Biomedical subjects

Bjørn Kvamme

Publications and source records attributed to Bjørn Kvamme.

4 recordsLinked to original sources

PubMed2006

Thermodynamic properties and phase transtions in the H2O/CO2/CH4 system.

The availability of free energy densities as functions of temperature, pressure and the composition of all components is required for the development of a three-component phase field theory for hydrate phase transitions. We have broadened the extended adsorption theory due to Kvamme and Tanaka (J. Phys. Chem., 1995, 99, 7114) through derivation of the free energy density surface in case of CO(2) and CH(4) hydrates. A combined free energy surface for the liquid phases has been obtained from a SRK equation of state and solubility measurements outside hydrate stability. The full thermodynamic model is shown to predict water-hydrate equilibrium properties in agreement with experiments. Molecular dynamics simulations of hydrates in contact with water at 200 bar and various temperatures allowed us to estimate hard-to-establish properties needed as input parameters for the practical applications of proposed theories. The 5-95 confidence interval for the interface thickness for the methane hydrate/liquid water is estimated to 8.54 A. With the additional information on the interface free energy, the phase field theory will contain no adjustable parameters. We provide a demonstration of how this theory can be applied to model the kinetics of hydrate phase transitions. The growth of hydrate from aqueous solution was found to be rate limited by mass transport, with the concentration of solute close to the hydrate approaching the value characterizing the equilibrium between the hydrate and the aqueous solution. The depth of the interface was estimated by means of the phase field analysis; its value is close to the interface thickness yielded by molecular simulations. The variation range of the concentration field was estimated to approximately 1/3 of the range of the phase field.

Carbon Dioxide↗

PubMed2005

Can dawsonite permanently trap CO2?

Thermodynamic calculations indicate that although dawsonite (NaAlCO3(OH)2) is favored to form at the high CO2 pressures associated with carbon dioxide injection into sandstone reservoirs, this mineral will become unstable as CO2 pressure decreases following injection. To assess the degree to which dawsonite will persist following its formation in sandstone reservoirs, its dissolution rates have been measured at 80 +/- 3 degrees C as a function of pH from 3 to 10. Measured dawsonite dissolution rates normalized to their BET surface area are found to be nearly independent of pH over the range of 3.5 < pH < 8.6 at 1.58 x 10(-9) mol/(m2 x s). Use of these dissolution rates in reactive transport calculations indicate that dawsonite rapidly dissolves following the decrease of CO2 pressure out of its stability field, leading mainly to the precipitation of secondary kaolinite. This result indicates that dawsonite will provide a permanent mineral storage host only in systems that maintain high CO2 pressures, whereas dawsonite may be an ephemeral phase in dynamic settings and dissolve once high CO2 pressure dissipates either through dispersion or leakage.

Aluminum Hydroxide↗

PubMed2005

Molecular dynamics simulations for selection of kinetic hydrate inhibitors.

Natural gas hydrates are ice-like structures composed of water and gas molecules that have long been a problem in petroleum industry. Heavy cost of alcohol and glycol injection has spurred an interest in called 'kinetic inhibitors' able to slow down the hydrate formation rather than prevent it. Since it is not possible to compare directly the macroscopic effects of different inhibitors on the kinetics of hydrate formation in computer experiments, a scheme capable of culling the list of candidates for experimental testing was proposed earlier [B. Kvamme, G. Huseby, O.K. Førrisdahl, Molecular dynamics simulations of PVP kinetic inhibitor in liquid water and hydrate/liquid water systems, Mol. Phys. 90 (1997) 979-991]. Molecular dynamics simulations were implemented to test several kinetic inhibitors in a multiphase water-hydrate system with rigid hydrate interface. In addition, a long-scale run was implemented for a system where the hydrate was free to melt and reform. Our conclusion that PVCap will outperform PVP as a kinetic hydrate inhibitor is supported by experimental data. We demonstrate that numerical experiments can be a valuable tool for selecting kinetic inhibitors as well as provide insight into mechanisms of kinetic inhibition and hydrate melting and reformation.

Computer Simulation↗

PubMed2001

Viabilty of atomistic potentials for thermodynamic properties of carbon dioxide at low temperatures.

Investigation into volumetric and energetic properties of several atomistic models mimicking carbon dioxide geometry and quadrupole momentum covered the liquid-vapor coexistence curve. Thermodynamic integration over a polynomial and an exponential-polynomial path was used to calculate free energy. Computational results showed that model using GROMOS Lennard-Jones parameters was unsuitable for bulk CO(2) simulations. On the other hand, model with potential fitted to reproduce only correct density-pressure relationship in the supercritical region proved to yield correct enthalpy of vaporization and free energy of liquid CO(2) in the low-temperature region. Except for molar volume at the upper part of the vapor-liquid equilibrium line, the bulk properties of exp-6-1 parametrization of ab initio CO(2) potential were in a close agreement with the experimental results. Copyright 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1772-1781, 2001

Journal Article↗