Martin B. Nemer

Sandia National Laboratories, Albuquerque, New Mexico, United States

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Publications (21)36.83 Total impact

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    ABSTRACT: A model system has been developed for enabling a multi-scale understanding of centrifugal-contactor liquid-liquid extraction. The system consisted of Nd(III) + xylenol orange in the aqueous phase buffered to pH = 5.5 by KHP, and dodecane + thenoyltrifluroroacetone (HTTA) + tributyphosphate (TBP) in the organic phase. Diffusion constants were measured for neodymium in both the organic and aqueous phases, and the Nd(III) partition coefficients were measured at various HTTA and TBP concentrations. A microfluidic channel was used as a high-shear model environment to observe mass transfer on a droplet scale with xylenol orange as the aqueous-phase metal indicator; mass transfer rates were measured quantitatively in both diffusion and reaction limited regimes on the droplet scale. The microfluidic results were comparable to observations made for the same system in a laboratory scale liquid-liquid centrifugal contactor, indicating that single drop microfluidic experiments can provide information on mass-transfer in complicated flows and geometries. © 2014 American Institute of Chemical Engineers AIChE J, 2014
    AIChE Journal 08/2014; 60(8). DOI:10.1002/aic.14510 · 2.58 Impact Factor
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    ABSTRACT: Liquid droplets flowing through a rectangular microfluidic channel develop a vortical flow field due to the presence of shear forces from the surrounding fluid. In this paper, we present an experimental and computational study of droplet velocities and internal flow patterns in a rectangular pressure-driven flow for droplet diameters ranging from 0.1 to 2 times the channel height. Our study shows excellent agreement with asymptotic predictions of droplet and interfacial velocities for infinitesimally small droplets. As the droplet diameter nears the size of the channel height, the droplet velocity slows significantly, and the changing external flow field causes a qualitative change in the location of internal vortices. This behavior is relevant for future studies of mass transfer in microfluidic devices.
    Physics of Fluids 03/2014; 26:032105. DOI:10.1063/1.4867695 · 2.04 Impact Factor
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    ABSTRACT: A study on the axisymmetric near-contact motion of drops with tangentially mobile interfaces under the action of a body force in a quiescent fluid is described. A long-time asymptotic analysis is presented for small-deformation conditions. Under these conditions the drops are nearly spherical, except in the near-contact region, where a flattened thin film forms. According to our analysis, a hydrostatic dome does not form in the near-contact region at long times, in contrast to the assumption underlying all previous analyses of this problem. Instead, the shape of the film in the near-contact region results from the absence of tangential stresses acting on it. As a result, the long-time behaviour of the system is qualitatively different than previously predicted. According to the theory presented herein, the minimum film thickness (rim region) decays with time as \${h}_{m} \sim {t}^{- 4/ 5} \$, and the thickness at the centre of the film decays as \${h}_{0} \sim {t}^{- 3/ 5} \$, which is a faster decay than predicted by prior analyses based on a hydrostatic dome. Numerical thin-film simulations quantitatively confirm the predictions of our small-deformation theory. Boundary-integral simulations of the full two-drop problem suggest that the theory also describes qualitatively the long-time evolution under finite-deformation conditions.
    Journal of Fluid Mechanics 08/2013; 728. DOI:10.1017/jfm.2013.288 · 2.29 Impact Factor
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    ABSTRACT: Subsurface containment of CO2 requires an effective caprock seal. Many previous studies on seals have relied on macroscopic measurements of capillary breakthrough pressure and other petrophysical properties without direct examination of solid phases that line pore networks and contact fluids. However, pore-lining phases strongly contribute to sealing behavior through interfacial interactions among CO2, brine, and the mineral or non-mineral phases. We examined continental and marine mudstones using high resolution (i.e., sub-micron), direct observations of pore-lining phases and X-ray diffraction (XRD). Our results indicate that sealing efficiency (i.e., breakthrough pressure) is governed by pore shapes and pore-lining phases that are not identifiable except through direct characterization of pores. Bulk XRD data do not indicate which phases line the pores and may be especially lacking for mudstones with organic material. Organics can line pores and may represent once-mobile organics that modified wettability of an originally clay-lined pore network. For shallow formations (i.e., <800 m depth), interfacial tension and contact angles result in breakthrough pressures that may be as high as those needed to fracture the rock—thus, in the absence of fractures, high capillary sealing efficiency is indicated. Deeper seals have poorer capillary sealing if some reduction in water-wetting occurs, with an increase in pressure and temperature, on minerals and/or pore-lining organic phases.
    International Journal of Greenhouse Gas Control 11/2012; 11:204-220. DOI:10.1016/j.ijggc.2012.08.001 · 3.82 Impact Factor
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    ABSTRACT: Understanding interfacial mass transport on a droplet scale is essential for modeling liquid-liquid extraction processes. A model system is investigated whereby neodymium is extracted from buffered aqueous droplets to a continuous phase of dodecane, tributyl phosphate and thenoyltrifluoroacetone. A thin flow-focusing channel is used to generate monodisperse aqueous phase droplets of varying size, with drop diameter to channel height ratios ranging from 0.5 to 2. Liquid streamlines within the droplets are inferred by particle tracking, revealing a fountain flow recirculation pattern. Larger droplets that are more confined in the channel move with a slower velocity relative to the continuous fluid and have a stronger recirculation pattern in the plane of the microfluidic chip. Knowledge of the recirculation pattern is then applied to understand species mass transfer from the droplet fluid. Quantitative mass transfer measurements are obtained using high speed imagery and spectrophotometry for various flow rates and droplet sizes. This research is supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
    12 AIChE Annual Meeting; 10/2012
  • Jeremy B. Lechman, Martin B. Nemer, David R. Noble
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    ABSTRACT: Particle suspensions play an important role in many engineering applications, yet their behavior in a number of respects remains poorly understood. In conjunction with careful experiments, modeling and simulation of these systems can provide key insight into their complex behavior. However, these two‐phase systems pose the challenge of simultaneously, accurately, and efficiently capturing the complex geometric structure, kinematics, and dynamics of the particulate discrete phase and the discontinuities it introduces into the variables (e.g., velocity, pressure, density) of the continuous phase. To this end, a new conformal decomposition finite element method (CDFEM) is introduced for solid particles in a viscous fluid. The method is verified in several simple test problems that are representative of aspects of particle suspension behavior. In all cases, we find the CDFEM to perform accurately and efficiently leading to the conclusion that it forms a prime candidate for application to the full direct numerical simulation of particle suspensions. Copyright © 2012 John Wiley & Sons, Ltd.
    International Journal for Numerical Methods in Fluids 04/2012; 68(11):1409-1421. DOI:10.1002/fld.3638 · 1.33 Impact Factor
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    ABSTRACT: A thin flow-focusing microfluidic channel is evaluated for generating monodisperse liquid droplets. The microfluidic device is used in its native state, which is hydrophilic, or treated with OTS to make it hydrophobic. Having both hydrophilic and hydrophobic surfaces allows for creation of both oil-in-water and water-in-oil emulsions, facilitating a large parameter study of viscosity ratios (droplet fluid/continuous fluid) ranging from 0.05 to 96 and flow rate ratios (droplet fluid/continuous fluid) ranging from 0.01 to 2 in one geometry. The hydrophilic chip provides a partially-wetting surface (contact angle less than 90°) for the inner fluid. This surface, combined with the unusually thin channel height, promotes a flow regime where the inner fluid wets the top and bottom of the channel in the orifice and a stable jet is formed. Through confocal microscopy, this fluid stabilization is shown to be highly influenced by the contact angle of the liquids in the channel. Non-wetting jets undergo breakup and produce drops when the jet is comparable to or smaller than the channel thickness. In contrast, partially-wetting jets undergo breakup only when they are much smaller than the channel thickness. Drop sizes are found to scale with a modified capillary number based on the total flow rate regardless of wetting behavior.
    Lab on a Chip 03/2012; 12(8):1540-7. DOI:10.1039/c2lc21197a · 5.75 Impact Factor
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    ABSTRACT: Understanding interfacial mass transport on a droplet scale is essential for modeling liquid-liquid extraction processes. A thin flow-focusing microfluidic channel is evaluated for generating monodisperse liquid droplets for microscale mass transport studies. Surface treatment of the microfluidic device allows creation of both oil in water and water in oil emulsions, facilitating a large parameter study of viscosity and flow rate ratios. The unusually thin channel height promotes a flow regime where no droplets form. Through confocal microscopy, this regime is shown to be highly influenced by the contact angle of the liquids with the channel. Drop sizes are found to scale with a modified capillary number. Liquid streamlines within the droplets are inferred by high speed imagery of microparticles dispersed in the droplet phase. Finally, species mass transfer to the droplet fluid is quantitatively measured using high speed imaging.
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    ABSTRACT: Pure-iron end-member hibbingite, Fe2(OH)3Cl(s), may be important to geological repositories in salt formations, as it may be a dominant corrosion product of steel waste canisters in an anoxic environment in Na–Cl- and Na–Mg–Cl-dominated brines. In this study, the solubility of Fe2(OH)3Cl(s), the pure-iron end-member of hibbingite (FeII, Mg)2(OH)3Cl(s), and Fe(OH)2(s) in 0.04 m to 6 m NaCl brines has been determined. For the reactionFe2(OH)3Cl(s) + 3H+ ↔ 3 H2O + 2 Fe2+ + Cl−,the solubility constant of Fe2(OH)3Cl(s) at infinite dilution and 25 °C has been found to be log10K = 17.12 ± 0.15 (95% confidence interval using F statistics for 36 data points and 3 parameters). For the reactionFe(OH)2(s) + 2H+ ↔ 2 H2O + Fe2+,the solubility constant of Fe(OH)2 at infinite dilution and 25 °C has been found to be log10K = 12.95 ± 0.13 (95 % confidence interval using F statistics for 36 data points and 3 parameters). For the combined set of solubility data for Fe2(OH)3Cl(s) and Fe(OH)2(s), the Na+–Fe2+ pair Pitzer interaction parameter θNa+/Fe2+ has been found to be 0.08 ± 0.03 (95% confidence interval using F statistics for 36 data points and 3 parameters). In nearly saturated NaCl brine we observed evidence for the conversion of Fe(OH)2(s) to Fe2(OH)3Cl(s). Additionally, when Fe2(OH)3Cl(s) was added to sodium sulfate brines, the formation of green rust(II) sulfate was observed, along with the generation of hydrogen gas. The results presented here provide insight into understanding and modeling the geochemistry and performance assessment of nuclear waste repositories in salt formations.Research Highlights► log10 K of Fe2(OH)3Cl(s) = 17.12 ± 0.15. ► log10 K of Fe(OH)2(s) = 12.95 ± 0.13. ► θNa+/Fe2+ = 0.08 ± 0.03. ► GR(II)SO4(s) and hydrogen were generated when Fe2(OH)3Cl was added to Na2SO4 brine under anoxic conditions.
    Chemical Geology 01/2011; 280(1-2):26-32. DOI:10.1016/j.chemgeo.2010.10.003 · 3.48 Impact Factor
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    ABSTRACT: Magnesium oxide (MgO) is the only engineered barrier certified by the EPA for emplacement in the Waste Isolation Pilot Plant (WIPP), a U.S. Department of Energy repository for transuranic waste. MgO will reduce actinide solubilities by sequestering CO2 generated by the biodegradation of cellulosic, plastic, and rubber materials. Demonstration of the effectiveness of MgO is essential to meet the U.S Environmental Protection Agency's requirement for multiple natural and engineered barriers. In the past, a series of experiments was conducted at Sandia National Laboratories to verify the efficacy of Premier Chemicals LLC (Premier) MgO as a chemical-control agent in the WIPP. Since December 2004, Premier MgO is no longer available for emplacement in the WIPP. Martin Marietta Magnesia Specialties LLC is the new MgO supplier. MgO characterization, including chemical, mineralogic, and reactivity analysis, has been performed to address uncertainties concerning the amount of reactive constituents in Martin Marietta MgO. Characterization results of Premier MgO will be reported for comparison. Particle size, solid-to-liquid ratio, and stir speed could affect the rate of carbonation of MgO slurries. Thus, it's reasonable to hypothesize that these factors will also affect the rate of hydration. Accelerated MgO hydration experiments were carried out at two or three levels for each of the above factors in deionized water at 70 °C. The Minitab statistical software package was used to design a fractional-factorial experimental matrix and analyze the test results. We also fitted the accelerated inundated hydration data to four different kinetic models and calculated the hydration rates. As a result of this study we have determined that different mechanisms may be important for different particle sizes, surface control for large particles and diffusion for small particles.
    MRS Online Proceeding Library 01/2011; 1124. DOI:10.1557/PROC-1124-Q05-05
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    ABSTRACT: In this study, the solubility constant of magnesium chloride hydroxide hydrate, Mg3Cl(OH)5·4H2O, termed as phase 5, is determined from a series of solubility experiments in MgCl2–NaCl solutions. The solubility constant in logarithmic units at 25°C for the following reaction, Mg3Cl(OH)5·4H2O+5H+=3Mg2++9H2O(l)+Cl- is calculated as 43.21±0.33 (2σ) based on the specific interaction theory (SIT) model for extrapolation to infinite dilution. The Gibbs free energy and enthalpy of formation for phase 5 at 25°C are derived as −3384±2 (2σ) kJmol−1 and −3896±6 (2σ) kJmol−1, respectively.MgO (bulk, pure MgO corresponding to the mineral periclase) is the only engineered barrier certified by the Environmental Protection Agency (EPA) for emplacement in the Waste Isolation Pilot Plant (WIPP) in the US, and an Mg(OH)2-based engineered barrier (bulk, pure Mg(OH)2 corresponding to brucite) is to be employed in the Asse repository in Germany. Phase 5, and its similar phase, phase 3 (Mg2Cl(OH)3·4H2O), could have a significant role in influencing the geochemical conditions in geological repositories for nuclear waste in salt formations where MgO or brucite is employed as engineered barriers. Based on our solubility constant for phase 5 in combination with the literature value for phase 3, we predict that the composition for the invariant point of phase 5 and phase 3 would be mMg=1.70 and pmH=8.94 in the Mg–Cl binary system. The recent WIPP Compliance Recertification Application Performance Assessment Baseline Calculations indicate that phase 5, instead of phase 3, is indeed a stable phase when the WIPP Generic Weep Brine (GWB), a Na–Mg–Cl-dominated brine associated with the Salado Formation, equilibrates with actinide-source-term phases, brucite, magnesium carbonates, halite and anhydrite. Therefore, phase 5 is important to the WIPP, and potentially important to other repositories in salt formations.
    Geochimica et Cosmochimica Acta 08/2010; 74(16):4605-4611. DOI:10.1016/j.gca.2010.05.029 · 4.25 Impact Factor
  • M. B. Nemer, D. W. Powers, A. E. Ismail
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    ABSTRACT: Halite from the upper Permian Salado Formation of the Permian basin has been extensively studied over the last century. Few researchers, however, have looked at these units at the nano-scale. This is partially due to the difficulty of preparing soft-ionic-crystal samples for TEM studies, and because of the inherent artifacts created in the sectioning and imaging process. We have ultramicrotomed and imaged halite from the Salado in a 200kV TEM. An interesting find is the presence of a &ap; 30 nm transition zone of crystal surrounding some (but not all) fluid inclusions in primary halite (chevron crystal). The transition-zone crystal appears to be oriented differently than the bulk halite crystal away from the transition zone. The thickness of the transition zone does not seem to be sensitive to the dimensions of the inclusion which rules out pressure-temperature changes in solubility in such a small volume. The cause of these transition zones is unknown. Several interesting petrofabrics can also be seen in the primary halite. Fluid-inclusion-banded halite contains bands of very small (< 100 nm) fluid inclusions. Some inclusions appear to have trails of smaller drops, as if due to a drop-breakup event. This is curious because we don't expect breakup events in a primary crystal. A ``myrmekite'' like texture has been observed that contains a series of indentations and spurs along the bedding plane. A turbulent fabric has been observed which contains small eddy-like structures . At this time, we are not able to interpret these fabrics with confidence or determine which are real and which are artifacts. This work is considered preliminary and should not be cited, as some samples were not collected under the Waste Isolation Pilot Plant (WIPP) Quality Assurance (QA) program. This work will be repeated in the future with full WIPP QA.
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    ABSTRACT: Assessing the performance of the U. S. Department of Energy's Waste Isolation Pilot Plant (WIPP), a deep geologic repository for defense-related transuranic waste in southeastern New Mexico, requires a detailed understanding of the response of concentrated brines to both minerals found in the surrounding rock formation and man-made materials that are emplaced in the repository. The geochemistry model developed for the WIPP is based on the activity coefficient model of Kenneth Pitzer. Parameter sets are available for many of the chemical species in the repository, including both common brine constituents such as Na+, Mg2+, HCO3, SO42 and Cl, as well as radionuclides such as Am(III) and Th(IV). In some scenarios iron and lead could be available in significant quantities in the repository through their use in waste packaging materials. There is limited information available in the literature for Pb(II) and Fe(II) in the complex brines observed at the WIPP. In addition, because of the basic pH and the strongly reducing conditions expected in the repository, both Pb(II) and Fe(II) are expected to form complexes with inorganic ligands such as hydroxide and chloride, and organic ligands such as EDTA and oxalate. Consequently, we have undertaken an experimental and modeling effort to determine Pitzer parameters for the interactions of Pb(II) and Fe(II) complexes with other major species in the brine (Na+, Mg2+, Cl, HCO3, and SO42). Experimental measurement of Pb(II) and Fe(II) solubilities in relatively simple solutions are combined with a free-energy minimization scheme to determine the new Pitzer parameters for each pair of species studied. Subsequent validation testing will assess the influence of the new parameters for Pb(II) and Fe(II) complexes on the WIPP geochemical model. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000. This research is funded by WIPP programs administered by the Office of Environmental Management of the U.S Department of Energy.
    2009 AIChE Annual Meeting; 11/2009
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    ABSTRACT: The linear viscoelastic response of an ordered dense emulsion is explored by numerical simulation. At concentrations below maximum packing, the stress relaxation is dominated by a single time scale associated with lubrication, which diverges at maximum packing. For concentrations above maximum packing, the stress relaxation is dominated by fast time scales of the order of the drop relaxation time. A slow time scale appears but does not dominate.
    05/2007: pages 75-84;
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    ABSTRACT: From an analysis of tangent spherical drops in straining flow, Baldessari and Leal conclude that the drop-scale internal circulation, driven by the ambient flow, has a negligible influence on the drainage of the thin liquid film between drops under small-deformation conditions [F. Baldessari, L.G. Leal, J. Colloid Interface Sci. 289 (2005) 262]. However, their conclusion is incorrect as explained in this letter.
    Journal of Colloid and Interface Science 05/2007; 308(1):1-3. DOI:10.1016/j.jcis.2006.10.028 · 3.55 Impact Factor
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    ABSTRACT: We analyze axisymmetric near-contact motion of two drops under the action of an external force or imposed flow. It is shown that hydrodynamic stresses in the near-contact region that are associated with the outer (drop-scale) flow can qualitatively affect the drainage of the thin fluid film separating the drops. If this far-field stress acts radially inward, film drainage is arrested at long times; exponential film drainage occurs if this stress acts outward. An asymptotic analysis of the stationary long-time film profile is presented for small-deformation conditions, and the critical strength of van der Waals attraction for film rupture is calculated. The effect of an insoluble surfactant is also considered. Hindered and enhanced drop coalescence are not predicted by the current theories, because the influence of the outer flow on film drainage is ignored.
    Physical Review Letters 04/2004; 92(11):114501. DOI:10.1103/PhysRevLett.92.114501 · 7.73 Impact Factor
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    ABSTRACT: Drop coalescence is a complex process due to the nonlinear dynamics of a system with deformable interfaces. In earlier studies the effect of an external flow on near-contact motion of drops was assumed to be equivalent to an external body force. Accordingly, the direct coupling between thin-film flow (in the near-contact region) and flow inside the drops was neglected. These assumptions have been used in calculations of collisional efficiencies and analyses of experimental results. Our investigations show that for drops with tangentially mobile interfaces the above assumptions do not hold. The velocity field produced inside the drops by the external flow couples to the film motion through tangential stress f (infinity) acting on the film interface. For sufficiently thin films (e.g., long times), this stress qualitatively alters the dynamics of the lubrication region by arresting or enhancing film drainage.
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    ABSTRACT: At long times, a thin liquid film between two deformable drops forms a central dimpled region which is separated from an outer hydrostatic region by a narrow rim region where the film thickness is minimal. We present a long-time asymptotic analysis of this problem. Previous scaling analyses were based on the assumption that the dimple assumes a hydrostatic shape at long times. Matching of the hydrostatic dimple to the inner rim solution requires that the film thickness in the matching region varies linearly with the distance x from the minimal gap. However, our solution of the integro-differential equation describing the rim indicates that nonlocal contributions give rise to a film thickness that varies as x^1/2. The dimple shape is governed by another integro-differential equation that minimizes the stresses due to the flow inside the drops. Based on the new matching conditions, we find that the central gap decreases as t-3/5 and the minimum gap as t-4/5, in contrast to the results of earlier studies. Evidence from thin film numerical simulations supports our assertions.
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    ABSTRACT: Imported oil exacerabates our trade deficit and funds anti-American regimes. Nuclear Energy (NE) is a demonstrated technology with high efficiency. NE's two biggest political detriments are possible accidents and nuclear waste disposal. For NE policy, proliferation is the biggest obstacle. Nuclear waste can be reduced through reprocessing, where fuel rods are separated into various streams, some of which can be reused in reactors. Current process developed in the 1950s is dirty and expensive, U/Pu separation is the most critical. Fuel rods are sheared and dissolved in acid to extract fissile material in a centrifugal contactor. Plants have many contacts in series with other separations. We have taken a science and simulation-based approach to develop a modern reprocessing plant. Models of reprocessing plants are needed to support nuclear materials accountancy, nonproliferation, plant design, and plant scale-up.