Carlos A. Nieto de Castro

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 ...

Reference data for the thermal conductivity of saturated liquid toluene over a wide range of temperatures

Efficient design of industrial processes and equipment requires accurate thermal conductivity data for a variety of fluids, such as alternative refrigerants, fuels, petrochemicals, aqueous systems, molten salts, and molten metals. The accuracy of experimental thermal conductivity data is a function of the operating conditions of the instrument. Reference data are required over a wide range of conditions to verify the claimed uncertainties of absolute instruments and to calibrate relative instruments, since either type may be used to measure the thermal conductivity of fluids. Recently, accurate experimental data for the thermal conductivity of liquid toluene near the saturation line have been obtained, which allow the upper temperature limit of the previous reference-data correlation to be extended from 360 to 553 K. The thermal conductivity was measured using two transient hot-wire instruments from 300 to 550 K, the first with a bare 12.7 μm platinum wire and the second using an anodized 25 μm tantalum wire. Uncertainties due to the contribution of thermal radiation and the purity of the samples are discussed. The proposed value of the thermal conductivity of liquid toluene at 298.15 K and 0.1 MPa is 0.13 088±0.000 85. The quality of the data is such that new improved recommendations and recommended values can be proposed with uncertainties at 95% confidence of 1% for 189

Hydrogen bonding and the dipole moment of hydrofluorocarbons by density functional theory

Recent measurements of the dielectric permittivity of hydrofluorocarbons in the liquid phase have allowed calculation of the dipole moments in a liquid environment. These values were based on Kirkwood theory, and were significantly greater than the corresponding gas phase dipole moments. In order to understand some features suggesting possible hindered rotation of the molecules in the liquid, density functional and self-consistent-reaction-field calculations for a series of HFC molecules including CHF2CF3 (HFC-125), CH2FCF3 (HFC-134a), CH3CF3 (HFC-143a), CH2F2 (HFC-32) and CHF2CH3 (HFC-152a) are reported. Particular emphasis has been given to the calculation of dimerisation energies, rotational potentials, polarisabilities and dipole moments. We discuss hydrogen bonding in hydrofluorocarbon dimers and the relationship between the structure and charge distribution of the dimers and the dipole moment in the liquid predicted by relative permittivity measurements. For HFC-32 we have calculated the average dipole moment in small clusters (n = 2–10). The structure of the clusters has been determined by density functional theory optimisations (n = 2–6) and Monte Carlo simulations (n = 2–10). The average dipole moment of the HFC-32 decamer is 2.35 D, which represents a 17% increase relative to the free monomer (2.0 D). We find that the enhancement of the monomer dipole induced by hydrogen bonding in HFC-32 clusters is much less pronounced in comparison with the considerable increase (50%) observed in water clusters.

Thermal conductivity of a moderately dense gas

Abstract Recent extensive measurements of the thermal conductivity of argon and nitrogen have enabled us to evaluate the first density correction as a function of temperature and to compare it with a theoretical prediction. The prediction follows from a previously published microscopically based theory, which includes effects due to collisional transfer, collisions among three molecules, and monomer-dimer collisions. The first density correction was evaluated for a Lennard-Jones interaction potential. An ad hoc modification of the theory accounts for contributions to the thermal conductivity from internal degrees of freedom. The comparison shows good agreement over a wide range of temperatures.

Nanofluids as Advanced Coolants

Nanofluids have attracted great interest from the researchers all over the world due to their superior thermal transports and potential applications in numerous important fields. From extensive research, nanofluids are found to exhibit significantly higher thermal conductivity than that of base fluids. However, besides thermal conductivity, investigations on convective and boiling heat transfer are also very important in order to exploit nanofluids as advanced coolants. In this chapter, experimental investigations on these two major cooling features, i.e., convective and boiling heat transfer, of nanofluids are reported together with critical review of recent research progress in these important areas of nanofluids. Nanofluid development background along with their potential benefits and applications are also briefly discussed. Despite of controversies and scattered experimental data on all these thermal features of nanofluids, it is undisputed that nanofluids exhibit substantially enhanced thermal conductivity, convective heat transfer coefficient, and boiling critical heat flux which further increase with increasing concentration of nanoparticles, and these clearly evince that nanofluids can potentially be used as advanced coolants in the future.

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.