Volume 36, Issue 1

In this study, experimental data of the kinetics of methane and ethane hydrate formation at constant volume were collected. The experiments were carried out in a batch reactor at different temperatures and pressures. The property of chemical affinity was used in the modeling of hydrate formation rate in a constant volume process. In this model a macroscopic driving force was defined which only needed the initial (experimental condition, temperature, and pressure) and final conditions (equilibrium conditions); thus, this model did not have the limitations of microscopic models, such as heat and mass transfer coefficients or population of particles, which may differ for each experiment. The experiments were carried out at temperatures 273, 274, 275.5, and 276 K for methane and 272, 273, 274, and 275 K for ethane with different initial pressures. The parameters of the model, A r and t K , were obtained for each experiment, and the results show that the parameter of for each gas has a constant value. Subsequently, parameters of the model were used to predict experimental data and the variation of pressures with time. The results indicated that this model can well predict constant volume experimental data for crystals I hydrate former.

The evaluation of the activation energy in Eyring's viscosity theory is of great importance in estimating the thermodiffusion coefficient for associating and non-associating fluid mixtures. Several methods were used to estimate the activation energies of pure components and then extended to mixtures of linear hydrocarbon chains. Results show that the recent model of Abbasi et al. [J. Chem. Phys. 131: 014502, 2009.] gives a good outcome in determining the activation energy of the components of a binary mixture. The activation energy model for pure components is shown to be useful for obtaining the activation energy of the mixture. In this paper, the activation energy model using alternative forms of Eyring's viscosity theory is used to estimate the thermodiffusion coefficient values for hydrocarbon binary mixtures. Comparisons of predicted thermodiffusion coefficients using different theoretical models with the experimental data show good capability of the activation energy model.

A one-dimensional numerical model of a compound piston shows that damping can occur if the gas is allowed to exchange heat with the walls of the system. The dynamics of the piston motion vary with the rate of heat flow, but the final position and the net work done by the gases on either side are found to be independent of this parameter. We find, however, that there is an optimum rate of heat flow for critical damping, and a rate of heat flow that is either larger or smaller than this significantly increases the damping time. We have investigated the thermodynamics of this intrinsic dissipation process and found that the net work done is given by the product of the final pressure and the volume change.

The thermodynamics of physicochemical processes in a reacting distributed kinetic system are considered, and the entropy balance equation for traveling waves of laminar combustion is derived for arbitrary Lewis number. Qualitative and numerical analysis of a dynamic system with a three-dimensional phase space and of the local and complete entropy production in the system were performed. It is shown that the complete entropy production in the system is a functional of the traveling wave solution of the problem, possessing extreme properties, whose minimum corresponds to the only physically meaningful traveling wave solution. The procedure of “cut-off” (zeroing) of the reaction rate is justified by methods of nonequilibrium thermodynamics. A variational formulation of the problem is presented for calculation of a steady laminar combustion wave.

A new approach for studying the influence of a thermal radiation field upon a rarefied neutral gas is introduced. We insert the radiation field effect in the force term of the Boltzmann equation. In a frame co-moving with the fluid, the BGK (Bhatnager–Gross–Krook) model kinetic equation is applied analytically. The one-dimensional steady problem is studied using the Liu–Lees model. We apply the moment method to follow the behavior of the macroscopic properties of the gas, such as the temperature and concentration. They are substituted into the corresponding two-stream Maxwellian distribution functions, permitting the investigation of the non-equilibrium thermodynamic properties of the system (gas + heated plate). The entropy, entropy flux, entropy production, thermodynamic forces and the kinetic coefficients are obtained. We verify the celebrated Onsager reciprocity relations for the system. The ratios between the different contributions of the internal energy changes based upon the total derivatives of the extensive parameters are estimated via the Gibbs formula. The results are applied to the Helium gas for various radiation field intensities due to different plate temperatures. Figures illustrating the calculated variables are drawn to predict their behavior and the results are discussed.