pvT Properties for R-227ea and HFE-7100 in the Liquid Phase

Article pubs.acs.org/jced

pvT Properties for R‑227ea and HFE-7100 in the Liquid Phase Baolin An, Longshan Tan, Yuanyuan Duan,* and Zhen Yang Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Beijing Key Laboratory for CO2 Utilization and Reduction Technology, Tsinghua University, Beijing 100084, China ABSTRACT: Liquid phase pvT properties of 1,1,1,2,3,3,3heptafluoropropane (R-227ea) and HFE-7100 were measured precisely using a constant-volume cell. The pvT property of R227ea was measured in the temperature range of (266 to 313) K and the pressure range of (0.823 to 17.014) MPa. The pvT property of HFE-7100 was measured in the temperature range of (275 to 303) K and the pressure range of (0.273 to 19.135) MPa. The temperature standard uncertainty was estimated to be 2.3 mK, the pressure standard uncertainty was estimated to be 15 kPa, and the density relative standard uncertainty was estimated to be 0.001. The experimental data for R-227ea were compared with an equation of state with a root-mean-square relative difference of 0.0003 for density. The liquid HFE-7100 pvT data were compared with available literature values, and the results show good agreements.

1. INTRODUCTION With increasing societal energy demands, the energy utilization efficiencies of all devices need to be improved.1−10 The utilization of low-grade heat sources which accounts for 50% or more of the total heat generated in the world greatly impacts the energy conservation.1 The organic Rankine cycle (ORC), which uses organic fluids as the working fluid, is good for the conversion of low-grade energy sources, rather than the conventional water-based steam Rankine cycles.1,5,6 The selection of the organic working fluid is very important, and previous studies have recommended a number of promising organic working fluids for the ORC systems. R-227ea and HFE7100 are promising working fluids.5−9 R-227ea has excellent thermal performance, is nonflammable, and has zero ozone depletion potential (ODP). HFE-7100 is nonflammable and has low GWP and zero ODP. The pvT property is a fundamental thermophysical property that has been widely researched.11−17 The liquid phase pvT property directly influences the pumping in organic Rankine cycle systems, and the pvT data are fundamental to the reference equations of state. The previous R-227ea pvT data for the liquid phase listed in Table 1 have obvious discrepancies.17−20 The previous HFE-7100 liquid pvT data listed in Table 2 were all measured with a vibrating tube densimeter.21−24 This paper presents the pvT properties of R-227ea and HFE-7100 measured in the liquid phase, using a constantvolume cell. The liquid R-227ea experimental data also show the reliability of the experimental system.

nonafluoroisobutyl ether and methyl nonafluorobutyl ether) with essentially identical properties according to 3 M Company. The R-227ea and HFE-7100 samples were used without further purification after being degassed. Before the measurements, the samples were transferred to a stainless steel vessel which was cooled by liquefied nitrogen to remove the noncondensable gases (such as air). The procedure was repeated several times to improve the sample purity. The HFE-7100 sample was measured with an ISQ Trance 1300 to test the main compositions and impurities. The initial temperature was set as 30 °C, the final temperature was set as 50 °C, and the heating rate was set as 2 °C·min−1. The result shows that the mole fraction of HFE-7100 is 0.9991, the mole fraction of 1,1,1,2,3,3,3,-heptafluoro-2-methoxypropane is 0.0003, and the mole fraction of 1,1,2,3,3,3-hexafluoropropyl methyl ether is 0.0006. A 19F nuclear magnetic resonance was performed on the purchased 3M HFE-7100 sample with a Bruker AVANCE III 400 HD NMR to measure the proportion of the two isomers. The NMR result shows that the methyl nonafluorobutyl ether to methyl nonafluoroisobutyl ether ratio was 37.7:62.3. Apparatus. A diagram of the apparatus is shown in Figure 1. The apparatus has been described in previous works, and only a brief description is given below.14,16,25 The system included thermostatic baths, a temperature measurement system, a pressure measurement system, a vacuum system, an analytical balance, and a data acquisition system. The temperature range for the thermostatic baths (Developed by Beijing Sensor Technology and Tsinghua University) was from (273 to 453) K. The temperature measurement system

2. EXPERIMENT Chemicals. The R-227ea was provided by DuPont with a state mole purity of 0.999. HFE7100 was supplied by the 3 M Company. Information of the two fluids was listed in Table 3. HFE-7100 consisted of two inseparable isomers (methyl © 2016 American Chemical Society

Received: September 13, 2015 Accepted: February 19, 2016 Published: March 7, 2016 1462

DOI: 10.1021/acs.jced.5b00784 J. Chem. Eng. Data 2016, 61, 1462−1467

Journal of Chemical & Engineering Data

Article

Table 1. Available pvT Data for R-227ea in the Liquid Phase range author 18

Klomfar et al. Ihmels et al.19 Scalabrin et al.20 Fedele et al.21

uncertainty

year

data point

purity

T/K

p/MPa

ΔT/mK

Δp

Δρ

1994 2002 2002 2007

83 257 10655 6155

0.9999 0.999 0.9999 0.995

205−315 278−373 253−363 283−333

0.6−52 0.9−30 0.9−20 0.9−35

20 30 20 23

0.001 6 kPa 2 kPa 23 kPa

0.001 0.2 kg m−3 0.0001 0.0005

Table 2. Available pvT Data for HFE-7100 in the Liquid Phase range

uncertainty

author

year

data point

purity

T/K

p/MPa

ΔT/mK

Δp/ kPa

Δρ

Piñeiro et al.18 Li et al.19 Qi et al.20 Rausch et al.21

2004 2011 2014 2015

100 22 141 19

0.998 0.995 0.995 0.995

283−313 279−321 283−363 273−363

0.1−40 0.1 0.1−100 0.9−35

50

50

16 10

192

0.1 kg m−3 0.005 kg m−3 0.6 kg m−3 0.0002

temperature measurement standard uncertainty was estimated to be 2.3 mK, including the 1 mK standard uncertainty of the platinum resistance thermometer, the 0.3 mK standard uncertainty of the thermometer bridge, and the 2 mK stability and uniformity of the thermostatic bath. The standard uncertainty of the pressure measurement was estimated to be 15 kPa, with 7 kPa for the pressure sensor and 8 kPa for the installation position. The uncertainty of the mass measurement was 0.001 g from the analytical balance. Procedure. The apparatus measured the density by measuring the mass of the sample liquid and the volume of the density measurement section consisted of B1 (shown in Figure 1, made from stainless steel 304), valve 5, and the connection between B1 and valve 5. Before the measurements, the constant-volume cell and connections were evacuated by the vacuum pump. The vacuum in the system was better than 10−4 Pa and was maintained for at least 6 h. Then, a selected amount of the sample was introduced into the constant-volume cell and connections. Valve 4 was closed, and the pvT measurements were started. The R-227ea and HFE-7100 vapor pressures were obtained from previous studies to verify that the samples were in the liquid phase.26,27 The thermostat bath temperature controlled the system to the designed temperatures. When the sample pressure was constant for at least 30 min, the sample was assumed to be in thermal equilibrium. Then, the sample temperatures and pressures were measured. The temperature and pressure at each state point was measured three times to reduce the experimental error, with the average of the three measurements used as the final value. When the temperature and pressure measurements along one isochore were finished, valve 5 was closed. The mass of B1, valve 5, and the connection were measured on the analytical balance. The sample mass was obtained by the mass difference of B1, valve 5, and the connection when filled with the sample and at a vacuum state. The procedure was repeated for several isochores. Volume of the Density Measurement Section (Constant Volume Cell B1, Valve 5, and the Connection). The volume of the constant volume cell B1, valve 5, and the connection was obtained by measuring the pvT property of R134a (1,1,1,2-tetrafluoroethane) in the liquid phase at of 294.899 K and 21.847 MPa. The information on R-134a sample was listed in Table 3. The volume was then calculated as

Table 3. Fluids Used in This Work fluid name

source

HFE-7100

3M

R-227ea

DuPont

R-134a

DuPont

chemicals methyl nonafluorobutyl ether/methyl nonafluoroisobutyl ether 37.7:62.3 1,1,1,2,3,3,3heptafluoropropane 1,1,1,2-tetrafluoroethane

mole purity

purification

0.9991

none

0.999

none

0.999

none

Figure 1. Apparatus for the pvT measurements in the liquid phase.

included platinum resistance thermometers (H. Tinsley & Co. Ltd.), a precise thermometer bridge (Measurements International Limited, MI: 6242T), a selector switch and a superthermometer (Fluke International Corporation, HART:1590). The temperature was determined on the basis of the International Temperature Scale of 1990 (ITS-90). The pressure was measured by a pressure sensor (Paroscientific, Inc., Type Model 9000−10K). A turbomolecular pump (KYKY Technology Co., LTD, KYKY: FD110) with a vacuum of 1•10−6 Pa provided the vacuum for the experimental apparatus. An analytical balance (MettlerToledo International Inc., Type PR1203) was used to measure the sample mass. Before the experiments, the platinum resistance thermometers, the thermometer bridge and the digital manometers were calibrated by the National Institute of Metrology (NIM), China. The overall temperature standard uncertainty including the variation of the thermostatic bath temperature, and the

Vref = mref /ρref 1463

(1) DOI: 10.1021/acs.jced.5b00784 J. Chem. Eng. Data 2016, 61, 1462−1467


Article

Table 4. pvT Data for R-227ea in the Liquid Phase

where Vref is the volume of the constant volume cell B1, valve 5, and the connection at the reference state, mref is the mass of R134a, and ρref is the density of the R-134a at reference state. The uncertainty in the constant volume cell volume was estimated as ΔVref = Vref

⎞2 ⎛ ∂ ln Vref ⎞2 ⎛ ∂ ln Vref Δmref ⎟ + ⎜⎜ Δρref ⎟⎟ ⎜ ⎝ ∂mref ⎠ ⎝ ∂ρref ⎠

(2)

The mass of R-134a was measured on the analytical balance, and the R-134a density was calculated from R-134a international equation of state with an relative uncertainty of 0.0005.28 The resulting volume was 31.013 mL (at 294.899 K, 21.847 MPa), and the relative standard uncertainty was 0.00056. The volume of the constant volume cell changes with temperature and pressure as V = Vref [1 + 3α(T − Tref ) + β(p − pref )]

(3)

where α = 1.6 × 10−5 K−1 is the temperature dilatation coefficient of the measuring cell material, β = 2.25 × 10−5 MPa−1 is the coefficient of the cell volume expansion with pressure, Tref is the reference temperature and pref is the reference pressure. Density Measurement. The density was then calculated: m ρ= Vref [1 + 3α(T − Tref ) + β(p − pref )] (4) where m is the mass of the investigated sample. The density relative uncertainty was estimated as u(ρ)2 =

⎛ ∂ρ ⎞2 u ( X ) ⎜ ∑ i ⎟ ⎝ ∂Xi ⎠

(5)

where u(ρ) is the density standard uncertainty and Xi are the input parameters in eq 4.

3. RESULTS AND DISCUSSION Liquid Phase pvT Data for R-227ea. The measurement results for the R-227ea liquid pvT property with 45 data points are shown in Table 4 and Figure 2. The measurements were made in the temperature range of (266 to 313) K and the pressure range of (0.823 to 17.014) MPa. The uncertainties of the coefficient α and β in eq 3 were both about 10% which is small enough to have little effect on the uncertainty of the sample cell temperature expansion and pressure expansion terms. The density relative standard uncertainty at the reference state was 0.00056, so the density relative standard uncertainty was estimated to be 0.001. The relative root-mean-square (RMS) deviation was defined as ⎡ 1 RMS = ⎢ ⎢⎣ n − 1

n

∑ (ρj ,exp /ρj ,cal j=1

⎤1/2 ⎥⎦

p/MPa

ρ/kg·m−3

279.512 281.323 283.419 285.367 287.364 289.407 291.465 293.405 295.288 297.178 299.382 301.398 302.937 268.918 271.830 274.295 277.704 280.801 283.611 286.698 289.311 286.426 289.142 292.001 294.978 297.852 300.889 303.821 306.881 310.047 312.948 286.668 288.433 290.440 292.977 294.612 296.721 298.699 300.868 302.736 304.795 306.954 308.997 311.053 312.852

0.839 1.993 3.331 4.577 5.848 7.162 8.474 9.717 10.924 12.136 13.527 14.839 15.829 1.786 3.840 5.598 8.059 10.284 12.288 14.495 16.361 1.142 2.747 4.466 6.251 7.978 9.788 11.544 13.381 15.281 17.014 1.203 2.193 3.367 4.875 5.846 7.101 8.273 9.562 10.686 11.916 13.205 14.427 15.654 16.727

1466.6 1465.2 1464.8 1464.6 1464.3 1464.1 1463. 9 1463.7 1463.5 1463.3 1463.1 1462.9 1462.8 1509.3 1508.5 1508.1 1507.7 1507.3 1507.0 1506.7 1506.4 1441.9 1440.7 1440.2 1439.8 1439.5 1439.2 1438.9 1438.6 1438.3 1438.0 1440.9 1440.0 1439.5 1439.1 1438.9 1438. 7 1438.5 1438.2 1438.1 1437.9 1437.7 1437.5 1437.3 1437.1

The temperature standard uncertainty was estimated to be 2.3 mK, the pressure standard uncertainty was estimated to be 15 kPa, and the density relative standard uncertainty was estimated to be 0.001.

2⎥

− 1)

T/K

above the R-227ea equation of state, with the differences increasing with pressure with a maximum relative difference of 0.005 near the critical region.19,23 The densities of Fedele et al. are below the R-227ea equation of state for most points with the absolute values of the differences increasing with pressure.21,23 The densities of Klomfar et al. agree well with the R-227ea equation of state with a maximum absolute deviation of less than 0.001.18,23 The RMS deviation of the R227ea data in this paper to the R-227ea equation of state is 0.0003, which shows good agreement with the R-227ea equation of state.26

(6)

where n is the number of experimental points, ρj,cal is the density calculated from the R-227ea equation of state,23 and ρj,exp is the measured density. The liquid pvT data for R-227ea was compared with the R227ea equation of state in Figures 3 and 4.23 The density differences between the measurements of Scalabrin et al. and the R-227ea equation of state are quite different from the other experimental results.20,23 The densities of Ihmels et al. are all 1464



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Table 5. pvT Data for HFE-7100 in the Liquid Phase

Figure 2. R-227ea experimental data: □, data points; , vapor pressures calculated from the R-227ea equation of state.26

Figure 3. R-227ea experimental data of Scalabrin et al. compared with the R-227ea equation of state.19,26

Figure 4. R-227ea experimental data compared with the R-227ea equation of state: ▼, this work; □, Fedele et al.; ○, Klomfar et al.; △, Ihmels et al.17,18,20,26

T/K

p/MPa

ρ/kg·m−3

275.017 277.094 279.259 281.337 283.500 285.493 287.586 289.564 291.625 293.525 295.589 291.672 289.599 287.538 286.257 284.437 281.924 279.746 279.434 279.748 280.461 282.377 283.651 285.416 288.039 289.600 291.665 287.535 286.256 292.609 294.314 296.289 298.566 300.654 302.596 302.596 301.342 299.645 295.319 293.435 291.665 289.721 287.675 285.935 284.037 281.940 280.941 292.704 287.265 281.546 280.365 286.607 289.600 288.898 286.953 285.095 283.210

1.984 3.723 5.543 7.289 9.101 10.769 12.510 14.156 15.869 17.446 19.153 10.101 8.448 6.789 5.757 4.290 2.278 0.524 0.273 0.527 1.101 2.648 3.673 5.083 7.178 8.425 10.070 6.765 5.744 10.815 12.183 13.751 15.560 17.215 18.786 18.751 17.761 16.411 12.982 11.481 10.052 8.502 6.872 5.471 3.949 2.249 1.442 10.872 6.535 1.942 0.972 5.994 8.462 7.893 6.330 4.838 3.315

1579.6 1579.2 1578.7 1578.3 1577.9 1577.5 1577.1 1576.7 1576.2 1575.9 1575.4 1562.0 1562.5 1562.9 1563.1 1563.5 1564.0 1564.4 1564.5 1564.4 1564.3 1563.9 1563.6 1563.3 1562.8 1562.5 1562.0 1562.9 1563.1 1561.9 1561.5 1561.1 1560.7 1560.3 1559.9 1559.9 1560.1 1560.5 1561.3 1561.7 1562.0 1562.4 1562.8 1563.2 1563.6 1564.0 1564.2 1561.2 1562.3 1563.5 1563.7 1562.5 1562.2 1562.5 1562.9 1563.3 1563.7

The temperature standard uncertainty was estimated to be 2.3 mK, the pressure standard uncertainty was estimated to be 15 kPa, and the density relative standard uncertainty was estimated to be 0.001.

Liquid Phase pvT Data for HFE-7100. The HFE-7100 liquid phase pvT data points were measured with the same 1465



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experimental system and procedure as for R-227ea. The measured HFE-7100 liquid pvT property with 57 data points are shown in Table 5 and Figure 5. The measurements were made in the temperature range (275 to 303) K and the pressure range (0.273 to 19.135) MPa. The density relative standard uncertainty in the measurement is estimated to be 0.001. Qi et al. measured HFE-7100 liquid pvT data with temperature from (283 to 363) K and pressure from (0.1 to 100) MPa and developed a correlation using their experimental data.23 The HFE-7100 liquid pvT data from Qi et al., Piñeiro et al., Li et al., and this work were compared with the correlation of Qi et al., and the results are shown in Figure 6. The RMS deviation of the experimental data from Qi et al., Piñeiro et al., Li et al., and this work to Qi’s correlation is 0.0009, 0.0010, 0.0042, and 0.0004, respectively. The deviations of the experimental data to the correlation for both this work and Piñeiro’s work increase with pressure. The maximum relative deviation for the experimental data to this correlation is less than 0.002 except for the data from the work of Li et al. Piñeiro et al. measured HFE-7100 liquid pvT data with temperature from (283 to 313) K and pressure from (0.1 to 40) MPa and developed a correlation using their experimental data.22 The HFE-7100 liquid pvT data from Qi et al., Piñeiro et al., Li et al., and this work were compared with the correlation of Piñeiro et al., and the results are shown in Figure 7. As this correlation was based on Piñeiro’s data with temperature from (283 to 313) K and pressure from (0.1 to 40) MPa, all the compared experimental data were selected within this region. The RMS deviation of the experimental data from Qi et al., Piñeiro et al., Li et al., and this work to Piñeiro’s correlation is 0.0007, 0.0001, 0.0037, and 0.0003, respectively. The maximum relative deviation for the experimental data to this correlation is less than 0.002 except for the data from the work of Li et al.

Figure 5. HFE-7100 experimental data: □, data points; , vapor pressures calculated from HFE-7100 vapor pressure equation.27

4. CONCLUSION R-227ea liquid pvT data was measured with a constant volume cell from (266 to 313) K with pressures from (0.823 to 17.014) MPa. HFE-7100 liquid pvT data was measured from (275 to 303) K with pressures from (0.273 to 19.135) MPa. The temperature standard uncertainty was estimated to be 2.3 mK, the pressure standard uncertainty was estimated to be 15 kPa and density relative standard uncertainty was estimated to be 0.001. The measured data of R-227ea data were compared with the R-227ea equation of state with an RMS deviation of 0.0003. The liquid HFE-7100 pvT data in this paper were compared with the correlations of Qi et al. and Piñeiro et al. The RMS deviation of the experimental data to the correlations of Qi and Piñeiro is 0.0004 and 0.0003, respectively.

Figure 6. HFE-7100 experimental data compared with the correlation from Qi et al: ■, this work; ○, Piñeiro et al.; △, Qi et al.; ◇, Li et al.21−23

■

AUTHOR INFORMATION

Corresponding Author

*Tel.: +86 10 6279 6318. E-mail: [email protected]. Funding

This work was supported by the National Natural Science Foundation of China (Grant Nos. 51236004 and 51321002). Notes

The authors declare no competing financial interest.

■

Figure 7. HFE-7100 experimental data compared with the correlation from Piñeiro et al: ■, this work; ○, Piñeiro et al.; △, Qi et al.; ◇, Li et al.21−23

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pvT Properties for R-227ea and HFE-7100 in the Liquid Phase

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