duncan Lockerby, University of Warwick
It's a pleasure to welcome three new starters to Warwick and the Micro Nano Flows team. Laura Cooper joins us as a post-doctoral researcher, and will be working on multi-phase flow in porous media with James Sprittles. Yixin Zhang and Jacqueline Misfud are in the first weeks of their PhDs. Yixin will be investigating nano film stability (with molecular dynamics) and Jacqui will be researching micro-bubble cavitation (with CFD) in partnership with Waters Limited. We wish all three the best of luck in their research!
Dr Juan C. Padrino, Research Fellow, University of Warwick
In an enlightening article published in 2015 in Physical Review Letters, Holtzman and Segre studied the effect of the contact angle (wettability) in immiscible two-phase flow in porous media in the unstable case of a less viscous invading fluid displacing a more viscous one. The title of the article “Wettability stabilizes fluid invasion into porous media via nonlocal, cooperative pore filling”, indicates the main conclusion of the work.
They carried out numerical experiments in a two-dimensional disordered medium constructed with an array of solid cylinders of varying diameter set within a large rectangular area. A degree of disorder was introduced by randomly selecting the cylinder’s diameter from a uniform distribution. The array of cylinders consisted of repeated triangular lattices of fixed spacing between vertexes (the cylinders’ centres). The fluid dynamics modelling at the pore scale took into account three types of meniscus instabilities, namely, bursting (Haines jumps), occurring when the curvature reaches a critical value; touching, when a meniscus intersects a third solid surface, and overlapping, when adjacent menisci encounter. The latter is essential in creating a compact, smooth, displacing front as it promotes non-local, cooperative pore filling. They used this porous medium model to simulate the experiments of Trojer, Szulczewski, and Juanes (2015). The radial fluid motion was produced by injecting air at a certain rate, in a small region of the domain initially saturated with a solution of water and glycerol. The simulations stopped when air reached one of the outer boundaries.
In various applications, it is of interest to have a compact moving front in immiscible two-fluid motion as this generates the more efficient displacement mechanism. This is desirable, for instance, in oil recovery processes.
An important contribution of the study by Holtzman and Segre is the introduction of two novel dimensionless parameters, namely, a modified capillary number, obtained by altering the classical capillary number (ratio of viscous to capillary forces) with a function of the contact angle and a dimensionless geometric ratio, and the so-called “cooperative number”, given as a function of these two parameters and the angle between two adjacent menisci. This number is a measured of the likelihood of filling the pores by menisci overlaps. In their simulations, the angle between two adjacent menisci was fixed to 120o.
By computing these two parameters for the same data used in the numerical study, Holtzman and Segre correlated their values with the salient features of the interfacial morphology from the simulations. These predictions followed the invasion regimes observed in the experiments referred to above. For modified capillary numbers greater than approximately 4 x 10-3, simulations showed viscous fingering, characterized by long and thin fingers, regardless of the magnitude of the cooperative number. On the other hand, for a modified capillary number smaller than 4 x 10-3 and positive cooperative numbers, indicating invasion by a wetting fluid, simulations predicted compact displacement, characterized by short and thick “fingers”. For the remaining sector, for which the cooperative number is negative (non-wetting invasion), results showed thinner, adjacent fingers within fractal, long interfaces, typical of the capillary fingering pattern. Therefore, their results showed that wetting invasion (imbibition) favors the formation of a compact front for low capillary numbers.
Finally, it is noteworthy that more recently, in 2016, Zhao, MacMinn, and Juanes, conducted a series of experiments by radially displacing a very viscous silicone oil in a porous system using water while systematically varying the wettability of the medium. They found a trend similar to the one described by Holtzman and Segre in that increasing the wettability of the invading fluid promotes cooperative pore filling and hence a more compact front displacement. Nonetheless, Zhao et al. surprisingly found that for a strongly wetting invading fluid, this trend is dramatically reversed and the displacement becomes markedly less efficient. They noted that this sudden change, not reported previously, is caused by the dominant presence of corner flow, for which the invading fluid moves without filling the pore bodies, over cooperative pore filling.
Dr Jianfei Xie, Research Associate, University of Edinburgh
During the past two decades, we see the fast development and wide applications of nanotechnologies, biological chips and lab-on-a-chip. Nanoscale transport governs the behaviour of a wide range of nanofluidic systems, but it remains less understood due to the enormous hydraulic resistance associated with the nano-confinement and the resulting minuscule flow rates in MEMS/NEMS. In addition, the huge surface-volume ratio (up to 106−109) signifcantly affects the mass and momentum transport in micro/nanoelements and makes this type of research challenging.
Obviously, the challenge is to overcome the large surface and viscous forces that prevent the fluid from flowing at the nanoscale, wherein other driving forces can be ignored in most microfluidic systems. In microfluidic biochip engineering, a driving force for driving microscale fluid motion has been introduced by employing the surface waves. The key of this novel technology is to make a micropump that is able to position reagents on the surface of chips or in microfluidic channels without the mechanical contact. This is implemented in terms of the surface acoustic waves (SAW) that are induced using radio frequency electric signals. These waves arise through the use of piezoelectric substrate materials in the chip. It is interesting that the SAW-induced effect has similarity in live nature, for example with the skin features of fast-swimming sea animals, such as dolphins. Dolphins use travelling waves on their skin surface to damp the turbulence in the boundary layers near the skin surface.
Our purpose is to present that the travelling surface waves propagating on the walls of nanochannels can offer a powerful method for inducing a host of extremely fast nanofluidic flow. We find that the flow rate is enlarged by increasing the amplitude of travelling surface waves and can be up to a sevenfold increase. However, the flow rate is only enhanced in the limited range of frequency of travelling surface waves such as low frequencies, and a maximum fivefold increase in flow rate is pronounced. In addition, the fluid-wall interaction (surface wettability) plays an important role in the nanoscale transport phenomena, and the flow rate is signifcantly increased under a strong fluid-wall interaction (hydrophilicity) in the presence of travelling surface waves. Moreover, the friction coefficient on the wall of nanochannels is decreased obviously due to the large slip length, and the shear viscosity of fluid on the hydrophobic surface is increased by travelling surface waves. It can be concluded that the travelling surface wave has a potential function to facilitate the fow in nanochannels with respect to the decrease in surface friction on the walls. Our results allow to defne better strategies for the fast nanofluidics by travelling surface waves. (more details please see: https://doi.org/10.1007/s10404-017-1946-z)
Livio Gibelli, Research Fellow, University of Warwick
On September 27th, the second Special Interest Group (SIG) meeting was hosted at the University of Warwick.
This series of meetings aims at bringing together theoreticians with experimental groups who share interest in the area of multiscale and non-continuum flows.
Beside the pleasure of seeing again many members of the Micro & Nano Flows group, the meeting was a good opportunity to meet other researchers across the United Kingdom.
After a welcome and 2-minute introductions by all the participants, four main lectures were given.
Dr. Kislon Voitchovsky (Durham University) discussed the liquid behaviour at nanoscale interfaces both from the numerical and, even more interestingly, experimental standpoints.
Dr. James Sprittles (University of Warwick) showed how non-equilibrium effects of the vapor flows can (unexpectedly) play a major role on the dynamics of the collisions between microdrops and on their impact/spreading on solid surfaces.
Dr. Sergey Karabasov and Dr. Ivan Korotkin (Queen Mary University of London) presented an interesting hybrid model which smoothly combines molecular dynamics with the Landau-Lifshitz fluctuating hydrodynamics.
I did appreciate the stimulating and constructive environment the meeting has created, as well as the main message of encouraging researchers to reflect on the impact that their studies may have beyond the academic community and to engage with industrial partners in collaborative research.