Nanoporous materials have been the subject of extensive research in recent years. This includes carbon nanotubes (CNTs) or porous graphene sheets used for water desalination or gas separation. Finding more efficient and cheaper methods of separating solutes from a solution can make these separation mechanisms more economically viable and accessible which makes it an important area of research.
Typically, fluid flow is described by the solutions to the Navier-Stokes equations, such as Hagen-Poiseuille flow through cylindrical pipes. However, these first of all do not take interactions between the fluid and the pore wall into account. Secondly, the NS equations are generally solved for incompressible Newtonian fluids which follow a linear stress-strain relation.
During my research I aim to find a description of fluid flow through nanochannels based on the continuum approach which nevertheless incorporates small-scale effects and can be generalised for different types of fluids. The following step is to look into solute rejection mechanisms, which factors contribute to them on a molecular level and finding a coherent description of such processes.
HOLD-UP IN HORIZONTAL AND INCLINED OIL-WATER FLOWS
Mixtures of oil and water are commonly encountered in oil transportation pipelines, especially for subsea developments. The extracted fluids from a well are processed in offshore platforms which have a limited processing capability. This limitation means that fluids are not fully separated and a residual water content is typically carried through export oil pipelines. For high oil flow rates, water is transported along the pipe as droplets in the oil phase. As the oil flow rate decreases, the water droplets coalesce to form slugs in the oil phase in which the water volume is unknown. This behaviour has not been widely studied for horizontal and slightly inclined pipes having small water fractions (i.e. <5%).
Experimental and theoretical investigations are being carried out to study the transition from stratified to non-stratified flow in oil-water mixtures at pipe inclinations between ±5°. The work is focused on the determination of the in-situ water fraction as a function of phase velocity, pipe inclination and inlet configurations. A number of measurement techniques are being used to characterise the flow, namely, Planar Laser Induced Fluorescence (PLIF), Particle Image Velocimetry (PIV) and pressure drop measurements. These techniques provide detailed information of the flow such as phase distribution, velocity vectors, velocity profiles, flow patterns, and turbulent measurements. This information will be used to develop a mechanistic model to predict the in-situ water fraction and the transition between stratified to non-stratified flows.
I research on the impact of droplets on a flowing liquid film. This experimental work allows me to study the various possible outcomes viz. bouncing, partial and total coalescence to splashing using high-speed imaging system. The effects of change of liquid, density ratios, viscosity of liquid and presence of surfactant on the overall process are studied as well. I also view the different wave-forms obtained on this flowing film, studying their evolution, propagation and eventual formation of coherent structures. The influence of these waves on the outcomes is monitored and the corresponding effects on the waves as well. Waves are allowed to form naturally and also induced artificially by externally imposing a specific frequency of vibration. Results obtained will be validated using numerical simulations with codes like BLUE and FLUIDITY.
My research focuses on developing fast, inexpensive and scalable approaches for surface patterning and microfabrication. Specifically, I study the mechanism of wrinkling as a way to impress regular patterns on polymers. Wrinkled surfaces can be applied for a wide range of applications including drag reduction, increased surface hydrophobicity, and photonics. We have successfully managed to obtain sinusoidal wrinkles with wavelength of 100 nm on plasma oxidised polydimethylsiloxane. Regarding microfabrication, I investigate the manifacturing of microfluidic devices using photolithographic techniques.
Mixing horizontal stratified liquid-liquid pipeline flows using transverse jets.
Researching the interaction of transverse jets with horizontal stratified pipeline flows. Monitoring the jet breakup and the evolution of the resulting dispersions through using PLIF, PIV, PTV laser based techniques. Experimental data is compared with CFD models to study the ability of the models to capture the important details in these complex flows.
Dynamics of Thin Liquid Film over a Spinning Disk
The flow of thin liquid films subjected to centrifugal forces is accompanied by the formation of large-amplitude waves which gives rise to intense mixing on the surface of the disk and considerable increase in heat and mass transfer, commonly referred as “process intensification”. Therefore, such flows have wide industrial applications, ranging from liquid atomisation to manufacturing of pharmaceuticals and fine chemicals.
We develop a mathematical model studying the hydrodynamics, mass and heat transfer and chemical reaction with regards to a thin liquid film flowing over a spinning disk. We apply the thin-layer approximation in conjunction with the Karman–Polhausen method to derive axisymmetric and non-axisymmetric evolution equations for the film thickness and the volumetric flow rates in both the radial and azimuthal directions satisfying boundary conditions and equation of state. We also use the integral method to derive evolution equations for the interfacial profiles as well as the spatio-temporal distributions of the reagent and product concentration surface assuming parabolic profile for velocity and concentration. Numerical solutions of these non-linear partial differential equations, which govern the hydrodynamics and the associated mass and heat transfer, reveal the existence and formation of large-amplitude waves and elucidate their substantial effect on the characteristics of mass and heat transfer and chemical reaction.
Additionally, we investigate 3D CFD (3 Dimensional Computational Fluid Dynamics) simulations of structure of the flow over the entire disk and the associated heat, mass transfer and chemical reaction using FLUENT and conduct relevant experiments in order to validate our model by comparing with the theoretical results obtained from the numerical methods.
Numerical Simulations of Gas-Liquid Flows in Large-Diameter Risers
Different distribution of phases, termed flow regimes, are encountered in gas-liquid flows through vertical pipes. One of these regimes is the ‘slug flow’. It occurs over a wide range of flow conditions and is characterised by the presence of bullet-shaped bubbles, known as Taylor bubbles, with diameter of about the same size as the pipe (Figure 1). For flows in sufficiently large diameter pipes (), this flow regime is not observed. My research seeks to numerically simulate gas-liquid flows in vertical ‘large-diameter’ pipes. A particular objective would be the investigation of the stability of Taylor bubbles under the flow condition encountered in these pipes. From this, we hope to be able to offer qualitative and quantitative explanations as to the nonexistence of slug flow regime in gas-liquid flows in large diameter risers.
Wax deposition is a phenomenon that plagues crude oilfields with significant economic impact that causes financial losses through the cost of prevention and remediation, reduced or deferred production, pipeline replacements and/or abandonments and equipment failures. A number of wax control technologies are currently being applied in the oilfield which includes mechanical methods for wax removal and thermal management strategies which primarily focuses on remediation rather than prevention. Chemical injection technology is a preventive, cost-effective alternative to combat wax deposition. The wax control chemicals currently in the market however are found not to be effective in preventing wax crystallization especially for crudes with high WAT and pour point temperatures. Therefore, there is a need to develop fundamental understanding of the wax crystallization mechanism at the molecular level and to develop a good and effective wax control chemical to suppress wax crystallization to the lowest possible temperature.
The aim of this study is to develop a framework of approaching the wax control chemical development in a systematic way. This will be done through a three-pronged approach: computer-aided molecular design; chemical synthesis and testing; embedding the molecular-scale chemistry into a continuum-scale model for simulations at the macro-scale. Coarse-grained molecular dynamics (MD) and the computational fluid dynamics (CFD) continuum-level simulation will be used to guide the synthesis of a new chemical, which will be tested against chemical systems from the oilfields. The MD-synthesis-testing steps will be iterative, culminating in the development of an effective wax inhibitor. Information from the MD step will be passed to the continuum-level modeling step for the development of simulation tools of wax formation/inhibition in flow processes, which is my main focus area.
The primary objective of my work is to obtain a fundamental understanding of the mechanism underlying the solid deposition within the oil and gas production system, and how chemical additives behave to inhibit the process. My research includes both computational approach of simulation and experimental procedure that are strongly linked to provide a comprehensive description of how the solid deposits are formed and in what way it can be suppressed. Molecular dynamics simulations of coarse-grained models based on the SAFT force-field is used to look into the formation of the solid deposits at molecular level as well as to study the phase behaviour and thermodynamic properties of the governing components of the targeted system. The experimental part of my work investigates how chemical additives work to prevent the formation of the deposits. Chemical of interest are synthesised, analysed and evaluated for its effectiveness in inhibiting the solid deposition. The chemical will then be modelled and incorporated into the molecular dynamics simulation to study the effect on precipitation boundary.
I am involved in the development of accurate, reliable, and efficient models for the direct simulation of the pattern formation associated with the drying of blood droplets (see Figure 1) whose complex stain morphologies are influenced by the original blood composition. The models will be formulated from the three-dimensional (3D) equations of mass, momentum and energy conservation, complemented by a 3D advective-diffusion equations for the concentrations of all species present within the drop. To simulate naturally crack-formation during drop drying, we will use a first-principles approach and couple the 3D fluid mechanical, and particle transport problem, to a mean-field, 3D solid mechanics problem by taking the densely-packed particles to be deformable Hertzian spheres; the latter are compressed by capillary pressure gradients due to non-uniform evaporation. These problems will, in turn, be coupled to Darcy flow in the interstices of the porous solid. A steady diffusion equation will be solved for the quasi-static vapour concentration to furnish the evaporative flux, and the energy equation will also be solved in the solid wall underlying the drop.
A hierarchy of models will be generated reflecting the increasing level of complexity. The models will account for all the relevant physical processes: evaporation, capillarity, Marangoni flow, diffusion, solidification/crystallisation, adsorption and changes of substrate wettability, contact line motion, sol-gel transition, and crack-formation. Thus, we will develop a simulation capability for the deposition morphology as a function of composition changes of the drying blood drops. This research will have application in the development of devices for rapid medical diagnosis.
This work will be carried out in collaboration with the group of Professor Khellil Sefiane (University of Edinburgh) who has world-leading expertise in evaporating, particle-laden drops, and with the group of Professor Rhodri Williams (University of Swansea) who has expertise in haemorheology.
Lee Rui Yan
The main objective of my work is to design and develop an effective fine sand consolidation solution to prevent or minimise its migration to the topside which will subsequently prevent equipment damage due to erosion or deposition of fines that may lead to production losses and deferment. My work is primarily experimental focusing on various physical and chemical methods to modify the surface properties of the particulate matter present within the formation to ensure that they conform to a state where they remain consolidated within the formation without causing any detrimental effects to the permeability of the reservoir. Experimental data from my work will be directly applied into the development of a comprehensive computational fluid dynamics model which will be capable of predicting the behavior of the fines within the formation and allow for optimization work to be carried out on the treatment of the formation.
Sand production is an inevitable challenge causing the oil and gas industry billions of dollars due to production loss, equipment damage and unscheduled shutdowns. A key control measure is by injecting sand control chemical into the formation. Recent development within the subject area focuses on developing chemical treatment which aims to agglomerate sand particles, primarily sand smaller than 50microns to form larger aggregates. The agglomerated particles are expected to maintain their size and strength under varying conditions whereas the chemical treatment should not induce formation damage and impair reservoir permeability.
My research attempts to understand sand particles dynamic behaviour and stability under the influence of agglomerating chemical and hydrocarbon flow, accounting for both agglomerate formation and breakage under varying parameters such as shearing effect, fluid and solid properties, and conditions representative of oil and gas reservoirs. Numerical simulation, Computational Fluid Dynamics (CFD) coupled with Discrete Element Method (DEM) are employed to simulate particle-particle interactions and particle-fluid interactions involved during the agglomeration process. A comparison with experimental data will also be made to assess the validity of the model.
My current research interests are non-intrusive reduced order modelling methods. Reduced order models (ROMs) have become prevalent in many fields of physics as they offer the potential to simulate dynamical systems with substantially increased computation efficiency in comparison to standard techniques. And, in most cases the source code describing the physical system has to be modified in order to generate the reduced order model. These modifications can be complex, especially in legacy codes, or may not be possible if the source code is not available (e.g. in some commercial software). To circumvent these shortcomings, non-intrusive approaches have been introduced into ROMs. The non-intrusive ROM (NIROM) is independent of the original physical system.
Over the past decade, two-dimensional (2D) nanomaterials have received considerable attention in the literature largely due to their truly remarkable properties; these include very high electrical and thermal conductivities, and tensile strength. Due to these properties, 2D nanomaterials are likely to play a central role in the future development of a number of applications that will generate tremendous economic and societal impact, which include opto-electronics, sensors, tissue engineering, drug delivery, and energy conversion and storage. There are a number of 2D materials that exhibit some of the aforementioned properties, the most celebrated one being undoubtedly graphene. The discovery of this material in 2004 by Geim and Novozelov resulted in their winning the Nobel Prize in 2010. In order to realise the potentially transformative effect of nanomaterials on industry, there is a need to overcome the considerable challenge of developing a large-scale, cost-effective and controllable (in terms of numbers of layers) process for their mass-production. This process must produce defect-free materials at rates that far exceed those associated with current methods such as growth and exfoliation.
The method proposed in this project uses a device involving the flow of a thin liquid layer (average thickness ~ 100 mm –1 mm) over a rapidly spinning disc(several hundred RPM). The shear imparted to the film due to the disc rotation leads to the development of large-amplitude, three-dimensional interfacial waves and an intense mixing environment on the surface of the disc. As a result of its process-intensifying properties, this device has previously been used as a spinning disc reactor (SDR) in the pharmaceutical industry as a potential replacement for the batch reactor. In the present project, the focus will be on harnessing the high-shear environment near the surface of the disc to accelerate the exfoliation of nanosheets from the 2D nanomaterial in the film.
I am research associate on numerical simulation of multiphase flows using front-tracking and domain decomposition methods. Our solver runs on a variety of computer architectures from laptops to supercomputers on 65536 threads or more (limited only by the availability to us of more threads). Our solver also includes modules for flow interaction with immersed solid objects, contact line dynamics, species and thermal transport with phase change.
Key words: Falling liquid film, droplet impact, direct numerical simulation, multiphase flow, parallel or distributed processing, interface dynamics and front tracking, atomization, Microfluidics,...
Coming soon :
Dr Qinghua Lei