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Surface Tension and Liquid Viscosity of R32+R1234yf and R32+R1234ze Junwei Cui, Shengshan Bi,* Xianyang Meng, and Jiangtao Wu Key Laboratory of Thermo-Fluid Science and Engineering, Ministry of Education, School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China ABSTRACT: The surface tension and liquid viscosity of two binary refrigerant mixtures 1,1,1,2-tetrafluoroethane (R32) (1) + 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) (2) and R32 (1) + trans-1,3,3,3-tetrafluoroprop-1-ene (R1234ze) (2) have been measured from 293 K to the critical point by using the surface light scattering (SLS) method. The experimental data were correlated as a function of temperature and mole fraction of the pure components. For the surface tension of R32+R1234yf and R32+R1234ze, the average absolute deviations are 0.053 and 0.029 mN·m−1, respectively. As for the liquid viscosity, the relative percentage average absolute deviations are 0.86 and 1.01%, respectively.

1. INTRODUCTION 2,3,3,3-Tetrafluoroprop-1-ene (R1234yf) with zero ozone depletion potential (ODP) and low global warming potential (GWP) of 4 (100 years) has been proposed as a drop-in substitute for 1,1,1,2-tetrafluoroethane (R134a). Trans-1,3,3,3tetrafluoro-1-propene (R1234ze) is anticipated to be an alternative to conventional refrigerant R410A (R125/R32 50/ 50% by mass) for air conditioning systems owing to its zero ODP and low GWP (100 year GWP = 6). However, pure R1234yf and R1234ze are inferior in the applications of air conditioning and heat pump systems due to their low operating pressure, small latent heat, and volumetric capacity. One of the proposed solutions is to add difluoromethane (R32) to them to improve the heat transfer characteristic1−5 and coefficient of performance (COP)6−10 of the air conditioner. Fujitaka et al.6 found the COP of the mixture R1234yf+R32 is increased as the concentration of R32 becomes richer. The COP of R1234yf +R32 (50/50% by mass) under the cooling and heating conditions reached 95% and 94% of that of R410A, respectively. Okazaki et al.7 tested R1234yf+R32 mixtures in a modified room air conditioning. When the concentration of R32 achieved 60%, the annual performance factor (APF) ratio of the mixture is 93.3% of R410A. Miyara et al.5 found the condensation heat transfer coefficient of R32+R1234ze (55/ 45% by mass) is comparable to that of R410A. Koyama et al.8 conducted a drop-in experiment of R410A, R1234ze, and R32+R1234ze (50/50% by mass) under heating conditions. The results revealed that the COP of R32+R1234ze (50/50% by mass) was weakly affected by the degree of subcooling at the condenser outlet and it was only about 10% lower than that of R410A at the same heating load of 2.8 kW. All the studies showed that R32+R1234yf and R32+R1234ze are promising candidates to R410A. © XXXX American Chemical Society

Thermophysical properties of the refrigerant are necessary for designing the condenser and the evaporator in refrigerator systems. The literature review of R32+R1234yf and R32+R1234ze were summarized in Table 1. Additionally, Akasaka et al. 13,20,21 measured the critical point of R32+R1234yf by a visual observation of meniscus disappearance and established the thermodynamic property models explicit in the Helmholtz energy for the R32+R1234yf and R32+R1234ze mixtures. For the surface tension and the liquid viscosity along the saturation line, only the surface tension of R32+R1234ze (50/50% by mass) were measured by Katsuyuki et al.18 with differential capillary rise method (DCRM) from 273 to 323 K. In this work, the surface tension and the liquid viscosity of R32+R1234yf and R32+R1234ze were measured by using the surface light scattering (SLS) method. The experimental data were correlated as a function of temperature and mole fraction of the pure components.

2. EXPERIMENTAL SECTION 2.1. Material. R32 was provided from Zhejiang Lantian Environmental Protection Hi-Tech Co., Ltd., and the stated mass fraction purity was more than 0.9996. R1234yf and R1234ze were obtained from Honeywell; the stated purities were more than 0.999 in mass fraction. The complete specifications for the three refrigerants are given in Table 2. The preparation of the refrigerants mixture was briefly described as follows: First, the two pure refrigerants were introduced to two different individual sample cylinders by Received: September 16, 2015 Accepted: December 28, 2015

A

DOI: 10.1021/acs.jced.5b00798 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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Table 1. Thermophysical Properties of R32+R1234yf and R32+R1234zea mixture

property

condition

T (K)

method

reference

R32+R1234yf

η″ ρ′ VLE VLE η′ VLE pvT σ λ′

atmosphere saturated

278−338 340 − Tc 273−333 273−313 283−323 273−313 310−380 273−323 283−353

falling-ball-type viscometer observation static method molecular simulation moving piston digital viscometer molecular simulation constant volume method differential capillary rise method transient hot-wire method

11, 12 13 14 15 16 15 17 18 19

R32+R1234ze

compressed

saturated saturated

a Notes: η″, the vapor viscosity; ρ′, the liquid density; VLE, the vapor liquid equilibrium; η′, the liquid viscosity; PVT, the pressure volume temperature property; σ, the surface tension; λ′, the liquid thermal conductivity.

Table 2. Specifications of Chemical Samples chemical

IUPAC name

source

purity (mass fraction)

purification method

R32 R1234yf R1234ze

1,1,1,2-tetrafluoroethane 2,3,3,3-tetrafluoroprop-1-ene trans-1,3,3,3-tetrafluoroprop-1-ene

Zhejiang Lantian Environmental Protection Hi-Tech co.Ltd., China Honeywell International Inc. Honeywell International Inc.

>0.9996 >0.999 >0.999

freeze−pump−thaw freeze−pump−thaw freeze−pump−thaw

through resistance heating and measured by two calibrated 100Ω platinum resistance probes with a standard uncertainty of 0.01 K. The temperature stability was better than 0.01 K during a single experiment run. The combined expanded uncertainty of temperature (k = 2) is 0.03 K. The incident angle was adjusted with an electric rotation table (DaHeng, GCD011080) with a standard uncertainty of 0.05%. For each temperature point, typically six measurements at different angles (±3.0°, ±3.1°, ±3.2°) of incidence were performed. The expanded uncertainty (k = 2) of the liquid kinematic viscosity data is estimated to be 2% at reduced temperatures Tr < 0.95. The expanded uncertainty (k = 2) is clearly larger near critical temperature and increases up to 6% when Tr gets close to 0.99. For the surface tension data, the expanded uncertainty (k = 2) is estimated to be 1.5% over the whole temperature range. A more detailed discussion regarding the accuracy achievable for liquid kinematic viscosity and surface tension from SLS can be found in refs 27 and 28.

freeze−pump−thaw cycles, respectively. An accurate electronic balance (Mettler Toledo ME3002) with a resolution of 0.01 g was used for the mass measurement. Then, the pure refrigerant R1234yf or R1234ze with a lower saturated pressure at room temperature was aspirated into the experimental cell with a hotair generator for at least 20 min. Also, the pure refrigerant R32 with a higher saturated pressure at room temperature was also aspirated into the experimental cell with the same procedure. Because the total mass of the refrigerants in the experimental cell was about 75 g, the standard uncertainty of the composition of the mixture was estimated to be better than 0.2% in mole fraction. Finally, R32 (1) + R1234yf (2) binary mixtures were prepared at nominal mole fractions x1 of 0.5193, 0.6988, and 0.7945, respectively. R32 (1) + R1234ze (2) binary mixtures were prepared at nominal mole fractions x1 of 0.2985, 0.5697, and 0.7501, respectively. 2.2. Surface Light Scattering. The surface light scattering (SLS) method has been successfully applied to the surface tension and the liquid viscosity measurement of ionic liquids and refrigerants.22−25 The main advantage of SLS relies on the possibility of simultaneously determining the surface tension and the liquid viscosity with low uncertainty in macroscopic thermodynamic equilibrium. The liquid kinematic viscosity and the surface tension were determined by solving the dispersion relation. In addition to the information on the dynamics of surface fluctuations at a given wave vector q⃗ obtained from the SLS apparatus, reference of dynamic vapor viscosity and density of both phase under saturation condition were utilized for this purpose. A detailed and comprehensive description of the fundamentals and methodological principles of SLS can be found in refs 26−28. The SLS apparatus employed in our former investigation for the surface tension and liquid viscosity of R1234yf, R1234ze,29 and R16130 was described thoroughly in ref 29. The experimental system consists of a diode-pumped solid state laser (Spectra-Physics Excelsior, 300 mW) with a wavelength of λ0 = 532 nm, a digital correlator with a single τ-structure (ALVLinCorr) for the computation of the pseudo cross-correlation function, optical path, and experimental cell (stainless steel and equipped with quartz windows; inner diameter, 70 mm; volume, 160 cm3). The temperature of the cell is regulated

3. RESULTS AND DISCUSSIONS 3.1. R32. The surface tension and the liquid kinematic viscosity of R32 were measured at the temperature range from 293 to 348 K and presented in Table 3. The saturated liquid, vapor densities, and the vapor viscosity of R32 were calculated with the NIST REFPROP9.0.31 A modified van der Waals type equation was used for the correlation of surface tension of R32 σ = σ0(1 − Tr)1.26 [1 + σ1(1 − Tr)0.5 + σ2(1 − Tr)]

(1)

where σ0, σ1, and σ2 are the fitting parameters listed in Table 4. In eq 1, Tr (= T/Tc) is the reduced temperature with Tc being the critical temperature. The surface tension of R1234yf and R1234ze were also correlated with eq 1 successfully in our previous work29 and the fitting parameters are also listed in Table 4. The surface tension of R32 in this paper is compared with the literature data and shown in Figure 1. Froeba et al.32 measured the surface tension by the same SLS method with a deviation less than 0.13 mN·m−1 compared with the values calculated from eq 1. Okada et al.33 and Zhu et al.34 measured B



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Table 3. Liquid Density ρ′, Vapor Density ρ″, Dynamic Viscosity of the Vapor Phase η″, Kinematic Viscosity of the Liquid Phase ν′, and Surface Tension σ of R32 under Saturation Conditionsa from 293 to 348 K by SLS T/K

ρ′/kg·m−3

ρ″/kg·m−3

η″/μPa·s

ν′/mm2·s−1

σ/mN·m−1

293.15 303.15 313.07 323.15 333.14 343.16 348.18

981.4 939.6 893.4 839.3 773.4 680.8 605.9

40.9 54.8 73.1 98.6 135.2 196.8 255.6

12.53 13.13 13.82 14.72 15.97 18.14 20.43

0.1295 0.1171 0.1079 0.0998 0.0930 0.0795 0.0750

7.40 5.94 4.35 2.96 1.67 0.57 0.14

the surface tension of R32 using DCRM with the estimated uncertainty of 0.2 mN·m−1.The deviations between their data and the values calculated from eq 1 are within the ±0.2 mN· m−1 with the exception of the surface tension of Zhu et al.34 at 334 K, where a discrepancy of 0.33 mN·m−1 can be found. Duan et al.35 and Heide et al.36 also measured the surface tension of R32 by DCRM with the estimated uncertainties of 0.15 and 0.1 mN·m−1, respectively. Their data are 0.13 to 0.27 mN·m−1 and 0.14 to 0.31 mN·m−1 larger than our data. With the exception of the data of given by Zhu et al. at 334 K and Heide et al. at 293 K, our surface tension data of R32 agree well with the other data sets within the combined uncertainty from 293 to 348 K. For the liquid viscosity of R32, a polynomial equation with an additional term

a

Directly measured values for frequency and damping at a defined wave vector of surface waves were combined with literature data for η″, ρ′, and ρ″ from ref 31 to derive ν′ and σ by an exact numerical solution of the dispersion relation. The combined expanded uncertainties Uc are Uc(T) = 0.03 K, Uc(ν′) = 0.02·ν′ for Tr < 0.95 and 0.06·ν′ for Tr close to 0.99, and Uc (σ) = 0.015. σ (level of confidence = 0.95)

3

v′ =

i=0

Tc/K

σ0/mN·m−1

σ1

σ2

R32 R1234ze29 R1234yf29

351.26 382.52 367.85

48.813 57.905 23.700

2.725 −0.054 6.196

−3.884 0.064 −8.185

⎝

T⎞ ⎟ Tc ⎠

n

(2)

was chosen to represent the viscosity over the complete investigated temperature range. νi (i = 0, 1, 2, 3, 4) and n are the fitting parameters listed in Table 5. The liquid kinematic viscosity of R1234yf and R1234ze were also correlated with eq 2 in our previous work29 and the fitting parameters are also listed in Table 5. Figure 2 represents the deviations of the experimental viscosity data for R32 and literature data are also included for

Table 4. Fitting coefficients of Equation 1 for R32, R1234yf, and R1234ze sample

⎛

∑ νiT i + ν4⎜1 −

Figure 1. Surface tension of R32 under saturated condition from SLS in comparison with literature data: ■, this work; − , the fitting equation with eq 1; △, ref 32; ○, ref 33; ▽, ref 34; ◁, ref 35; ▷, ref 36

Figure 2. Liquid kinematic viscosity for R32 under saturated condition from SLS in comparison with literature data: ■, this work; − , the fitting equation with eq 2; ○, ref 32; ◁, ref 37; ▷, ref 38, ◇, ref 39; ▽, ref 40; △, ref 41.

Table 5. Fitting Coefficients of Equation 2 for R32, R1234yf, and R1234ze sample

ν0/mm2·s−1

ν1 × 102/mm2·s−1·K−1

ν2 × 105/mm2·s−1·K−2

ν3 × 107/mm2·s−1·K−3

ν4/mm2·s−1

n

R32 R1234yf29 R1234ze29

15.71648 0.00473 −1.52231

−18.0110 0.34750 0.20014

62.65041 −1.86891 −0.66278

−6.84753 0.25140 0.31591

4.92544 0.11835 2.94438

1.14918 0.14707 0.82509

C



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Table 6. Liquid Density ρ′, Vapor Density ρ″, Dynamic Viscosity of the Vapor Phase η″, Kinematic Viscosity of the Liquid Phase ν′, and Surface Tension σ of R32 (1) + R1234yf (2) with Mole Factions x1 of 0.5193, 0.6988, and 0.7945 of R32 under Saturation Conditionsa from 293 to 343 K by SLS T/K

ρ′/kg·m−3

ρ″/kg·m−3

η″/μPa·s

293.16 303.16 313.14 323.17 333.14 343.14

1062.9 1024.2 982.0 934.7 880.3 813.3

34.4 45.9 60.8 80.6 107.1 145.0

12.19 12.66 13.27 14.00 14.92 16.26

293.21 303.20 313.21 323.19 333.21 343.16

1038.7 999.1 955.4 906.4 848.7 776.6

36.0 48.1 63.9 84.8 113.6 155.6

12.40 12.94 13.58 14.34 15.34 16.80

293.15 303.14 313.26 323.20 333.21 343.18

1023.5 983.3 938.3 888.3 828.6 752.2

37.2 49.7 66.3 88.0 118.5 164.1

12.47 13.03 13.70 14.49 15.54 17.12

ν′/mm2·s−1 x1 = 0.5193 0.1311 0.1197 0.1094 0.1010 0.0915 0.0818 x1 = 0.6988 0.1280 0.1188 0.1094 0.0991 0.0898 0.0793 x1 = 0.7945 0.1279 0.1183 0.1082 0.0982 0.0885 0.0771

(ν′exp − νb)/ν′exp·100

σ/mN·m−1

σexp − σb/mN·m−1

−1.59 −2.75 −4.02 −4.29 −6.52 −9.88

6.55 5.29 4.10 2.96 1.91 0.97

−0.30 −0.21 −0.13 −0.09 −0.07 −0.07

−0.04 0.19 −0.55 −3.03 −5.41 −10.33

6.90 5.49 4.10 2.82 1.66 0.66

−0.11 −0.10 −0.15 −0.19 −0.22 −0.24

1.73 1.45 −0.03 −2.48 −5.57 −12.08

7.04 5.57 4.14 2.83 1.62 0.59

−0.11 −0.11 −0.15 −0.18 −0.22 −0.23

Directly measured values for frequency and damping at a defined wave vector of surface waves were combined with literature data for η″, ρ′, and ρ″ from ref 31 to derive ν′ and σ by an exact numerical solution of the dispersion relation. The combined expanded uncertainties Uc are Uc(T) = 0.03 K, Uc(x) = 0.002·x, Uc(ν′) = 0.02·ν′ for Tr < 0.95 and 0.06·ν′ for Tr close to 0.99, and Uc(σ) = 0.015. σ (level of confidence = 0.95). bCalculated from NIST REFPROP9.0.31 a

comparisons. Laesecke et al.,37 Sun et al.,38 and Ripple et al.39 measured the viscosity of R32 by a capillary viscometer with a stated uncertainty of 2.4, 3, and 5%, respectively. Their data agree well with our results with the maximum deviation of 3.05, 5.13, and 2%, respectively. Oliveira et al.40 obtained the experimental data using vibrating-wire viscometer with an estimated uncertainty of 0.5∼1, and 0.5%, respectively. Their data are consistent with our results except for the viscosity at 343.14 K (Tr = 0.977) by Oliveira, which a deviation larger than 12% can be found and might be due to the measurement being taken in the proximity of the critical point and the larger uncertainty of the density data. Froeba et al.32 measured the viscosity of R32 by SLS with an accuracy of 5%. As illustrated in Figure 2, the discrepancy is within 6.6%. Assael et al.41 obtained the experimental data using vibrating-wire viscometer with an estimated uncertainty of 0.5%, where a deviation of 3.07 and 2.81% from eq 2 can be found at 293.15 and 313.5 K, respectively. 3.2. R32+R1234yf and R32+R1234ze. The surface tension and liquid viscosity of the mixtures of R32 (1) + R1234yf (2) at three mole fractions x1 of 0.5193, 0.6988, and 0.7945 were measured from 293 to 343 K, and the experimental data were given in Table 6. The surface tension and liquid viscosity of the mixtures of R32 (1) + R1234ze (2) with x1 of 0.2985, 0.5697, and 0.7501 were measured from 293 to 348 K, and the experimental data were listed in Table 7. The saturated liquid, vapor densities, and the vapor viscosity of mixtures were calculated with the NIST REFPROP9.031 in which the saturated liquid and vapor densities were determined by the Helmholtz energy equation of state, and the vapor viscosity were estimated with the extended corresponding state method. A more detailed information can be found in refs 42−44.

The comparisons of the experimental surface tension and the liquid viscosity of the two binary mixtures with those calculated from NIST REFPROP9.0 are also included in Tables 6 and 7. For the surface tension of R32+R1234yf, the experimental results agree well with the prediction from NIST REFPROP9.0 with a maximum absolute deviation (MAD) of 0.30 mN·m−1. For the liquid kinematic viscosity of R32+R1234yf, the MAD and the average absolute deviations (AAD) are 7.73 and 4.37%, respectively. Also, the percentage deviations increase dramatically when the temperature reach 348 K. For the surface tension of R32+R1234ze, the discrepancies between the experimental results and the NIST REFPROP9.0 are larger, especially at 293 K where a deviation is larger than 1.1 mN·m−1. For the liquid kinematic viscosity of R32+R1234ze, the MAD and AAD are 7.73 and 4.37%, respectively. 3.3. Correlation. For the mixture refrigerants, the Redlich− Kister polynomial equation45 was used for the correlation of the surface tension σmix = x1σ1 + x 2σ2 + x1x 2(a + bT )

(3)

where σmix denotes the surface tension of the mixture, σ1 and σ2 are the surface tension of the pure components, x1 and x2 are mole fractions of the pure compounds, and a and b are the fitting parameters shown in Table 8. The surface tension data for the pure refrigerants R1234yf and R1234ze were adopted from our previous study in ref 29. Figures 3 and 4 show the experimental surface tension and the deviations from eq 3 for R32+R1234yf and R32+R1234ze, respectively. The AAD and the MAD between the experimental results and the values reproduced by eq 3 for R32+R1234yf are 0.083 and 0.117 mN·m−1, respectively. Also, those for R32+R1234ze are 0.029 and 0.109 mN·m−1, respectively. D



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Table 7. Liquid Density ρ′, Vapor Density ρ″, Dynamic Viscosity of the Vapor Phase η″, Kinematic Viscosity of the Liquid Phase ν′, and Surface Tension σ of R32 (1) + R1234ze (2) with Mole Factions x1 of 0.2985, 0.5697, and 0.7501 of R32 under Saturation Conditionsa from 293 to 348 K by SLS T/K

ρ′/kg·m−3

ρ″/kg·m−3

η″/μPa·s

293.16 303.17 313.13 323.13 333.16 343.12 348.17

1120.6 1084.0 1044.6 1001.1 951.8 894.7 860.9

31.6 42.1 55.6 73.0 96.0 126.7 146.9

12.77 13.21 13.71 14.38 15.18 16.23 16.92

293.14 303.16 313.12 323.14 333.14 343.11 348.19

1068.1 1028.4 984.9 935.7 878.3 807.1 761.1

36.6 49.0 65.0 86.3 115.4 157.4 187.7

12.82 13.31 13.99 14.77 15.78 17.23 18.32

293.15 303.17 313.08 323.13 333.11 343.12 348.18

1033.2 992.0 946.7 894.4 832.1 750.0 692.5

39.0 52.2 69.5 93.0 125.9 176.7 217.1

12.77 13.34 14.04 14.89 16.02 17.80 19.30

ν′/mm2·s−1 x1 = 0.2985 0.1606 0.1432 0.1319 0.1227 0.1113 0.1019 0.0963 x1 = 0.5697 0.1471 0.1338 0.1220 0.1126 0.1028 0.0931 0.0874 x1 = 0.7501 0.1368 0.1281 0.1144 0.1041 0.0975 0.0896 0.0858

(ν′exp − νb)/ν′exp·100

σ/mN·m−1

σexp − σb/mN·m−1

4.74 1.93 2.13 3.24 1.97 1.85 0.77

8.46 7.17 5.93 4.75 3.62 2.54 2.06

−1.17 −1.01 −0.84 −0.66 −0.49 −0.35 −0.25

7.69 6.46 5.34 5.36 4.52 3.33 1.77

8.02 6.63 5.34 4.15 2.89 1.83 1.34

−1.18 −1.01 −0.80 −0.56 −0.46 −0.26 −0.17

6.67 7.73 4.35 2.66 3.95 3.95 4.30

7.74 6.30 4.91 3.62 2.41 1.32 0.83

−0.92 −0.78 −0.62 −0.46 −0.32 −0.17 −0.10

Directly measured values for frequency and damping at a defined wave vector of surface waves were combined with literature data for η″, ρ′, and ρ″ from ref 31 to derive ν′ and σ by an exact numerical solution of the dispersion relation. The combined expanded uncertainties Uc are Uc(T) = 0.03 K, Uc(x) = 0.002·x, Uc(ν′) = 0.02·ν′ for Tr < 0.95 and 0.06·ν′ for Tr close to 0.99, and Uc(σ) = 0.015. σ (level of confidence = 0.95). bCalculated from NIST REFPROP9.0.31 a

Table 8. Fitting Coefficients of Equation 3 for R32+R1234yf and R32+ R1234ze sample

a/mN·m−1

b × 102/mN·m−1·K−1

R32+R1234yf R32+R1234ze

−8.8331 −6.6940

0.0232 0.0207

Tanaka et al. 18 measured the surface tension for R32+R1234ze (50/50% by mass) by DCRM with an estimated uncertainty of 0.3 mN·m−1. The AAD and the MAD between their data and the values calculated by eq 3 are 0.239 and 0.432 mN·m−1, respectively. As it can be seen from Figure 4, there is a big discrepancy among their results. Most of the deviations were still within the declared uncertainty. From Figures 3 and 4, the surface tension of the R32+R1234ze mixture seems to vary almost linearly with respect to the mole fraction of the component R32, while in case of R32+R1234yf mixtures that seems to be strongly dominated by the presence of R32. Lin46 found the same trend for the surface tension of R32+R134a and R32+R227ea measured by DCRM. It is maybe related to the molecular structure, size, and polarity difference of two components, which should affect nonideal degree of the mixtures and lead to a nolinear relation. The Redlich−Kister polynomial equation45 was also used for the correlation of the liquid viscosity of binary mixtures ′ = x1η1′ + x 2η2′ + x1x 2(c + dT ) ηmix

Figure 3. Surface tension measured by SLS and deviations calculated from eq 3 in comparison with experimental data for R32+R1234yf: □, x1 = 5193; ○, x1 = 6988; △, x1 = 0.7945; ---, R32, correlation with eq 1; , R1234yf, correlation with eq 1; - −, R32+R1234yf, correlation with eq 3.

where ηmix is the liquid dynamic viscosity of the mixture, η1′ and η′2 (η′ = ρ′ν′) are the liquid dynamic viscosity of the pure

(4) E



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Figure 5. Liquid viscosity measured by SLS and deviations calculated from eq 4 in comparison with experimental data for R32+R1234yf: □, x1 = 0.5193; △, x1 = 0.6988; ○, x1 = 0.7945; ---, R32, correlation with eq 2; , R1234yf, correlation with eq 2; - −, R32+R1234yf, correlation with eq 4.

Figure 4. Surface tension measured by SLS and deviations calculated from eq 3 in comparison with experimental data for R32+R1234ze: ■, x1 = 2985; ●, x1 = 0.5697; ▲, x1 = 7501; ▼, ref 18; ---, R32, correlation with eq 1; , R1234ze, correlation with eq 1; - −, R32+R1234ze, correlation with eq 3.

components, x1 and x2 are mole fractions, and c and d are the fitting parameters shown in Table 9. The liquid density ρ′ Table 9. Fitting Coefficients of Equation 4 for R32+R1234yf and R32+ R1234ze sample

c/μPa·s

d × 102/μPa·s·K−1

R32+R1234yf R32+R1234ze

−47.2484 −87.5908

0.1179 0.2212

comes from NIST REFPROP 9.0.,31 the kinematic viscosity ν′ (the experimental data cited from ref 29) was represented by eq 2, and the fitting coefficients were listed in Table 5. The experimental viscosities and deviations from eq 4 for R32+R1234yf and R32+R1234ze are shown in Figures 5 and 6, respectively. The AAD and the MAD between the experimental results and the values reproduced by eq 4 for R32+R1234yf are 0.86 and 1.72%, respectively. Those for R32+R1234ze are 1.01 and 2.80%, respectively. From Figures 5 and 6, the liquid viscosities of the two mixtures behave similarly with respect to the mole fraction of R32 compared with their surface tension. The liquid viscosity of R32+R1234yf seems strongly dominated by the presence of R32 component, which may be ascribed to the stronger association effects between the R32 and R1234yf molecules.

Figure 6. Liquid viscosity measured by SLS and deviations calculated from eq 4 in comparison with experimental data for R32+R1234ze: ■, x1 = 2985; ●, x1 = 0.5697;▲, x1 = 7501; ---, R32, correlation with eq 2; , R1234yf, correlation with eq 2; - −, R32+R1234ze, correlation with eq 4.

The experimental surface tension and viscosity of R32+R1234yf and R32+R1234ze were correlated as a function of temperature and mole fraction of the pure components by using the Redlich−Kister polynomial equation. For the surface tension of R32+R1234yf and R32+R1234ze, the AAD are 0.083 and 0.029 mN·m−1, respectively. For liquid viscosity, corresponding values of 0.86 and 1.01% can be found. The results can be used to evaluate the heat transfer, flow and phase change of two binary mixture refrigerants.

4. CONCLUSIONS In this work, the surface tension and the liquid viscosity of R32 were measured under saturated conditions by SLS and compared with the literature data. The surface tension and liquid viscosity of the mixtures of R32 (1) + R1234yf (2) at three mole fractions x1 of 0.5193, 0.6988, and 0.7945 were measured from 293 to 343 K. The surface tension and liquid viscosity of the mixtures of R32 (1) + R1234ze (2) with x1 of 0.2985, 0.5697, and 0.7501 were measured from 293 to 348 K. F



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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: +86-29-82663737. Funding

This study was supported by the National Natural Science Foundation of China (Grant Nos. 51276142 and 51476130) and the Specialized Research Fund for the Doctoral Program of Higher Education (20130201110046). Notes

The authors declare no competing financial interest.

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LIST OF SYMBOLS n; fitting parameter, exponent r; radius of capillary T; temperature xi; mole fraction of component i

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GREEK LETTERS ρ′; the saturated liquid density ρ″; the saturated vapor density σ; the surface tension ν′; kinematic viscosity of the liquid phase η″; dynamic viscosity of the vapor phase η′; dynamic viscosity of the liquid phase λ′; the liquid thermal conductivity

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