Experimental pressure-volume-temperature data and an equation of state for trifluoroiodomethane (CF3I) in gaseous phase

ELSEVIER

Fluid Phase Equilibria 131 (1997) 233-241

Experimental pressure-volume-temperature data and an equation of state for trifluoroiodomethane (CF3I) in gaseous phase Yuan-Yuan Duan, Ming-Shan Zhu *, Lin Shi, Li-Zhong Han Dept. of Thermal Engineering, Tsinghua University, Beijing 100084, China Received 29 July 1996; accepted 17 November 1996

Abstract

Some 175 pressure-volume-temperature data points in gaseous phase for trifluoroiodomethane (CF3I) have been measured using Burnett/isochoric methods. Bumett expansion measurements were made both at 353.15 K and at 323.15 K. Based on the pressure-volume relationships established both at 353.15 K and at 323.15 K isotherms, data were collected along isochores. Data along eight isochores were measured at the temperature range from 323.15 K to 393.15 K. Data along five isochores were measured at the temperature range from 278.15 K to 323.15 K. The pressure range is from 0.19 to 1.75 MPa. The maximum total temperature uncertainty in this work is estimated to be within _ 10 mK, the maximum total pressure uncertainty in this work is estimated to be within + 500 Pa. The present data have been correlated with a virial equation of state. This equation has a root-mean-square deviation (RMS) deviation of 0.11% in pressure and a RMS deviation of 0.12% in density. The purity of the sample used in this work is 99.95 wt.% with 3.4 ppm of water. © 1997 Elsevier Science B.V. Keywords: PVT properties; Equation of state; CF31; Trifluoroiodomethane; Alternatives

1. Introduction According to the Nov. 25, 1992 Copenhagen revision of the Montreal Protocol, CFCs have already been phased out in developed countries. As a traditional and effective refrigerant, CFC-12 is widely used in numerous applications. Alternatives to CFC-12 must be developed that are environmentally acceptable and can be used in high capacity, high efficiency applications. So far many achievements have been made in developing alternatives to CFCs. HFC-134a has been widely used as a replacement for CFC-12, especially in the USA, Japan, U K and France. However, it requires physical retrofitting of equipment and does not mix with conventional lubricants. It also has a higher global warming

* Corresponding author. 0378-3812/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PH S0378-38 12(96)03227-X

E-Y. Duan et al. / Fluid Phase Equilibria 131 (1997) 233-241

234

potential (GWP) value. Even though they are flammable, hydrocarbons are considered to be another promising alternative, especially in Germany. CF3I has been found to be non-ozone depleting, miscible with mineral oil and compatible with refrigeration system materials. It also has an extremely low GWP value and very low acute toxicity. Therefore, it is also been considered as a promising alternative, especially as a component in mixtures, to replace CFC-12 (Lankford and Nimitz, 1993; Zhao et al., 1995). However there has been no reliable data published in recent years. Therefore, the thermophysical properties of CF3I are of great interest, especially the pressure-volume-temperature (PVT) properties.

2. Apparatus The Burnett apparatus has been thoroughly documented in earlier publications (Zhu et al., 1992; Fu et al., 1995), and is only briefly described here. A modified Burnett apparatus shown in Fig. 1 is used in this work. It includes a high-accuracy thermostat bath, a temperature-measurement system, a pressure-measurement and control system, a vacuum system and a sample cell. The temperature of the bath can be varied from 223 to 453 K. Silicone oil, distilled deionized water or alcohol is used as the fluid in the bath depending on the temperature range. The temperature instability is less than + 5 mK in 8 h. The overall temperature uncertainty for the bath and temperature-measurement is less than + 10 mK.

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Y.-Y. Duan et al. / Fluid Phase Equilibria 131 (1997) 233-241

235

Table 1 Experiment PVT data for CF3I by Burnett expansions T (K)

P (MPa)

p (kg m - 3)

T (K)

P (MPa)

p (kg m - 3)

353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15

1.3626 1.0921 0.8617 0.6723 0.5200 0.4002 0.3067 0.2342 0.1784

113.497 85.852 64.941 49.124 37.158 28.108 21.262 16.083 12.166

323.15 323.15 323.15 323.15 323.15 323.15 323.15

0.9034 0.7225 0.5665 0.4399 0.3393 0.2604 0.1993

80.333 60.766 45.965 34.770 26.301 19.895 15.049

353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15 353.15

1.7507 1.4526 1.1708 0.9275 0.7257 0.5624 0.4329 0.3318 0.2540

163.108 123.380 93.328 70.596 53.401 40.394 30.555 23.113 17.483

323.15 323.15 323.15 323.15 323.15 323.15 323.15

0.8888 0.7092 0.5557 0.4313 0.3325 0.2551 0.1951

78.622 59.472 44.986 34.029 25.741 19.471 14.728

The pressure-measurement system includes a piston-type pressure gauge, a pressure transducer and an atmosphere pressure gauge. The whole pressure-measurement system has an uncertainty of + 500 Pa in the pressure range of 0.1 to 6 MPa. The extremely high vacuum is about 1 × 10 -6 torr. 100.00

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Y.-Y. Duan et al. / Fluid Phase Equilibria 131 (1997) 233-241

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238

Y.-E Duan et al. / Fluid Phase Equilibria 131 (1997) 233-241

Table 2 Experiment PVT data for CF3I by isochoric method T (K)

P (MPa)

p (kg m-3)

T (K)

P (MPa)

p (kg m-3)

313.15 318.15 323.15 303.15 308.15 313.15 318.15 323.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15 283.15 288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15 278.15 283.15 288.15 293.15 298.15 303.15 308.15 313.15 318.15 323.15 353.15 358.15 363.15 368.15 373.15 378.15 383.15 388.15 393.15 338.15 343.15 348.15 353.15

0.6497 0.6652 0.6797 0.4978 0.5100 0.5210 0.5317 0.5423 0.3716 0.3805 0.3889 0.3969 0.4049 0.4126 0.4204 0.2750 0.2816 0.2878 0.2941 0.3003 0.3060 0.3117 0.3174 0.3231 0.2080 0.2128 0.2175 0.2220 0.2264 0.2306 0.2346 0.2390 0.2432 0.2474 1.5481 1.5863 1.6239 1.6610 1.6977 1.7342 1.7705 1.8065 1.8424 1.1737 1.2020 1.2297 1.2570

56.592 56.582 56.572 43.800 43.792 43.784 43.776 43.768 33.144 33.139 33.133 33.127 33.121 33.115 33.109 25.008 25.003 24.999 24.994 24.990 24.985 24.981 24.976 24.972 18.880 18.876 18.873 18.870 18.866 18.863 18.860 18.856 18.853 18.849 135.260 135.235 135.209 135.183 135.157 135.132 135.106 135.080 135.053 102.084 102.065 102.046 102.027

358.15 363.15 368.15 373.15 378.15 383.15 388.15 393.15 328.15 333.15 338.15 343.15 348.15 353.15 358.15 363.15 368.15 373.15 378.15 383.15 388.15 393.15 328.15 333.15 338.15 343.15 348.15 353.15 358.15 363.15 368.15 373.15 378.15 383.15 388.15 393.15 323.15 328.15 333.15 338.15 343.15 348.15 353.15 358.15 363.15 368.15 373.15

1.2838 1.3104 1.3368 1.3630 1.3891 1.4151 1.4410 1.4668 0.8957 0.9160 0.9361 0.9557 0.9750 0.9941 1.0130 1.0320 1.0508 1.0696 1.0884 1.1072 1.1259 1.1444 0.7095 0.7239 0.7381 0.7521 0.7660 0.7802 0.7941 0.8078 0.8216 0.8355 0.8493 0.8630 0.8767 0.8905 0.5442 0.5545 0.5647 0.5751 0.5855 0.5958 0.6063 0.6165 0.6268 0.6368 0.6469

102.007 101.988 101.969 101.949 101.930 101.910 101.890 101.871 76.689 76.675 76.661 76.646 76.632 76.618 76.603 76.589 76.574 76.560 76.545 76.530 76.516 76.501 58.074 58.064 58.053 58.042 58.031 58.020 58.009 57.998 57.987 57.976 57.965 57.954 57.943 57.932 43.935 43.927 43.919 43.911 43.903 43.895 43.887 43.878 43.870 43.862 43.853

239

Y.- Y. D u a n et al. / Fluid Phase Equilibria 131 (1997) 233-241 Table 2 (continued)

T (K)

P (MPa)

p (kg m - 3)

T (K)

P (MPa)

p (kg m-3)

378.15 383.15 388.15 393.15 323.15 328.15 333.15 338.15 343.15 348.15 353.15 358.15 363.15 368.15 373.15 378.15 383.15 388.15 393.15 323.15 328.15 333.15 338.15 343.15 348.15

0.6571 0.6671 0.6771 0.6871 0.4220 0.4297 0.4373 0.4450 0.4526 0.4601 0.4679 0.4755 0.4830 0.4904 0.4979 0.5054 0.5129 0.5205 0.5283 0.3251 0.3308 0.3365 0.3423 0.3479 0.3535

43.845 43.836 43.828 43.819 33.189 33.183 33.177 33.171 33.165 33.158 33.152 33.146 33.140 33.133 33.127 33.121 33.114 33.108 33.102 25.080 25.075 25.071 25.066 25.062 25.057

353.15 358.15 363.15 368.15 373.15 378.15 383.15 388.15 393.15 323.15 328.15 333.15 338.15 343.15 348.15 353.15 358.15 363.15 368.15 373.15 393.15 378.15 383.15 388.15

0.3593 0.3649 0.3706 0.3762 0.3818 0.3875 0.3931 0.3987 0.4044 0.2490 0.2533 0.2576 0.2618 0.2661 0.2704 0.2746 0.2789 0.2832 0.2875 0.2917 0.3088 0.2959 0.3002 0.3045

25.052 25.047 25.043 25.038 25.033 25.028 25.024 25.019 25.014 18.963 18.959 18.956 18.952 18.949 18.945 18.941 18.938 18.934 18.931 18.927 18.912 18.923 18.920 18.916

manufacturer stated that the sample purity of CF3I was 99.95 wt.% with 3.4 ppm of water. The sample was used without further purification.

3. Experimental result Burnett expansion measurements were made both at 353.15 K and at 323.15 K. Fourteen pressures were measured in two separate runs totalling twelve expansions ranging in density from 14 to 80 kg m -3 at 323.15 K, and eighteen pressures were measured in two separate runs totalling sixteen expansions ranging in density from 12 to 160 kg m - 3 at 353.15 K. Results are given in Table 1. The densities were calculated using the cell constant, and then the data were fit with a polynomial so that they could be interpolated to calculate densities where the isochores intersected the Burnett isotherms. The pressure-density relationship along the 323.15 K isotherm is shown in Fig. 2. The pressure-density relationship along the 353.15 K isotherm is shown in Fig. 3. After the pressure-density relationships were established both at 353.15 K and at 323.15 K, data were collected along isochores. Data along eight isochores were measured at the temperature range from 328.15 K to 393.15 K, the

240

Y.-Y. Duan et al. / Fluid Phase Equilibria 131 (1997) 233-241

pressure m e a s u r e m e n t for each isochore at 353.15 K was used to determine the density. Data along five isochores were measured at the temperature range from 278.15 K to 323.15 K, the pressure m e a s u r e m e n t for each of the isochores at 323.15 K was used to determine the density. A temperature correction to the densities was made to compensate for the thermal expansion of the sample cell. Results of the isochoric m e a s u r e m e n t s are given in Table 2. Fig. 4 shows the location in pressure and temperature of the present data and of the vapor pressure data of Duan et al. (1996).

4. E q u a t i o n The data published in this article were represented with a three term virial equation: PV RT

B

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V

C -~

D

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0.91431903E-1 - 0.31870392 0.39270880 -0.17814376 0.13502054E- 1 -0.21136215E-2, - 0.10251536E-5 0.88130506E-6 0.96930547E-8 - 0.93767383E-8 395.05 K

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= 42.4402 J K - l k g - i Pa K kg m -3

The suitable range of this equation is f r o m 0.19 to 1.75 M P a in pressure, f r o m 278.15 K to 393.15 K in temperature and f r o m 12 to 163 kg m - 3 in density. This equation has a RMS deviation of 0.11% in pressure and a RMS deviation of 0.12% in density (see Figs. 5 and 6). The critical temperature ( Tc) needed in this equation c o m e s f r o m data ( Tc = 395.05 K) published by U N E P (1995).

Y.-E Duan et al. / Fluid Phase Equilibria 131 (1997)233-241

241

5. Conclusion Some 175 P V T data points in gaseous phase for trifluoroiodomethane (CF3I) have been measured using B u r n e t t / i s o c h o r i c methods. The pressure range is from 0.19 to 1.75 MPa and the temperature range is from 278.15 K to 393.15 K. The maximum total temperature uncertainty in this work is estimated to be within ± 10 inK, the m a x i m u m total pressure uncertainty in this work is estimated to be within + 500 Pa. The present data have been correlated with a virial equation of state. This equation has a RMS deviation of 0.1 1% in pressure and a RMS deviation of 0.12% in density.

Acknowledgements This work is supported by the State Education Commission of P.R.C., W e are grateful to Dr. Nimitz, I K O N Co. and Pacific Scientific, USA for providing the CF3I sample. W e also thank Yi-Dong Fu for providing useful help in measurements.

References Y.Y. Duan, M,S. Zhu and L.Z. Han, Experimental vapor pressure data and a vapor pressure equation for trifluoroiodomethane (CF3I), Fluid Phase Equil., 121 (1996) 227-234. Y.D. Fu, L.Z. Han and M.S. Zhu, PVT properties, vapor pressures and critical parameters of HFC-32, Fluid Phase Equil., I l 1 (1995) 273-286. L. Lankford and J. Nimitz, A new class of high-performance, environmentally sound refrigerants, The Int. CFC and Halon Alternatives Conf., Washington, DC, USA. 1993. UNEP, 1995. 1994 Report of the Refrigeration, Air Conditioning and Heat Pumps Technical Option Committee, Chapter 2, Refrigerant Data, UNEP, 1995, p.40. X.Y. Zhao, L. Shi, M.S. Zhu and L.Z. Han, L.Z., A new generation of long-term refrigerants as CFC-12 alternatives, Proceedings of The Int. CFC and Halon Alternatives Conf., Washington, DC, USA, 1995, pp. 286-293. M.S. Zhu, Y.D, Fu and L.Z, Han, An experimental study of PVT properties of CFC alternative HFC-134a, Fluid Phase Equil., 80 (1992) 149-156.