Multiscale Interfacial Transport (MIT) Laboratory

Our group focuses on theoretical, numerical and experimental research on fundamental mechanisms of transports (fluid mechanics, mass diffusion and dispersion, heat transfer, electro-kinetics…) with applications in energy resources exploration and exploitation, waste protection and utilization, interactions with life and health systems, space propulsion, and new materials.

¨ Micro/nanoscale fluid mechanics;

¨ Electrokinetics and ion transport;

¨ Transports in porous media and disordered systems;

¨ Complex fluids and soft matter;

¨ Heat transfer Physics and non-equilibrium thermodynamics at extreme scales (time and space);

¨ Multiscale and hierarchical modeling for transport and coupling mechanisms.

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Recent highlights

Self-adaptive preferential flow control using dispersed polymers in heterogeneous porous media

Abstract: Preferential flow which leads to non-uniform displacement, especially in heterogeneous porous media, is usually unwelcome in most practical processes. We propose a self-adaptive preferential flow control mechanism by using dispersed polymers, which is supported strongly by experimental and numerical evidences. Our experiments are performed on a microchip with heterogeneous porous structures where oil is displaced by dispersed polymer microsphere particles. Even though the size of particles is much smaller than the pore-throat size, the diversion effect by the dispersed microspheres is still proved. Therefore, the plugging effect is not the major mechanism for preferential flow control by dispersed polymers. The mechanisms are further investigated by pore-scale modelling, which indicates that the dispersed polymers exhibit an adaption ability to pressure and resistance in the porous flow field. In such an intelligent way, the displacing fluid with dispersed polymers smartly controls the preferential flow by inducing pressure fluctuations, and demonstrates better performances in both efficiency and economy aspects rather than the traditional way with simply increasing the viscosity. These insights can be applied to improve techniques in the fields, such as enhanced oil recovery and soil wetting.

Publication: C.Y. Xie, W. Lei, M. Balhoff, M. Wang* and S. Chen. Journal Fluid Mechanics 906: A10, 2021 (Cover Page)

Enhanced oil recovery mechanism and recovery performance of micro-gel particle suspensions by microfluidic experiments

Abstract: Micro-gel particle suspensions (MGPS) have been proposed for enhanced oil recovery (EOR) in reservoirs with harsh conditions in recent years, yet the mechanisms are still not clear because of the complex property of MGPS and the complex geometry of rocks. In this paper, the micro-gel particle-based flooding has been studied by our microfluidic experiments on both bi-permeability micromodels and reservoir-on-a-chip. A method for reservoir-on-a-chip design has been proposed based on QSGS (Quartet Structure Generation Set) to ensure that the flow geometry on chip owns the most important statistical features of real rock microstructures. In the micromodel experiments with heterogeneous microstructures, even if the MGPS has the same macroscopic rheology as the hydrolyzed polyacrylamides (HPAM) solution for flooding, MGPS may lead to significant fluctuations of pressure field caused by the non-uniform concentration distribution of particles. In the reservoir-on-a-chip experiments, clustered oil trapped in the swept pores can be recovered by MGPS because of pressure fluctuation, which hardly happens in the HPAM flooding. Compared with the water-flooding, the HPAM solution flooding leads to approximately 17% incremental oil recovery, while the MGPS results in approximately 49.8% incremental oil recovery in the laboratory.

Publication: W. Lei, T. Liu, C.Y. Xie, H.E. Yang, T.J. Wu, M. Wang*. Energy Science and Engineering 8: 986-998, 2020 (Cover Page)

Does low-viscosity fracturing always create complex fractures?

Abstract: Lower-viscosity fluids are commonly believed to be able to create more complex fractures in hydraulic fracturing, however, the mechanism remains stubbornly unclear. We use a new grain-scale model with accurate coupling of hydrodynamic forces to simulate the propagation of fluid-driven fracturing. The results clarify that fracturing fluid with a lower viscosity does not always create more complex fractures. The heterogeneity in the rock exerts the principal control on systematic evolution of fracture complexity. In homogeneous rock, low viscosity fluids result in low breakdown pressure, but viscosity exerts little influence on fracture complexity. However, in heterogeneous rock, lower viscosity can lead to more complex network of fracturing. A regime map shows the dependence of fracture complexity on the degree of rock heterogeneity where low viscosity fracturing fluid more readily permeates weak defects and creates complex fracture networks.

Publication: Z.Q. Chen, D. Elsworth and M. Wang*. Journal Geophysical Research-Solid Earth 125(9): e2020JB020332, 2020

Temperature effects on electrical double layer at solid-aqueous solution interface

Abstract: Despite the significant influence of solution temperature on the structure of electrical double layer, the lack of theoretical model intercepts us to explain and predict the interesting experimental observations. In this work, we study the structure of electrical double layer as a function of thermo-chemical properties of the solution by proposing a phenomenological temperature dependent surface complexation model. We found that by introducing a buffer layer between the diffuse layer and Stern layer, one can explain the sensitivity of zeta potential to temperature for different bulk ion concentration. Calculation of the electrical conductance as function of thermo-chemical properties of solution reveals the electrical conductance not only is a function of bulk ion concentration and channel height but also the solution temperature. The present work model can provide deep understanding of micro and nanofluidic devices functionality at different temperatures.

Publication: A. Alizadeh and M. Wang*. Electrophoresis 41, 1067-1072, 2020 (cover page inside)

Dispersion of Charged Solute in Charged Micro- and Nanochannel with Reversible Sorption

Abstract: We study dispersion of a charged solute in a charged micro- and nanochannel with reversible sorption and derive an analytical solution for mass fraction in the fluid, transport velocity and dispersion coefficient. We discuss the effect of sorption and electrical double layer (EDL) on solute transport and show that the coupling between sorption and EDL gives rise to charge-dependent transport even for a thin double layer. However, in this case it can be reduced to a simple non-charge-dependent case by introducing the intrinsic sorption equilibrium constant.

Publication: L. Zhang, M.A. Hesse and M. Wang*. Electrophoresis 40: 838-844, 2019 (Cover page)

Transport mechanism of deformable micro-gel particle through micropores with mechanical properties characterized by AFM

Abstract: Deformable micro-gel particles (DMP) have been used to enhanced oil recovery (EOR) in reservoirs with unfavourable conditions. Direct pore-scale understanding of the DMP transport mechanism is important for further improvements of its EOR performance. To consider the interaction between soft particle and fluid in complex pore-throat geometries, we perform an Immersed Boundary-Lattice Boltzmann (IB-LB) simulation of DMP passing through a throat. A spring-network model is used to capture the deformation of DMP. In order to obtain appropriate simulation parameters that represent the real mechanical properties of DMP, we propose a procedure via fitting the DMP elastic modulus data measured by the nano-indentation experiments using Atomic Force Microscope (AFM). The pore-scale modelling obtains the critical pressure of the DMP for different particle-throat diameter ratios and elastic modulus. It is found that two-clog particle transport mode is observed in a contracted throat, the relationship between the critical pressure and the elastic modulus/particle-throat diameter ratio follows a power law. The particle-throat diameter ratio shows a greater impact on the critical pressure difference than the elastic modulus of particles.

Publication: W.H. Lei, C. Xie, T.J. Wu, X.C. Wu and M. Wang*. Scientific Reports 9: 1453, 2019

Direct simulation of electroosmosis around a spherical particle with inhomogeneously acquired surface charge

Abstract: Uncovering electroosmosis around an inhomogeneously acquired charge spherical particle in a confined space could provide detailed insights into its broad applications from biology to geology. In the present study, we developed a direct simulation method with the effects of inhomogeneously acquired charges on the particle surface considered, which has been validated by the available analytical and experimental data. Modeling results reveal that the surface charge and zeta potential, which are acquired through chemical interactions, strongly depend on the local solution properties and the particle size. The surface charge and zeta potential of the particle would significantly vary with the tangential positions on the particle surface by increasing the particle radius. Moreover, regarding the streaming potential for a particle-fluid-tube system, our results uncover that the streaming potential has a reverse relation with the particle size in a micro or nanotube. To explain this phenomenon, we present a simple relation that bridges the streaming potential with the particle size and tube radius, zeta potential, bulk and surface conductivity. This relation could predict good results specifically for higher ion concentrations and provide deeper understanding of the particle size effects on the streaming potential measurements of the particle-fluid-tube system.

Publication: A. Alizadeh and M. Wang*. Electrophoresis 38: 580-595, 2017 (cover page)

Electrokinetic mechanism of wettability alternation at oil-water-rock interface

Abstract: Design of ions for injection water may change the wettability of oil-brine-rock (OBR) system, which has very important applications in enhanced oil recovery. Though ion-tuned wettability has been verified by various experiments, the mechanism is still not clear. In this review paper, we first present a comprehensive summarization of possible wettability alteration mechanisms, including fines migration or dissolution, multicomponent ion-exchange (MIE), electrical double layer (EDL) interaction between rock and oil, and repulsive hydration force. To clarify the key mechanism, we introduce a complete frame of theories to calculate attribution of EDL repulsion to wettability alteration by assuming constant binding forces (no MIE) and rigid smooth surface (no fines migration or dissolution). The frame consists of three parts: the classical Gouy-Chapman model coupled with interface charging mechanisms to describe EDL in oil-brine-rock systems, three methods with different boundary assumptions to evaluate EDL interaction energy, and the modified Young-Dupré equation to link EDL interaction energy with contact angle. The quantitative analysis for two typical oil-brine-rock systems provides two physical maps that show how the EDL interaction influences contact angle at different ionic composition. The result indicates that the contribution of EDL interaction to ion-tuned wettability for the studied system is not quite significant. The classical and advanced experimental work using microfabrication is reviewed briefly on the contribution of EDL repulsion to wettability alteration and compared with the theoretical results. It is indicated that the roughness of real rock surface may enhance EDL interaction. Finally we discuss some pending questions, perspectives and promising applications based on the mechanism.

Publication: H. Tian and M. Wang*. Surface Science Reports 72: 369-391, 2017 (cover page)

Phonon hydrodynamics and its applications in nanoscale heat transport

Abstract: Phonon hydrodynamics is an effective macroscopic method to study heat transport in dielectric solid and semiconductor. It has a clear and intuitive physical picture, transforming the abstract and ambiguous heat transport process into a concrete and evident process of phonon gas flow. Furthermore, with the aid of the abundant models and methods developed in classical hydrodynamics, phonon hydrodynamics becomes much easier to implement in comparison to the current popular approaches based on the first-principle method and kinetic theories involving complicated computations. Therefore, it is a promising tool for studying micro- and nanoscale heat transport in rapidly developing micro and nano science and technology. However, there still lacks a comprehensive account of the theoretical foundations, development and implementation of this approach. This work represents such an attempt in providing a full landscape, from physical fundamental and kinetic theory of phonons to phonon hydrodynamics in view of descriptions of phonon systems at microscopic, mesoscopic and macroscopic levels. Thus a systematical kinetic framework, summing up so far scattered theoretical models and methods in phonon hydrodynamics as individual cases, is established through a frame of a Chapman-Enskog solution to phonon Boltzmann equation. Then the basic tenets and procedures in implementing phonon hydrodynamics in nanoscale heat transport are presented through a review of its recent wide applications in modeling thermal transport properties of nanostructures. Finally, we discuss some pending questions and perspectives highlighted by a novel concept of generalized phonon hydrodynamics and possible applications in micro/nano phononics, which will shed more light on more profound understanding and credible applications of this new approach in micro- and nanoscale heat transport science.

Publication: Y.Y. Guo and M. Wang*. Physics Reports 595: 1-44, 2015 (cover page)

Predictions of effective physical properties of complex multiphase materials

Abstract: Theoretical prediction of effective properties for multiphase material systems is very important not only to analysis and optimization of material performance, but also to new material designs. This review first examines the issues, difficulties and challenges in prediction of material behaviors by summarizing and critiquing the existing major analytical approaches dealing with material property modeling. The focus then shifts to some recent advances in numerical methodology that are able to predict more accurately and efficiently the effective physical properties of multiphase materials with complex internal microstructures. A random generation-growth algorithm is highlighted for reproducing multiphase microstructures, statistically equivalent to the actual systems, based on the geometrical and morphological information obtained from measurements and experimental estimations. Then a high-efficiency lattice Boltzmann solver for the corresponding governing equations is described which, while assuring energy conservation and the appropriate continuities at numerous interfaces in a complex system, has demonstrated its numerical power in yielding accurate solutions. Various applications are provided to validate the feasibility, effectiveness and robustness of this new methodology by comparing the predictions with existing experimental data from different transport processes, accounting for the effects due to component size, material anisotropy, internal morphology and multiphase interactions. The examples given also suggest even wider potential applicability of this methodology to other problems as long as they are governed by the similar partial differential equation(s). Thus, for given system composition and structure, this numerical methodology is in essence a model built on sound physics principles with prior validity, without resorting to ad hoc empirical treatment. Therefore, it is useful for design and optimization of new materials, beyond just predicting and analyzing the existing ones.

Publication: M. Wang and N. Pan*. Materials Science and Engineering: R: Reports 63: 1-30, 2008 (cover page)