Isabel M. A. Fonseca

Measurements and Correlation of High-Pressure Densities of Imidazolium-Based Ionic Liquids

In the present work, experimental density measurements are reported along with the derived thermodynamic properties, such as the isothermal compressibility (κT), the isobaric expansivity (Rp), and the thermal pressure coefficient (γV) for imidazolium-based ionic liquids (ILs), namely, 1-ethyl-3-methylimidazolium methylsulfate [C2mim][MeSO4], 1-ethyl-3-methylimidazolium ethylsulfate [C2mim][EtSO4], 1,3-diethylimidazolium bis(trifluoromethylsulfonyl)imide [C2eim][Tf2N], and 1-decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C10mim][Tf2N] in the pressure (0.10 < P/MPa < 35.00) and temperature (293.15 < T/K < 393.15) domains. It is shown that experimental densities are in good agreement with the predicted densities obtained by the Gardas and Coutinho method and the correlation using the Tait equation and Sanchez-Lacombe equation of state.

Thermodynamics of liquid mixtures of xenon and methyl fluoride

Experimental determinations of the vapour—liquid equilibria of Xe + CH3F at 161.39, 182.33, and 195.48 K are presented together with the evaluation of the excess Gibbs energy GE over the entire composition range. The system exhibits a positive azeotrope for solutions richer in the more volatile component (x1 ≈ 0.1). The excess molar enthalpy estimated from the G E values for the equimolar mixture is relatively large and positive (HE = 867 J mol−1). The molar volumes of the liquid mixtures measured at 161.39 K show that for this system VE is small and positive. The experimental results are compared with those obtained by using the Soave and the Peng—Robinson equations of state.

Thermodynamic and Transport Properties of CNT-Water Based Nanofluids

Carbon nanotubes (CNTs) – perhaps the most enticing class of nano-materials, can be added in small volume fractions to enhance the thermal properties of fluids when process intensification or even device miniaturization is required. This work reports on the results obtained when measuring viscosity, and thermal conductivity of homogenous CNTs – water based nanofluids. The influence of CNTs volume concentration on the nanofluid thermo-physical properties is studied and measurements are undertaken at different temperatures, ranging from 283.15 K to 333.15 K. The nanofluids have been prepared by adding different volume concentrations of treated CNTs to water. The latter has been then sonicated for one hour and the colloidal stability monitored via UV – vis spectrophotometer. The absorbance of the nanofluid was observed at 263 nm, and the average concentration of CNTs was maintained at 9.35 mg/l, even after 200 hours, over 97% when compared with the initial concentration. The viscosity was measured using a controlled stress rheometer, and the measurements were performed in the shear rate ranging from 0 to 600 sec-1. At the same shear rate and temperature, the viscosity was observed to rise with increasing CNTs volume concentration. In what concerns thermal conductivity, it was assessed with a KD2 pro thermal property tester from Decagon Devices and the results clearly show that thermal conductivity rises with CNTs volume fraction, reaching its maximum at 2.5%vol where it represents more than 100% enhancement when the comparison is established with the corresponding value for the base fluid, at the same temperature conditions (i.e. 283.15 – 303.15 K). Furthermore, at higher temperatures (i.e. 313.15 – 333.15 K), the latter, for up to 1%vol concentration represents a 70% enhancement in thermal conductivity.

EG/CNTs Nanofluids Engineering and Thermo-Rheological Characterization

The research work presented here intends to contribute to the overall research effort towards nanofluids engineering and characterization. To accomplish the latter, multiwalled carbon nanotubes (MWCNTs) are added to an ethylene glycol (EG) based fluid. Different aspects concerning the nanofluids preparation and its thermal characterization will be addressed. The study considers and exploits the relative influence of CNTs concentration on EG based fluids, on the suspension effective thermal conductivity and viscosity. In order to guarantee a high-quality dispersion it was performed a chemical treatment on the MWCNTs followed by ultrasonication mixing. Furthermore, the ultrasonication mixing-time is optimized through the UV-vis spectrophotometer to ensure proper colloidal stability. The thermal conductivity is measured via transient hot-wire within a specified temperature range. Viscosity is assessed through a controlled stress rheometer. The results obtained clearly indicate an enhancement in thermal conductivity consistent with carbon nanotube loading. The same trend is observed for the viscosity, which decreases with temperature rise and its effect is nullified at higher shear rates.

Some thermodynamic properties of liquid hydrogen sulphide and deuterium sulphide

Abstract The orthobaric densities of liquid H 2 S and D 2 S have been measured from about 197 to 265 K. Over the whole of this range, liquid H 2 S has the larger molar volume. The difference of the vapour pressures of the two compounds has been measured from about 208 to 248 K. At 225.05 K the two liquids have the same vapour pressure. At lower temperatures than this, H 2 S has the higher vapour pressure. The available vapour pressures for H 2 S have been fitted to a Wagner equation. By combining vapour pressures for H 2 S derived from this equation with the differential measurements, values for the vapour pressure of D 2 S have been obtained. These values have also been fitted to a Wagner equation. The material presented in this paper has been used to estimate the enthalpy of vaporization of H 2 S and of D 2 S each from its triple-point temperature to 270 K. Throughout this temperature range, the enthalpy of vaporization of D 2 S exceeds that of H 2 S, the difference decreasing with rising temperature.

Solubilities of some new refrigerants in water

Solubility data for the refrigerants HFC23 (CHF3), HFC32 (CH2F2) and HFC125 (C2HF5) in water have been determined as a function of the temperature in the range of temperatures 288‐303 K at atmospheric pressure. These hydrofluorocarbons (HFCs) are good substitutes of the chlorofluorocarbons (CFCs), which have significant impact to stratospheric ozone depletion. The ‐ approach has been used to predict the experimental results. The fugacity coefficients were calculated using a modified version of the Peng‐Robinson equation of state.

Some thermodynamic properties of liquid ammonia and trideuteroammonia

Abstract The orthobaric density of liquid NH 3 has been measured from about 200 to 287 K, and for liquid ND 3 from about 205 to 273 K. The molar volume of liquid NH 3 exceeds that of ND 3 by between 0.8 and 0.9 per cent. The difference of the vapour pressures of the two compounds has been measured from about 200 to 266 K, and the vapour pressure of NH 3 from the triple-point temperature to 234 K. Liquid NH 3 has the higher vapour pressure, the difference being relatively large for a pair of isotopic compounds. At 200 K, the ratio of the vapour pressure of NH 3 to that of ND 3 is about 1.2. The available vapour pressures for NH 3 have been fitted to a Wagner equation. By combining vapour pressures derived from this equation with the differential measurements, values for the vapour pressure of ND 3 have been obtained. These values have likewise been fitted to a Wagner equation. The material presented in this paper has been used to estimate the molar enthalpies of vaporization of NH 3 (l) and of ND 3 (l) from the triple-point temperatures to 290 K. The molar enthalpy of vaporization of ND 3 exceeds that of NH 3 throughout this range. The difference amounts to about 3.5 per cent at the triple-point temperatures, and decreases with rising temperature.

Some thermodynamic properties of hydrogen chloride and deuterium chloride

Abstract The molar volume V m l of HCl(l) has been measured from 162 to 236 K, and of DCl(l) from 160 to 218 K. The difference in V m l of the two compounds in this range does not exceed 0.1 per cent. At lower temperatures, V m l (HCl) > V m l (DCl), but from 192 K upwards V m l (HCl) V m l (DCl). Direct measurements of the vapour pressure of HCl have been made from 159 to 220 K, and of DCl from 158 to 188 K. In addition, the difference in the vapour pressure of the two isotopic forms has been measured from 159 to 226 K. At lower temperatures, the vapour pressure of HCl exceeds that of DCl but above 223.35 K that position is reversed. The vapour pressure of each substance has been fitted to a Wagner equation. These equations have been used in conjunction with the Clapeyron equation to calculate the molar enthalpies of vaporization Δ l g H m . If r is the ratio of the vapour pressure of HCl to that of DCl, the values of r conform very closely to the equation T ln r = − A + C T , where A and C are constants. This has been used in an alternative way of estimating the difference in Δ l g H m for the two compounds. At 160 K, Δ l g H m of DCl exceeds that of HCl by 260 J · mol −1 . This difference decreases with rising temperature, being 138 J · mol −1 at 230 K. If the estimate of Δ l g H m for DCl is combined with the results of Chihara and Inaba, the calorimetric (third-law) entropy of DCl in the ideal-gaseous state at 101 325 Pa and 188.50 K, its normal boiling temperature, is 179.25 J · K −1 · mol −1 , in agreement with the statistical value.

VLE for cryogenic methyl fluoride + nitrous oxide + xenon at 182.33 K

An apparatus for accurate VLE measurements on ternary cryogenic systems is briefly described. It is a modified version of that introduced and developed by Staveley and co-workers for binary mixtures. The apparatus was tested against published results for CH 3F + Xe and N20 + Xe, at 182.33 K, the agreement being much satisfactory for both systems. The mixture CH3F + N20 + Xe at the same temperature was selected for the first measurements on a ternary system carried out using the modified experimental arrangement, the operation of which is also summarized. VLE results for 61 ternary points are presented together with the evaluation of the excess molar Gibbs free energy G E for the liquid mixture at that temperature. No ternary azeotrope has been found. G E for the three component liquid mixture is not an additive function of the G~ for its constituent binary mixtures. For the equimolar (ternary) mixture G~/3 = (500 -4- 6) J mol -~ , at 182.33 K.

Solubility of methyl fluoride in some alcohols

The solubilities of methyl fluoride in some polar solvents (methanol, ethanol, propanol and n-butanol) have been measured at temperatures ranging from about 280 to 300 K, and at atmospheric pressure. The solubility is the lowest in methanol, increasing with the C-content of the alcohols. H-bonding factors, based on the ideal gas solubilities and the solubilities in the alcohols, appear to be linearly dependent on the H-bonding factor in methanol. The molar Gibbs energy, enthalpy and entropy of solution were calculated from the experimental results (at 1 atm partial pressure of the gas and 298 K).