1068
J. Chem. Eng. Data 2003, 48, 1068-1072
Surface Tension Measurements of Difluoromethane (R-32) and the Binary Mixture Difluoromethane (R-32) + 1,1,1,2-Tetrafluoroethane (R-134a) from (253 to 333) K Yuan-Yuan Duan,* Hong Lin, and Zhong-Wei Wang Department of Thermal Engineering, Tsinghua University, Beijing 100084, China
The surface tensions of binary mixtures of difluoromethane (R-32) + 1,1,1,2-tetrafluoroethane (R-134a) and pure difluoromethane (R-32) were measured over the temperature range (253 to 333) K using a differential capillary rise method (DCRM) under vapor-liquid equilibrium conditions. The temperature and surface tension uncertainties were estimated to be within (10 mK and (0.15 mN‚m-1, respectively. The present data were used to develop a van der Waals-type surface tension correlation for pure R-32. Correlations for pure R-32 and R-134a were used to develop a surface tension correlation for the experimental data of the R-32 + R-134a mixtures as a function of the mass fraction.
Introduction Because of the ozone layer depletion and global warming caused by chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants, hydrofluorocarbon (HFC) mixtures are expected to be interim and long-term replacements for HCFC refrigerants (such as chlorodifluoromethane (R-22)) and R-502. Surface tension is a basic thermophysical property, related to vapor-liquid interfacial effects that must be known to analyze the heat transfer through heatexchanging surfaces with bubbles or fluid drops. This paper presents surface tension measurements for pure R-32 and binary mixtures of R-32 + R-134a in the temperature range from (253 to 333) K. The experimental results for pure R-32 were represented with a van der Waals-type surface tension correlation. The experimental mixture data were then used to develop a surface tension correlation for R-32 + R-134a mixtures as a function of the mass fraction using the correlations for pure R-32 and R-134a. Experimental Section Mixture Preparation. The sample of pure R-32 was purchased from Zhejiang Fluoro-Chemical Technology Research Institute and was used without further purification. The manufacturer stated that the purity was more than 99.95 mass %. R-134a was obtained commercially from Honeywell and used without further purification. The sample purity stated by the manufacturer was more than 99.95 mass %. A gas chromatograph with a thermal conductivity detector (TCD) and an ODPN column was used to examine the samples, and no impurities were detected. The mixtures were gravimetrically prepared using an accurate electronic balance with a resolution of (0.001 g. Four R-32 (1) + R-134a (2) binary mixtures were prepared at nominal mass fractions (the liquid and vapor average composition) w′1 of 0.2379, 0.4017, 0.6235, and 0.7628. Apparatus and Procedure. The surface tension was measured using the direct optical measurement system * Corresponding author. Telephone: +86-10-6278-2484. Fax: +86-106277-0209. E-mail address:
[email protected].
Figure 1. Surface-tension apparatus: MCF, movable coordinate frame; OL, optical level instrument; ADS, accurate displacement sensor; DR, digital readout; EC, experimental cell; TB, thermostated bath; H, heater; CP, cooling pipe; D, dynamic-electric stirrer; S, thermal-sensitive resistance sensor; C, controller; PRT, platinum resistance thermometer; SW, selector switch; BR, automatic thermometer bridge; COM, computer; W, window; LS, light source; VP, vacuum pump; SB, sample bottle.
shown in Figure 1 based on the differential capillary rise method. The apparatus has been described in detail1-5 and is only briefly described here. The measurement system includes a moveable coordinate frame, a telescope, and an accurate displacement sensor. The sample cell contained three capillaries with inner radii of r1 ) (0.390 ( 0.001) mm, r2 ) (0.259 ( 0.001) mm, and r3 ) (0.125 ( 0.001) mm. The three capillary radii were determined by partially filling the capillaries with mercury slugs of different masses. The sample cell was installed in a thermostated bath. The bath temperature could be varied from (233 to 453) K. The temperature instability in the bath is less than (5 mK in 8 h. The temperature measurement system includes platinum resistance thermometers (Tinsley: 5187SA) with an uncertainty of (2 mK, a precision thermometer bridge (Tinsley: 5840D) with an accuracy within (1 mK, a select switch (Tinsley: 5840CS/6T), and a personal computer. The temperatures were determined on the international tem-
10.1021/je030137f CCC: $25.00 © 2003 American Chemical Society Published on Web 06/21/2003
Journal of Chemical and Engineering Data, Vol. 48, No. 4, 2003 1069 Table 1. Experimental Surface Tension Data and Capillary Constants for R-32 σ/mN‚m-1
a2/mm2 T/K 252.74 257.00 260.46 265.04 268.75 273.28 276.85 281.50 285.79 294.05 297.58 301.42 305.30 309.50 315.58 319.38 319.84 323.29 327.23 332.00
Fl
/kg‚m-3
1121.9 1108.5 1097.4 1082.6 1070.3 1054.9 1042.4 1025.7 1009.8 977.8 963.4 947.1 930.1 910.7 880.8 860.6 858.1 838.4 814.3 781.8
Fv/kg‚m-3
(3,2)
(3,1)
(3,2)
(3,1)
10.99 12.82 14.47 16.92 19.14 22.18 24.85 28.74 32.77 41.96 46.56 52.09 58.31 65.88 78.67 88.01 89.23 98.97 111.72 130.15
2.688 2.563 2.480 2.374 2.296 2.176 2.097 1.965 1.840 1.645 1.552 1.454 1.358 1.245 1.081 0.967 0.947 0.852 0.748 0.601
2.686 2.568 2.484 2.378 2.296 2.176 2.102 1.972 1.840 1.647 1.554 1.453 1.356 1.245 1.084 0.970 0.948 0.852 0.746 0.601
14.631 13.760 13.160 12.396 11.825 11.011 10.455 9.600 8.809 7.543 6.972 6.377 5.801 5.154 4.249 3.661 3.568 3.087 2.575 1.919
14.621 13.787 13.182 12.417 11.825 11.011 10.480 9.634 8.809 7.552 6.981 6.373 5.792 5.154 4.260 3.672 3.571 3.087 2.568 1.919
Table 2. Experimental Surface Tension Data and Capillary Constants for Nominal Mass Fraction w′1 ) 0.2379 for R-32 (1) + R-134a (2) with Liquid Mass Fraction w1 a2/mm2 T/K 255.03 256.94 258.87 260.74 263.04 264.63 266.53 268.90 271.05 273.66 278.13 282.42 286.04 288.32 292.49 295.14 296.81 298.62 300.47 302.58 304.89 306.90 308.95 310.59 311.21 313.15 315.19 317.10 318.71 319.34 321.24 323.11 325.33 327.26 329.46 331.37 333.53
Fl/kg‚m-3 Fv/kg‚m-3 1287 1281 1275 1269 1262 1256 1250 1242 1235 1227 1211 1196 1184 1175 1160 1150 1143 1136 1129 1121 1111 1103 1094 1087 1085 1076 1067 1058 1051 1048 1039 1030 1018 1009 996.9 986.4 974.3
10.77 11.54 12.36 13.20 14.30 15.09 16.09 17.41 18.68 20.33 23.40 26.70 29.78 31.86 35.97 38.82 40.70 42.84 45.12 47.85 51.01 53.90 57.00 59.60 60.61 63.85 67.48 71.03 74.16 75.42 79.35 83.42 88.52 93.22 98.89 104.10 110.40
σ/mN‚m-1
w1
(3,2)
(3,1)
(3,2)
(3,1)
0.2324 0.2321 0.2318 0.2315 0.2311 0.2309 0.2305 0.2301 0.2297 0.2292 0.2283 0.2274 0.2266 0.2261 0.2251 0.2245 0.2240 0.2236 0.2232 0.2227 0.2221 0.2216 0.2210 0.2206 0.2204 0.2199 0.2193 0.2188 0.2184 0.2182 0.2177 0.2172 0.2166 0.2161 0.2155 0.2150 0.2144
2.244 2.210 2.185 2.151 2.083 2.067 2.026 1.980 1.941 1.890 1.805 1.729 1.660 1.628 1.526 1.475 1.439 1.406 1.359 1.334 1.295 1.249 1.223 1.188 1.173 1.141 1.077 1.065 1.034 1.012 0.983 0.942 0.895 0.868 0.822 0.780 0.725
2.244 2.208 2.185 2.152 2.086 2.067 2.026 1.981 1.946 1.897 1.814 1.729 1.660 1.628 1.529 1.473 1.434 1.407 1.360 1.339 1.298 1.244 1.223 1.188 1.170 1.139 1.078 1.061 1.033 1.016 0.984 0.942 0.895 0.870 0.820 0.778 0.724
14.033 13.747 13.518 13.236 12.735 12.568 12.250 11.881 11.568 11.175 10.504 9.906 9.388 9.119 8.405 8.031 7.772 7.531 7.218 7.015 6.726 6.421 6.214 5.981 5.888 5.659 5.275 5.151 4.949 4.823 4.622 4.369 4.076 3.895 3.617 3.372 3.069
14.033 13.735 13.518 13.242 12.753 12.568 12.250 11.887 11.598 11.216 10.556 9.906 9.388 9.119 8.421 8.020 7.745 7.537 7.223 7.041 6.742 6.395 6.214 5.981 5.873 5.649 5.280 5.131 4.944 4.842 4.627 4.369 4.076 3.904 3.608 3.364 3.065
perature scale of 1990 (ITS-90). The overall temperature uncertainty including the bath instability and the temperature measurement system was less than (10 mK. The differences between the capillary rise heights were determined by measuring the meniscus locations in each capillary through a transparent window of the sample cell using a traveling telescope with an uncertainty of (10 µm. The differential capillary rise between two capillaries was
Table 3. Experimental Surface Tension Data and Capillary Constants for Nominal Mass Fraction w′1 ) 0.4017 for R-32 (1) + R-134a (2) with Liquid Mass Fraction w1 a2/mm2 T/K 254.88 256.82 259.08 261.21 262.98 265.09 266.90 269.06 271.09 275.81 278.11 280.06 282.23 283.25 286.27 289.25 291.23 293.41 295.48 297.23 299.20 301.19 303.43 305.51 307.34 309.23 311.60 313.64 315.26 317.40 319.24 321.49 323.44 325.43 327.18 329.24 331.50
Fl/kg‚m-3 Fv/kg‚m-3 1246 1240 1233 1226 1220 1213 1207 1200 1193 1177 1170 1163 1155 1151 1141 1130 1122 1114 1106 1099 1091 1083 1074 1066 1058 1050 1039 1030 1023 1012 1004 992.5 982.6 972.2 962.9 951.5 938.6
11.63 12.47 13.50 14.54 15.44 16.58 17.61 18.91 20.20 23.47 25.21 26.76 28.59 29.48 32.26 35.21 37.30 39.72 42.14 44.28 46.81 49.49 52.67 55.78 58.66 61.77 65.90 69.65 72.78 77.12 81.06 86.15 90.82 95.87 100.60 106.40 113.20
σ/mN‚m-1
w1
(3,2)
(3,1)
(3,2)
(3,1)
0.3944 0.3940 0.3935 0.3930 0.3926 0.3921 0.3916 0.3911 0.3905 0.3892 0.3885 0.3879 0.3872 0.3869 0.3859 0.3849 0.3842 0.3835 0.3827 0.3821 0.3813 0.3805 0.3797 0.3788 0.3781 0.3773 0.3764 0.3755 0.3748 0.3739 0.3731 0.3721 0.3713 0.3704 0.3697 0.3687 0.3677
2.302 2.281 2.225 2.188 2.137 2.109 2.070 2.034 1.976 1.896 1.842 1.811 1.740 1.736 1.684 1.617 1.575 1.513 1.467 1.447 1.395 1.365 1.327 1.278 1.241 1.216 1.151 1.106 1.080 1.025 0.986 0.951 0.899 0.863 0.818 0.768 0.723
2.302 2.280 2.225 2.188 2.143 2.108 2.070 2.033 1.978 1.898 1.845 1.815 1.743 1.738 1.686 1.616 1.576 1.515 1.471 1.447 1.398 1.364 1.328 1.280 1.239 1.214 1.148 1.102 1.079 1.022 0.983 0.950 0.901 0.862 0.820 0.767 0.723
13.923 13.720 13.296 12.988 12.613 12.364 12.064 11.771 11.356 10.717 10.333 10.083 9.604 9.540 9.149 8.674 8.371 7.964 7.647 7.478 7.138 6.913 6.641 6.326 6.077 5.888 5.488 5.205 5.029 4.695 4.459 4.224 3.928 3.706 3.456 3.180 2.924
13.923 13.714 13.296 12.988 12.649 12.358 12.064 11.766 11.367 10.728 10.349 10.105 9.620 9.551 9.160 8.669 8.376 7.975 7.668 7.478 7.153 6.908 6.646 6.336 6.067 5.879 5.474 5.186 5.024 4.682 4.446 4.219 3.937 3.701 3.465 3.176 2.924
sensed by a height transducer on the telescope using a digital readout. The contact angle, θ, was assumed to be zero, since the inner walls of the capillaries were carefully washed before the measurements. All of the measurements were carried out under equilibrium conditions between the liquid and its saturated vapor. A total error analysis gave the estimated surface tension and temperature measurement accuracies to be within (0.15 mN‚m-1 and (10 mK, respectively. The binary mixture of R-32 + R-134a in the sample cell was prepared by placing the requested amounts of R-32 and R-134a in separate gas cylinders. The two cylinders were precisely weighed on an accurate electronic balance with a resolution of (0.001 g (Mettler Toledo PR1203). The sample cell and connections were then evacuated by a vacuum pump (KYKY FD110) to remove impurities. The system vacuum was
