The paper presents a complete theory for a new method for the determination of the thermal diffusivity of a bulk solid in the form of a cylinder using a pulse of energy of finite duration delivered on one face and the subsequent temperature rise detected on a parallel face. It is an important feature of the method that the departure from equilibrium in the solid sample is small so that the temperature rise is no more than a few degrees Kelvin. The energy pulse may be of any temporal distribution and the detection of the temperature rise can be conducted at any point on the opposing face of the sample. The theory explicitly accounts for heat losses at all the surfaces of the sample and enables absolute measurement of the thermal diffusivity of the sample. A prototype instrument is described to realize this theory in which the heating pulse is generated by an array of light emitting diodes in a circular configuration which is then guided by a light pipe so that a uniform distribution is ensured across the flat face of the solid sample being tested. The instrument is designed for operation over the temperature range from ambient to 1300 K but, in the current proof of principle, measurements are conducted at room temperature on a sample of Pyroceram™ 9606.1 In this case, the detection is performed with a micro-thermocouple at the center of the sample. Several different rectangular heating pulse durations are employed to show that the theory provides an appropriate description of the experiment. The potential for future applications of the technique is demonstrated.

The paper summarizes the conditions that are necessary to secure accurate measurements of the thermal conductivity of fluids using the transient hot-wire technique. The paper draws upon the development of the method over five decades to produce a prescription for its use. The purpose is to provide guidance on the implementation of the method to those who wish to make use of it for the first time. It is shown that instruments of the transient hot-wire type can produce measurements of the thermal conductivity with the smallest uncertainty yet achieved (± 0.2%). This can be achieved either when a finite element method (FEM) is employed to solve the relevant heat transfer equations for the instrument or when an approximate analytic solution is used to describe it over a limited range of experimental times from 0.1 s to 1 s. As well as establishing the constraints for the proper operation of the instrument we consider the means that should be employed to demonstrate that the experiment operates in accordance with the theoretical model of it. If the constraints are all satisfied then an uncertainty in thermal conductivity measurements of as little as ± 0.2–0.5% can be obtained for gases and liquids over a wide range of thermodynamic state from 0.1 MPa to 700 MPa and temperatures from 70 K to 500 K with the exception of near critical conditions. It is observed that many applications of the transient hot-wire technique do not conform to the constraints set out here and therefore may be burdened with very much greater uncertainties, sometimes large enough to render the results meaningless.

There are three mechanisms whereby energy can be transported from one region of space to another under the influence of a temperature difference. One is by transmission in the form of electromagnetic waves (radiation); the second is the process of convection, in which a bulk or local motion of the material effects the transport; and the final process is that of thermal conduction, when energy is transported through a medium. In most practical situations, energy transport is accomplished by all three processes to some extent, but the relative importance of each contribution varies markedly. For example, within an evacuated region, radiation is the sole mechanism of transport; whereas, in an opaque solid, conduction is the only mechanism possible. The fact that in most practical situations all three heat transfer mechanisms are present gready complicates the process of measurement of the thermal conductivity.

New measurements of the thermal conductivity of n -docosane, n -tetracosane, 1,6-hexanediol, and 1,8-octanediol, in the solid and liquid phase, are presented. The technique employed is the transient hot-wire technique, based on a full theoretical model. The technique is absolute and is characterized by an uncertainty of 1%. At the 95% confidence level, the standard deviations of the thermal conductivity measurements of n -docosane, are 0.40% for the solid phase (267 K to 308 K), and 0.60% for the liquid phase (330 K to 360 K); of n -tetracosane, 0.60% for the solid phase (265 K to 306 K), and 0.30% for the liquid phase (339 K to 363 K); of 1,6-hexanediol, 0.70% for the solid phase (263 K to 296 K), and 0.40% for the liquid phase (327 K to 351 K); and of 1,8-octanediol 1.1% for the solid phase (265 K to 312 K), and 0.50% for the liquid phase (344 K to 356 K), respectively.

From the time levulinic acid was listed as one of the top-12 building blocks for the sugars-high value compounds conversion, the interest in this compound increased. As part of its possible production route, the definition of viable separation schemes appears of paramount importance in the overall development of levulinic acid exploitation. Hybrid sequences where liquid-liquid extraction is followed by distillation were considered proving how the direct and direct -indirect separation schemes appeared to be the best alternatives in terms of total annual cost and environmental impact. These alternatives were further analyzed to improve their design by complementing the process simulator database with thermophysical experimental values. After obtaining a reliable design for the hybrid direct and direct-indirect configurations used as benchmarks, two intensified alternatives were generated. The first intensified configuration is classified as thermodynamically equivalent sequence, while the second one includes a divided wall column. For both, it was achieved a reduction of the total annual cost of 11% without any penalty for the environmental impact compared to the reference case.

New measurements of the thermal conductivity of hexadecan-1-ol and octadecan-1-ol, in the solid and liquid phases, are presented. The technique employed is the transient hot-wire technique, based on a full theoretical model with equations solved both by the approximate analytic solution and by finite elements for the exact geometry of the sensor. The technique is absolute and is characterized by an uncertainty of 1 %. At the 95% confidence level, the standard deviations of the thermal conductivity measurements of hexadecan-1-ol, are 0.65 % for the solid phase (266 K to 315 K), and 0.16 % for the liquid phase (334 K to 361 K); while in the case of octadecan-1-ol, are 0.46 % for the solid phase (259 K to 324 K), and 0.33 % for the liquid phase (340 K to 364 K), respectively.

Ionic liquids have been suggested as new engineering fluids, specifically in the area of heat transfer, and as alternatives to current biphenyl and diphenyl oxide, alkylated aromatics and dimethyl polysiloxane oils, which degrade above 200 °C, posing some environmental problems. Addition of nanoparticles to produce stable dispersions/gels of ionic liquids has proved to increase the thermal conductivity of the base ionic liquid, potentially contributing to better efficiency of heat transfer fluids. It is the purpose of this paper to analyze the prediction and estimation of the thermal conductivity of ionic liquids and IoNanofluids as a function of temperature, using the molecular theory of Bridgman and estimation methods previously developed for the base fluid. In addition, we consider methods that emphasize the importance of the interfacial area IL-NM in modelling the thermal conductivity enhancement. Results obtained show that it is not currently possible to predict or estimate the thermal conductivity of ionic liquids with an uncertainty commensurate with the best experimental values. The models of Maxwell and Hamilton are not capable of estimating the thermal conductivity enhancement of IoNanofluids, and it is clear that the Murshed, Leong and Yang model is not practical, if no additional information, either using imaging techniques at nanoscale or molecular dynamics simulations, is available.

New measurements of the thermal conductivity of argon, nitrogen and carbon monoxide within the temperature range 83 K to 387 K and for pressures up to 10MPa have been performed. The experimental data have an estimated accuracy of ±0.5% and are used in this paper to derive values of the first coefficient of the density expansion of the thermal conductivity of unprecedented accuracy over such a wide range of temperature. The results are compared with a theoretical evaluation of the coefficient for argon and with several empirical estimations for nitrogen and carbon monoxide. The agreement with the theoretical calculation of Rainwater and Friend for argon is good while for nitrogen and carbon monoxide the same theory with a semi-empirical addition to account for the internal energy proves more successful than the Modified Enskog Theory.

A complete theoretical analysis of the fluid and solid dynamics of the torsional quartz crystal viscometer is presented which for the first time, establishes a firm theoretical basis for two working equations whereby the viscosity of a fluid may be determined from measurements of the resonant frequency of the crystal and the width of the resonance when immersed in the fluid. Modern instrumentation means that it is possible to achieve higher resolution in the measurement of these two quantities than hitherto and the new theory opens the way to securing a concomitant accuracy in the determination of viscosity.

The paper seeks to answer a question posed in a recent paper by Hasselman [1] in this journal concerning the application of the transient hot-wire method to the measurement of the thermal conductivity of fluids in general, and the effective thermal conductivity of nanofluids, in particular. At the same time, the paper corrects a number of errors of fact and assertion made in that paper.

The initial explosion of interest in the opportunities created by the ready availability of nanoscale particles of a variety of materials generated many claims for potential applications of their suspensions in liquids in the context of enhanced heat transfer. Calmer, objective reflection prompted by more careful experimentation and simulation has revealed that most of these claims were ill-founded. This paper explores some of the opportunities that may yet lead to real applications in the particular context of fluid heat transfer. In order to provide an appropriate direction for future studies, we show here there are some special situations in which the modest enhancement of the apparent thermal conductivity that can be achieved by nanofluids over the base fluid may be sufficient to be technically useful. In addition, we consider what is almost the opposite circumstance where, instead of exploiting the enhancement of the heat transfer between fluid and solid particles, processes use the poor heat transfer between the two phases to drive phase changes within the fluid phase itself. The applications of this phenomenon seem to have even greater potential. (C) 2019 Elsevier Ltd. All rights reserved.

K. Α. Tasidou,1 Ch. D. Chliatzou,1 M. J. Assael,1,a) K. D. Antoniadis,1 S. K. Mylona,2 M. L. Huber,3 W. A. Wakeham4 1Chemical Engineering Department, Aristotle University, Thessaloniki 54646, Greece 2ThermTest, Fredericton, Canada 3Applied Chemicals and Materials Division, National Institute of Standards and Technology, Boulder, Colorado 80305-3337, USA 4Chemical Engineering Department, Imperial College London, Prince Consort Road, London SW7 2BY, United Kingdom.

In 1988, reference correlations for the viscosity of a selection of molten inorganic salts were proposed by Janz and have been used extensively. During the last 31 years, many additional measurements have been published. In a very recent paper, new reference correlations for the thermal conductivity of 13 inorganic molten salts were proposed. In this paper, reference correlations for the viscosity of those same salts are proposed. All available experimental data for the viscosity of 13 inorganic molten salts have been critically examined with the intention of establishing improved or new reference viscosity correlations. All experimental data have been categorized into primary and secondary data according to the quality of measurement specified by a series of criteria. Standard reference correlations are proposed for the following molten salts (with estimated uncertainties at the 95% confidence level given in parentheses): LiNO3 (6.7%), NaNO3 (3.0%), KNO3 (3.0%), NaBr (1.6%), KBr (2.0%), RbBr (2.2%), LiCl (3.7%), NaCl (2.4%), KCl (1.6%), RbCl (3.6%), CsCl (1.1%), NaI (1.5%), and RbI (1.5%).

This article presents new density data and some theological studies on tris(2-ethylhexyl) trimellitate (TOTM) which has recently been proposed as a reference fluid for viscosity at high temperatures and high pressures. The density data have been obtained with the aid of an Anton Paar DMA HP U-tube instrument, covering temperatures from 328 to 423 K and pressures up to 70 MPa, and they are aimed at extending the temperature range of previous results. They are also used to check the effect of interlot consistency of the density data for TOTM. The present density measurements are compared with previously published data. Rheological tests were carried out to complement earlier studies. Particular attention is given to the shear rate range of greatest interest for the proposed use of TOTM as an industrial reference fluid for viscosity: the tests include shear stresses up to 750 Pa and shear rates up to 4000 s(-1) under atmospheric pressure. The tests were carried out using a Parallel Plate Rheometer AR1500ex10C4298. The results at a temperature of 298 K corroborate the previous findings that TOTM is Newtonian below a shear rate of 600 s(-1) which is entirely compatible with its use as an industrial calibrating fluid for viscosity. At shear rates higher than 600 s(-1) a shear-thinning like behavior is observed.

The available experimental data for the thermal conductivity of 13 inorganic molten salts have been critically examined with the intention of establishing thermal conductivity reference correlations. All experimental data have been categorized into primary and secondary data according to the quality of measurement specified by a series of criteria. Standard reference correlations are proposed for the following molten salts (with estimated uncertainties at the 95 % confidence level given in parentheses): LiNO3 (7 %), NaNO3 (7 %), KNO3 (15 %), NaBr (15 %), KBr (15 %), RbBr (15 %), LiCl (17 %), NaCl (20 %), KCl (17 %), RbCl (17%), CsCl (10 %), NaI (17 %), and RbI (20 %).

The aim of this paper is to investigate in depth whether adding nanoparticles or nanotubes to a fluid enhances its heat transfer capabilities. For this reason, the thermal conductivities and viscosities of a selection of nanofluids were thoroughly examined. The systems studied were (a) ethylene glycol with added CuO, TiO2, or Al2O3 nanoparticles and (b) water with TiO2 or Al2O3 nanoparticles or multiwall carbon nanotubes (MWCNTs). All of the measurements were conducted at 298.15 K. In a very recent paper, it was shown that instruments employing the transient hot-wire technique can produce excellent measurements when a finite element method (FEM) is employed to describe the instrument for the geometry of the hot wire. Furthermore, it was shown that an approximate analytic solution can be employed with equal success, over the time range from 0.1 to 1 s, provided that four specific criteria are satisfied. Subsequently a transient hot-wire instrument was, designed, constructed, and employed for the measurement of the thermal conductivities of nanofluids with an uncertainty of about 2%. A second, validated technique, namely, a hot-disk instrument, was also employed to conduct measurements on some of the systems to provide mutual support for the tesults of the thermal conductivity measurements. To investigate the effect of any enhancement Of the thermal conductivity of the fluids on their application in practical heat transfer, the viscosities of typical concentrations of:several of the nanofluids were also measured. A parallel-plate rotational rheometer, able to measure the viscosities of Newtonian and non-Newtonian liquids with an uncertainty of better than 5%, was employed for, these measurements because most of the nano fluids considered showed behavior comparable to a Bingham plastic. All of these measurements have:allowed an investigation of the change in the heat transfer capability of the base fluid when nanoparticles or MWCNTs are added to it for a typical heat exchanger. It is shown that in general the combined changes in physical properties that accompany suspension of nanoparticles in fluids mean that the heat transfer benefits are all rather modest, even when they are achieved.

This paper presents a reference correlation for the-viscosity of tris(2-ethylhexyl) trimellitate designed to serve in industrial applications for the calibration of viscometers at elevated temperatures and pressures such as those encountered in the exploration of oil reservoirs and in lubrication. Tris(2-ethylhexyl) trimellitate has been examined with respect to the criteria necessary for an industrial standard reference material such as toxicity, thermal stability, and variability among manufactured lots. The viscosity correlation has been based upon all of the data collected in a multinational project and is supported by careful measurements and analysis of all the supporting thermophysical property data that are needed to apply the standard for calibration to a wide variety of viscometers. The standard reference viscosity data cover temperatures from 303 to 473 K, pressures from 0.1 to 200 MPa, and viscosities from approximately 1.6 to 755 mPa s. The uncertainty in the data provided is of the order of 3.2% at 95% confidence level, which is thought to be adequate for most industrial applications.

This work was supported by the Strategic Project PEstOE/QUI/UI0100/2013 funded by Fundacao para a Ciencia e a Tecnologia (FCT, Portugal).

The available experimental data for the thermal conductivity of liquid copper, gallium, indium, iron, lead, nickel, and tin has been critically examined with the intention of establishing thermal conductivity reference correlations. All experimental data have been categorized into primary and secondary data according to the quality of measurement specified by a series of criteria. The proposed standard reference correlations for the thermal conductivity of liquid copper, gallium, indium, iron, lead, nickel, and tin are respectively characterized by uncertainties of 9.8, 15.9, 9.7, 13.7, 16.9, 7.7, and 12.6% at the 95% confidence level.