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  • 1
    Publication Date: 2018-12-06
    Description: The precipitation of calcium carbonate as a binding salt for the consolidation of loose sand formations is a promising approach. The heterogeneous nucleation and growth of calcite were investigated in supersaturated solutions. The ionic activities in the solutions tested were selected so that they included both supersaturations in which crystal growth took place only following the introduction of seed particles and supersaturations in which precipitation occurred spontaneously past the lapse of induction times. In the latter case the supersaturation conditions were sufficiently low to allow the measurement of induction times preceding the onset of precipitation. The stability domain of the calcium carbonate system was established at pH 8.50, 25 °C, measuring the induction times in the range between 30 min and 2 h. The rates of precipitation following the destabilization of the solutions were measured from the pH and/or concentration–time profiles. The induction times were inversely proportional and rates proportional to the solution supersaturation as expected. The high-order dependence of the rates of precipitation on the solution supersaturation suggested a polynuclear growth mechanism. Fitting of the induction time–supersaturation data according to this model yielded a value of 64 mJ/m2 for the surface energy of the calcite nucleus. In the concentration domain corresponding to stable supersaturated solutions, seeded growth experiments at constant supersaturation showed a second-order dependence on the rates of crystal growth of calcite seed crystals. Inoculation of the stable supersaturated solutions with quartz seed crystals failed to induce nucleation. Raising supersaturation to reach the unstable domain showed interesting features: calcite seed crystals yielded crystal growth kinetics compatible with the polynuclear growth model, without any induction time. The presence of quartz seed crystals reduced the induction times and resulted in nucleation in the bulk solution. The kinetic data in the latter case were consistent with the polynuclear growth model and the surface energy for the newly forming embryo was calculated equal to 31.1 mJ/m2, because of the dominantly heterogeneous nature of the process.
    Type: Article , PeerReviewed
    Format: text
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  • 2
    ISSN: 1573-1634
    Keywords: two-phase flow ; ganglion dynamics ; immiscible displacement ; relative permeability ; enhanced oil recovery
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A comparative experimental study of ‘steady-state’ two-phase flow in two types of model porous media is made to determine the effects of nonplanarity on the flow mechanisms and the mesoscopic flow behavior. The two model porous media have virtually the same pore geometry, but one has a planar network skeleton, whereas the other has a nonplanar (two-layer) skeleton. The latter is a new type of model porous medium that permits detailed visual observation and quantitative measurements without sacrificing the 3D character of the pore network topology. The capillary number and the flowrate ratio are changed systematically, whereas the viscosity ratio and the wettability (contact angle) are kept constant. Conventional relative permeabilities are determined and correlated with the porescale flow phenomena. In the range of parameter values investigated, the flow mechanism observed was ganglion dynamics (intrinsically unsteady, but giving a time-averaged steady-state). The nonplanarity is shown to have small qualitative but significant quantitative effects. In the nonplanar porous medium, the ganglion size distribution is wider, the mean ganglion size larger, and the stranded ganglia are fewer than those in the planar one, under the same flow conditions.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-1634
    Keywords: two-phase flow ; relative permeabilities ; ganglion dynamics ; viscous coupling ; coupling indices
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A parametric experimental investigation of the coupling effects during steady-state two-phase flow in porous media was carried out using a large model pore network of the chamber-and-throat type, etched in glass. The wetting phase saturation,S 1, the capillary number,Ca, and the viscosity ratio,k, were changed systematically, whereas the wettability (contact angleθ e ), the coalescence factorCo, and the geometrical and topological parameters were kept constant. The fluid flow rate and the pressure drop were measured independently for each fluid. During each experiment, the pore-scale flow mechanisms were observed and videorecorded, and the mean water saturation was determined with image analysis. Conventional relative permeability, as well as generalized relative permeability coefficients (with the viscous coupling terms taken explicitly into account) were determined with a new method that is based on a B-spline functional representation combined with standard constrained optimization techniques. A simple relationship between the conventional relative permeabilities and the generalized relative permeability coefficients is established based on several experimental sets. The viscous coupling (off-diagonal) coefficients are found to be comparable in magnitude to the direct (diagonal) coefficients over board ranges of the flow parameter values. The off-diagonal coefficients (k rij /Μ j ) are found to be unequal, and this is explained by the fact that, in the class of flows under consideration, microscopic reversibility does not hold and thus the Onsager-Casimir reciprocal relation does not apply. Thecoupling indices are introduced here; they are defined so that the magnitude of each coupling index is the measure of the contribution of the coupling effects to the flow rate of the corresponding fluid. A correlation of the coupling indices with the underlying flow mechanisms and the pertinent flow parameters is established.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-1634
    Keywords: two-phase flow ; ganglion dynamics ; relative permeability ; population balance equations ; oil recovery ; soil remediation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Recent experimental work has shown that the pore-scale flow mechanism during steady-state two-phase flow in porous media is ganglion dynamics (GD) over a broad and practically significant range of the system parameters. This observation suggests that our conception and theoretical treatment of fractional flow in porous media need careful reconsideration. Here is proposed a mechanistic model of steady-state two-phase flow in those cases where the dominant flow regime is ganglion dynamics. The approach is based on the ganglion population balance equations in combination with a microflow network simulator. The fundamental information on the cooperative flow behavior of the two fluids at the scale of a few hundred pores is expressed through the system factors, which are functions of the system parameters and are calculated using the simulator. These system factors are utilized by the population balance equations to predict the macroscopic behavior of the process. The dependence of the conventional relative permeability coefficients not only on the wetting fluid saturation Swbut also on the capillary number, Ca, the viscosity ratio κ the wettability (θ0 a, θ0 r), the coalescence factor, Co, as well as the porous medium geometry and topology is explained and predicted on a mechanistic basis. Sample calculations have been performed for steady-state fully developed (SSFD) and steady-state nonfully developed (SSnonFD) flow conditions. The number distributions of the moving and the stranded ganglia, the mean ganglion size, the fraction of the nonwetting fluid in the form of mobile ganglia, the ratio of the conventional relative permeability coefficients and the fractional flows are studied as functions of the system parameters and are correlated with the flow phenomena at pore level and the system factors.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 19 (1973), S. 58-67 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new model for porous media comprised of monosized, or nearly monosized grains, is developed. In applying this model to a packed bed, the bed is assumed to consist of a series of statistically identical unit bed elements each of which in turn consists of a number of unit cells connected in parallel. Each unit cell resembles a piece of constricted tube with dimensions which are random variables. The problem of flow through each unit cell is reduced, subject to reasonable assumptions, to the determination of the flow in an infinitely long periodically constricted tube. The solution of this flow problem is given in a companion publication. This model, together with the solution of the flow through it, can be used for the modeling of processes which take place in the void space of a bed.As a preliminary test, theoretical friction factor values, based on the proposed model, were compared with experimental ones for two different beds and found to be in good agreement even in the region of high Reynolds numbers where the nonlinear inertia terms are significant.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 19 (1973), S. 1036-1039 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A collocation solution of creeping Newtonian flow through periodically constricted tubes is obtained. The profile of the wall of the type of tube considered is piecewise continuous, composed of symmetric parabolic segments. A transformation of the domain of interest into a rectangular one is obtained, which allows satisfaction of all boundary conditions. The collocation solution gives the stream function in terms of the new independent variables and can easily be converted to the original cylindrical coordinates. Axial and radial velocity components are obtained in analytical form, and the pressure drop is calculated from a volume integration of the viscous dissipation function as well as from line integration of the Navier-Stokes equation. The results are compared with the finite-difference solution by Payatakes et al. (1973b) and are found in good agreement. Differences between the two solutions are attributed mainly to discretization error in the finite-difference solution. The analytical expressions obtained from the collocation solution can be used together with porous media models of the constricted unit cell type for the modeling of processes taking place in granular porous media.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The problem of immiscible displacement of oil ganglia arises in connection with oil bank formation and attrition during enhanced oil recovery with flooding. A stochastic simulation method is developed here, which enables prediction of the fate of solitary ganglia during immiscible displacement in water-wet unconsolidated granular porous media. This method takes into account the local topology of the porous medium; the initial size, shape and orientation of the oil ganglion and the capillary number. For each ganglion size, hundreds of realizations are performed with random ganglion shapes for a 100 × 200 sandpack. These results are averaged to obtain probabilities of mobilization, breakup and stranding as functions of capillary number and ganglion size. Axial and lateral dispersion coefficients are obtained as functions of the average ganglion velocity. The results from the solitary ganglion analysis can be used with the ganglion population balance equations developed in a companion publication (Payatakes, Ng and Flumerfelt, 1980) to study the dynamics of oil bank formation.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 26 (1980), S. 430-443 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A model is formulated in order to study the transient behavior of oil ganglion populations during immiscible displacement in oil recovery processes. The model is composed of three components: a suitable model for granular porous media; a stochastic simulation method capable of predicting the expected fate (mobilization, breakup, stranding) of solitary oil ganglia moving through granular porous media; and two coupled ganglion population balance equations, one applying to moving ganglia and the other to stranded ones. The porous medium model consists of a regular network of randomly sized unit cells of the constricted tube type. Based on this model and a mobilization-breakup criterion, computer aided simulations provide probabilistic information concerning the fate of solitary oil ganglia. Such information is required in the ganglion population balance equations, the solution of which delineates the conditions under which oil bank formation suceeds or fails. Successful oil bank formation depends on the outcome of the competition between the process of oil ganglion deterioration through breakup and stranding on one hand and the process of oil ganglion collision and coalescence on the other. The parameters entering the system of population balances are initial ganglion number concentration, average ganglion velocity, ganglion dispersion coefficients, ganglion stranding coefficient, ganglion breakup coefficient and probability of coalescence given a collision. These parameters are, in turn, functions of the porous medium geometry, capillary number, ganglion size distribution, flood velocity, oil saturation and flood composition.
    Additional Material: 11 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 1122-1134 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The problem of mass transfer from a Newtonian fluid to a swarm of spheroidal adsorbers under creeping flow conditions is considered using the spheroid-in-cell model to represent the swarm. The flow field within the fluid envelope for the Kuwabara type of boundary conditions is obtained form the analytical solution of Dassios et al. (1994). The complete convective diffusion equation is used to describe mass transport within the envelope so that moderate and strong diffusional terms can be taken into account. A new set of boundary conditions is used that respects mass flux and concentration continuity across the outer surface of the cell and maximizes the applicability of the spheroid-in-cell model in the convection-to-diffusion transition regime. The resulting elliptic problem in two dimensions is solved numerically. Results for the upstream and downstream concentration profiles reveal that tangential diffusion is very significant and should not be neglected for moderate and low Peclet number values. Also, the classical Levich-type of formulation, which is theoretically valid for very weak diffusional terms only, can in practice be modified to predict with fair accuracy the overall Sherwood number and the adsorption efficiency of prolate and oblate spheroids-in-cell even in moderate Peclet number cases.
    Additional Material: 13 Ill.
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