PVTx Measurements Research Articles

Virial Coefficients from Burnett Measurements for the Carbon Dioxide + Fluoromethane System

This work reports the experimental results for the carbon dioxide (CO2) + fluoromethane (R41) system obtained using the Burnett method. The apparatus was calibrated using helium. For mixtures, the composition was found by gas chromatographic analysis of the sample collected during expansions. The gas chromatograph was calibrated precisely using samples prepared by the gravimetric method. From the PVT data collected, the second and third virial coefficients were derived for R41 covering the temperature range from 303 to 343 K. The second and third cross virial coefficients were derived from the PVTx measurements for the CO2 + R41 system at T = (303, 313, 323, 333, and 343) K. The second virial coefficients for pure R41 show a good consistency with the literature. Due to lack of experimental data in the literature for the CO2 + R41 system, our density measurements were compared with the REFPROP 6.01 prediction, the differences being within 0.6%, which would confirm the good predictive power of the model for this system and property.

PVTx measurements for H 2O+D 2O mixtures in the near-critical and supercritical regions

The PVTx relationships of H 2O+D 2O mixtures were measured in the near-critical and supercritical regions. Measurements were made using a constant-volume piezometer immersed in a precision thermostat. The volume of the piezometer V PT was corrected for both temperature and pressure expansions. The uncertainty of the density measurements was estimated to be 0.05–0.10%, depending on the experimental pressure and temperature. The uncertainty of the temperature, pressure, and composition measurements were respectively 10 mK, 0.05%, and 0.001 mol fraction. Measurements were made along various near-critical and supercritical isotherms between 517 and 680 K at pressures from 3 to 38 MPa and densities from 97 to 466 kg m −3 for two compositions, namely 0.5 and 0.6 mol fraction of H 2O. The measured PVTx data for H 2O+D 2O mixtures were compared with values calculated from a six-term Landau expansion and from parametric crossover equations of state. The accuracy of the method was confirmed by PVT measurements for pure water in the critical and supercritical regions. The values of partial molar volumes for dilute H 2O+D 2O mixtures near the critical point of pure H 2O and the Krichevskii parameter were calculated using a parametric crossover equation of state and the critical locus data. Using measured values of molar volumes and corresponding values for pure components, we derived the values of excess molar volumes as a function of pressure for the supercritical isotherms.

CO 2 + R23 Binary System: Virial Coefficients Derived from Burnett Measurements

Burnett PVT measurements were performed on trifluoromethane (R23) and mixtures of R23 with carbon dioxide (CO2). The Burnett apparatus was calibrated using helium. Fourteen expansions were performed for 5 isotherms and in a pressure range from 130 kPa to 6 MPa for R23. Second and third virial coefficients were derived from the collected data and compared with literature values; good agreement was found between them. PVTx measurements for the binary CO2+R23 system were carried out for five isotherms (303, 313, 323, 333, and 343 K). In all, 18 runs were performed in a pressure range from 150 kPa to 5.9 MPa. The composition of the mixtures was measured with a gas chromatograph after it had been calibrated using samples prepared gravimetrically. Second and third virial coefficients for the system were derived, together with the second and third cross virial coefficients, from experimental results using virial coefficients for CO2 from previous measurements (for the same sample as used in the present study). Samples for composition measurements were collected during the first Burnett expansion. Second virial coefficients for the system showed positive deviations from ideal values, while the third virials were negative. No previous experimental results were found for the PVTx properties of this binary system.

Burnett Measurements for the Difluoromethane + Carbon Dioxide System

As part of our ongoing research program on PVTx measurements using the isochoric and Burnett methods for hydrofluorocarbon + hydrocarbon and/or inorganic compound systems, this work reports on the experimental results for the difluoromethane (R32) + carbon dioxide (CO2) system obtained by the Burnett method. The apparatus was calibrated using helium, and its performance was confirmed by measurements for pure R32. The second and third virial coefficients were derived, and a good consistency was found after comparison with data in the literature. A new experimental procedure for mixture measurements was developed, on the basis of the gas chromatographic analysis of the sample collected during expansions. The gas chromatograph was calibrated precisely using samples prepared by the gravimetric method. PVTx measurements were performed for the binary R32 + CO2 system at T = (303, 313, 323, 333, and 343) K. The second and third cross virial coefficients were derived from the experimental results. No experimental data could be found in accessible literature sources on the PVTx for the R32 + CO2 system. Results were compared with the prediction obtained using REFPROP 6.01.

PVTx measurements for the R125 + CO 2 system by the Burnett method

The PVTx behaviour for the carbon dioxide (CO 2)+pentafluoroethane (R125) system was measured by the Burnett method within the range 323–363 K and at pressures from 10 to 5000 kPa. The apparatus was calibrated by means of helium and its performance was checked by measurements of PVT for the mixture components. Their second and third virial coefficients were found to be in good agreement with data available in the literature. A new experimental procedure for assessment of the mixture composition has been implemented, based on gas chromatographic analyses of the sample collected during expansions. The derived second and third virial coefficients and respective cross virial coefficients were compared also with correlating methods adapted from the literature. No experimental data on the PVTx for the CO 2+R125 system could be found in the literature.

PVTxMeasurements for Water + Toluene Mixtures in the Near-Critical and Supercritical Regions

The PVTx relationships of dilute (1 − x) water + x toluene mixtures were measured in the near-critical and supercritical regions, with a constant-volume piezometer immersed in a precision thermostat. The ITS-90 temperature was measured with a 10 Ω platinum resistance thermometer (PRT-10) with an uncertainty of 10 mK. Pressure was measured by means of a dead-weight gauge with an uncertainty of 1.5−2.0 kPa. Uncertainties of the density measurements are estimated to be 0.05−0.15%, depending on the experimental pressure and temperature. The uncertainty in composition measurement is 0.001 mole fraction. Measurements were made on near-critical and supercritical isotherms between 623 and 673 K at pressures from 11 to 46 MPa and densities between 54 and 579 kg·m-3 for three composition mole fractions of toluene (0.0008, 0.0022, and 0.0085). The measured PVTx data for (1 − x) water + x toluene mixtures were compared with values calculated from a recently developed crossover equation of state and published measurements. The PVTx measurements were used to derive values of the Krichevskii parameter, excess volumes, and apparent molar volumes. The method of isochoric break points was used to extract the phase transition temperatures and pressures for each measured isochore. The critical anomalies of the supercritical (1 − x) water + x toluene mixtures and the behavior of the Krichevskii function near the solvent's (water) critical point are discussed.

Equation of State and Thermodynamic Properties of Pure Toluene and Dilute Aqueous Toluene Solutions in the Critical and Supercritical Regions

In this paper, we report new PVTx measurements for water + toluene binary mixtures at 11 near-critical and supercritical isotherms T = 623, 627, 629, 631, 633, 643, 645, 647, 649, 651, and 673 K and pressures up to 39 MPa at a fixed concentration of x = 0.0287 mole fraction of toluene. Using these PVTx data together with data obtained earlier by other authors, we developed a crossover Helmholtz free-energy model (CREOS) for pure toluene and dilute aqueous toluene solutions in a wide range of the parameters of state around the vapor−liquid critical points. In the temperature range 593 K ≤ T ≤ 680 K and density range 100 kg·m-3 ≤ ρ ≤ 500 kg·m-3, the CREOS reproduces the PVT data for pure toluene with an average absolute deviation (AAD) of about 0.5%, the CP data with an AAD of about 1%, and the sound velocity data with an AAD of about 2.6%. In water + toluene mixtures, the CREOS yields an adequate description of all available experimental data in the region bounded by 0.35ρc(x) ≤ ρ ≤ 1.65ρc(x) and 0.98Tc(x)...

PVTx measurements for dilute water+ n-hexane mixtures in the near-critical and supercritical regions

The PVTx relationship of four binary dilute (water+ n-hexane) mixtures (0.0021, 0.0050, 0.0850 and 0.0138 mole fraction of n-hexane) were measured with a constant-volume method. Measurements were made at five near-critical and supercritical temperatures of pure water: 643.05, 645.05, 647.05, 649.05 and 651.05 K. The range of pressures was from 8 to 35 MPa. The total uncertainty of density, pressure, concentration, and temperature measurements were estimated to be less than ±0.2%, ±5 kPa, 0.001 mole fraction, and 10 mK, respectively. The derived PVTx data have been differentiated to yield infinite dilution partial molar volumes V ̄ 2 ∞ . Asymptotic properties for V ̄ 2 ∞ along the critical isotherm–isobar of the pure solvent (water) are experimentally studied. We show that PVTx measurements for the dilute water+ n-hexane mixture confirm the non-classical power-law behavior of V ̄ 2 ∞ along the experimental path of constant T C– P C with a critical exponent of 0.79. The values of the Krichevskii parameter of 96.4 MPa for the dilute water+ n-hexane mixture was estimated from PVTx measurements and compared with values calculated from the initial slopes of the T C – x and P C– x critical lines and the slope of the vapor-pressure P S– T S curve at the pure solvent critical point. The excess molar volumes of the mixture near the critical point of pure water are calculated using measured PVTx properties for mixtures and pure components.

PVTx measurements and partial molar volumes for water–hydrocarbon mixtures in the near-critical and supercritical conditions

By means of a constant-volume piezometer, measurements have been made of the PVTx properties of water+hydrocarbon ( n-heptane, n-octane, and benzene) mixtures at near-critical and supercritical conditions. The measurements cover the pressure range from 5 to 40 MPa and densities between 20 and 450 kg m −3 for six compositions from 0 to 0.614 mole fraction of hydrocarbon. Tests on the piezometer and consistency tests on the measurements suggest that the results are free from significant `dead volume' error. The experimental errors of the present PVTx measurements are estimated to be within ±0.01 K in temperature, ±0.15% in density, ±2 kPa in pressure, and ±0.002 mole fraction in composition. Good agreement was obtained with values reported in the literature for pure components (water, n-heptane, n-octane, and benzene), measured using other techniques. Values of partial molar volumes and the Krichevskii parameter have been obtained from these measurements. Analysis of the results for dilute water–hydrocarbon mixtures shows that partial molar volumes of the hydrocarbon (solute) near the critical point of pure water (solvent) exhibit remarkable anomalies. The experimental results have been interpreted in terms of modern molecular thermodynamic models for the partial molar volumes of the solute near the solvent critical point and Kirkwood–Buff fluctuation theory of solutions in terms of direct correlation function integral.

Study of intermolecular interactions and microstructure of supercritical mixtures water +n-heptane and water +n-hexane based onPVT x measurements

The partial molar volumes of n-heptane and n-hexane in super- and nearly critical water are determined based on the PVTx mesurements of the binary mixtures water + n-heptane and water + n-hexane near the critical point (CP) of the pure solvent (water). The partial molar volumes of n-heptane and n-hexane $$\bar V_2^\infty $$ show nonclassical (scaling) behavior ( $$\bar V_2^\infty \approx x^{ - \gamma /\beta \delta } $$ ) as the system asymptotically approaches (x → 0) the CP of pure water along the critical isobar-isotherm (Tc, Pc). The microstructure of the supercritical mixture is studied based on our experimental (PVTx, $$\bar V_2^\infty $$ ) data and Kirkwood-Buff’s fluctuation theory of dilute solutions; the dependence of the cluster size (N 1 ∞ ) on thermodynamic conditions (T, P) is established. With minor variations of temperature and pressure near the CP of pure water, the cluster size changes anomalously abruptly. The parameters of the equation of state of the SPHCT model are determined based on the PVTx measurements, and direct solvent-solute correlation integrals C 12 ∞ (of water + n-heptane and water + n-hexane) are calculated. The Krichevskii parameter (∂P / ∂x) VT C , adequately defining the behavior and structure of an infinitely dilute mixture near the CP of the pure solvent, is calculated. The effects of interactions between the solvent and solute molecules on the structure of a supercritical fluid are examined.

Volumetric Properties of Near-Critical and Supercritical Water + Pentane Mixtures: Molar, Excess, Partial, and Apparent Volumes

We present new PVTx measurements for water (A) + pentane (B) mixtures at the critical temperature of water (TC = 647.05 K) in the pressure range 4 MPa to 41 MPa at xb = 0, 0.028, 0.042, 0.061, 0.088, 0.184, 0.391, 0.694, and 1.0. The measurements were performed with a constant-volume piezometer. The sample was confined to a 36.8 cm3 cylindrical cell of a corrosion-resistant steel alloy, provided with a steel ball for stirring. The cell was separated from the rest of the fill and pressure measurement system by a diaphragm-type null indicator. The temperature was measured by a 10 Ω platinum resistance thermometer. The uncertainty in the temperature measurement is less than ±5 mK. Pressure was measured by means of a dead-weight gauge with a precision of ±2 kPa. The composition was determined with an uncertainty of ±0.002 in mole fraction. The volume of the cell was corrected for temperature expansion and elastic deformation by means of the known expansion coefficients of the cell. Taking into account the err...

PVTx study of binary system R22/R152a with Burnett method

This paper reports the PVTx properties of R22/R152a system in the ranges of temperature from 298.15 K to 353.15 K and pressure from 0.288 MPa to 1.288 MPa. Sixty seven PVTx measurements for three compositions, i.e., 0.2712, 0.4094 and 0.7911 mole fraction of R22, have been measured along 16 isotherms. The uncertainties of temperature and pressure measurements are less than 0.01 K and ±500 Pa respectively. The reliability of the experimental measurements is confirmed by using REFPROP program, a computer program suggested by Morrison et al[4].

Measurements of PVTx properties for the binary refrigerant HCFC 142b + HCFC 22 system

This paper reports PVTx properties for the HCFC 142b + HCFC 22 system in a wide range of temperatures from 297 to 443, of pressures from 0.5 to 10.0 MPa, and of densities from 72 to 1079 kg/m[sup 3]. For 4 compositions, i.e., 20, 40, 60, and 80 wt % HCFC 142b, 422 PVTx measurements have been made along 31 isochores. The uncertainties of the temperature, pressure, and density measurements are less than [plus minus]10 mK, [plus minus]3.0 kPa, and [plus minus]0.1%, respectively. From the PVTx measurements for 20, 40, 60, and 80 wt % HCFC 142b, the authors determine dew points and bubble points, enabling us to construct the dew- and bubble-points curves for each composition. The authors also compare the vapor-liquid equilibrium data along three isotherms, where the experimental data are reported by others, with the vapor-liquid equilibrium curve calculated from the Raoult's law.

Thermodynamic state surface and cycle analysis for refrigerant 22+refrigerant 114 system.

In order to examine thermophysical properties and cycle analysis for a nonazeotropic mixture of the Refrigerant 22 (CHCIF2) + Refrigerant 114 (CCIF2 CCIF2) system, an equation of state coupled with empirical mixing rules was formulated based on the available PVTx measurements taking thermodynamic consistency into consideration. The developed equation of state is expressed by the Helmholtz function as a function of temperature, density and composition, and is effective for a range of temperatures from 250 to 500 K and of pressures up to 10 MPa, which corresponds to the density range up to the critical value. With the aid of the proposed equation, the cycle analysis on the heat pump and refrigeration systems was theoretically carried out, and it became clear that the Refrigerant 22 + Refrigerant 114 system is suitable for industrial heat pump systems or air-conditioning and hot-water-supply heat pump systems. It was confirmed that the effect of change in composition on the theoretical coefficient of performance had the same behavior as that reported by an experimental testing.

Analysis of PVTx measurements for binary mixtures of R115 and R114

We have made PVTξ measurements of R115 and R114 at temperatures from 296 to 443 K, pressures from 0.4 to 9.8 MPa, and densities from 153 to 1387 kg·m−3, for four compositions, namely, 25, 50, 75, and 100 wt% R115. The data were obtained along isochores. The uncertainties in temperature, pressure and density are less than ±8 mK, ±2.2 kPa and ±0.1%, respectively. Using the experimental measurements on 100 wt% R115, we have validated our experimental apparatus and measurements. Furthermore, from the PVTξ measurements for 75wt% R115, 50wt% R115, and 25wt% R115, we have determined dew points and bubble points enabling us to construct the dew- and bubble-point curves for each composition. Our measurements also yield the critical point of R115 and R114 as a function of the concentration of the mixture.

Measurements of the PVTx Properties of Binary Refrigerant R 12 + R 22 System : Second Report: PVTx State-surface and Composition Dependence of the Thermodynamic Properties

For representing PVTx state-surface of a binary refrigerant R 12+R 22 system, B-W-R equations of state for both pure components in combination with mixing rules for the coefficients were applied. Proposed B-W-R equations of state with new mixing rules for the system of interest were developed based on the PVTx measurements for seven different compositions obtained by a constant-volume method coupled with several isothermal expansion procedures. The dew- and bubble-point curves of the present system were determined by analyzing these PVTx measurements graphically. The B-W-R equations of state with the mixing rules proposed here represent the PVTx measurements with an average pressure-deviation of 0.67% over a wide range of temperatures 300 to 420 K, of pressures up to 9 MPa and of densities up to 900 kg/m3. The composition dependence of the thermodynamic properties of density, isobaric specific heat capacity, enthalpy and entropy is discussed in detail.

Temperature-entropy Diagrams and Cycle Analysis for a Refrigerant Mixture of the R 12 + R 22 System

With an aid of Helmholtz function in combination with new mixing rules based on our PVTx measurements, the thermodynamic state-surface for a refrigerant mixture of the R 12+R 22 system was described in the range of 240≤T≤420 K, P≤9 MPa and ρ≤900 kg/m3. Using T-s diagrams for several compositions illustrated, the coefficient of performance for the standard refrigeration cycle using the present binary mixture system as refrigerant was calculated. Analysis of the coefficient of performance was explained by the composition dependence of cycle performance was explained by the composition dependence of the thermodynamic state-surface of the present system.

Measurements of the PVTx Properties of Binary Refrigerant R12+R22 System : First Report : A Mixture of 80 wt% R12+20 wt% R22

A new method of measuring the PVTx properties of fluid mixtures was proposed and a new apparatus was designed and constructed. The apparatus constructed here was examined for its performance by the measurements of the PVT properties of R22. Then the PVTx properties of a mixture of 80 wt% R12+20 wt% R22 were measured in the range of temperatures 293 to 418K, of pressures 0.7 to 9.6 MPa and of densities 141 to 1049kg/m3. Twohundred PVTx measurements were made along the 13 isochores. Based on the obtained data, dew- and bubble-point curves were determined and the available estimation methods were discussed.