Papers by S. Hassanizadeh
Current theories of multiphase flow rely on capillary pressure and saturation relationships that ... more Current theories of multiphase flow rely on capillary pressure and saturation relationships that are commonly measured under static conditions. Recently, new multiphase flow theories have been proposed that include a new capillary pressure-saturation relationship that is valid under dynamic conditions. In this relationship, the difference between the two fluid pressures is called dynamic capillary pressure, and is assumed to be a function of the saturation and its time rate of change: Pc,dyn = Pn - Pw = Pc,stat - L dS/dt The dynamic effect is governed by the coefficient L that, in general, may be a function of saturation. In this work, we test this relationship using a pore-scale network model. Our model consists of a three-dimensional network of tubes (pore throats) connected to each other by pore bodies. Both pore bodies and pore throats are assumed to have square cross sections. We perform numerical experiments wherein both static and dynamic procedures for measurements of capillary pressure-saturation curves are simulated. We show that the dynamic correction term may indeed be important when large pressure gradient are imposed on the fluids. We determine the value of the coefficient L and investigate its dependence on soil and fluids properties.
Traditional and Modern Modeling Approaches, 2012
Numerical Methods in Geotechnical Engineering, 2014
Quantitative Microbiology
Experiments with batch suspensions, recirculating columns and¯ow-through columns have been carrie... more Experiments with batch suspensions, recirculating columns and¯ow-through columns have been carried out involving a sandy soil and ®ve bacteriophages: MS2, PRD1, fX174, Qb and PM2. In batch and recirculating column experiments, attachment and detachment rate coef®cients were determined by ®tting a twoparameter (attachment and detachment) model. In general, attachment and detachment rate coef®cients were not found to be signi®cantly different between the two kinds of experiments. There was one exception, however: MS2 appeared to detach faster in the presence of strong advective¯ow. In the case of¯ow-through column experiments, it is shown that a two-site model, with adsorption to equilibrium and kinetic sites, ®ts the breakthrough curves of all the phages, except PM2, satisfactorily. A one-site kinetic model was found to be appropriate for phage PM2. A small proportion of bacteriophages MS2, PRD1, and Qb adsorbed to equilibrium sites, whereas a large proportion of fX174 adsorbed to equilibrium sites. Such a distinction between adsorption to equilibrium and kinetic sites cannot be made in the case of batch or recirculating column experiments. Kinetic attachment rate coef®cients were found to be signi®cantly higher for the bacteriophages with presumably stronger negative charge. This may be ascribed to the presence of multivalent cations. Under these conditions, bacteriophage fX174 appears to behave more conservatively than more negatively charged viruses, and may then be a better choice as a relatively conservative tracer for virus transport through the subsurface.
In order to investigate the significance of incorporating interfacial area as a separate variable... more In order to investigate the significance of incorporating interfacial area as a separate variable in the governing equations of two-phase flow, an experimental setup was constructed to study and visualize two-phase flow in a micro-model under quasi-static and dynamic conditions. In this setup, a combination of lenses, three beam splitters and four cameras were used to visualize flow in a two-dimensional micro-model. PDMS micro-models with 2000, 3000 and 6000 pore bodies and 6000, 9000 and 20000 throats respectively, were used. The mean pore size of the flow-network varied between 40 μm, 50 μm and 70 μm. The mean depth of the micro-models was kept close to their mean pore size. The size of the flow network was 5 mm x 35 mm in all micro-models. With the use of four identical cameras equipped with CCD sensors, visualization of the distribution of phases in the micro-models took place. The effective area that has been visualized was 5 mm x 30 mm. Given the overall size and the pixel siz...
The main objective of this research is to gain a better understanding of the relation between por... more The main objective of this research is to gain a better understanding of the relation between porosity-permeability evolution at the local scale and its manifestation at larger (REV) scales. Continuum pore space changes during the progress of chemical reactions in porous media. Such phenomena takes place in reservoir rock in which CO2 is to be stored. In the present approach, the microscopic pore space is modeled using a Multi-Directional Pore Network (MDPN), which allows for a distribution of pore coordination number ranging between one and 26. This topological property, together with geometrical distributions of pore sizes are used to mimic the microstructure of real porous media at the REV scale. In order to simulate transport of multi-component chemical species, mass balance equations are solved within each element of the network (i.e., pore body and pore throat). We have considered both advective and diffusive transport processes within the pore spaces and have used a Reaction ...
Coupled Phenomena in Environmental Geotechnics, 2013
International Journal of Multiphase Flow, 1989
Springer Proceedings in Physics, 2005
ABSTRACT Recent theories indicate that capillary pressure is perhaps not only a function of satur... more ABSTRACT Recent theories indicate that capillary pressure is perhaps not only a function of saturation but may also depend on the time rate of change of saturation. This is known as the dynamic or non-equilibrium effect. There is compelling experimental evidence reported in the literature that the non-equilibrium effect is observable, quantifiable, and significant. However, almost all reported experiments relate to unsaturated systems. In this work, we report on a recent series of experiments involving water and PCE. Quasi-static as well as dynamic capillary pressure curves for primary drainage, main drainage, and main imbibition, are measured. The data are used to estimate the non-equilibrium capillary pressure coefficient. Finally, a continuum-scale two-phase flow model has been employed to simulate the experiments. Variations of average pressures and average water saturation with time are calculated and compared with measured curves. It is found that the displacement process takes place much faster in simulations than in experiments. This is believed to be due to presence of dynamic effects not captured with the numerical model.
Lab on a Chip, 2014
In the study of non-equilibrium heat transfer in multiphase flow in porous media, parameters and ... more In the study of non-equilibrium heat transfer in multiphase flow in porous media, parameters and constitutive relations, like heat transfer coefficients between phases, are unknown. In order to study the temperature development of a relatively hot invading immiscible non-wetting fluid and, ultimately, approximate heat transfer coefficients, a transparent micro-model is used as an artificial porous medium. In the last few decades, micro-models have become popular experimental tools for two-phase flow studies. In this work, the design of an innovative, elongated, PDMS (polydimethylsiloxane) micro-model with dimensions of 14.4 Ă— 39 mm(2) and a constant depth of 100 microns is described. A novel setup for simultaneous thermal and optical imaging of flow through the micro-model is presented. This is the first time that a closed flow cell like a micro-model is used in simultaneous thermal and optical flow imaging. The micro-model is visualized by a novel setup that allowed us to monitor and record the distribution of fluids throughout the length of the micro-model continuously and also record the thermal signature of the fluids. Dynamic drainage and imbibition experiments were conducted in order to obtain information about the heat exchange between the phases. In this paper the setup as well as analysis and qualitative results are presented.
Water Resources Research, 2014
ABSTRACT The goal of this research was to investigate the difference in behavior of hydrophilic a... more ABSTRACT The goal of this research was to investigate the difference in behavior of hydrophilic and hydrophobic colloids during transport in two-phase flow, in general, and their attachment and remobilization characters, in particular. Experiments were performed in a hydrophobic Polydimethylsiloxane (PDMS) micro-model. Water and fluorinert-FC43 were used as the two immiscible liquids. Given the fact that PDMS is a hydrophobic material, fluorinert was the wetting phase and water was the non-wetting phase in this micro-model. As model colloids, we used hydrophilic polystyrene carboxylate-modified microspheres (dispersible in water) and hydrophobic fluorous-modified silica microspheres (dispersible in fluorinert) in separate experiments. Using a confocal laser scanning microscope, we directly observed fluid distribution and colloid movement within pores of the micro-model. We also obtained concentration breakthrough curves by measuring the fluorescent intensities in the outlet of the micro-model.The breakthrough curves during steady-state flow showed that the colloid attachment rate is inversely related to the background saturation of the fluid in which the colloids were dispersed. Our visualization results showed that the enhanced attachment of hydrophilic colloids at lower water saturations was due to the retention at the fluorinert-water interface and fluorinert-water-solid contact lines. This effect was observed to be much less in the case of hydrophobic colloids (dispersed in fluorinert). In order to explain the colloids behavior, we calculated interaction potential energies of colloids with PDMS surfaces, fluid-fluid interfaces, and fluid-fluid-solid contact lines. Also, balance of forces that control colloid, including DLVO, hydrodynamic, and surface tension forces, were determined. Our calculations showed that there is a stronger repulsive energy barrier between hydrophobic colloids and fluorinert-water interface and solid-fluid interface, compared with the hydrophilic colloids. Moreover, hydrophobic colloids were seen to aggregate due to strong attractive forces among them. These aggregates had even less tendency to attach to various interfaces, due to an increase in the corresponding energy barrier. For the colloid retention at fluid-fluid-solid contact lines, we found that the role of DLVO interactions was less important than capillary forces.During transient events, we found that attached colloids become remobilized. The colloids deposited on the solid-fluid interface were detached by the moving fluid-fluid-solid contact lines. But, this happened only when the liquid containing colloids was being displaced by the other liquid. We simulated breakthrough curves using a model based on a coupled system of equations for two-phase flow, advection-dispersion of colloids, adsorption to and desorption from fluid-fluid interfaces and fluid-solid interfaces. Very good agreements were obtained among measured breakthrough curves, visualization results, and numerical modeling.
ABSTRACT Several experiments have evidenced the occurrence of saturation overshoots for flows in ... more ABSTRACT Several experiments have evidenced the occurrence of saturation overshoots for flows in homogeneous porous media. Such phenomena are ruled out by standard mathematical models, which are based on equilibrium assumptions. In this presentation we discuss nonequilibrium models, in particular including dynamic effects in the capillary pressure. This leads to extensions of the classical Buckley-Leverett (BL) equation, a commonly accepted model for two-phase flow in porous media. For this extended equation we investigate the existence of traveling wave solutions. Based on this we explain the occurrence of saturation overshoots, and discuss the profiles obtained for one phase or two phase flow models.
Water Resources Research, 2014
Recent computational studies of two-phase flow suggest that the role of fluid-fluid interfaces sh... more Recent computational studies of two-phase flow suggest that the role of fluid-fluid interfaces should be explicitly included in the capillarity equation as well as equations of motion of phases. The aim of this study has been to perform experiments where transient movement of interfaces can be monitored and to determine interfacial variables and quantities under transient conditions. We have performed two-phase flow experiments in a transparent micromodel. Specific interfacial area is defined, and calculated from experimental data, as the ratio of the total area of interfaces between two phases per unit volume of the porous medium. Recent studies have shown that all drainage and imbibition data points for capillary pressure, saturation, and specific interfacial area fall on a unique surface. But, up to now, almost all micromodel studies of two-phase flow have dealt with quasi-static or steady state flow conditions. Thus, only equilibrium properties have been studied. We present the first study of two-phase flow in an elongated PDMS micromodel under transient conditions with high temporal and spatial resolutions. We have established that different relationships between capillary pressure, saturation, and specific interfacial area are obtained under steady state and transient conditions. The difference between the surfaces depends on the capillary number. Furthermore, we use our experimental results to obtain average (macroscale) velocity of fluid-fluid interfaces and the rate of change of specific interfacial area as a function of time and space. Both terms depend on saturation nonlinearly but show a linear dependence on the rate of change of saturation. We also determine macroscale material coefficients that appear in the equation of motion of fluid-fluid interfaces. This is the first time that these parameters are determined experimentally.
International Journal of Multiphase Flow, 2011
We have developed a Dynamic Pore-network model for Simulating Two-phase flow in porous media (DYP... more We have developed a Dynamic Pore-network model for Simulating Two-phase flow in porous media (DYPOSIT). The model is applicable to both drainage and imbibition processes. Employing improved numerical and geometrical features in the model facilitate a physically-based pore-scale simulator. This computational tool is employed to perform several numerical experiments (primary and main drainage, main imbibition) to investigate the current capillarity theory. Traditional two-phase flow formulations state that the pressure difference between the two phase is equal to the capillary pressure, which is assumed to be a function of saturation only. Many theoretical and experimental studies have shown that this assumption is invalid and the pressure difference between the two fluids is not only equal to the capillary pressure but is also related to the variation of saturation with time in the domain; this is referred to as the non-equilibrium capillarity effect. To date, non-equilibrium capillarity effect has been investigated mainly under drainage. In this study, we analyze the non-equilibrium capillarity theory under drainage and imbibition as a function of saturation, viscosity ratio, and effective viscosity. Other aspects of the dynamics of two-phase flow such as trapping and saturation profile are also studied.
Ima Journal of Applied Mathematics, 2012
Water Research, 2003
In a field study on the efficiency of dune recharge for drinking water production, bacteriophage ... more In a field study on the efficiency of dune recharge for drinking water production, bacteriophage MS2 was shown to be removed 8 log 10 by passage through the dune sand. The question of whether pathogenic viruses would be removed as much as MS2 was studied by comparing complete breakthrough curves of MS2 with those of the human viruses Coxsackievirus B4 (CB4) and Poliovirus 1 (PV1) in laboratory columns. The columns were designed to closely simulate the field conditions: same sand, water, porewater velocity and temperature. Employing a two-site kinetic model to simulate breakthrough curves, attachment/detachment to two types of kinetic sites as well as inactivation of free and attached viruses were evaluated. It was found that attachment to only one of the sites is of significance for determining overall removal. At field scale, removal of the less negatively charged PV1 was extrapolated to be about 30 times greater than that of MS2, but removal of CB4 would be only as much as that of MS2. Also, removal of spores of Clostridium perfringens D10, a potential surrogate for Cryptosporidium oocysts, was studied. The attachment rate coefficient of the spores was 7.5 times greater than that of MS2. However, this does not imply that the removal of the spores is 7.5 times greater than that of MS2. Due to negligible inactivation in combination with detachment of previously attached spores, the actual removal rate of the spores depends on the duration of contamination and eventually all spores will break through. Provided no irreversible attachment or physical straining occurs, this may also be the case for other persistent microorganisms, like oocysts of Cryptosporidium. r
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Papers by S. Hassanizadeh