Molecular dynamics simulations of a hydrophilic MIL-160-based membrane demonstrate pressure-dependent selective uptake of industrially relevant greenhouse
Oral presentation for ACS Spring Meeting
Chapman, Jordan↗
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Temperature- and Pressure-Dependent Kinetics of CH 2 OO + CH 3 COCH 3 and CH 2 OO + CH 3 CHO: Direct Measurements and Theoretical Analysis: TEMPERATURE- AND PRESSURE-DEPENDENT KINETICS OF CH 2 OO + CH 3 COCH 3 AND CH 2 OO + CH 3 CHO
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Elsamra, Rehab M. I.↗
Effect of energy dependence of the density of states on pressure-dependent rate constants
The F E integral for the normalized Boltzmann-weighted number of unimolecular states above the threshold energy is the key quantity for computing the collision efficiency in the pressure-dependent unimolecular rate theory developed by Troe, who calls this the energy dependence factor of the density of states. By using the Whitten–Rabinovitch approximation and assuming that the Whitten–Rabinovitch a(E) function is independent of energy, F E can be approximated by an analytical formula; this approximate formula is widely used because of its convenience and computational efficiency. Here we test its validity by comparing the rate constants computed by using the approximate F E to the ones determined by using the numerically integrated F E . For small-sized molecules and for reactions with high threshold energies E 0 , the differences are negligible at all temperatures, but in other cases, the approximate formula tends to underestimate F E and thus overestimates the collision efficiency, and this leads to smaller pressure falloff. When a(E) at high energies differs appreciably from a(E 0 ), we find that the underestimation of pressure-dependent rate constants by using the approximate formula can be greater than a factor of 5 at high temperatures. The physical insight we draw from this study is that, for reactions with threshold energies below about 30 kcal mol -1 , the rate of collisional energy transfer can be appreciably slowed down by the increase in the density of states at higher energies, and this increases the falloff effect by which finite-pressure rate constants become lower than the high-pressure limit, especially at higher temperatures.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Pressure Dependence of the Boson Peak of Glassy Glycerol
The pressure dependence of the Boson peak (BP) of glycerol, including its behavior across the liquid-glass transition, has been studied under pressure using Raman scattering. A significant increase of the BP frequency was observed with pressure up to 11 GPa at room temperature. The pressure dependence of BP frequency ν BP is proportional to (1+P/P 0 ) 1/3 , where P and P 0 are the pressure and a constant, respectively, the spectra are consistent with a soft potential model. The characteristic length of medium range order is close in size to a cyclic trimer of glycerol molecules, which is predicted as the medium range order of a BP vibration using molecular dynamics simulations. The pressure dependence of a characteristic length of medium range order is nearly constant. The pressure induced structural changes in glycerol can be understood in terms of the shrinkage of voids with cyclic trimers remaining up to at least 11 GPa. Lastly, the pressure dependence of intermolecular O-H stretching mode indicates that the intermolecular hydrogen bond distance gradually decreases below the glass transition pressure of ~5 GPa, while it becomes nearly constant in the glassy state indicating the disappearance of the free volume in the dense glass.
36 MATERIALS SCIENCE↗
Validation of a Pressure Dependent PBX 9501 Cookoff Model
A pressure dependent cookoff model for PBX 9501 was developed. This cookoff model was implemented in the finite element (FE) heat transfer code Aria and was used to simulate a set of cookoff experiments. This set is called the Large Scale Annular Cookoff (LSAC) experiments. Three dimensional and axisymmetric heat conduction FE models were implemented to simulate these experiments. The predictive ability of the PBX 9501 pressure dependent cookoff model was evaluated using Latin Hypercube sampling (LHS). Predictions of the thermal times to ignition and temperatures are compared with the experiments.
42 ENGINEERING↗
Addressing spreading pressure dependence of real adsorbed solution theory with generalized Langmuir isotherm
This work addresses spreading pressure dependence of Real Adsorbed Solution Theory (RAST) for mixed-gas adsorption equilibria using generalized Langmuir (gL) isotherm. Considering vacant sites as an integral part of competitive multicomponent adsorption on a constant adsorbent surface area, the gL isotherm properly accounts for surface heterogeneity and loading, adsorbate composition, and temperature dependence. We show the spreading pressure dependence of adsorbate activity coefficient expression in the RAST framework can be generated from the gL isotherm. The procedure is illustrated with a spreading pressure dependent adsorption Nonrandom Furthermore, two-Liquid activity coefficient model, and the results are validated for ten binary mixed-gas adsorption equilibria systems including two highly nonideal azeotropic systems.
42 ENGINEERING↗
Density functional and theoretical study of the temperature and pressure dependency of the plasmon energy of solids
The temperature and pressure dependency of the volume plasmon energy of solids was investigated by density functional theory calculations. The volume change of crystal is the major factor responsible for the variation of valence electron density and plasmon energy in the free electron model. Hence, to introduce the effect of temperature and pressure for the density functional theory calculations of plasmon energy, the temperature and pressure dependency of lattice parameter was used. Also, by combination of the free electron model and the equation of state based on the pseudo-spinodal approach, the temperature and pressure dependency of the plasmon energy was modeled. The suggested model is in good agreement with the results of density functional theory calculations and available experimental data for elements with the free electron behavior.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Dissociation-induced depletion of high-energy reactant molecules as a mechanism for pressure-dependent rate constants for bimolecular reactions
In 1922, Lindemann proposed the now-well-known mechanism for pressure-dependent rate constants for unimolecular reactions: reactant molecules with sufficiently high energies dissociate more quickly than collisions can reestablish the Boltzmann distribution of the internal energies of the molecule during its dissociation at low pressures – yielding pressure-dependent rate constants for unimolecular reactions due to the preferential depletion of the high energy states capable of dissociation. In the last century, incredible progress has been made in achieving a far greater understanding of and quantitative predictions for unimolecular and association reactions. In the modern era, pressure-dependent phenomenological rate constants are now nearly universally used to describe the rates of unimolecular and associative reactions in phenomenological kinetic modeling. However, there is a second, more indirect, implication of Lindemann’s mechanism that relates to how these dissociation-induced non-equilibrium distributions impact bimolecular reactions, including non-associative bimolecular reactions – which are generally not considered to have pressure-dependent rate constants. Yet, as we show herein, the same high energy states depleted due to dissociation would otherwise react most rapidly in high-activation-energy bimolecular reactions – yielding a mechanism for pressure-dependent rate constants for bimolecular reactions (including non-associative reactions). Here, we present results from a case study for CH 2 O dissociation, isomerization, and bimolecular reaction with O2 to explore this question. Results from our master equation calculations indicate that the effect of dissociation-induced non-equilibrium distributions on bimolecular reactions can be substantial – even when chemical timescales are well separated from internal energy relaxational timescales (i.e. when the traditional rate constant description would be thought to apply). This effect is found to be more pronounced – and more complex – for bimolecular reactions involving molecular entities whose chemical timescales are merged with the internal energy relaxational timescales. Lastly, we present some ideas for discussion regarding what should be considered as “chemical species” in phenomenological kinetic models.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Impact of Pressure-Dependent Interfacial Tension and Contact Angle on Capillary Heterogeneity Trapping of CO2 in Storage Aquifers
Summary Carbon dioxide (CO2) capillary trapping increases the total amount of CO2 that can be effectively immobilized in storage aquifers. This trapping, manifesting itself as accumulated CO2 columns at a continuum scale, is because of capillary threshold effects that occur below low-permeability barriers. Considering that capillary pressure is dictated by heterogeneous pore throat size, the trapped CO2 column height and associated CO2 saturation will vary spatially within a storage aquifer. This variation will be influenced by two pressure-dependent interfacial parameters—CO2/brine interfacial tension (IFT) and CO2/brine/rock contact angle. Our objective is to understand how the pressure dependence of these two parameters affects the heterogeneity of capillary trapped CO2 at a continuum scale. Our conceptual model is a 1D two-zone system with the upper zone being a flow barrier (low permeability) and the lower zone being a flow path (high permeability). The inputs to this model include microfacies-dependent capillary pressure vs. saturation curves and permeability values. The input capillary pressure curves were collected in the literature that represents carbonate microfacies (e.g., dolograinstone) in a prevalent formation in the Permian Basin. We then used the Leverett j-function to scale the capillary pressure curve for the two zones that are assigned with the same or different microfacies. During scaling, we considered the influence of pressure on both the IFT and contact angle of CO2/brine/dolomite systems. We varied the zone permeability contrast ratio from 2 to 50. We then assumed capillary gravity equilibriums and calculated the CO2 saturation buildup corresponding to various trapped CO2 column heights. The CO2 saturation buildup is defined as the CO2 saturation in the lower layer minus that in the upper one. We found that the saturation buildup can be doubled when varying pressure in a storage aquifer, after considering pressure-dependent IFT and contact angles. Thus, assuming these two parameters to be constant across such aquifers would cause large errors in the quantification of capillary trapping of CO2. The whole study demonstrates the importance of considering pressure-dependent interfacial properties in predicting the vertical distribution of capillary trapped CO2. It has important implications in developing a better understanding of leakage risks and consequent storage safety.
Engineering↗
Development of a Pressure-Dependent Constitutive Model with Combined Multilinear Kinematic and Isotropic Hardening
The development of a pressure-dependent constitutive model with combined multilinear kinematic and isotropic hardening is presented. The constitutive model is developed using the ABAQUS user material subroutine (UMAT). First the pressure-dependent plasticity model is derived. Following this, the combined bilinear and combined multilinear hardening equations are developed for von Mises plasticity theory. The hardening rule equations are then modified to include pressure dependency. The method for implementing the new constitutive model into ABAQUS is given.
Allen Phillip A.↗
THE INFLUENCE OF PRESSURE-DEPENDENT VISCOSITY ON THE THERMAL EVOLUTION OF SUPER-EARTHS
We study the thermal evolution of super-Earths with a one-dimensional (1D) parameterized convection model that has been adopted to account for a strong pressure dependence of the viscosity. A comparison with a 2D spherical convection model shows that the derived parameterization satisfactorily represents the main characteristics of the thermal evolution of massive rocky planets. We find that the pressure dependence of the viscosity strongly influences the thermal evolution of super-Earths-resulting in a highly sluggish convection regime in the lower mantles of those planets. Depending on the effective activation volume and for cooler initial conditions, we observe with growing planetary mass even the formation of a conductive lid above the core-mantle boundary (CMB), a so-called CMB-lid. For initially molten planets our results suggest no CMB-lids but instead a hot lower mantle and core as well as sluggish lower mantle convection. This implies that the initial interior temperatures, especially in the lower mantle, become crucial for the thermal evolution-the thermostat effect suggested to regulate the interior temperatures in terrestrial planets does not work for massive planets if the viscosity is strongly pressure dependent. The sluggish convection and the potential formation of the CMB-lid reduce the convective vigor throughout the mantle, thereby affecting convective stresses, lithospheric thicknesses, and heat fluxes. The pressure dependence of the viscosity may therefore also strongly affect the propensity of plate tectonics, volcanic activity, and the generation of a magnetic field of super-Earths.
79 ASTRONOMY AND ASTROPHYSICS↗
Pressure dependence of the infrared absorption of calcite.
Calcite IR absorption dependence on pressure, discussing calcite-aragonite transformation
Katz, S.↗
Pressure dependence of Poisson’s ratio of glassy Baltic amber studied by Brillouin scattering spectroscopy
Amber is a typical natural glass with very long aging time. Elastic properties of amber at high pressures have been studied using Brillouin scattering and a diamond anvil cell. Both longitudinal and transverse acoustic modes have been observed up to 12 GPa. The pressure dependences of longitudinal, shear, Young’s, and bulk moduli, compressibility, and Poisson’s ratio were determined. The longitudinal, shear, Young’s, bulk moduli show the remarkable increase, and compressibility shows a marked decrease with increasing pressure. However, it is found that the pressure dependence of Poisson’s ratio is very small. The mechanism of this small pressure dependence was discussed. Finally, the Cauchy type relation between longitudinal and shear moduli was examined. Its coefficients show the deviation from the Cauchy relation owing to the coexistence of different intermolecular interactions in amber.
07 ISOTOPE AND RADIATION SOURCES↗
Numerical investigation of the pressure-dependence of yield sooting indices for n-alkane and aromatic species
The pressure-dependence of the Yield Sooting Index (YSI), as a measure of sooting tendency, is numerically investigated for pressures ranging from 1 atm to 15 atm. Straight-chain alkanes, including ethane, propane, n-hexane, n-heptane, and n-dodecane, and aromatic species, including benzene, toluene, xylene, and ethylbenzene, are selected as test fuels. A detailed chemical mechanism is used for all test fuels considered, and a flamelet-based YSI simulation methodology is employed, where the YSI values are computed based on the Polycyclic Aromatic Hydrocarbon (PAH) dimer production rate at each pressure. It is found that the maximum flame centerline soot volume fraction increases with increasing pressure for all test compounds. However, the pressure dependence of the maximum soot volume fraction is similar for the hydrocarbons within the same class (n-alkane or aromatics). As a consequence, the YSI values computed at pressures up to 15 atm show only small deviations from their values computed and measured at atmospheric pressure. These results suggest that YSI is robust also at elevated pressures, close to those found in practical combustion devices. This study is entirely based on numerical simulations without any experimental measurements available for direct validation. Experimental YSI measurements at high pressures would be required to fully confirm the conclusions reported in this manuscript. Still, our numerical results provide some guidelines for the design of such experiments in the future.
42 ENGINEERING↗
The role of a pressure-dependent rheology in the dynamics of mantle circulation
A thermomechanical model for upper mantle convection was constructed such that the thickness and the structure of the lithosphere are determined self consistently by the heat transported by convection. In this study of the interaction between the lithosphere and upper mantle, strongly temperature and pressure dependent rheologies for both Newtonian and non-Newtonian creep mechanisms are employed. For a strictly temperature dependent rheology an insignificant amount of heat, less than 12.5 mW/sq m, can be transported convectively for an interior viscosity, 0(10 sup 21 Pas), compatible with post glacial rebound. On the other hand, for similar values of the interior viscosity, steady heat fluxes between 20 and 40 mW/sq m are produced by introducing pressure dependence into the rheology. For the temperature and pressure dependent flow law the horizontally averaged interior temperature displays very little variation with the amount of heat evacuated, once all of the rheological parameters are fixed. This finding may have important ramifications for parameterized convection.
Yuen, D. A.↗
Modeling study on pressure dependence of plasma structure and formation in 110 GHz microwave air breakdown
Recent experimental studies of 110 GHz microwave air volume breakdown have shown that as pressure is decreased from atmosphere to a few torr, the discharge transitions from a well-defined array to a smeared-out array and finally to a diffuse plasma. In this letter, a two-dimensional model coupling plasma fluid equations and Maxwell equations is used to simulate the pressure dependence of plasma structure and formation under conditions similar to the experiments. The modeling pressure dependence of plasma structures in H plane and E plane is qualitatively consistent with the experimental observation. The quantitative discrepancy between modeling and experimental results is explained. The simulations allow a good understanding of plasma structure at different pressures in microwave volume breakdown.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Mantle convection with internal heating and pressure-dependent thermal expansivity
Recent laboratory work suggests that the thermal expansivity alpha of the mantle decreases strongly with pressure. alpha determines the buoyancy of plumes and the rate at which plumes lose their thermal signature as they rise, and so may be expected to have a strong influence on the temperature and velocity structure of the mantle. Numerical simulations were conducted on convection in an internally heated, compressible mantle including constant and pressure-dependent alpha and thermal conductivity kappa. They show that a pressure-dependent alpha allows the existence of thermal plumes rising from the core-mantle boundary, however the plumes are weak and dissipate higher in the mantle.
Leitch, A. M.↗