F. J. V. Santos

Standard Reference Data for the Viscosity of Toluene

Viscosity is an important transport property for the optimum design of a chemical process plant and for the development of molecular theories of the liquid state. A large amount of experimental viscosity data has been produced for all types of liquids, from alternative refrigerants to molten salts and molten metals. The accuracy of these data is related to the operating conditions of the instrument and, for this purpose as well as for the calibration of relative instruments, standard reference data for viscosity are necessary over a wide range of temperatures. New experimental data on the viscosity of liquid toluene along the saturation line have been obtained recently, mostly at low temperatures. The quality of the data is such that recommended values can be proposed with uncertainties of 0.5% (95% confidence level) for 260 K⩽T⩽370 K and 2% for 210 K⩽T<260 K and 370 K<T⩽400 K. A discussion about the uncertainties in the measurements and about the purity of the samples is made. The proposed value for the ...

Dielectric constant measurements of toluene and benzene

Abstract Preliminary measurements of the dielectric constant of toluene and benzene have been performed along the saturation line, up to 100°C. A capacitance bridge operating with a three terminal arrangement was used. A new capacitor was designed for these measurements. A general description of the instrument is made which includes the temperature control and measurement systems, pressure and vacuum lines, dielectric constant cell and pressure vessel.

Alkyl deoxy-arabino-hexopyranosides: Synthesis, surface properties, and biological activities

Octyl and dodecyl glycosides possessing 2-deoxy-arabino-hexopyranoside moieties belonging to the D- and L-series in their alpha- and beta-forms were synthesized by reaction of an acetyl protected glycal with octanol or dodecanol, catalyzed by triphenylphosphine hydrobromide, followed by deprotection. Their surface properties were studied and discussed in terms of the adsorption and aggregation parameters, pC(20), CMC, and gamma(CMC). The antimicrobial activities were assessed using the paper disk diffusion and broth dilution methods. Both the octyl and dodecyl 2-deoxy beta-D-glycosides inhibited significantly Enterococcus faecalis, a microbe also highly susceptible to dodecyl 2,6-dideoxy-alpha-L-arabino-hexopyranoside. This compound was particularly active against Bacillus cereus and Bacillus subtilis, presenting for both Bacillus species a minimal inhibitory concentration of the same order of magnitude and a minimal lethal concentration even smaller than that obtained for chloramphenicol, a bioactivity which remained unaltered after 1 year solution storage at 4 degrees C. In addition, activity over Listeria monocytogenes was also observed. Direct cytotoxicity and genotoxicity of the glycosides were determined by proliferative index (mitotic index) evaluation in peripheral human lymphocytes of healthy donors. All compounds induced acute toxicity effects, and the response was dose dependent for the alpha-anomer of both the alkyl 2-deoxy-arabino-hexopyranosides and for the corresponding dodecyl beta-anomer, what suggests that non-toxic but still bioactive concentrations may be found for these compounds.

A high-temperature viscometer for molten materials

An oscillating-cup viscometer for the measurement of the viscosity of molten materials from room temperature to 1400 K was developed. The instrument is described in detail and the working equations are presented. The operational behavior was tested with water at room temperature. Preliminary measurements show that the new viscometer is capable of measuring the viscosity of water at room temperature to within 0.2%. As the primary objective of this work is the establishment of standard reference data for high-temperature viscosity measurements in molten salts, molten metals, and molten semiconductors, references of earlier viscosity measurements of molten KNO3 are given.

Gradient flow titration for the determination of fluoride ion in natural waters

The determination of fluoride ions in water samples was accomplished by using a gradient flow titration. A standard commercial combined electrode is used in a cell configuration that combines the gradient chamber and the electrode in a single unit. The methodology developed gives results with a relative standard deviation of about 3%. The average recoveries after spiking natural samples with fluoride are in the range 100-102%. The method was used successful in determining the fluoride concentration in water samples.

Dipole moments of isomeric alkoxyalcohols in cyclohexane. Comparison of Hedestrand and Fröhlich procedures with a new formula

Limiting dipole moments of four isomeric alkoxyalcohols dissolved in cyclohexane at 298.15 K were determined from measurements of the relative permittivity of at least 17 dilute solutions up to solute mole fraction of 0.03. In addition, 5 to 7 data points were obtained up to a mole fraction of 0.1. A stepwise dilution device ensured dielectric measurements to be performed in highly dilute solutions with accurately determined concentrations. Densities of these solutions and refractive indices of the pure liquids were independently measured. Limiting dipole moments were calculated using Hedestrands equation and an improved method of implementing Fröhlichs equation, which circumvents extrapolation difficulties referred to in the literature. A new formula, based on the one-liquid approach for extending the Onsager-Kirkwood-Fröhlich equation to liquid mixtures, is introduced and shown to yield a reliable and robust procedure for estimating dipole moments of polar molecules dissolved in non-polar solvents. Limiting dipole moment values for 2-tert-butoxyethanol (2.31 D), 1-propoxypropan-2-ol (2.14 D), 2-butoxyethanol (2.14 D) and 2-isobutoxyethanol (2.08 D) are recommended. The relative order of these values appears to determine the order of hydrophilicity of these four alkoxyalcohols as suggested by their recently reported limiting partial molar volumes and isentropic compressions in aqueous solutions.

Dielectric properties of alternative refrigerants

This paper gives an overview of our research, from experimental measurements of the relative permittivity on new and alternative refrigerants, to theoretical interpretation of the data and density functional and density functional self-consistent reaction field calculations for a series of HFC molecules. Experimental measurements were obtained as a function of temperature and pressure for Class B refrigerants-HCFC-123, HCFC-142b, HCFC-141b, Class A refrigerants-HFC-32, HFC-134a, HFC-152a, HFC-143a, HFC-227ea, HFC-245fa, HFC-365mfc and some mixtures of them: HFC-125/143a/134a (R-404A), HFC-32/125/134a (R-407C), HFC-125/143a (R-507), HFC-32/125 (R-410A). Density functional and density functional self-consistent reaction field calculations were performed for CHF2CF3 (HFC-125), CH2FCF3 (HFC-134a), CH3CF3 (HFC-143a), CH2F2 (HFC-32), and CHF2CH3 (HFC-152a). A particular emphasis has been given to the calculation of dimerisation energies, rotational potentials, polarisabilities and dipole moments

Synthesis, properties and physical applications of ionanofluids

Ionic liquids have proved to be one of the most impressive classes of fluids, due to their properties and applications to chemistry and engineering. One of the most recent applica‐ tions of complex systems of ionic liquids and nanomaterials are IoNanofluids, from heat transfer to catalysis, solar absorbing panels, lubricants or luminescent materials. These novel materials belong to the class of nanofluids proposed in the last years and are a mixture of ionic liquid and nanomaterial, in the form of nanoparticle dispersion, and have already re‐ sulted in a number of publications in chemical and physical journals.

Ionanofluids: New Heat Transfer Fluids for Green Processes Development

Ionanofluids represent a new and innovative class of heat transfer fluids that encompass multiple disciplines like nanoscience, mechanical, and chemical engineering. Apart from fascinating thermophysical properties, the most compelling feature of ionanofluids is that they are designable and fine-tunable through base ionic liquids. Besides presenting results on thermal conductivity and specific heat capacity of ionanofluids as a function of temperature and concentration of multiwall carbon nanotubes, findings from a feasibility study of using ionanofluids as replacement of current silicon-based heat transfer fluids in heat transfer devices such as heat exchangers are also reported. By comparing results on thermophysical properties and estimating heat transfer areas for both ionanofluids and ionic liquids in a model shell and tube heat exchanger, it is found that ionanofluids possess superior thermophysical properties particularly thermal conductivity and heat capacity and require considerably less heat transfer areas as compared to those of their base ionic liquids. This chapter is dedicated to introducing, analyzing, and discussing ionanofluids together with their thermophysical properties for their potential applications as heat transfer fluids. Analyzing present results and other findings from pioneering researches, it is found that ionanofluids show great promises to be used as innovative heat transfer fluids and novel media for the exploitation of green energy technologies.

Current research and future applications of nano- and ionano-fluids

An overview of several important aspects of nanofluids and ionanofluids, their background, as well as key experimental findings on their thermophysical properties is presented in this study. While nanofluids are prepared by dispersing nanoparticles in traditional heat transfer fluids, ionanofluids are engineered by dispersing nanoparticles in ionic liquids only. Some representative results of various thermal features and properties of both fluids are also briefly discussed. Although there are inconsistencies in experimental data from various groups, nanofluids possess significantly higher thermal conductivity, convective heat transfer coefficient and boiling critical heat flux compared to their base fluids and these properties further increase with increase concentration of nanoparticles. On the other hand, based on results from very limited studies ionanofluids are found to show superior thermophysical properties compared to their based ionic liquids. In addition, numerical results on heat transfer areas from a model study indicated that ionanofluids are better heat transfer fluids for heat exchangers or other heat transfer devices than ionic liquids. Future research direction and applications of these novel fluids are also outlined. Review reveals that both nanofluids and ionanofluids show great promises to be used as advanced heat transfer fluids and novel media for many thermal management systems as well as green solvent-based applications.