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- A novel non-intrusive microcell for sound-speed measurements in liquids. Speed of sound and thermodynamic properties of 2-propanone at pressures up to 160 MPaPublication . Azevedo, R. Gomes de; Szydlowski, J.; Pires, P. F.; Esperança, J. M. S. S.; Guedes, H. J. R.; Rebelo, L. P. N.A novel high-pressure, ultrasonic cell of extremely reduced internal dimensions ( 0.8 10 6 m3) and good precision for the determination of the speed of propagation of sound in liquids was conceived and built. It makes use of a non-intrusive methodology where the ultrasonic transducers are not in direct contact with the liquid sample under investigation. The new cell was used to carry out speed of sound measurements in 2-propanone (acetone) in broad ranges of temperature (265 < T =K < 340) and pressure (0:1 < p=MPa < 160). (p; q; T ) data for acetone were also determined but in a narrower T ; p range (298 to 333 K; 0.1 to 60 MPa). In this interval, several thermodynamic properties were thus calculated, such as: isentropic (js) and isothermal (jTÞ compressibility, isobaric thermal expansivity (ap), isobaric (cp) and isochoric (cv) specific heat capacity, and the thermal pressure coefficient (cv). Comparisons with values found in the literature generally show good agreement.
- Thermophysical and thermodynamic properties of ionic liquids over an extended pressure range: [bmim][NTf2] and [hmim][NTf2]Publication . Azevedo, R. Gomes de; Esperança, J. M. S. S.; Szydlowski, J.; Visak, Z. P.; Pires, P. F.; Guedes, H. J. R.; Rebelo, L. P. N.The current study focuses on 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, [bmim][NTf2], and 1-hexyl-3- methylimidazolium bis(trifluoromethylsulfonyl)amide, [hmim][NTf2]. The objective is to study the influence of pressure as well as that of the cation s alkyl chain length on several properties of this type of ionic liquids. Speed of propagation of ultrasound waves and densities in pure ionic liquids (ILs) as a function of temperature and pressure have been determined. Several other thermody namic properties such as compressibilities, expansivities and heat capacities have been obtained. Speed of sound measurements have been carried out in broad ranges of temperature (283 < T/K < 323) and pressure (0.1 < p/MPa < 150), using a non-intrusive micro cell. Density measurements have been performed at broad ranges of temperature (298 < T/K < 333) and pressure (0.1 < p/MPa < 60) using a vibrating tube densimeter. The pressure dependence of heat capacities, which is generally mild, is highly dependent on the curvature of the temperature dependence of density.
- Ultrasonic speed of sound and derived thermodynamic properties of liquid 1, 1, 1, 2, 3, 3, 3-heptafluoropropane (HFC227ea) from 248 K to 333 K and pressures up to 65 MPaPublication . Pires, P. F.; Esperança, J. M. S. S.; Guedes, H. J. R.This work reports experimental data of the speed of sound in liquid 1,1,1,2,3,3,3-heptafluoropropane (HFC227ea) from 248 K to 333 K and pressures up to 65 MPa, measured with a pulse-echo method. The results are fitted with a rational approximant. Derived thermodynamic properties are calculated, combining our experimental data with density and isobaric heat capacity values published by other authors. The results were compared with the data available in the literature.