Thermal Conductivity of Ionic Liquids and IoNanofluids. Can Molecular Theory Help?

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.

KINETICS AND MECHANISM OF SORPTION OF COPPER (II) IONS BY ION EXCHANGER

In this article the kinetics of the process of sorption of copper (II) ions from aqueous solutions by polymer sulfonic cation exchanger, an elementary unit containing a heterocycle and a sulfonic group, under static conditions at a temperature of 298 K and a copper concentration of 2 mmol / mg is investigated. The sulfonic cation exchanger was preliminarily obtained by the reaction of polycondensation of diphenyl oxide and furfural with further sulfonation to obtain functional ionogenic groups in order to increase the extraction efficiency. The obtained kinetic curves of the dependence of the degree of extraction of copper ions from solution on time were processed using the Boyd, Adamson, and Myers equation, which describes diffusion in a limited volume of solution. The kinetic parameters of the sorption process (effective diffusion coefficient, etc.) are calculated, and the results obtained are compared with the data for the traditionally used industrial cation exchanger, which is a copolymer of styrene and divinyl benzene. It has been established that the process of sorption of copper (II) ions in the sulfonic cation exchanger phase is of an intra diffusion nature and corresponds to second-order kinetic equations.

Thermal Conductivity of Metastable Ionic Liquid [C2mim][CH3SO3]

Ionic liquids have been suggested as new engineering fluids, namely in the area of heat transfer, as alternatives to current biphenyl and diphenyl oxide, alkylated aromatics and dimethyl polysiloxane oils, which degrade above 200 °C and pose some environmental problems. Recently, we have proposed 1-ethyl-3-methylimidazolium methanesulfonate, [C2mim][CH3SO3], as a new heat transfer fluid, because of its thermophysical and toxicological properties. However, there are some interesting points raised in this work, namely the possibility of the existence of liquid metastability below the melting point (303 K) or second order-disorder transitions (λ-type) before reaching the calorimetric freezing point. This paper analyses in more detail this zone of the phase diagram of the pure fluid, by reporting accurate thermal-conductivity measurements between 278 and 355 K with an estimated uncertainty of 2% at a 95% confidence level. A new value of the melting temperature is also reported, Tmelt = 307.8 ± 1 K. Results obtained support liquid metastability behaviour in the solid-phase region and permit the use of this ionic liquid at a heat transfer fluid at temperatures below its melting point. Thermal conductivity models based on Bridgman theory and estimation formulas were also used in this work, failing to predict the experimental data within its uncertainty.