Browsing by Author "Sousa, Ana T."
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- Density of 1,1-dichloro-1-fluoroethane (HCFC 141b) as a function of temperature and pressure.Publication . Sousa, Ana T.; Fialho, Paulo; Nieto de Castro, Carlos A.; Tufeu, R.; Neindre, B. LeThe density of HCFC 141b has been measured at several temperatures between 260 and 320 K, Mid pressures up to 20 MPa, with a mechanical oscillator densimeter. The densimeter was calibrated with 2,2,4-trimethylpentane, whose density was obtained from a correlating cyuation with 0.3% uncertainty. The density data obtained for HCFC 14H) hits a reproducibility of 0.05% and an uncertainty of 0.3%. The data obtained were fitted to a Tait-type equation which reproduced the experimental densities within 0.11 % and were compared with the data obtained in other works.
- The density of 1,1-dichloro-1-fluoroethane (HCFC 141b).Publication . Sousa, Ana T.; Fialho, Paulo; Nieto de Castro, Carlos A.In this Note we present the density of HCFC 141b, measured between 293.15 and 300.15 K, with an mechanical oscillator densimeter, with an uncertainty of 0.007%. The results are compared with the densities estimated by the reduced hard-sphere-DeSantis equation of state and with the experimental data obtained by several authors.
- The density of environmentally acceptable refrigerants and their mixtures: its measurement, correlation and estimation.Publication . Fialho, Paulo; Sousa, Ana T.; Nieto de Castro, Carlos A.The density of liquid refrigerants is very important for the design of compression cycles in the refrigeration and air-conditioning industries. The density of pure liquids as well as binary mixtures proposed as alternatives to the chlorofluorocarbons (CFCs) [the hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs)] is not well known, in spite of some international effort in recent years to measure them. Some of the methods of easurement, correlation and estimation of the densities of pure HCFCs, HFCs and binary mixtures are reviewed. The correlation of the densities is based on the hard-sphere - DeSantis equation of state (HSDS), the misture being assumed to obey a 1-fluid approach. The equation is shown to be universal for pure fluids and suitable for estimating their densities within 1% for T/Tc < 0.9, where Tc is critical temperature, for both Class B and Class A refrigerants. The estimation scheme was extended to binary mixtures, using only pure component properties and combination rules for 'pseudo' critical parameters, with the same uncertainty.
- Density of HCFC 142b and of its mixture with HCFC 22Publication . Sousa, Ana T.; Fialho, Paulo; Nieto de Castro, Carlos A.; Tufeu, R.; Le Neindre, B.The density of the binary mixture 40/60 wt% of monochlorodifluoromethane (HCFC 22) and 1-chloro-1,1-difluoroethane (HCFC 142b) in the liquid phase, has been measured between 300 and 370 K and pressures up to 19 MPa, with an oscillating fork sendimeter, operating in a relative mode. Toluene and vacuum have been used as calibrating fluids. The accuracy of the data is 0.08 %. An equation for the dependence of density in temperature and pressure for HCFC 142b and for this mixture is also presented.
- The thermal conductivity of 1-chloro-1,1-difluoroethane (HCFC-142b)Publication . Sousa, Ana T.; Fialho, Paulo; Nieto de Castro, Carlos A.; Tufeu, R.; Le Neindre, B.The thermal conductivity of 1-chloro-l,l-difluoroethane (HCFC-142b) has been measured in the temperature range 290 to 504 K and pressures up to 20 MPa with a concentric-cylinder apparatus operating in a steady-state mode. These temperature and pressure ranges cover all fluid states. The estimated accuracy of the method is about 2 %. The density dependence of the thermal conductivity has been studied in the liquid region.
- Thermophysical Properties of Alternative Refrigerants.Publication . Gurova, A. N.; Barão, M. T.; Sousa, Ana T.; Nieto de Castro, Carlos A.; Mardolcar, Umesh V.; Fialho, PauloThe need for new environrnentally acceptable refrigerants, with low or zero ozone depletion potential and low global warming potential, led the industrial and the scientific community to launch a significant research effort on the thermophysical properties of these compounds. It is the purpose of this paper to give an overall view of the current research in this field, started in 1990 by our group, in collaboration with the LIMHPCNRS, Villetaneuse, France, and the NIST, Boulder, USA. The effort has been concentrated in developing equipments to measure density dielectric constant and thermal conductivity in the liquid phase, covering the temperature and pressure ranges necessary for the normal duty of these fluids. The dielectric constant and the thermal conductivity of three provisional replacements, HCFC 123, HCFC 141b, HCFC 142b and two c1ass A fluids, HFC 134a and HFC 152a, have been measured in the temperature range 200 to 300 K and pressures up to 20 MPa, using a direct capacitance method, by measuring the capacitance of a cylinder filled with the sample and in vacuum, using an impedance analyzer, and the polarized hot wire technique. The density of HCFC 142b, HCFC 22 + HCFC 142b and HCFC 14lb was measured with a vibrating fork densimeter, calibrated with toluene, 2,2,4-trimethylpentane and vacuum. The instruments are capable of obtaining the dielectric constant with an absolute uncertainty of 0.1 %, the thermal conductivity with 0.5 % and the density with 0.1 %. An Hard Sphere De Santis equation of state has been used to develop an universal estimation scheme for the density of pure refrigerants and of their mixtures, based only upon the properties of pure fluids, capable of calculating the density of the liquid phase with an uncertainty better than 1.5 % for T/Tc < 0.9. The density dependence of the dielectric constant has been studied using the concept of Eulerian strain and the Onsager-Kirkwood theories. The dipole moments of the several refrigerants in the liquid phase were obtained.