There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

An introduction to heat transfer

Organic Carbonates as Solvents in Synthesis and Catalysis

This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

A Benchmark Study on the Thermal Conductivity of 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.

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

One of the potential applications of the ionic liquids (ILs) is their use as lubricants or lubricant additives. The choice of the cation and the anion of the ILs, as well as the side chain design, determine their fundamental properties, which permits us to create tailor-made lubricants and lubricant additives among other functional fluids. In this work we have studied 10 ILs for which we report densities and viscosities from 283.15 K (and for some ILs at lower temperatures) up to 373.15 K. The viscosities of the ILs fall in the range of the applications of hydraulic fluid or lubricants. Four of these ILs were composed by the anion tris(pentafluoroethyl)trifluorophosphate [(C2F5)3PF3]− and one of the following cations: 1-butyl-2,3-dimethylimidazolium [C4C1C1min]+, 1-butyl-1-methylpyrrolidinium [C4C1Pyrr]+, 1-(2-methoxyethyl)-1-methyl-pyrrolidinium [C1OC2C1Pyrr]+, and trihexyl(tetradecyl)phosphonium [P6,6,6,14]+. Furthermore, three of the ILs contain the anion bis(trifloromethylsulfonyl)imide [NTf2]− and on...

Influence of Molecular Structure on Densities and Viscosities of Several Ionic Liquids

Homogeneous stable suspensions obtained by dispersing dry TiO2 nanoparticles in pure ethylene glycol were prepared and studied Two types of nanocrystalline structure were analyzed, namely anatase and rutile phases, which have been characterized by scanning electron microscopy The rheological behavior was determined for both nanofluids at nanoparticle mass concentrations up to 25%, including flow curves and frequency-dependent storage and loss moduli, using a cone-plate rotational rheometer The effect of temperature over these flow curve tests at the highest concentration was also analyzed from 28315 to 32315 K Furthermore, the influence of temperature, pressure, nanocrystalline structure, and concentration on the volumetric properties, including densities and isobaric thermal expansivities, were also analyzed

/pdf/rheological-and-volumetric-properties-of-tio2-ethylene-4bfj1ycycm.pdf

Rheological and volumetric properties of TiO2-ethylene glycol nanofluids

The rheological behaviour of ethylene glycol-based nanofluids containing hexagonal scalenohedral-shaped α-Fe2O3 (hematite) nanoparticles at 303.15 K and particle weight concentrations up to 25% has been carried out using a cone-plate Physica MCR rheometer. The tests performed show that the studied nanofluids present non-Newtonian shear-thinning behaviour. In addition, the viscosity at a given shear rate is time dependent, i.e. the fluid is thixotropic. Finally, using strain sweep and frequency sweep tests, the storage modulus G', loss modulus G″ and damping factor were determined as a function of the frequency showing viscoelastic behaviour for all samples.

/pdf/rheological-non-newtonian-behaviour-of-ethylene-glycol-based-50k5l2ih72.pdf

Luis Lugo

Papers

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

Influence of Molecular Structure on Densities and Viscosities of Several Ionic Liquids

Rheological and volumetric properties of TiO2-ethylene glycol nanofluids

Rheological non-Newtonian behaviour of ethylene glycol-based Fe2O3 nanofluids

Automated densimetric system: Measurements and uncertainties for compressed fluids