Alejandro J. García-Cuéllar

A perturbation density functional theory for hydrogen bonding cyclic molecules

Using the framework of Wertheims thermodynamic perturbation theory, a new polyatomic density functional theory is developed to account for the intermolecular association of cyclic molecules in interfacial systems. To test the theory, Monte Carlo simulations in the canonical ensemble were performed for the specific case of an associating triatomic ring with one association site next to a hard wall. The theory and simulation results were found to be in good agreement.

Theory and simulation for associating cyclic molecules

A successful equation of state for ring molecules [J. Chem. Phys. 101, 6880 (1994); Phys. Rev. E 50, 386 (1994)] is extended using Wertheims first-order thermodynamic perturbation theory to predict the degree of bonding and thermodynamic properties of associating cyclic molecules. This new theory is tested against molecular simulation results for pure fluids of cyclic trimers with either one or three association sites. The trimers’ association potential of interaction is modeled by an orientation-dependent square-well, and the segment–segment interactions are of the hard-sphere type. A wide range of densities and temperatures is studied. Values for fraction of molecules not bonded, configurational internal energy and compressibility factor were obtained using Metropolis Monte Carlo simulations in the canonical and isothermal–isobaric ensembles. The theory predictions are in excellent agreement with these simulation results.

Formulation techniques for nanofluids.

Fluids with suspended nanoparticles, commonly known as nanofluids, may be formulated to improve the thermal performance of industrial heat transfer systems and applications. Nanofluids may show enhanced thermal and electrical properties such as thermal conductivity, viscosity, heat transfer coefficient, dielectric strength, etc. However, stability problems may arise as nanoparticles usually have the tendency to agglomerate and sediment producing deterioration in the increment of these properties. In this review, we discuss patents that report advances in the formulation of nanofluids including: production methods, selection of components (nanoparticles, base fluid and surfactants), their chemical compositions and morphologies, and characterization techniques. Finally, current and future directions in the development of nanofluid formulation are discussed.

Thermal analysis of a solar distillation system for ethanol-water solutions

The dimensions, volumetric flow rates, and thermal capacities of an ethanol distillation system where solar energy is used as primary energy are examined in this article. A rigorous thermodynamic equilibrium analysis is applied to obtain the critical design parameters for the solar distillation of an ethanol-water solution with different feed stream concentrations (5%, 7%, and 10% wt. ethanol) to obtain a distillate product of 95% wt. ethanol. The volumetric flow of the feed stream is varied and a sensitivity analysis is performed to study its impact on the design of the solar distillation system. Important technical details, such as the configuration of the solar distillation system, the size of the distillation columns, reboiler heat duty, energy consumption per unit mass of distillate product, solar fraction, and collector area, among others, are evaluated and presented as a guideline for designers. The methodology developed herein is used to design the solar ethanol distillation system and can be exte...

Theory and simulation of chain molecules with multiple bonding sites in an associating solvent

Although polyethylene oxide (PEO) is soluble in water, polymethylene oxide (PMO) is not, even though PMO has more association sites. Some suggest this is due to orientation effects in the water hydrogen-bond network. A simulation and theory study of the effect of bonding site density on thermodynamic properties and extent of bonding of a linear flexible chain in a hydrogen-bonding solvent is performed. Predictions from Wertheims theory are compared against simulation results. Thermodynamic properties and extent of bonding were obtained. The solvent molecules are modeled as hard spheres with four association sites in a tetrahedral arrangement. The chains are flexible and consist of six tangent segments of hard spheres with bonding sites that interact with the solvent molecules. A solvent molecule can also form a bond with a second solvent molecule. The association interaction is modeled with an orientation-dependent square-well. The total number of bonding sites on each chain is varied and the effects studied. This is another test of the theory for the case of mixtures of associating molecules of different sizes. The Metropolis Monte Carlo technique was chosen to perform simulations in the canonical and isothermal–isobaric ensembles. Good agreement was found between theory and simulation.