Carlos Casanova

A study on stability and thermophysical properties (density and viscosity) of Al2O3 in water nanofluid

The dispersion and stability of nanofluids obtained by dispersing Al2O3 nanoparticles (obtained from different sources) in water have been analyzed. The differences arising from different dispersion techniques, the resulting particle size distribution, and time stability among the different samples are evaluated. Then the volumetric behavior up to high pressures (25 MPa) and atmospheric pressure viscosity were experimentally determined. It has been found that the influence of particle size in density is subtle but not negligible, but the differences in viscosity are very large and must be taken into account for any practical application. These viscosity differences can be rationalized by considering a theory describing the aggregation state of the nanofluid.

Application of the zeroth approximation of the DISQUAC model to cyclohexane + n-alkane mixtures using different combinatorial entropy terms

Abstract Literature data on molar excess functions, Gibbs energy GE, enthalpy HE, and heat capacity CpE, on activity coefficients γi∞, and partial molar excess enthalpies HiE,∞, at infinite dilution and on solid-liquid equilibria, SLE, of the cyclohexane + n-alkane mixtures are examined on the basis of the zeroth approximation of the DISQUAC group contribution model. The model provides a quite satisfactory description of the thermodynamic properties for the mixtures under study, although the symmetry of the calculated excess functions differs from the experimental one for systems containing long-chain n-alkanes. This may be due to the so-called Patterson effect. The influence of different combinatorial entropy terms (Flory-Huggins, Stavermann-Guggenheim or Kikic equations) on the prediction of thermodynamic properties such as GE, lnγi∞ and SLE is also examined. HE, CPE or HiE,∞ are represented by an interactional term only. The results calculated using the Flory-Huggins term are slightly better than those obtained applying the Stavermann-Guggenheim equation. Results based on the Kikic expression are poorer than those given by Flory-Huggins, particularly at high concentration of cyclohexane in systems containing the longer n-alkanes. So, the Kikic equation leads to poorer results for lnγ2∞ for these systems. SLE predictions are determined mainly by the physical constants of the pure compounds. So, essentially they do not depend on the combinatorial term used. A comparison between the zeroth approximation of DISQUAC and the modified UNIFAC model (Lyngby version) is also presented. Such comparison shows that both methods lead to similar results; although the latter gives poorer predictions on the temperature dependence of the excess functions than the former. On the other hand, the number of interaction parameters needed in modified UNIFAC is larger than when the zeroth approximation of DISQUAC is applied and, more important, they change with the number of carbon atoms of the n-alkane in a rather erratic way for the first members of the series. This makes the predictive task of UNIFAC more difficult.

Calorimetric investigation of the interactions between oxygen and hydroxyl groups in (alcohol+ether) at 298.15 K☆☆☆

Abstract Flow-calorimetric measurements of excess enthalpies at 298.15 K are reported for 17 mixtures of (an alcohol + an ether). The alcohol is methanol, ethanol, propan-1-ol, or heptan-1-ol; the ether is butyl ether, methyl butyl ether, diethylether, 3,6-dioxaoctane, or 2,5,8-trioxanonane. The results indicate that interactions between alcohol and ether which are a consequence of the interactions between the hydroxyl and the oxygen groups increase almost linearly with the surface fraction of oxygen in the ether molecule. These interactions are more important in the case of short-chain alcohols.

Excess properties of mixtures of some n-alkoxyethanols with organic solvents: III. VE and CEp with butan-1-ol at 298.15 K

The excess molar volumes, VE, and the excess molar heat capacities, CEp are determined as a function of mole fraction, X, at atmospheric pressure and 298.15 K for 2-methoxyethanol (1), 2-ethoxyethanol (1), 2-butoxyethanol (1), 2-(2-methoxyethoxy)ethanol (1), 2-(2-ethoxyethoxy)ethanol (1), 2-(2-butoxyethoxy)ethanol (1) with butan-1-ol (2) mixtures. The VE values decrease in magnitude as the alkyl chain length of the n-alkoxyethanol increases for the two homologous series; they are positive except for the mixtures containing 2-butoxy-ethanol and 2-(2-butoxyethoxy)ethanol for which they are negative over the whole mole-fraction range. The CEp values are positive and relatively small for all the mixtures studied.

DISQUAC predictions of phase equilibria, molar and standard partial molar excess quantities for 1-alkanol+cyclohexane mixtures

Literature data for phase equilibria: vapor-liquid VLE, liquid-liquid LLE, and solid-liquid SLE; molar excess Gibbs energies GE, molar excess enthalpies HE; activity coefficients γi∞ and partial molar excess enthalpies HiE,o at infinite dilution for 1-alkanol (1)+cyclohexane (2) mixtures are examined by the DISQUAC group contribution model. For a more sensitive test of DISQUAC, the azeotropes, obtained from the reduction of the original isothermal VLE data, are also examined for systems characterized by hydroxyl, alkane and cyclohexane groups. The alkane/cyclohexane and alkane/hydroxyl interaction parameters have been estimated previously. The cyclohexane/hydroxyl interaction parameters are reported in this work. The first dispersive parameters increase regularly with the size of the alkanol; from 1-octadecanol they are constant; an opposite behavior is encountered for the third dispersive parameters, which are constant from 1-dodecanol. The second dispersive parameters decrease as far as 1-propanol and then increase regularly; from 1-octadecanol they are constant. The quasichemical parameters are equal to those for the alkane/hydroxyl interactions. Phase equilibria, the molar excess functions, and activity coefficients at infinite dilution are reasonably well reproduced. Poor results are found for HiE,o and DISQUAC predictions for HiE,o are strongly dependent on temperature.

Thermochemical behaviour of mixtures of n-alcohol + aliphatic ether: heat capacities and volumes at 298.15 K

Abstract Molar excess volumes VE at 298.15 K were obtained as a function of mole fraction for each of the binary mixtures formed from methyl n-butylether, 3,6-dioxaoctane, and 2,5,8-trioxanonane + methanol, and + ethanol, and also for 2,5,8-trioxanonane+1-propanol. In addition, a Picker flow calorimeter was used to determine molar excess heat capacities CPE at 298.15 K for the same mixtures. All the excess heat capacities are positive and the excess volumes are negative. Values of VE of mixtures with a given ether become less negative with increasing chain length of the alcohol.

Calorimetric and phase equilibrium data for linear carbonates + hydrocarbons or + CCl4 mixtures. Comparison with DISQUAC predictions

Abstract The disquac interaction parameters for the linear organic carbonate—alkane, carbonate—cyclohexane, carbonate—benzene or —toluene, and carbonate—CCl 4 contacts are revised on the basis of new experimental data on vapor—liquid equilibria for dimethyl or diethyl carbonate + n -alkane mixtures. The new parameters differ slightly from the previous ones. The main conclusions remain valid. The quasichemical interchange coefficients for carbonate—alkane or —cyclohexane contacts, and the purely dispersive interchange coefficients for carbonate—benzene or —toluene and carbonate—CCl 4 contacts, show a relatively weak steric effect. The model provides a fairly consistent description of low pressure fluid phase equilibria (vapor—liquid, liquid—liquid and solid—liquid) and related excess functions (Gibbs energy and enthalpy) using the same set of parameters.

Excess properties of mixtures of some n-alkoxyethanols with organic solvents I. HmE with di-n-butylether at 298.15 K

Abstract The excess molar volumes and excess molar heat capacities have been determined as functions of mole fraction x at atmospheric pressure and 298.15 K for six (an alkoxyethanol + di-n-butylether) mixtures. The alkoxyethanols were 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, 2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)ethanol, and 2-(2-butoxyethoxy)ethanol. The VmEs decrease in magnitude as the alkyl chain length of the alkoxyethanol increases for the two homologous series. They are positive except for the mixtures containing 2-butoxyethanol and 2-(2-butoxyethoxy)ethanol. For these they are positives only at low mole fractions of alkoxyethanol. A parallel, almost linear, decrease is also observed for the Cp, mEs; they are strongly positive and smaller for the components with higher alkyl chain length.

Characterization of the alkanol/alkanol contacts and prediction of excess functions of ternary systems of two n-alkan-1-ols and one n-alkane using DISQUAC

Abstract Gonzalez, J.A., Garcia de la Fuente, I., Cobos, J.C. and Casanova, C., 1992. Characterization of the alkanol/alkanol contacts and prediction of excess functions of ternary systems of two n-alkan-1-ols and one n-alkane using DISQUAC. Fluid Phase Equilibria, 78: 61-80. The data available in the literature on the molar excess Gibbs energies GE, molar excess enthalpies HE, and activity coefficients at infinite dilution γ∞i, for mixtures of two n-alkan-1-ols are examined on the basis of the DISQUAC group contribution model. Using the available interaction parameters for the hydroxyl/aliphatic contacts, the interchange coefficients for the hydroxyl/hydroxyl contacts CDISh1h2,l (l = 1, 2, 3)were fitted. One set of GE ternary data and 21 sets of HE ternary data for n-alkan-1-ol(1)+ n-alkan-1-ol(2) + n-alkane(3) systems are also investigated in the framework of this model. The relative standard deviations for the excess enthalpies are less than 0.1 for most of the mixtures.

Excess molar volumes of diethyl carbonate with hydrocarbons or tetrachloromethane at 25°C

The excess molar volumes VmE at atmospheric pressure and at 25°C for binary mixtures of diethyl carbonate with n-heptane, n-decane, n-tetradecane, 2,2,4-trimethylpentane, cyclohexane, benzene, toluene, or tetrachloromethane have been obtained over the whole mole-fraction range from densities measured with a vibrating-tube densimeter. The VmE are positive for all the systems investigated, except for the mixture with toluene which is negative. The results for VmE together with data previously published on excess molar enthalpies HmE and excess molar Gibbs energies GmE, suggest interactions between carbonate and hydrocarbons which are stronger with aromatic than with aliphatic hydrocarbons.