Volume 233, Issue 4 - Special Issue: Dedicated to Ulrich Deiters on the occasion of his 65th birthday / Guest Editors: Thomas Kraska and Kai Leonhard

The cross second virial coefficient and three dilute gas transport properties (shear viscosity, thermal conductivity, and binary diffusion coefficient) of mixtures of hydrogen sulfide (H 2 S) and nitrogen (N 2 ) were determined with high accuracy at temperatures up to 1200 K using statistical thermodynamics and the kinetic theory of molecular gases, respectively. The required intermolecular potential energy surface (PES) for the H 2 S–N 2 interaction is presented in this work, while the H 2 S–H 2 S and N 2 –N 2 PESs were reported previously. All three PESs are based on high-level quantum-chemical ab initio (i.e. first-principles) calculations. There is only very limited experimental information available on the second virial coefficients of H 2 S–N 2 mixtures, and there appear to be no experimental data at all for the transport properties. Thus, the present predictions constitute a substantial increase in our knowledge of the thermophysical properties of this system, which are of practical relevance for modeling sour natural gas.

In this work, we have been carried out GEMC-NVT simulations in the temperature range 18 K–32 K for fluid hydrogen and in range 60 K–140 K for fluid fluorine using four our developed ab initio 5-site intermolecular potentials for dimers H 2 -H 2 and F 2 -F 2 , respectively. The thermodynamic properties of vapor-liquid equilibria and the critical points of fluids hydrogen and fluorine were calculated with the obtained densities of coexisting phases and vapor pressures. The simulation results drived from ab initio pair potentials were compared with those from ab initio potential plus three-body Axilrod-Teller potential and experimental data as well as those from Monte Carlo simulation using Lennard-Jones potentials, Deiters equation of state (D1-EOS) and Benedict-Webb-Rubin equation of state (EOS) reported in the literature.

Carbohydrate complexes are crucial in many various biological and medicinal processes. The impacts of N-acetyl on the glycosidic linkage flexibility of methyl β -D-glucopyranose, and of the glycoamino acid β -D-glucopyranose-asparagine are poorly understood at the electronic level. Furthermore, the effect of D- and L-isomers of asparagine in the complexes of N-acetyl- β -D-glucopyranose-(L)-asparagine and N-acetyl- β -D-glucopyranose-(D)-asparagine is unknown. In this study, we performed density functional theory calculations of methyl β -D-glucopyranose, methyl N-acetyl- β -D-glucopyranose, and of glycoamino acids β -D-glucopyranose-asparagine, N-acetyl- β -D-glucopyranose-(L)-asparagine and N-acetyl- β -D-glucopyranose-(D)-asparagine for studying their linkage flexibilities, total solvated energies, thermochemical properties and intra-molecular hydrogen bond formations in an aqueous solution environment using the COnductor-like Screening MOdel (COSMO) for water. We linked these density functional theory calculations to deep learning via estimating the total solvated energy of each linkage torsional angle value. Our results show that deep learning methods accurately estimate the total solvated energies of complex carbohydrate and glycopeptide species and provide linkage flexibility trends for methyl β -D-glucopyranose, methyl N-acetyl- β -D-glucopyranose, and of glycoamino acids β -D-glucopyranose-asparagine, N-acetyl- β -D-glucopyranose-(L)-asparagine and N-acetyl- β -D-glucopyranose-(D)-asparagine in agreement with density functional theory results. To the best of our knowledge, this study represents the first application of density functional theory along with deep learning for complex carbohydrate and glycopeptide species in an aqueous solution medium. In addition, this study shows that a few thousands of optimization frames from DFT calculations are enough for accurate estimations by deep learning tools.

We carry out extensive computer simulations to study the phase equilibrium, thermodynamics, and diffusion coefficient of three-center Lennard-Jones (3CLJ) fluids with an emphasis on the effects of bond angle on these properties. We take into account several bond angles ranging from θ 0 = 60 to 180 degrees and two equilibrium bond elongations l e = 1.0 and 0.5 (in Lennard-Jones length unit). Moreover, we study the fully flexible (FF) 3CLJ fluids for molecules with bond length 1.0. Gibbs ensemble Monte Carlo (MC) simulations are performed to compute the densities of the vapor-liquid coexisting phases and the vapor pressure, and direct three-phase (vapor-liquid-vapor) molecular dynamics (MD) simulations are carried out to calculate the surface tension. We then apply constant NVT MC simulations to obtain the internal energy, the pressure, and the pair correlation function, and utilize equilibrium MD simulations to compute the diffusion coefficient of systems with l e = 1.0. In addition to MD simulations, the modified Cohen-Turnbull (mCT) theory is used to to compute the diffusion coefficient and the mean free volume appearing in the mCT relation is provided by the results of the Generic van der Waals (GvdW) theory. We show that the mCT theory is capable of reproducing the MD simulation values quite well over a wide range of density with slight overestimations at medium range. The angle dependence of different thermophysical properties are analyzed and discussed in details.

For energy production and conversion, the use of thermodynamic cycles is still the most common way. To find the optimal solution is a multiparametric optimization problem, where some parameters are related to thermodynamic and physical chemistry, while others are associated with costs, safety, or even environmental issues. Concerning the thermodynamic aspects of the design, the selection of the working fluid is one of the crucial points. Here, we are going to show different types of adiabatic expansion processes in various pure working fluids, pointing out the ones preferred in Organic Rankine Cycles or in Trilateral Flash Cycles. The effect of these expansions on the layout of the cycles will also be presented. Finally, we are giving a few thumb-rules, derived from thermodynamic studies, useful for energy engineers to select the proper working fluid for a given thermal system.