Self-consistent cluster approach to the homogeneous kinetic nucleation theory

\u3cp\u3eAn alternative, self-consistent formulation of the homogeneous nucleation theory has been proposed. This approach differs from the classical Becker-Döring-Zeldovich theory in two respects: (i) evaporation rates are evaluated by referring to the stable equilibrium of a saturated vapor rather than to the constrained metastable equilibrium of a supersaturated vapor; and (ii) for the reference stable equilibrium state the Fisher theory of condensation is used in order to obtain a self-consistent definition of the free-energy barrier for l-cluster formation, where l is the number of molecules in the cluster. A comparison of the expressions for the nucleation rate and critical cluster size with the corresponding classical expressions has been made for the different parts of the phase diagram (temperature-supersaturation) and the domain where both theories are close has been found. Predictions of the present theory have been compared with the experimental results on nucleation of n-nonane for the three sets of experiments (diffusion cloud chamber, fast-expansion cloud chamber, and two-piston cloud chamber). It has been shown that the present theory has a much better agreement with experimental results for n-nonane than the classical theory.\u3c/p\u3

Fluid of hard spheres with dipolar-like patch interaction and effect of adding an isotropic adhesion

International audienceWe compare two fluid models of spherical molecules with anisotropic, purely surface interactions. Both models admit an analytical solution of the molecular Ornstein-Zernike integral equation, within the Percus-Yevick approximation plus orientational linearization. In the first model, the molecular surface corresponds to a unique nonuniform patch, with a potential obtained by truncating a long-ranged dipolar interaction exactly at the contact distance between two hard sphere particles. In the second model, a further isotropic adhesion is added to the intermolecular potential. The study is focused on the local orientational ordering. Differences and similarities with respect to hard spheres with full long-ranged dipolar forces are analysed in detail. The effect of the competition between anisotropic patch interaction and isotropic adhesion is investigated through the pair correlation function as well as via two novel anisotropic order parameters

Physical and Chemical Properties of Oil and Gas Under Reservoir and Deep-Sea Conditions

Petroleum is one of the most complex naturally occurring organic mixtures. The physical and chemical properties of petroleum in a reservoir depend on its molecular composition and the reservoir conditions (temperature, pressure). The composition of petroleum varies greatly, ranging from the simplest gas (methane), condensates, conventional crude oil to heavy oil and oil sands bitumen with complex molecules having molecular weights in excess of 1000 daltons (Da). The distribution of petroleum constituents in a reservoir largely depends on source facies (original organic material buried), age (evolution of organisms), depositional environment (dysoxic versus anoxic), maturity of the source rock (kerogen) at time of expulsion, primary/secondary migration, and in-reservoir alteration such as biodegradation, gas washing, water washing, segregation, and/or mixing from different oil charges. These geochemical aspects define the physical characteristics of a petroleum in the reservoir, including its density and viscosity. When the petroleum is released from the reservoir through an oil exploration accident like in the case of the Deepwater Horizon event, several processes are affecting the physical and chemical properties of the petroleum from the well head into the deep sea. A better understanding of these properties is crucial for the development of near-field oil spill models, oil droplet and gas bubble calculations, and partitioning behavior of oil components in the water. Section 3.1 introduces general aspects of the origin of petroleum, the impact of geochemical processes on the composition of a petroleum, and some molecular compositional and physicochemical background information of the Macondo well oil. Section 3.2 gives an overview over experimental determination of all relevant physicochemical properties of petroleum, especially of petroleum under reservoir conditions. Based on the phase equilibrium modeling using equations of state (EOS), a number of these properties can be predicted which is presented in Sect. 3.3 along with a comparison to experimental data obtained with methods described in Sect. 3.2