J.L. Legido

Thermal conductivity and viscosity measurements of ethylene glycol-based Al2O3 nanofluids

The dispersion and stability of nanofluids obtained by dispersing Al2O3 nanoparticles in ethylene glycol have been analyzed at several concentrations up to 25% in mass fraction. The thermal conductivity and viscosity were experimentally determined at temperatures ranging from 283.15 K to 323.15 K using an apparatus based on the hot-wire method and a rotational viscometer, respectively. It has been found that both thermal conductivity and viscosity increase with the concentration of nanoparticles, whereas when the temperature increases the viscosity diminishes and the thermal conductivity rises. Measured enhancements on thermal conductivity (up to 19%) compare well with literature values when available. New viscosity experimental data yield values more than twice larger than the base fluid. The influence of particle size on viscosity has been also studied, finding large differences that must be taken into account for any practical application. These experimental results were compared with some theoretical models, as those of Maxwell-Hamilton and Crosser for thermal conductivity and Krieger and Dougherty for viscosity.

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.

Enhancement of thermal conductivity and volumetric behavior of FexOy nanofluids

Homogeneous and stable magnetic nanofluids containing iron oxide nanoparticles, α-Fe2O3 (hematite) and Fe3O4 (magnetite) in ethylene glycol, were prepared at concentrations up to 25% in mass fraction. Commercial Hexagonal Scalenohedral-shaped α-Fe2O3 nanoparticles were selected while Fe3O4 nanoparticles were synthesized using a coprecipitation method. The products were characterized by transmission and scanning electron microscopy and x-ray diffraction. The thermal conductivity of both nanofluids was measured as a function of volume fraction and temperature. The results illustrate that the enhanced thermal conductivity of the nanofluids increases with volume fraction but is temperature independent. The experimental results show that both types of nanoparticles in this base fluid present no significant aggregation. These experimental values were also compared with theoretical models. Moreover, the density of these nanofluids was measured as a function of volume fraction, temperature, and pressure. The volu...

Effect of temperature on W-shaped excess molar heat capacities and volumetric properties : Oxaalkane-nonane systems

Excess molar volumesVmf of the mixtures diglyme (2,5,8-trioxanonane: TON), triglyme (2.5,8,11-tetraoxadodecane: TODD), or tetraglyme (2,5,8,11,14-pen-taoxapentadecane: POPD; E181)+n-nonane have been obtained from density measurements at 278.15, 288.15,298.15, and 308. 15 K. In addition, a micro DSC II differential scanning calorimeter was used to obtain excess molar heat capacitiesCpE at constant pressure for the same mixtures except for TON+n-nonane and at the same temperatures except for 278.15 K. These results allowed us to calculate the following mixing quantities in the complete range of concentration: α(∂Vmυ/∂T)p, and (∂Hυ/∂p)nT at 298.15K. The excess molar volumes are positive with large maximum values located in the central concentration range with the exception of POPD +n-nonane at 278.15 K, which has a central miscibility gap. For these mixtures,CpF has a W-shaped concentration dependence: two minima separated by a maximum.

Analysis of thermodynamic properties of 1-alkanol + n-alkane mixtures using the nitta—chao group contribution model

Abstract In 1977, Nitta et al. published a group contribution molecular model for thermodynamic properties of polar and non-polar liquids and their solutions, including energy of vaporization, pVT relationships, excess properties and activity coefficients. At the same time they reported the corresponding characteristic parameters for methyl, methylene, hydroxyl and carbonyl groups and for their mutual interactions. Since the values predicted by the Nitta et al. model for certain excess properties of alcohol + alkane systems using these parameters differ significantly from experimental findings, we have recalculated the relevant parameters using data for a larger number of mixtures and for properties such as excess volumes that were not included in the original database.

Description of PVT behaviour of hydrofluoroethers using the PC-SAFT EOS

A description of the volumetric behaviour of segregated hydrofluoroethers has been carried out using PC-SAFT EOS. Characteristic parameters for several molecules were calculated where experimental data were available, and accurate results were obtained for compressed and saturated liquid density estimation, as well as for saturation curves. A functional group contribution scheme is proposed also for the calculation of the mentioned PC-SAFT EOS characteristic parameters, and this approach reproduces adequately the dependence on molecular structure of the parameters calculated in this work, and also gives good estimations when the parameters are extrapolated for other molecules of the same family.

PρT Measurements of Nonafluorobutyl Methyl Ether and Nonafluorobutyl Ethyl Ether Between 283.15 and 323.15 K at Pressures Up to 40 MPa

In this paper, experimental densities for nonafluorobutyl methyl ether and nonafluorobutyl ethyl ether from 283.15 to 323.15 K at pressures up to 40 MPa are reported. The density measurements were performed by means of a high pressure vibrating tube densimeter. Data reliability was checked by comparing experimental results obtained for tetrachloromethane—whose density is close to those of the fluids studied—with recommended literature data. Furthermore, the isobaric thermal expansion, isothermal compressibility, and internal pressure have been calculated from these density data.

Viscosity deviations of ternary mixtures di-n-butyl ether + 1-propanol + n-octane at several temperatures

Abstract Viscosities and densities of {x1 di-n-butyl ether+x2 1-propanol+(1−x1−x2) n-octane} and their corresponding binary mixtures were measured at the temperatures of 293.15, 298.15, 303.15 and 308.15 K under atmospheric pressure. Kinematic viscosities were determined using a capillary viscosimeter, and densities were measured by a vibrating tube densimeter. The viscosity deviations and Gibbs free energies of activation for flow were evaluated. All the experimental values were compared with the results obtained with different predictive methods.

Analysis of excess enthalpies of ethyl formate + n-alkane or 1-alkanol with two group contribution models

Abstract We present experimental values of enthalpies of mixing at 298.15 K for mixtures composed of ethyl formate with n-alkanes (from n-hexane to n-decane) or 1-alkanols (from 1-propanol to 1-decanol). Then hE data for the latter mixtures have been used to determine characteristic formate-alkanol interaction parameters for three group contribution models: the UNIFAC model with and without consideration of 1-alkanol association effects, and the Nitta-Chao model. The experimental data are reproduced within mean errors of less than 6% by all the used models.

Application of the UNIFAC and Nitta-Chao models to describing the behavior of methyl ester/alkane mixtures, and experimental data for (methyl n-alkanoates + n-heptadecane) binary mixtures

Abstract J. Ortega and J.L. Legido, 1994. Application of the UNIFAC and Nitta-Chao models to describing the behavior of methyl ester/alkane mixtures, and experimental data for (methyl n-alkanoates+n-heptadecane) binary mixtures. Fluid Phase Equilibria, 95: 175-214. Excess molar properties, hE and vE, were determined based on the composition of binary mixtures of fourteen methyl esters (from ethanoate to n-pentadecanoate) and n-heptadecane at 298.15 K. The results showed all the mixtures to be endothermic and to undergo positive changes in excess volume. Both these effects decreased in a quasi-regular manner with the chain length of the methyl alkanoate. The excess enthalpies of the mixtures were compared with the values estimated by two group-contribution models, two different versions of the UNIFAC model, and the model of Nitta et al. [Nitta, T., Turek, E.A., Greenkorn, R.A. and Chao, K.C., 1977. A group contribution molecular model of liquids and solutions. AIChE J., 23: 144-160]. Using the UNIFAC model, the best prediction was achieved when all the methyl esters were considered to be alkyl ethanoates, which yielded a mean overall error of less than 5%. Application of the model of Nitta et al. to the mixtures considered yielded hE and vE values that differed substantially from the experimental values, with mean overall errors of 14% for the hE values and 34% for the vE values. Therefore, a comprehensive database of thermodynamic quantities for 368 binary mixtures was used to recalculate the alkane-ester interaction parameters and group parameters, which were then reapplied in the above-mentioned molecular model. This substantially improved the estimates of the properties for the pure components as well as those for the mixing quantities, achieving mean errors of less than 4% for hE and 17% for vE.