Browsing by Author "Nieto de Castro, Carlos A."
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- Applications of the hard sphere DeSantis equation of state to the estimation of the density of compressed alternative refrigerants.Publication . Fialho, Paulo; 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 increasing concern with the environmental protection leads the governments to legislate in order to banish in the short term the use of the CFC's and in the long run the HCFC's. Considering those decisions, the industries need to find new replacements for those compounds, and suitable substitutes seam to be HFC's, fluorinated ethers, their mixtures and mixtures with small quantities of HCFC's. The only problem in using those alternative refrigerants is the lack of knowledge about their properties. Among them, the density is one of the most important. It is the propose of this paper to show the use of a model that allows the user to estimate the liquid density for the refrigerants. The uncertainty of this model is of ± 2.0 % for reduced values of temperature less then 0.95 and reduced values of density less then 1.0. This model needs the information for the critical parameters and the pressure of the saturated liquid-vapour line. The Hard-Sphere DeSantis equation of state Ref. /1/ is use to give physical support to the model. The corrections to the attractive and repulsive part, a and b, have been calculated from a few experimental pure refrigerants Ref. /1/ (HCFC 152a, HCFC 22, HCFC 142b, HCFC 123, HCFC 114).
- The correlation of transport properties of alkali metal vapours and noble gases.Publication . Apelblat, Alexander; Fialho, Paulo; Nieto de Castro, Carlos A.It was found that transport properties of gases (viscosity η, thermal conductivity λ, and diffusion coefficients D) in the form of the quantity: C = ηD λT α are temperature independent in the 700–2000K temperature interval. Although the exponent α seems to be independent inside the group for all the monoatomic vapours it seems to change between different groups (α = 1.909±0.015 for alkali metal vapours – Li, Na, K, Rb and Cs; α = 1.72±0.05 for noble gases – He, Ne, Ar, Kr, and Xe). In this approach, transport properties of gases are correlated using only different values of C. This fact was extended to the properties of the binary mixtures of monoatomic and diatomic molecules in the alkali metal vapours, to obtain the mutual diffusion coefficients D12(T, p) and the self-diffusion coefficients of diatomic molecules, D22(T).
- 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.
- Erratum to 'Prediction of halocarbon Liquid Densities by a Modified Hard Sphere-De Santis Equation of State'.Publication . Fialho, Paulo; Nieto de Castro, Carlos A.This is a correction note to the papers entitled "Prediction of halocarbon liquid densities by a modified hard sphere-De Santis equation of state" (Fialho and Nieto de Castro, 1996a), and "Prediction of liquid densities for halocarbon mixtures by a modified hard sphere-De Santis equation of state" (Fialho and Nieto de Castro, 1996b). Recently we found some printing mistakes that are important to correct in order to allow others to take advantage of the described technique and use the proposed equations.
- Prediction of halocarbon liquid densities by a modified hard Sphere-De Santis equation of state.Publication . Fialho, Paulo; Nieto de Castro, Carlos A.The present paper describes a general scheme for the prediction of halocarbon liquid state densities based on a modified hard sphere De Santis equation of state. It is shown that it is possible to estimate the density of pure liquids solely from the critical constants and relative molecular mass to better than 1.5% for T∗ < 0.9 and from saturation vapour pressures up to 20 MPa.
- Prediction of liquid densities for halocarbon mixtures by a modified Hard Sphere-De Santis equation of state.Publication . Fialho, Paulo; Nieto de Castro, Carlos A.In a companion paper, we dealt with the problem of predicting the liquid behaviour of pure refrigerants. It is the purpose of the present paper to extend the use of the Hard Sphere De Santis (HSDS) model by associating it with mixing and combination rules to predict the liquid state densities for mixtures of halocarbon refrigerants. The deviations obtained between the experimental data, available for binary and ternary mixtures, and the HSDS model have shown an uncertainly of 1.5% for T∗ ≤ 0.9. This was the uncertainty claimed for the model, when applied to pure fluids.
- Prediction of the vapor pressure of environmentally acceptable halocarbons.Publication . Fialho, Paulo; Nieto de Castro, Carlos A.The vapor pressure and its dependence on temperature of halocarbons for 0.002< p R<1 have been analyzed in terms of universal behavior. Results for CFC-114, HCFC-123, HCFC-141b, HCFC-142b, HCFC-143a, HFC-23, HFC-32, HFC-134, HFC-125, HFC-134a, and HFC-152a for reduced temperatures between 0.55 and 1.0 show that the reduced vapor pressure can be expressed as a function of 1−T R by a Padé approximant. Deviations of the correlated data from the universal function do not amount to more than ±0.06 MPa, with an average deviation of 0.025 MPa. Predictions of the saturation vapor pressures of HCFC-124, HCFC-225ca, and HCFC-225cb, which are the systems used to test the capability of this scheme, agree within 0.025 MPa, that is, within the accuracy of the corresponding states correlation. However, for HFC-236ea, the deviations are as large as -0.07 MPa. The present scheme can be used to calculate the Pitzer acentric factor, and an average value of ω=0.269±0.015 is obtained for all the fluids.