Department of Applied Mechanics and Engineering Sciences

Premixed Turbulent Combustion

Investigator(s)	Libby, P.A.			$55,000
Phone	619-534-3168
E-mail	libby@ames.ucsd.edu

This project is primarily concerned with flames in stagnating turbulence. Such flames are rich in problems of fundamental interest, e.g., the extinction of turbulent flames under high rates of strain. As a consequence, there are five or six laboratories in Western Europe and several in the United States carrying out relevant experiments. Although our effort is primarily theoretical, we pay close attention to experimental results coming from these laboratories. In addition we have carried out and published in the proceedings of the Twenty-fifth Symposium (International) on Combustion the results of our own experiment on turbulent flames in impinging streams. Our principal focus during the past year has been on a Reynolds stress formulation for such flames. This configuration is the most widely studied experimentally but to date there has been no satisfactory theoretical treatment of them. Although totally convincing solutions have not to date been obtained, several important findings have resulted from this effort. In particular we have shown that the calculated mean axial velocity is in excellent agreement with data despite highly inaccurate predictions for the Reynolds stresses. The implications are that the mean velocities are determined by the mean pressure and that the Reynolds stresses are to be calculated in a known mean velocity field. In addition we have found that the models for pressure-rate-of-strain effects derived for constant density flows must be altered to account for the variations of density associated with heat release. This effort is continuing. During the past contract year we have published three journal articles related to analyses of highly idealized flames in a channel, of laminar Couette flow involving premixed combustion and of the extinction of premixed turbulent flames under nonisenthalpic conditions.

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Department of Chemical Engineering and Petroleum Refining

Composition of Dependence of Fluid Thermophysical Properties Theory and Modeling

Investigator(s)	Ely, J.F.			$116,500
Phone	303-273-3885
E-mail	jely@mines.edu

The objective of this research is to develop high accuracy predictive models that describe the physical property behavior of complex mixtures. The work is currently progressing along three fronts: (1) development of improved corresponding states models for asymmetric mixtures through reference fluid equation of state design and improved mixing rules; (2) investigation of the phenomenological behavior of the viscosity of molecular (e.g., structured) mixtures through nonequilibrium computer simulation techniques; and (3) development of ultrahigh accuracy equations of state for complex fluids and fluid mixtures through the use of stepwise regression and simulated annealing optimization. The ultimate goal of this research is to develop improved computer-based models for process design that provide accurate predictions of phase transitions and bulk-phase properties in systems that have large size and/or polarity differences. Current work is focused on non-equilibrium simulations of large structured molecules and their mixtures. The ultimate goal of this part of the study is to develop improved predictive models for the viscosity of high molecular weight fluids.

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Department of Chemical Engineering

Study of Improved Methods for Predicting Chemical Equilibria

Investigator(s)	Lenz, T.G.			$90,000
Phone	970-491-5252
E-mail	lenz@lance.colostate.edu

The primary goal of this project is to develop an accurate, yet inexpensive, molecular-based computational model for predicting thermodynamic properties of nontrivial molecules. Accomplishments to date have included accurate prediction of chemical equilibria for a wide range of hydrocarbons as well as very accurate prediction of the heat capacities for heteroatomic alternative refrigerants. Software developed within this project has been provided to the Quantum Chemistry Program Exchange, and is available as programs QCPE593 and QCMP145. The computational model within these programs is based on molecular mechanics. A consistent force field is the heart of this molecular mechanics program (QCFF), and substantial effort has been devoted to parameterization of this force field. Several experimental studies have been undertaken within this project to provide structural information for the force field parameterization. The most recent experimental studies have dealt with lactic acid. This work has involved isolation and characterization of the d and l enantiomers of lactic acid, as well as the racemic mixture of this molecule. The structure of l-lactic acid has been obtained using single-crystal x-ray crystallography, and a similar study for the racemic material is currently in progress.

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School of Chemical Engineering

Simulation of Fluid Behavior in Well-Characterized Porous Materials

Investigator(s)	Gubbins, K.E.			$227,000
Phone	607-255-4385
E-mail	KEG@CHEME.CORNELL.EDU

This work is developing new and rigorous theoretical and simulation methods for the study of the adsorption behavior of fluids in well-characterized porous materials. In particular, fluids in porous carbons, aluminosilicates (particularly MCM-41), aluminophosphates, and buckytubes are being studied. Simulations of carbon dioxide/methane and nitrogen/methane mixtures in zeolites have been carried out, and are being compared with experimental data; in both of these mixtures inversion of selectivity has been found in certain materials. Both selective adsorption and melting/freezing studies have been made for a range of gases adsorbed in buckytubes and MCM-41. Both increases and decreases of melting temperature have been observed, depending on the material and conditions. Studies of the adsorption and filling behavior of water and water/hydrocarbon mixtures in activated carbons are being carried out. The Presence of active chemical sites on the carbon surface has been shown to give rise to a completely different pore filling mechanism from that for simple fluids, and to lead to continuous filling as opposed to the capillary condensation observed for more simple systems.

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School of Chemical Engineering

Molecular Simulation of Phase Equilibria for Complex Fluids

Investigator(s)	Panagiotopoulos, A.Z.			$132,000
Phone	607-255-8243
E-mail	azp2@cornell.edu

The objective of this project is the investigation of phase equilibria for complex fluids using molecular simulation techniques. The long-range goal is development of improved modeling techniques for rational design of efficient industrial chemical processes. Current research encompasses three main classes of systems, namely polymeric, surfactant, and ionic systems. A major methodological development during the past year has been the introduction of histogram reweighting Monte Carlo sampling methods. The methods allow significantly more accurate determination of phase coexistence properties than previously available techniques. They also can be used to locate critical points for strongly interacting fluids with high precision. We are presently applying these methods to polar and polarizable fluids, primitive electrolyte models, and lattice models for surfactants and polymers. For surfactant systems, the methods allow determination of aggregation properties in addition to transitions between structured phases. A related method, Hamiltonian-Scaling Gibbs ensemble Monte Carlo, has been developed to allow determination of properties for a series of related models from a single simulation.

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Department of Mechanical and Aerospace Engineering

Reaction and Diffusion in Turbulent Combustion

Investigator(s)	Pope, S.B.			$101,000
Phone	607-255-4314
E-mail	pope@mae.cornell.edu

Fundamental processes in non-premixed turbulent combustion are being studied using direct numerical simulations (DNS). Previously, we have performed studies (on grids up to 128³) of reactions in homogeneous turbulence, over a broad range of Damkohler numbers and reaction-zone thicknesses. In the last year, three aspects of the project have come to fruition. First, the DNS code has been implemented to run in parallel on the IBM SP2. This allows grid sizes up to at least 256³, and hence a wider parameter range. Second, we have completed a comprehensive and fundamental study of the mixing of two passive scalars. This study extends in a significant way an earlier study of the mixing of a single scalar which, for the last decade, has served as a standard test case. Third, as a prelude to studying reaction in inhomogeneous turbulence, we have completed a study of the mixing of a passive scalar with an imposed mean gradient. In progress is work on reactive scalar mixing layers, and periodic reaction zones. These studies are providing essential information for the construction and testing of models of turbulent combustion that are applicable to practical devices.

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Department of Chemical Engineering

New Generation of Group Contribution and Equation-of-State Models

Investigator(s)	Sandler, S.I.			$114,000
Phone	302-831-2945
E-mail	SANDLER@che.UDEL.EDU

To make intelligent, cost-effective decisions for the design of new chemical processes, for the development of synthetic fuels and other new technologies, and for estimating the environmental fate and bioaccumulation of chemicals, accurate methods of predicting and correlating thermodynamic properties and phase equilibria are needed. The research being conducted under this grant addresses this problem from three different directions. First, the Wong-Sandler mixing rules, which have greatly expanded the range of application of equations of state to highly nonideal mixtures, are being further developed to apply to collections of mixtures that previously could not be accurately described over large ranges of temperature and pressure. This includes hydrogen-containing mixtures and mixtures with strongly polar compounds. The second area of research is the use of ab initio molecular orbital calculations to compute the effect of hydrogen-bonding and other strong association phenomena. The results of these calculations have been incorporated into equations of state to reduce the number of adjustable parameters that must be used. Following completion of the EOS work, the quantum mechanically-derived information will be used in the development of a new generation of group contribution methods (such as UNIFAC) to improve the accuracy of these important prediction methods. We have also been using computer simulation and statistical mechanical theory to develop an accurate thermodynamic description of long chain hydrocarbons, polymers, and mixtures involving these components.

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Department of Chemical Engineering

Computer Simulation of Osmosis and Reverse Osmosis in Solutions.

Investigator(s)	Murad, S.			$85,000 (15 months)
Phone	312-996-5593
E-mail	MURAD@UIC.EDU

Computer simulation studies are being carried out to study the phenomena of osmosis and reverse osmosis in solutions. These studies have been carried out using both a molecular dynamics method recently developed by us, as well as a modified Gibbs ensemble Monte-Carlo (GEMC) method. Both gas mixtures and liquid (including aqueous) solutions are being investigated, since reverse osmosis is considered an attractive technique for separations in these systems. Our results show that computer simulations could prove to be a useful tool for determining the feasibility of reverse osmosis as a possible technique for many industrial separations problems. Our studies on aqueous electrolyte solutions have also suggested a new mechanism for reverse osmosis separations of salts from aqueous solutions. It was previously thought that ions are prevented from crossing the semi-permeable membrane, despite their smaller size (compared to water), because of surface interactions between the membrane and the ions. Our work seems to suggest that water molecules strongly cluster around the ions, thus effectively increasing their size and preventing them from permeating the semi-permeable membrane. We are also studying the phenomenon of electro-osmosis at the molecular level using the method of molecular dynamics in an effort to better understand it. This will ultimately allow separations carried out using these techniques, to be carried out more efficiently.

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Department of Chemical Engineering

Prediction of Thermodynamic Properties of Complex Molecules

Investigator(s)	Donohue, M.D.			$89,000
Phone	410-516-7761
E-mail	donohue@jhu.edu

The goal of this research program is to improve our understanding of the factors that cause deviations from ideal behavior in complex fluids (i.e. molecules whose size, shape, or interaction energy cause them to behave differently from spherical, non-polar molecules). We are particularly interested in understanding the properties of mixtures of such molecules. Our program includes a combination of theory, molecular simulations, and experiments. In the past, most of our work was concerned with developing equations of state for spherical molecules and molecules that can be considered strings or chains of spherical molecules. Being able to predict the properties of such molecules is important because most organic molecules are chain molecules. While we have continued to work in this area, our work has broadened considerably. In particular, we have put considerable effort into understanding how small molecules interact with polymers and how small molecules interact with surfaces. We also have tried to develop a much deeper understanding of how macroscopic properties depend on the detail of molecular packing and geometry. For example, a 2-D hexagonal lattice has the same coordination number as a 3-D cubic lattice, but they have different energies. We have developed a new theory that can predict the energetic differences as a function of both coordination number and lattice structure. Future work will be directed at generalizing this theory to polymer solutions.

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Institute for Physical Science and Technology

Thermophysical Properties of Fluids and Fluid Mixtures

Investigator(s)	Sengers, J.V.			$135,000
Phone	301-405-4805
E-mail	js45@umail.umd.edu

Critical fluctuations affect the thermodynamic and transport properties of fluids and fluid mixtures in a wide range of temperatures and densities. Equations that incorporate the effects of these critical fluctuations on the thermodynamic and transport properties are being developed. Specifically, we are investigating the crossover from Ising-like to mean-field critical behavior in fluids and fluid mixtures including ionic systems. We are developing and applying a general isomorphism approach to describe thermodynamic properties of mixtures with complex phase diagrams. We are in the process of extending the theory to high-temperature aqueous salt solutions. We are also developing equations for the transport properties of mixtures like carbon-dioxide+ethane and methane+ethane by extending the mode-coupling theory to include the nonasymptotic critical behavior of the transport properties.

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Department of Chemical Engineering

Theoretical Studies of Solid--Fluid Phase Equilibria

Investigator(s)	Monson, P.A.			$96,000
Phone	413-545-0661
E-mail	monson@ecs.umass.edu

In this project statistical thermodynamics is applied to the calculation of solid-fluid phase equilibrium. In our recent work a study of solid-fluid equilibrium for flexible chain molecules has been initiated. A method for calculating the free energy in Monte Carlo simulations of chain molecules in the solid phase has been developed. This method has been used to calculate the solid-fluid phase diagrams of freely jointed chains of tangent hard spheres. The methodology is being extended to the case of chains with bond angle constraints and torsional intramolecular potentials. The results of this work will be used to analyze the solid-fluid equilibrium in chain molecules, such as the normal alkanes, from a corresponding states perspective, and to develop generalized van der Waals theories of solid-fluid equilibrium. In our work on mixtures we have shown that hard sphere mixtures exhibit five of the six most important classes of solid-fluid phase behavior for binary organic mixtures. Theoretical results for hard sphere mixtures have also been used to assess some methods from classical thermodynamics that are commonly used to estimate solid-fluid phase diagrams for mixtures. We have extended our theory of solid solutions to the treatment of attractive intermolecular interactions. The predictions of the theory agree quite well with experimental data for binary mixtures involving argon, krypton and methane.

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Department of Chemical Engineering

Theoretical Treatment of the Bulk and Surface Properties of Fluids Containing Long, Flexible Molecules

Investigator(s)	Hall, C.K.			$104,000
Phone	919-515-3571
E-mail	hall@turbo.che.ncsu.edu

This research program is designed to enhance understanding of the behavior of fluids and fluid mixtures containing chain-like molecules. The objective is to develop a theory that is capable of predicting the experimentally observed thermophysical properties, including phase equilibria and transport properties, of fluids and fluid mixtures containing chain-like molecules ranging in length from alkanes to polymers. Highlights of this year's accomplishments include: (1) the extension of the Generalized Flory Dimer theory to fluids containing hard heteronuclear chains, i.e. block, alternating and random copolymers, (2) the completion of a very large scale simulation of the dynamics of very long (n=192) polymer melts and analysis of evidence for knot formation, (3) simulation of the static and dynamic properties of double-tethered chain molecules at interfaces, and (4) the simulation of the sorption and diffusion of model penetrants into model polymer membranes (including facilitated transport membranes) in the presence of a chemical potential gradient. Work is continuing on extracting activity coefficients from the Generalized Flory Dimer theories, with the aim being to use this as a basis for developing a new group contribution approach to estimate the properties of mixtures when experimental data are unavailable.

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Department of Chemical Engineering

Molecular and Polymeric Fluids in Microporous Media

Investigator(s)	Glandt, E.D.			$100,956
Phone	215-898-6928
E-mail	eglandt@eniac.seas.upenn.edu

The distribution of dissolved macromolecules between a bulk solution and the interior of a porous substrate occurs in a variety of technologically important systems. The partition coefficient K, which is the ratio of concentration in the pores to that in the bulk, is primarily determined by the effective size of the polymer molecules. For dilute solutions, K decreases rapidly as the effective polymer dimensions exceed the average pore size. We have used liquid-state theory to construct a rigorous integral equation model for the structure of concentrated flexible linear polymers in the presence of a rigid matrix of discrete repulsive obstacles. We have used the structural information to calculate the thermodynamic properties of the polymer in these model porous materials. In particular we have been able to calculate the partition coefficient as a function of concentration. The model provides good agreement with thermodynamic properties obtained from previous computer simulations of bulk polymer solutions, as well as with our own simulations of polymers in porous materials.

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Department of Chemical Engineering

Computational and Theoretical Studies of Homogeneous Nucleation in Supercritical Fluids

Investigator(s)	Debenedetti, P.G.			$72,000
Phone	609-258-5480
E-mail	pdebene@pucc.princeton.edu

We have studied the influence of fluid-phase non-idealities on the precipitation of solids from ternary supercritical mixtures. We are also investigating, theoretically and computationally, the properties of fluids under extreme temperatures and pressures. Water can form two glassy phases that are separated by an apparently first-order phase transition. This unusual phenomenon is known as polyamorphism. We developed a microscopic model of a network-forming fluid that exhibits polyamorphism. We are testing this theoretical prediction by computer simulation. We showed that the simplest explanation of the anomalous properties of supercooled water does not require the existence of spinodal curves or metastable critical points. We have measured the evaporation rates of amorphous and crystalline water at 150K, and used this to estimate the entropy difference between vitreous and crystalline water. We showed that glassy water is connected to ordinary liquid water by a thermodynamically reversible path at atmospheric pressure. We are studying the potential energy hypersurface of superheated liquids, and find that even at the triple-point density, local potential energy minima (inherent structures) contain very large voids. The equation of state of the superheated liquid is highly sensitive to the maximum size of voids that can form in the inherent structure.

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Department of Chemical Engineering

Fundamental Studies of Fluid Mechanics and Stability in Porous Media

Investigator(s)	Homsy, G.M.			$80,000 (18 months)
Phone	415-723-2419
E-mail	bud@chemeng.stanford.edu

This research project treats flow and transport problems in porous media, which are of interest in energy recovery processes. Both macroscopic Darcy scale and pore scale flows are studied. In the former case, current work is focused on the interactions between fingering instabilities and flows driven by permeability heterogeneity. Current Darcy scale analyses are devoted to analyzing the fingering process in the presence of strong permeability heterogeneity. Current pore-scale work focuses on the propagation of interfaces of wetting and nonwetting viscoelastic fluids. Theory shows that the instability of interface propagation depends on contact angle dynamics, capillary number, and Weissenberg number. Perturbation theory for small Weissenberg numbers has shown how viscoelastic thin-film dynamics differs from the Newtonian case. In the wetting case, the hydrodynamically entrained film is thinner due to the increased resistance to elongational flow, and viscoelastic forces destabilize the interface. In the nonwetting case the main effect of elasticity is to stabilize the dynamic contact line against rivulet formation. The stabilization mechanism is related to the increased resistance to streamwise acceleration accompanying the rivulet formation. Recent experimental studies on the instability of dynamic contact lines have demonstrated that elasticity is a stabilizing force, in agreement with the theoretical predictions. Some ancillary studies of the effect of chaotic mixing in viscoelastic liquids were also undertaken and have been recently published.

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Chemical Engineering Department

Molecular Simulation of Phase Coexistence, with Application to Ordered Phases

Investigator(s)	Kofke, D.A.			$65,000
Phone	716-645-2911

The aims of this research are the development of simulation tools that can be used by researchers in molecular thermodynamics, and the application of these tools to understand phase equilibria involving ordered phases, particularly solids. Phase equilibria play a central role in modern technology - particularly in the development, manufacture, and performance of materials - and as a consequence the study of phase coexistence occupies the activities of a wide array of engineers and scientists. Empirical, phenomenological modeling of these phenomena long ago reached its limits, and modern approaches employ a molecular viewpoint. Model substances, defined in terms of molecular interactions, are used to understand complex phenomena observed in real substances. Accurate evaluation of phase equilibria properties in model substances requires computer simulation. This has proved a difficult prospect, particularly in connection with ordered phases such as solids and liquid crystals. Thus there is a great need to develop new simulation techniques that can treat these systems. In this work two approaches are being developed to extend our abilities to evaluate coexistence by molecular simulation. The first method employs thermodynamic integration in new ways and with great efficiency. The second represents a significant departure from standard practice in simulation, and in fact constitutes something of a hybrid of simulation and numerical technique. The first method is well-grounded in theory, and has proven effectiveness; the second is more tentative, and requires significant development before it may be used routinely. Thus this research strikes a balance between incremental and radical advances in technique. The methods developed in this work are used to study phase equilibria of ordered phases. Phase diagrams describing coexistence between fluids, liquid crystals, plastic crystals, and oriented crystals are computed to examine the effects of a wide array of basic molecular features: composition, polydispersity, electrostatics, shape, and flexibility.

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Department of Chemistry

Thermophysical Properties of Fluids and Fluid Mixtures

Investigator(s)	Stell, G.R.			$120,000
Phone	516-632-7899
E-mail	george.stell@sunysb.edu

Theoretical research continues on the thermophysical properties of fluids using a statistical mechanics-based approach to do molecular modelling. Current emphasis is on the study of phase separation in ionic fluids, on fluids of associating particles, and on fluids in porous media. The work on ionic fluids includes studies in which the assumptions of the mean spherical approximation are augmented by new treatments of ionic association to yield phase diagrams in which the location of phase separation is more accurately predicted. The work on association includes studies of dimerization and polymerization in model liquids of reacting atoms in which the core volume of the product molecules is considerably smaller than the sum of the core volumes of the reacting monatomic particles. The work on fluids in porous media includes a general study of thermodynamic relations for a simple fluid in such a medium that is assumed to have a realistically irregular pore structure, in contrast to earlier studies of fluids in single pores of a particular shape. In addition to the above, new work on colloidal systems has begun.

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Department of Chemical Engineering

Theoretical and Experimental Study of Mixed Solvent Electrolyte Systems

Investigator(s)	Cummings, P.T.			$149,021
Phone	423-974-0227
E-mail	ptc@utk.edu

The objective of this project is to develop fundamentally-based predictive theories for the thermodynamic properties and phase equilibria in mixed solvent electrolyte systems and supercritical aqueous solutions. During the current year, a new model for water has been under development in our research group. The model features polarizability and has the property that the isolated water molecule has the bare dipole moment of water (1.85D) unlike almost all other models for water. The goal of this model is to reproduce the properties of water over wide ranges of density and temperature, so that it will yield an accurate vapor-liquid phase envelope, as well as be effective in the high-temperature, high-pressure supercritical regime. We have also developed a molecular dynamics simulation of water/alcohol/tetrabutylammonium halide salt systems. We are performing simulations with this code to probe the molecular basis of experimental measurements of phase equilibria and densities in alcohol/water/organic salt systems performed in our laboratory. Many of the simulation codes written in our group for this project have been developed to run on the massively parallel supercomputers in the Center for Computational Sciences at Oak Ridge National Laboratory.

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Department of Mechanical Engineering

Computational and Experimental Study of Laminar Premixed and Diffusion Flames

Investigator(s)	Smooke, M.D.; Long, M.B.			$206,000
Phone	203-432-4344
E-mail	smooke%smooke@biomed.med.yale.edu

Our research has centered on an investigation of the effects of complex chemistry and detailed transport on the structure and extinction of hydrocarbon flames in coflowing axisymmetric configurations. We have pursued both computational and experimental aspects of the research in parallel. The computational work has focused on the application of accurate and efficient numerical methods for the solution of the boundary value problems describing the various reacting systems. Detailed experimental measurements have been performed on axisymmetric coflow flames using two-dimensional imaging techniques. Spontaneous Raman scattering and laser-induced fluorescence are used to measure the temperature, major and minor species profiles. Our goal is to obtain a more fundamental understanding of the important fluid dynamic and chemical interactions in these flames so that this information can be used effectively in combustion modeling.

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