PVTx Measurements Research Articles

PvTx properties for carbon dioxide (CO2)/difluoromethane (R32)/1,1,1,2-tetrafluoroethane (R134a) ternary mixture measured in the compressed liquid, superheated vapour, and two-phase regions

In low-temperature refrigeration applications, mixtures containing carbon dioxide and refrigerants with low triple points are considered potential substitutes for the refrigerant R23, characterised by a very high global warming potential. This study provides pvTx measurements for the ternary mixture of carbon dioxide (CO2), difluoromethane (R32), and 1,1,1,2-tetrafluoroethane (R134a) carried out in the compressed liquid, superheated vapour, and two-phase regions. A vibrating tube densimeter was used to measure the compressed liquid density along eight isotherms evenly spaced from (283.15 to 353.15) K and for pressures from near saturation up to 35 MPa. An isochoric apparatus was used to measure the two-phase and superheated vapour pvTx properties along three isochores from (223.15 to 303.15) K. The measurement uncertainties were estimated to be lower than 1 kg∙m − 3 for the liquid density and 0.02 m3∙kg−1 for the vapour specific volume. All the presented properties were compared with the calculations of the multi-fluid Helmholtz-energy explicit model. Both the default binary interaction parameters available in REFPROP 10.0 and new binary interaction parameters tuned on the presented data and the experimentally-determined thermodynamic properties collected from the literature have been used in the model. The tuned parameters provided lower deviations than the default parameters used in REFPROP 10.0.

Two-Phase and Vapor Phase PvTx Properties of the Difluoromethane + cis-1,3,3,3-Tetrafluoroprop-1-ene Binary System

This paper provides 84 two-phase and 66 vapor phase PvTx measurements for binary blends comprising difluoromethane (R32) and cis-1,3,3,3-tetrafluoroprop-1-ene (R1234ze(Z)). The data are for seven i...

Vapor-Phase PvTx Measurements of Binary Blends of cis-1,2,3,3,3-Pentafluoroprop-1-ene + Isobutane and 3,3,3-Trifluoropropene + Isobutane

Ninety-seven vapor-phase PvTx measurements are reported for six binary blends of cis-1,2,3,3,3-pentafluoroprop-1-ene (R1225ye(Z)) and isobutane (R600a), and sixty-six vapor-phase PvTx measurements ...

PVTx and thermal-pressure coefficient measurements of the binary CO2 + n-decane mixtures in the critical and retrograde regions

Abstract PVTx and temperature derivative of pressure (thermal-pressure coefficient), γ VX = ( ∂ P / ∂ T ) VX , of binary CO2 + n-decane mixtures have been measured in the critical, supercritical, and retrograde condensation regions (near the critical and cricondenterm points). Most measurements were made in the immediate vicinity of the dew-, bubble, and the critical point curves (in the single – and two-phase regions) to precisely determine the phase boundary properties, T S , P bub , P dew , ρ S ′ , ρ S ″ , ( ∂ P / ∂ T ) VX ′ , and ( ∂ P / ∂ T ) VX ″ .The measurements have been made using a high-temperature, high-pressure, nearly constant-volume adiabatic piezo-calorimeter for three concentrations of 0.095, 0.178, and 0.263 mol fraction of n-decane over the temperature range: (for mixture-1, x = 0.095) from (292 to 567) K along the liquid and vapor densities between (89 and 659) kg·m−3 at pressures up to 28.3 MPa; (for mixture-2, x = 0.178) from (302 to 557) K along the liquid and vapor densities between (85 and 467) kg·m−3 at pressures up to 24.3 MPa; and (for mixture-3, x = 0.263) from (361 to 568) K along the liquid and vapor densities between (298 and 520) kg·m−3 at pressures up to 25.4 MPa. The combined expanded uncertainty of the density, ρ , pressure, P, temperature, T, concentration, x, and the thermal-pressure coefficient, γ VX , measurements at the 68% confidence level with a coverage factor of k = 2 is estimated to be (0.2–0.5)%, (0.5–1.0)%, 15 mK, 0.01 mol%, and (0.2–2.0)% (depending on temperature and pressure), respectively. The critical (the critical temperature, T C , the critical pressure, P C , and the critical density, ρ C ), cricondentherm, and cricondenbar point data of CO2 + n-decane mixture were derived as a function of concentration from phase boundary properties studied. The Krichevskii parameter and isomorphism of the critical behavior of the mixture were studied using the critical curve data for the mixture and vapor pressure data for the pure solvent (CO2). Features of the P S - T S phase boundary diagram and thermodynamic behavior of the mixture near the critical and cricondentherm points and in the retrograde region were observed.

PVTx measurements of mixed clathrate hydrates in batch conditions under different crystallization rates: Influence on equilibrium

Abstract Notwithstanding the numerous studies about classical temperature and pressure equilibrium of mixed gas hydrates, few provide hydrate composition and volume at local and final equilibrium under batch conditions. Therefore, required new phase equilibrium data for mixed gas hydrates including CO2-C3H8, C2H6-nC4H10, CH4-nC4H10, CO2-C2H6-C3H8, CH4-C2H6-nC4H10 and CH4-C2H6-C3H8-nC4H10 are presented in this paper. Moreover, results contain hydrate phase properties such as hydrate volume and density, storage capacity, water conversion and guest composition in all phases (et al., liquid and hydrate). Importantly, effect of crystallization rate on final state has been evaluated. Finally the experimental results were compared to the thermodynamic model of van der Waals and Platteeuw to investigate kinetic effects. Experimental results show that equilibrium pressures at final state are dissimilar with respect to the crystallization rate. Furthermore, the hydrate volume formed at slow crystallization rate is noticeably lower than at quick. Noticeably, storage capacity in the case of slow crystallization is higher which could be crucial for industry. Also, the guest composition in hydrate phase at final state differs. Enclathration of heavier molecules is more significant at slow crystallization rate, and the hydrate phase seems to be more homogeneous according to the thermodynamic study. Indeed, modelling results, that assume the hydrate phase to be homogeneous in composition, show better agreement with the slow crystallization results for both equilibrium pressure and guest distribution in hydrate phase. This elucidates that, at quick crystallization rate, thermodynamic equilibrium cannot be reached. In conclusion, how kinetics influence the design of clathrate hydrate based industrial applications such as energy storage and transportation, carbon capture sequestration etc. are demonstrated.

Gaseous PvTx measurements of HFO-1234yf + HFC-32 binary mixture by single-sinker magnetic suspension densimeter

The measurements of PvTx properties of HFO-1234yf/HFC-32 binary mixture in the vapor phase were carried out by single-sinker magnetic suspension densimeter in the range of temperatures from 279.8 to 347.9 K, pressures from 0.10 to 2.66 MPa, densities from 2.30 to 66.02 kg m−3, and mole fractions of HFO-1234yf from 0.062 to 0.610. The experimental expanded uncertainty (k = 2) in temperature, pressure, and mole fraction are estimated to be 12 mK, 1.4 kPa, and 0.0002, respectively. The relative expanded uncertainty (k = 2) in density is 0.029–0.104%. On the basis of the experimental PvTx properties data, a truncated virial equation of state was developed for the binary HFO-1234yf/HFC-32 system. It reproduces the experimental values with average absolute deviations of 0.10% and 0.11% for pressure and density, respectively.

PVTx measurements and other derived volumetric properties of the binary ((1-propanol + n-pentane)) mixtures in the critical and supercritical regions

The PVTx properties of binary (1-propanol+n-pentane) mixture have been measured over wide temperature and pressure ranges from (306.15 to 573.15)K for densities between (15.52 and 663.69)kg·m−3 up to 49.09MPafor four concentrations (0.2, 0.5, 0.8, and 0.9mol fraction of n-pentane). The well-known high-temperature and high-pressure constant-volume piezometer technique was used for measurements of the PVTx relationship. The measurements were concentrated in the critical and supercritical regions in order to study the features of the mixture critical curve behaviour (critical phenomena in the (1-propanol+n-pentane) mixture and other derived thermodynamic properties near the liquid-gas critical points. The combined expanded uncertainty of the density (ρ), pressure (P), temperature (T), and concentration (x), measurements at the 95% confidence level with a coverage factor of k=2 is estimated to be 0.2% (density in the liquid phase), 0.3% (density in the gas phase); 0.5% (density in the critical and supercritical regions); 0.05% (pressure), 15mK, and 0.01mol%. The critical curve values (TC-x), (PC-x), and (ρC-x), were determined from the measured PVTx results. The value of the Krichevskii parameter (∂P/∂x)TCVC∞=7.985MPafor (1-propanol+n-pentane) mixture was estimated from the present and reported critical curve and the directly measured P-x results along the critical isochore-isotherm of pure 1-propanol. The critical curve values were also used to study the critical phenomena (isomorphism in the binary mixture) in the (1-propanol+n-pentane) mixture. In particular, the characteristic reduced temperature and density differences, which determine the isomorphic thermodynamic behaviour (pure-like and mixture-like critical behaviour) of the mixture, were estimated using the critical curve values. The measured PVTx values were also used to calculate the derived volumetric properties such as excess and partial molar volumes of n-pentane near the critical point of pure 1-propanol.

Vapor Phase PvTx Measurements of Binary Blends of 2,3,3,3-Tetrafluoroprop-1-ene + Propane and cis-1,2,3,3,3-Pentafluoroprop-1-ene + Propane

The paper presents 86 PvTx measurements in the vapor phase for blends of 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) and propane and 62 PvTx measurements in the vapor phase for blends of cis-1,2,3,3,3-pentafluoroprop-1-ene (R1225ye(Z)) and propane. The R1234yf and propane blends were measured along four isochores (0.047, 0.048, 0.072, 0.095) m3·kg–1 for (268 < T < 363) K for four propane mole fractions (0.230, 0.505, 0.611, 0.709) mol·mol–1. The R1225ye(Z) and propane blends were measured along five isochores (0.032, 0.038, 0.042, 0.067, 0.090) m3·kg–1 for (303 < T < 363) K for five propane mole fractions (0.225, 0.516, 0.593, 0.690, 0.855) mol·mol–1. The data are well-predicted when fitted (1) with Fundamental Helmoltz Equations of State (EoS), Peng–Robinson EoS, and Extended Corresponding States EoS when each are coupled with a modified van der Waals one-fluid linear mixing model, and (2) with a truncated Virial EoS.

Gaseous pVTx measurements for (HFC134a + HC290) by a compact single-sinker densimeter

Comprehensive gaseous pVTx measurements for {1,1,1,2-tetrafluoroethane (HFC134a)+propane (HC290)} were carried out by a compact single-sinker densimeter, based on the Archimedes’ buoyancy principle, at temperatures from (258 to 294)K, pressures up to 0.86MPa, and mole fractions of HFC134a from (0.2391 to 0.7989). The overall experimental standard uncertainty in temperature, pressure, mole fraction and density were estimated to be less than 5mK, 176Pa, (0.02 and 0.05)%, respectively. A truncated virial equation of state was employed to correlate the experimental pVTx data of (HFC134a+HC290) mixtures. This equation represented the experimental pressures and densities with average absolute relative deviations of (0.043 and 0.046)%, respectively.

Alternative biofuels

This study presents the experimental results for the dimethyl ether (DME) + propane system obtained using the Burnett method. The apparatus was calibrated using helium. PVTx measurements were taken for four isotherms (344, 354, 364, and 375 K), performing 16 Burnett expansions in pressures ranging from about 3,000 to 70 kPa. The second and third virial coefficients were derived from experimental results. The experimental uncertainty in the second and third virial coefficients was estimated to be within ±5 cm 3 /mol and ± 1,000 cm 6 /mol 2 , respectively.

PVTx measurements in the gas phase for binary mixtures of HFC-161 and HFC-227ea

The gaseous PVTx properties of ethyl fluoride (HFC-161) + 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) mixtures were measured at temperatures from 318.180 to 403.205 K and corresponding pressures from 961.3 to 3129.8 kPa using the isochoric method. The uncertainties in the present measurements were estimated to be ±1.5 kPa for pressure and ±6 mK for temperature. On the basis of the experimental PVTx property data, a truncated virial equation of state was developed for the binary HFC-161/227ea system. This equation reproduced the experimental data in the gas phase within ±0.164% in pressure and within ±0.178% in density.

Burnett Measurements and Virial Coefficients for the R32 + N2O System

Experimental results for the difluoromethane (R32) + nitrous oxide (N2O) system are presented in this paper. The Burnett apparatus was calibrated using helium, and its performance was confirmed by measurements for pure N 2O. The values of the virial coefficients for R32 were adopted from previous measurements as the same sample was used in the present study. PVTx measurements were performed for the binary R32 + N2O system for four isotherms (303, 323, 343, and 364 K). Twenty Burnett expansions were performed in a pressure range from 5000 to 150 kPa. The second and third virial coefficients along with the cross second and third virial coefficients were derived from experimental results.

Isochoric PVTx Measurements for the Carbon Dioxide + 1,1-Difluoroethane Binary System

PVTx measurements for carbon dioxide (CO2, R744) + 1,1-difluoroethane (CH3CHF2, R152a) for both the two-phase and the superheated vapor regions are presented. The measurements were taken with a constant volume apparatus at temperatures ranging from (223 to 343) K and pressures from (60 to 3890) kPa along eight isochores. The data obtained in the two-phase region were used to derive vapor−liquid equilibrium (VLE) parameters using a flash method with the Carnahan−Starling−De Santis equation of state (CSD EOS). The dew point was also found for each isochore from the intersection of the P−T sequences. Results from the superheated region were compared with those predicted from the CSD EOS. The complete set of data was also compared with the REFPROP 7.0 prediction.

Isochoric PVTx Measurements for the N2O + R125 Binary System

Isochoric PVTx measurements are reported for nitrous oxide (N2O, R744A) + pentafluoroethane (CHF2CF3, R125) for both the two-phase and the superheated vapor regions at temperatures ranging from (217 to 363) K and pressures from (160 to 1853) kPa along six isochores. The data obtained in the two-phase region were used to derive vapor−liquid equilibrium (VLE) parameters using a flash method with the Carnahan−Starling−De Santis equation of state (CSD EOS). The dew point was also found for each isochore from the intersection of the P−T sequences. The dew points were then used to derive VLE parameters from CSD EOS. Results from the superheated region were compared with those predicted from the virial EOS and from the CSD EOS.

Virial Coefficients from Burnett Measurements for the R23 + N2O System

This paper presents experimental results for the trifluoromethane (R23) + nitrous oxide (N2O) system, which has been chosen as a working fluid for low-temperature applications since it might be a valid option for the low-temperature stage in a cascade cycle. The thermodynamic properties of the binary mixture’s constituents are well known from the literature, but no experimental results have been published to date on the PVTx properties of this binary system. PVTx measurements were obtained for the binary R23 + N2O system for three isotherms (303, 323, and 343 K), performing 15 Burnett expansions in a range of pressures from about 4400 to 80 kPa. The second and third virial coefficients were derived from experimental results together with the second and third cross virial coefficients. The experimental uncertainties in the second and third virial coefficients were estimated to be within ±1 cm3·mol−1 and ±500 cm6·mol−2, respectively.

Isochoric PVTx Measurements for the C2H6 + N2O Binary System

In the search for fluids potentially suitable for low-temperature refrigeration applications, we have turned our attention to systems consisting of natural fluids, nitrous oxide (N2O) and ethane (C2H6) in particular. Isochoric PVTx measurements are reported for nitrous oxide + ethane for both the two-phase and the superheated vapor regions at temperatures ranging from (216 to 358) K and pressures from (494 to 5261) kPa along 11 isochores. The data obtained in the two-phase region were used to derive VLE parameters using a flash method with the Carnahan−Starling−De Santis equation of state (CSD EOS). The dew point was also found for each isochore from the intersection of the P−T sequences. The dew points were then used to derive VLE parameters from CSD EOS. Results from the superheated region were compared with the predicted from the virial EOS and CSD EOS.

PVTx measurements for N 2O + CH 3F, N 2O + CH 2F 2, and N 2O + CHF 3 binary systems

Isochoric PVTx measurements have been performed for the binary system of nitrous oxide + CH 3F (R41), +CH 2F 2 (R32), and +CHF 3 (R23) using a new experimental set-up. The experiments covered both the two-phase region and the superheated vapor region and were performed within the temperature range 214–358 K and within a pressure range from 270 to 5600 kPa. Data have been collected for not less than four compositions for each system. The vapor–liquid equilibrium data were derived correlating the experimental data by means of the Carnahan–Starling–De Santis equation of state. The studied systems show a positive deviation from the Raoult's law. The results obtained were compared with the Burnett PVTx data. The two methods showed a mutual consistency within an acceptable margin of error. No other experimental PVTx data were found in the literature for these binary systems.

PVTx Measurements for the R116 + CO2 and R41 + CO2 Systems. New Isochoric Apparatus

A new isochoric apparatus was built for PVTx measurements in an extended temperature range from (210 to 360) K and at pressures up to 6.0 MPa. The setup was used to measure PVTx properties for the R116 + CO2 and R41 + CO2 systems, both in the two-phase and superheated vapor regions. The binary interaction parameters were derived from experimental data in the two-phase region by applying the flash method and the Carnahan−Starling−DeSantis equation of state (CSD EOS). The dew-point parameters were found by interpolating the P−T isochoric sequences, again applying the CSD EOS. A composition-dependent mixing rule implemented in the CSD EOS improved the VLE data representation of both binary systems. The resulting binary interaction parameters were used for VLE parameter derivation. The superheated vapor region data were compared with those obtained by the Burnett method and using REFPROP 7.

Second and third virial coefficients for the R41+N 2O system

As a part of our ongoing research program on the PVTx measurements by the Burnett method for HFC + hydrocarbon and/or inorganic compound systems, in this work the experimental results for the nitrous oxide (N 2O) + fluoromethane (R41) system will be described. The system was chosen as an alternative refrigerant mixture. The thermodynamic properties of both mixture constituents are well known from the literature, but no experimental results have been published so far on the PVTx properties of this specific binary system. PVTx measurements were performed for the binary N 2O + R41 system for four isotherms (283, 303, 323 and 343 K). In total, 17 runs were performed in a pressure range from 4600 to 150 kPa. The second and third virial coefficients along with the second and third cross-virial coefficients were derived from experimental results. The experimental uncertainty in second and third virial coefficients is estimated to be within ±2 cm 3/mol and ±500 cm 6/mol 2, respectively.

PVTx Measurements for a H2O + Methanol Mixture in the Subcritical and Supercritical Regions

PVTx relationships for a H2O + CH3OH mixture (0.36 mole fraction of methanol) were measured in a range of temperatures from 373 to 673 K and pressures between 0.042 and 90.9 MPa. The density ranged from 37.76 to 559.03 kg · m−3. Measurements were made with a constant-volume piezometer surrounded by a precision thermostat. The temperature inside the thermostat was maintained uniform within 5 mK. The volume of the piezometer (32.68 ± 0.01 cm3) was previously calibrated from well-established PVT values of pure water (IAPWS), and was corrected for both temperature and pressure expansions. Uncertainties of the density, temperature, and pressure measurements are estimated to be 0.16%, 30 mK, and 0.05%, respectively. The uncertainty in composition is 0.001 mole fraction. The method of isochoric and isothermal break points was used to extract the phase transition temperatures, pressures, and densities for each measured isochore and isotherm. The values of the critical temperature, pressure, and density of the mixture were also determined from PVTx measurements in the critical region.