Dielectric properties of alternative refrigerants

IEEE Transactions on Dielectrics and Electrical Insulation Vol. 13, No. 3; June 2006

1070-9878/06/$20.00 © 2006 IEEE

503

Dielectric properties of alternative refrigerants

F. J. V. Santos, R. S. Pai-Panandiker, C. A. Nieto de Castro Departamento de Química e Bioquímica and Centro de Ciências Moleculares e Materiais

Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal

and U. V. Mardolcar Instituto Superior Técnico, Departamento de Física e Núcleo de Termofísica,

Av. Rovisco Pais, 1049-001 Lisboa, Portugal and Centro de Ciências Moleculares e Materiais

Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal

ABSTRACT This paper gives an overview of our research, from experimental measurements of the relative permittivity on new and alternative refrigerants, to theoretical interpretation of the data and density functional and density functional self-consistent reaction field calculations for a series of HFC molecules. Experimental measurements were obtained as a function of temperature and pressure for Class B refrigerants – HCFC-123, HCFC-142b, HCFC-141b, Class A refrigerants – HFC-32, HFC-134a, HFC-152a, HFC-143a, HFC-227ea, HFC-245fa, HFC-365mfc and some mixtures of them: HFC-125/143a/134a (R-404A), HFC-32/125/134a (R-407C), HFC-125/143a (R-507), HFC-32/125 (R-410A). Density functional and density functional self-consistent reaction field calculations were performed for CHF2CF3 (HFC-125), CH2FCF3 (HFC-134a), CH3CF3 (HFC-143a), CH2F2 (HFC-32), and CHF2CH3 (HFC-152a). A particular emphasis has been given to the calculation of dimerisation energies, rotational potentials, polarisabilities and dipole moments.

Index Terms — Cooling, dielectric liquids, dielectric measurements.

1 INTRODUCTIONTHE measurement of the relative permittivity allows the

study of fluid molecular behavior when subjected to an electric field, related to chemical structure and molecular interactions. In industry, measurements of relative permittivity of these fluids give operational values for design parameters of machinery used in the air conditioning and refrigeration industry. This property also affects the electric properties of compressor lubricants, where the refrigerants are soluble. The search for the replacement of harmful halocarbons used in the refrigeration, air conditioning and foam blowing industries lead the international community to the establishment of a concerted effort to determine the thermophysical properties of the alternative compounds, chosen to have a small or zero ozone depletion potential and small global warming potential. Since 1990, our research group has done a considerable work on dielectric properties environmentally acceptable refrigerants. The current international agreements addressing global environmental issues (the Montreal and Kyoto Protocols) provide the guidelines needed to ensure that all refrigerant and blowing agent solutions are environmentally safe.

The Montreal Protocol has provided a phase-out of all ozone depleting substances, inducing the utilization of substances with zero ozone depletion potential. Our work started with the study of Class B compounds, evolving to Class A compounds, those with zero ozone depletion potential1.

An instrument for the determination of absolute values of relative permittivity was designed and constructed to operate in an extended thermodynamic range, from 170 K up to 370 K, at pressures up to 30 MPa. The measurements use the direct capacitance method. The description of the cell has been presented before by Mardolcar et al. [1] and the sample handling, vacuum and pressure system by Gurova et al. [2]. The measuring process uses a fully automated instrumentation, operated from a computer graphics user interface, described elsewhere [3]. Vacuum capacitance was measured as a function of temperature before filling the cell with the fluid.

1 Ozone Depletion Potential – capacity of destruction of a given number of ozone molecules by chlorine atoms, calculated through a chemical model for the stratospheric ozone, assuming the stationary state of emission and destruction. Relative to CFC-11 (trichlorofluoromethane). Manuscript received on 15 July 2005, in final form 26 December 2005.

F. J. V. Santos et al.: Dielectric properties of alternative refrigerants504

An impedance gain-phase analyzer (Schlumberger, model SI 1260) has been used with an uncertainty of 5x10-4 pF. This equipment was calibrated by Laboratório de Metrologia Eléctrica da Companhia Portuguesa Radio Marconi, Lisbon, using the standards of capacitance of 1 pF, 10 pF, 100 pF, 1000 pF, 0.01 mF, 0.1 mF and 1 mF, with an uncertainty of 0.01%. The technique employed a four terminal connection to the cell in order to compensate for parasitic impedances. The mean value of a 10-dimensional sample taken at a 10 kHz frequency provides the experimental value of relative permittivity, which proved to be properly suited to the working accuracy. As referred above the measuring process is now completely automatic and operated from a computer graphics user interface, making the data analysis faster and statistically more significant. Relative permittivity ε of the fluid is determined from the ratio between C(p,T) - the geometric capacitance at pressure p and temperature T - and C0(T) - the capacitance under vacuum at a temperature T, equation (1):

)(),(

0 TCTpC

=ε (1)

The cell temperature was measured with a calibrated platinum resistance thermometer (100 Ω at 0 ºC) located near the sample, and which resistance was determined with a four-wire measurement, by a digital multimeter (Keithley, model 199 DMM), calibrated with three standard resistors, giving an uncertainty for the temperature measurement of 0.01 K. The pressure vessel is immersed in a cylindrical copper vessel cooled by a cryostat (Julabo Model FPW90-SC), filled with ethanol and operative in the range from 183 to 373 K with an uncertainty of 0.1 K. A high-pressure system composed of a HIP manual liquid-pressure generator and an air-operated, diaphragm-type compressor (Newport Scientific) was used. The pressure was measured with a pressure transducer (Setra Systems) with an uncertainty of 0.01 MPa. Vacuum points were stable at the level of 10-4 pF over the duration of this study. The presence of impurities causes an extra source of uncertainty, can amount to a maximum of 0.5 mass %, with a maximum contribution to the uncertainty budget of the order of 1 part in 103. The uncertainty of the experimental measurements of the relative permittivity with the present apparatus was found to be better than 0.16%, for a confidence interval of 95%2.

The schematic diagram of the apparatus set-up for the measurements of the relative permittivity in the liquid phase is presented in Figure 1. All the experimental points measured at a given temperature T, were adjusted to nominal temperatures Tn, close to T, by using:

(2)

2 ISO definition of uncertainty, with k = 2 (95% confidence) was used. Using current calculations for uncertainty (accuracy), the values reported here must be divided by two.

Density was obtained from the best available equations of state or reference databases, like REFPROP© [4]. The results were expressed as functions of temperature, and pressure or density. Figure 2 shows the results obtained for 1,1,1,3,3-pentafluoropropane (HFC-245fa). The behavior is qualitatively identical for all the pure fluids and mixtures

studied, as TP∂

∂ ε is positive and PT∂

∂ ε is negative.

However, T∂

∂ρε is always positive.

Figure 1. Schematic diagram of the apparatus. The figure is self contained.

Figure 2. The relative permittivity of 1,1,1,3,3-pentafluoropropane, ε, as a function of density, ρ, for the different isotherms. + 303.84 K; - 293.23 K; - 283.19 K; - 273.12 K; × - 263.00 K;− - 253.01 K; - 243.02 K; - 233.12 K; - 224.16 K; - 218.53 K

( ) ( ) ( )TTT

p,Tp,T np

n −∂∂+= εεε

6

7

8

9

10

11

1300 1350 1400 1450 1500 1550 1600

ρ / kg.m-3

εεεε

IEEE Transactions on Dielectrics and Electrical Insulation Vol. 13, No. 3; June 2006 505

2 DATA ANALYSIS An analysis of the experimental data of relative permittivity

as a function of density is also presented in this paper. The Vedam formalism was applied based on the work of Vedam etal. [5,6] and Diguet [7]. According to this theory, the variation of the relative permittivity with pressure is a function of the deformation of the volume, showing a non-linear behavior in the case of liquids. This non-linearity can be reduced when the variation of ε, Δ, defined by equation (3) is analyzed as a function of the Eulerian deformation, Σ, also named the Eulerian strain, defined by equation (4). It is possible to verify that Σ provides a linear relation for Δ independently of the type of molecules that compose the fluid.

(3)

(4)

In these equations, ρ0 is the reference density, taken in this case as the saturation value for each isotherm. The calculations made show that the function Δ indeed represents a linear variation with the Eulerian Strain Σ, as can be seen in Figure 3, for liquid pentafluoropentane (HFC-125)[8]. The same result has been obtained for all pure fluids, and mixtures of fixed composition. This behavior is really remarkable and can be used as a predictive tool, as the intercept B of equation (3) is nearly zero, with a decrease in the accuracy of the data predicted. See, p.e., [8].

Figure 3. Variation of Δ with the Eulerian strain, Σ (equations (3) and 4)) for liquid pentafluoropentane (HFC-125) [8].

The molecular theories developed to interpret the relation between the dipole moment of a liquid of polar molecules and the electric permittivity are based on the definition of Onsager`s local field [9]. The most important are those based on the statistical theories of polarizability, namely the theories of Kirkwood [10] and of Frölich [11]. Unfortunately, in the absence of information about the refractive index of the liquids studied, and of its dependence on density and frequency, the only molecular theory that can be applied to the data of all

refrigerants measured, is the theory of molecular polarizability developed by Kirkwood [10]. In this theory, the apparent dipole moment of the liquid μ* is calculated from the following relation:

( )( ) ( )+=

+−Tk

NM

B

*A

0

2

339121

εμα

ρεεε

(5)

where M is the relative molar mass of the fluid, NA is the Avogadro constant, α is the molecular polarizability of the molecule, ε0 is the electric permittivity in vacuum, T is the absolute temperature, kB is the Boltzmann constant and ρ is the density, evaluated for each thermodynamic state of the liquid. The apparent dipole moment is μ*=g1/2 μ, where μ is the dipole moment in the ideal gas state and g is the Kirkwood correlation parameter, which represents the restriction to rotation imposed by a cage of molecules surrounding a given molecule (the model assumes a spherical cavity, see Figure 7). Kirkwood, on the basis of a quasi-crystalline model, defined this parameter g as:

(6)

where zi is the number of neighbors to the central molecule under consideration in the i-th coordination shell, and

icosγ is the average cosine angle γ formed by the dipole moments of molecules in the i-th shell with the dipole of the central molecule, exemplified in Figure 4, with schematic dipoles.

Figure 4. Schematic representation of the first coordination shell, for zi = 5.

For non-polar or non-associated liquids g ≈ 1, but for polar liquids it considerably differs from unity (for water a value of 2.6, for zi = 4 was found). The greater the value of g, the bigger the orientational order imposed by the neighbors. Equation (5) shows that, if the theory is correct, the value of μ* can be calculated by a linear regression of the left-hand side of equation (7) as a function of 1/T. Figure 5 shows the variation of the Kirkwood function, equation (5), with the reciprocal temperature, for 1,1,1,3,3-penta-fluoropropane

( ) ( )02

12

1ρερε −=Δ

−=Σ3

2

0

121

ρρ

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040 0.045−Σ−Σ−Σ−Σ

ΔΔΔΔ

303.74 K 294.08 K 283.21 K 273.19 K 263.32 K253.29 K 243.31 K 233.19 K 223.20 K 214.32 K

∞

=

+==1

21

2

iii

*

coszg γμμ

γi

First coordination shell


(HFC-245fa) [12]. A value of μ* = 2.688 D is obtained. Using the value of the dipole moment (μ =1.549 D) in the gas phase [13], the value of the Kirkwood parameter g was found to be equal to 3.01, a value which demonstrates a complete hindered rotation of these molecules in the liquid state.

Looking to the values obtained for the apparent dipole moments in the liquid phase, the corresponding values for the dipole moments in the gaseous phase and the Kirkwood factors, it was found that the HFC’s and the HCFC’s exhibit gas phase dipole moments (μg) in the following order [14,15]:

(1) 123 < 125 < 134a < 32 < 141b < 142 b < 152a < 143a

Figure 5. Variation of the Kirkwood function (equation (8)) with the reciprocal temperature for 1,1,1,3,3-pentafluoropropane (HFC-245fa). Experimental values; line – (equation (5)).

The values obtained for the liquid phase (μ*), based on the Kirkwood theory have a slightly different trend given by:

(2) 123 < 125 < 141b < 142b < 143a < 134a < 32 < 152a

As a consequence of these differences, the Kirkwood correlation factor g, has an interesting behavior:

(3) 143a < 141b < 142b < 125 < 123 < 152a < 32 < 134a

Since g is indicative of the restriction to rotation imposed by a cage of surrounding molecules on a given molecule, the results may suggest that the HFC 143a has the greatest rotational mobility in the liquid state, whereas HFC 134a has the greatest rotational hindrance. The values obtained are displayed in Table I, along with values obtained with the Kirkwood-Frölich theory [11], using only refractive index data for the gas phase. Although this is a simplification, it might suggest that the apparent dipole moments obtained with the Kirkwood theory are overestimated. In fact and as previously mentioned, the relationship between the apparent dipole moments and the effective dipole moment in the liquid is not direct and involves statistical-mechanical theories of relative permittivity. In this sense, some of the more recent studies on liquid water [16-18] have contributed to a better definition of

the meaning and value of the dipole moment in the liquid state. As an example, Silvestrelli and Parrinello [16] estimated the dipole moment of liquid water to be 2.95 D, using classical molecular dynamics calculations, Gregory et al. [17] using abinitio cluster calculations estimated it to be 2.7 D and Baydal et al. [18] from the x-ray structure measured with synchrotron radiation to be 2.9 ± 0.6 D. The value obtained for water using Kirkwood theory is 2.98, in excellent agreement with these calculations, a strong indication that Kirkwood model is a simple and reliable calculation procedure.

There is a strong correlation between the apparent dipole moment in Kirkwood theory and the dipole moment of the same compound in the gas phase, given by equation (6). If we represent μ* as a function of μg, we can obtain the plot of Figure 6.

A line is sketched in the plot, just dividing the zones for free rotation and restricted rotation of the molecules in the liquid phase, the number of fluorine atoms being significant in this decision (the more fluorine atoms, or the bigger the ratio between fluorine and hydrogen atoms in the molecule, the more restricted the rotation in the liquid phase).

Figure 6. Plot of μ* as a function of μg for the liquids studied.

All these facts suggested the development of a density functional theory approach and self-consistent-reaction field calculations for these five molecules and HFC-32, the methane fluorinated compound [19], to try to understand better this behavior. The SCRF calculations were based in the polarized continuum model (PCM) and on the self-consistent isodensity polarized continuum model (SCIPCM). The “solvent” is modeled as a continuum of uniform dielectric constant. The main difference between these two models is the cavity shape definition, or the cage that surrounds a test or “solvent” molecule, as illustrated in Figure 7. Dimerisation energies, rotational potentials, polarisabilities and dipole moments were calculated. Hydrogen bonding in hydrofluorocarbon dimmers was also studied and the relationship between the structure and charge distribution of the dimers and the dipole moment in the liquid predicted by dielectric constant measurements. Details of the DFT geometrical optimizations and basis sets used can

1.2

1.4

1.6

1.8

2

3 3.5 4 4.5 5

103/T / K-1

104 .( εε εε

-1)*

(2εε εε+

1)/9

εε εε*(M

/ ρ)ρ) ρ)ρ)

// / /m3.

mol

-1

0

1

2

3

4

0 1 2 3μμμμ

μ∗μ∗μ∗μ∗123

32

143a134a

152a

141b142b

125245fa

Free Rotation

Restricted Rotation


be found in Cabral et al. [19]. The values obtained for the dipole moments in the gas-phase agree very well with the experimental values, for different theoretical levels, reproducing the experimental order (1). Results obtained using the SCIPCM model, with B3PW91/D95V(d,p) level, are also displayed in Table 1. The effective dipole moments obtained confirm that the Kirkwood theory overestimates the dipole moments in the liquid phase, by inducing less mobility of the molecules. The order (2) of the dipoles in the liquid agrees with the experimental ones, except for HFC-143a, where the calculated value is the greater one.

Kirkwood-Onsager Model

Polarized Continuum

Model (PCM)

Self-consistent isodensity polarizedcontinuum

model (SCIPCM)

Figure 7. Schematic of the models referred in this work, illustrating the cavity shape. All the models assume the “solvent” as a continuous media (no local structure).

Table 1. Experimental dipole moments and Kirkwood factors for several refrigerants

Refrigerant μK* gK μKF* μT* μg Class

HCFC-141b 2.96 2.17 - - 2.01 B HCFC-123 2.13 2.48 - - 1.36 B HCFC-142b 3.17 2.20 - - 2.14 B HFC-32 3.60 3.31 2.61 2.35 1.98 A HFC-125 2.48 2.46 1.84 1.94 1.56 A HFC-134a 3.54 3.44 2.67 2.61 2.06 A HFC-143a 3.34 2.04 2.63 2.75 2.34 A HFC-152a 3.69 2.67 2.55 2.77 2.26 A HFC-245fa 2.69 3.01 - - 1.55 A

μT* for the liquid phase was obtained using the SCIPCM model, with B3PW91/D95V(d,p) level [19]

It is noteworthy to refer here the calculations with difluoromethane (HFC-32). HFC 32 clusters (n=2 10), where n is the number of molecules have been generated by Monte Carlo simulations at a temperature T=50K. For some clusters (n=2 6) full geometry optimizations at the B3LYP/D95V(d,p) level have been carried out. Figure 8 shows the DFT optimized structures for n=3 6. These calculations indicate a small reduction of some F...H distances from the trimer (2.43 Å) to the hexamer (2.39 Å) indicating some cooperative polarization effects typical of hydrogen bonding systems [20]. Comparison

between the results for the HFC 32 and water clusters shows a much stronger polarization effect in water [19]. Moreover, the procedure used provides a reliable estimation of the average dipole moment in water clusters that is similar, in the case of the water hexamer, to the measured dipole moment of bulk water. Thus, our DFT results show that the large dipole moments of HFC’s based on dielectric constant measurements and Kirkwood theory cannot be fully explained by polarization effects induced by hydrogen bonding. Reasons for this discrepancy are probably related to limitations of the Kirkwood theory and to the eventual formation in the liquid phase of dimers and small clusters in all the liquids studied, carrying large dipoles3.

Figure 8. Difluoromethane (HFC 32) clusters optimized structures from B3LYP/D95V(d,p) calculations: (a) n=3; (b) n=4; (c) n=5; (d) n=6. F...H distances in Å.

In addition, the occurrence of hydrogen bonding in HFC-134a and HFC-143a can be easily seen in Figure 9, were electronic densities are shown around the different atoms. For HFC-134a, the distances between the active fluor and hydrogen atoms in the different dimmers vary between 2.53 and 2.95 Å. For HFC-143a, the same distances vary between 2.51 and 2.94 Å, exactly the same type of interaction.

The experimental studies were extended to mixtures of fixed composition. Two binary systems (HFC-32/HFC-125 (R410A) [3] and HFC-125/HFC-143a (R-507)) and two ternary systems HFC125/143a/134a (R-404A), HFC32/125/134a (R-407C) [21] in the liquid phase was measured at temperatures from 217 to 303K and pressures up to 16 MPa. Kirkwood theory was applied to these systems and the value of the apparent dipole moment in the liquid state was obtained for the first time for these mixtures, considering the mixture as a single fluid, with a molar fraction dependent dipole moment.

The relation between the dipole moment of a binary mixture in the liquid state with the dipole moments of its components is

3 A complete discussion of this problem is found in section 4.3 of reference [19], namely in its Figure 6.


not well understood, except for dilute solutions of polar components in non-polar solvents. In the case of R410A we have a 50/50 mass % mixture of HFC-32 and HFC-125, which corresponds to a molar fraction of R32 x32 = 0.6976.

Figure 9. Electronic contour diagrams for 1,1,1,2-Tetrafluoroethane (HFC-134a) and 1,1,1-Trifluoroethane (HFC-143a). F-light green, H-blue, C-gray. Hydrogen bonding is shown in the regions of overlapping electronic density of the two molecules. The zones in red show deficiency in electronic density.

As it has been proven that the volumetric properties of the refrigerant mixtures are nearly ideal, an ideal combination law for the dipole moment of the binary mixture can be assumed:

***mix xx 2211 μμμ += (7)

The values of the dipole moments in the liquid phase have been calculated by the authors and found to be 2.48 Debye for HFC-125 and 3.60 Debye for HFC-32 [8,14]. The value calculated from equation (7) is 3.26 Debye, a value that is in excellent agreement with the value found experimentally. This result seems to support the use of a law of the type of equation (6) to estimate the dipole moments of these types of binary mixtures in the liquid state. Table II shows the results obtained for all the five mixtures measured.

Agreement is very good for R407A and R410A. For mixtures that contain HFC-143a, probably caused by some

systematic error in the determination of μexp* for this refrigerant, the “linear model” has bigger errors (around 10%). This conclusion seems to support the results obtained with the density functional theory. Further investigations are needed in more mixtures to text this hypothesis more extensively.

Table 2. Effective Dipole Moments of the mixtures (1-fluid approximation).

Mixture Components μexp* μcalc

* Deviation / %

R404A R125, R143a, R134a

3.36 3.02 - 10.1

R407A R32, R125, R134a

3.43 3.38 - 1.5

R410A R32, R125 3.31 3.26 - 1.5 R507 R125, R143a 3.32 2.96 - 10.8

3 CONCLUSION Experimental and theoretical work on the dielectric

properties of environmentally safe refrigerants developed by the authors since 1990 was reviewed. Although substantial data of dielectric constant (relative permittivity) as a function of temperature and pressure in the liquid state has been obtained for pure liquids and some mixtures, the theoretical calculations using density functional theory (DFT), based on self–consistent reaction field (SCRF) approach for a continuous media, showed that Kirkwood theory is just an approximation to obtain the effective dipole moments in the liquid phase. Further calculations have to be performed with greater degrees of theoretical basis, but the lack of experimental information about refractive indices and structural factors for the liquid local structure, restrains the results completely. A possible solution will be the determination of the structure functions of the liquid phases with Neutron Diffraction studies (normal and small angles), but the chemical difficulty of obtaining/producing the deuterated compounds has yet to be solved. The predicted values of the dipole moments in the condensed phase can be useful to derive effective and pair- additive intermolecular potential models. These models may be used to discuss the liquid state properties by means of computer simulations based on Monte Carlo or molecular dynamics techniques. This is a research line that we look forward pursuing in the near future.

APPENDIX

The publication of the experimental results for the different liquids has been made in several journals, and they complete the ones cited during the text of this paper. Table A1 shows the liquids measured, the range of temperature and pressure covered, the origin of the liquid and the publication media.

HFC-134a

HFC-143a


Table A1. Fluids studied, origin, purity, ranges of measurement

Fluid /Mixture Origin/Purity Temperature range / K Pressure range/ MPa

Reference

HCFC-123 Solvay Fluor und Derivative, Germany/99.8%

204.04 – 312.91 0.21 – 15.13 [2, 24,26]

HCFC-141b Solvay Fluor und Derivative, Germany/99.8%

202.25 – 298.25 0.10 – 15.14 [15]

HCFC-142b Solvay Fluor und Derivative, Germany/99.9%

206.62 – 303.75 0.32 – 18.23 [23]

HCFC-134a Solvay Fluor und Derivative, Germany/99.8%

298.15 – 323.15 (g) 205.59 – 308.16 (l)

0.1245 – 1.2486 (g) 0.64 – 16.51 (l)

[22]

HFC-32 ICI, UK/99.8% 208.42 – 303.48 2.00 – 16.10 [14] HFC-152a Solvay Fluor und

Derivative, Germany/99.9%

207.08 – 297.84 0.50 – 17.93 [24,26]

HFC-143a Elf Atochem (France)/99.5%

218.25 – 294.11 2.00 – 15.00 [25]

HFC-125 Elf Atochem (France)/>99.5%

214.32 – 303.72 2.00 – 16.00 [8]

R-410A Solvay Fluor und Derivative, Germany/>99.5%

217.15 – 303.65 2.00 – 16.00 [3]

R-404A Solvay Fluor und Derivative, Germany/>99.5%

217.65 – 303.15 2.00 – 16.00 [21]

R-407C Solvay Fluor und Derivative, Germany/>99.5%

220.15 – 303.15 2.00 – 16.00 [21]

R-507 Solvay Fluor und Derivative, Germany/>99.5%

219.15 – 303.15 2.00 – 16.00 [21]

HFC-245fa Honeywell Fluorochemical, Italy/99.9%

218.53 – 302.84 1.00 – 16.00 [27]

HFC-227ea Ausimont, Italy/99.9% 223.15 – 302.00 1.00 – 16.00 [28] HFC-236ea Lancaster Inc,

USA/99% 223.15 – 302.00 1.00 – 16.00 [28]

HFC-365mfc Solvay Fluor und Derivative, Germany/>99.5%

223.15 – 302.00 1.00 – 16.00 [28]


ACKNOWLEDGMENT

The authors would like to thank all our co-workers along the years, namely Teresa Barão, Anélia Gurova, Filipe Brito, Luís Pereira, and Ana Paula Ribeiro that had a fundamental contribution to the work on dielectric properties of refrigerants. Especially thanks are also for Professor J. M. St-Arnaud (Université du Québec à Trois-Rivières, Canada) for very enlightening collaborations and Professor B. Cabral (Faculdade de Ciências da Universidade de Lisboa, Portugal) for having conducted the density functional theory and SCRF calculations and subsequent discussions.

REFERENCES

[1] U. V. Mardolcar, C. A. Nieto de Castro, F. J. V. Santos, “Dielectric Constant of Toluene and Benzene”, Fluid Phase Equil., Vol. 79, pp. 255-264, 1992.

[2] A. N. Gurova,, M. T.Barão, U. V. Mardolcar, C. A. Nieto de Castro, “The Thermal Conductivity and Dielectric Constant of HCFC 141b, HCFC 123, HCFC 142b and HFC 134a” High Temp.- High Press., Vol. 26, pp. 25-34, 1994.

[3] F. E. de Brito, A. N. Gurova, U. V. Mardolcar, C. A. Nieto de Castro, “Dielectric Constant of Nearly Azeotropic Mixture R-410A”, Int. J. Thermophys., Vol.21, pp. 415-427, 2000.

[4] M. Huber, J. Gallagher, M. McLinden, G. Morrison, “REFPROP”, NIST Standard Reference Database 23, version 5.0, 1996.

[5] K. Vedam, “CRC Critical Reviews in Solid and Materials Science”, Vol. 11, pp.1-17, 1983.

[6] K. Vedam and C. Chen, “Importance of Using Eulerian Representation of Strain in High-Pressure Studies in Liquids”, J.Chem. Phys., Vol. 77, pp.1461-1463, 1982.

[7] R. Diguet, “Density Dependence of Refractive Index and Static Dielectric Constant”, Physica B & C, Vol. 139-140, pp. 126-130, 1986.

[8] L. M. Pereira, F. E. de Brito, A. N. Gurova, U. V. Mardolcar, C. A. Nieto de Castro, “Dielectric Properties of Liquid Pentafluoropentane (HFC-125)”, Int. J. Thermophys., Vol. 22, pp. 887-899, 2001.

[9] L. Onsager, “Electric Moments of Molecules in Liquids”, J.Am.Chem.Soc., Vol. 58, pp. 1486-1491, 1936.

[10] J. G. Kirkwood, “The Dielectric Polarization of Polar Liquids”, J.Chem.Phys. , Vol. 7, pp. 911-919, 1939.

[11] H. Frölich, “Theory of Dielectrics”, Oxford University Press, 1958.

[12] A. N. Gurova, F. E. de Brito, U. V. Mardolcar, C. A. Nieto de Castro, “Dielectric Properties of 1,1,1,3,3-pentafluoropropane (HFC-245fa)”, J. Chem. Eng. Data, Vol.46, pp. 1072-1077, 2001.

[13] M. O. McLinden, S. A Klein, E. W. Lemmon, A. P. Peskin, “REFPROP - Thermodynamic and transport properties of refrigerant and refrigerant mixtures”, NIST Standard Reference Database 23- version 6.01, 1998.

[14] C. A. Nieto de Castro, F. J. V. Santos, U. V. Mardolcar, “The Dielectric Constant of Liquid HFC 32”, Proc. 19th Congress International Institute of Refrigeration (IIR/IIF), The Hague, The Netherlands, Vol. IVa, pp. 436-442, 1995.

[15] M. T. Barão, C. A. Nieto de Castro, U. V. Mardolcar, “Molecular Properties of Alternative Refrigerants Derived from Dielectric Constant Measurements”, Int. J. Thermophys., Vol. 18, pp. 419-438, 1997.

[16] P. L. Silvestrelli, M. Parrinello, “Structural, electronic, and bonding properties of liquid water from first principles”, J. Chem. Phys., Vol. 111, pp. 3572-3580, 1999.

[17] J. K. Gregory, D. C. Clary, K. Liu, M. G. Brown, R. J. Saykally, Science, “The Water Dipole Moment in Water Clusters” Vol. 275, pp. 814-817, 1997.

[18] Y. S. Baydal, M.-L. Saboungi, D. L. Price, S. D. Shastri, D. R. Haeffner, A. K. Soper, “Electron Distribution in Water”, J. Chem. Phys., Vol. 112, pp. 9206-9208, 2000

[19] B. J. Costa Cabral, R. C. Guedes, R. S. Pai-Panandiker, C. A. Nieto de Castro, “Hydrogen Bonding and Internal Rotation of Hydrofluorocarbons by Density Functional Theory”, Phys. Chem. Chem. Phys., Vol. 3, pp. 4200-4207, 2001.

[20] S. Scheiner, “Hydrogen Bonding. A Theoretical Prospective”, Oxford University Press, Oxford, 1997.

[21] F. E. Brito, A. N. Gurova, C. A. Nieto de Castro, U. V. Mardolcar, “Dielectric Constant and Dipole Moment of Hydrofluorocarbon refrigerant mixtures R404A, R407C and R507”, High Temperatures-High Pressures, Vol. 32, pp. 631-651, 2000.

[22] T. Barão, C. A. Nieto de Castro, U. V. Mardolcar, R. Okambawa, J. M. St-Arnaud, “Dielectric Constant, Dielectric Virial Coefficients and Dipole Moments of HFC 134a”, J. Chem. Eng. Data, Vol. 40, pp. 1242-1248, 1995.

[23] M. T. Barão, C. A. Nieto de Castro, U. V. Mardolcar, "The Dielectric Constant of Liquid HFC 134a and HCFC 142b", Int. J. Thermophys., Vol. 17, pp. 573-585, 1996.

[24] M. T. Barão, “Dielectric Properties of Environmentally Acceptable Refrigerants”, PhD Thesis, Faculdade de Ciências da Universidade de Lisboa, pp. 173-176, 1995.

[25] A. N. Gurova, L. M. Pereira, F. E. de Brito, C. A. Nieto de Castro, U. V. Mardolcar, “Dielectric Constant and Dipole Moment of HFC 143a", Proceedings of the 4th General Conference of the Balkan Physical Union, Veliko Tarnovo, Bulgaria, ed. Balkan Physical Union, 2000.

[26] M. T. Barão, U. V. Mardolcar, C. A. Nieto de Castro, “Dielectric Constant and Dipole Moments of 1,1,1-Trifluoro-2,2-Dichloroethane (HCFC 123) and 1,1-Difluoroethane (HFC 152a) in the Liquid Phase”, Fluid Phase Equil., Vol. 150-151, pp. 753-762, 1998.

[27] A. N. Gurova, F. E. de Brito, C. A. Nieto de Castro and U. V. Mardolcar, “Dielectric Properties of 1,1,1,3,3-Pentafluropropane (HFC-245fa)”, J. Chem. Eng. Data, Vol. 46, pp. 1072-1077, 2001.

[28] A. P. C. Ribeiro, U. V. Mardolcar, C. A. Nieto de Castro, “Relative Permitivity of 1,1,1,2,3,3,3-Heptafluoropropane (HFC-227ea), 1,1,1,2,3,3-Hexafluoropropane (HFC-236ea) and 1,1,1,3,3-Pentafluorobutane (HFC-365mfc) in the Liquid Phase”, to be submitted 2006.

Fernando J. V. Santos was born in Lisbon, Portugal in 1958. He received the B.Sc. degree in Chemistry (1979), the M.Sc. degree in Chemistry (Physical-Chemistry/Inorganic Chemistry) (1981) and the Ph.D. degree in Chemistry (Physical-Chemistry) (1993) from the Faculdade de Ciências of the Universidade de Lisboa, in Lisbon, Portugal. He has been since 1993 Professor Auxiliar at the Faculdade de Ciências of the Universidade de Lisboa. Current

memberships include the Portuguese Chemistry Society, and the Portuguese Metrology Society. Actual research interests include the study and characterization of materials (ionic liquids included) through accurate measurements of thermophysical properties for extensive ranges of temperature and pressure; study of molecular interactions in pure fluids and binary mixtures; development of accurate measurement methods of metrological quality and property estimation by molecular thermodynamics methods; and the development of instruments for the accurate measurement of thermophysical properties and automatic systems of data acquisition and analysis based on microcomputers and standard interfaces.


Rahool S. Pai-Panandiker was born inMarzagão, India, in 1971. He received the B.Sc. degree in chemical engineering, minor in chemistry and materials science, in 1992 from the Karnataka Regional Engineering College, India, and the Ph.D. degree from the Colorado School of Mines, Golden, GO, USA in 1997. He has been since 1998 post-doctoral fellow in the Center for Molecular Sciences and Materials and Instructor at the Department of Chemistry

and Biochemistry of the Faculdade de Ciências da Universidade de Lisboa. He worked for several projects in industry in Goa, India, namely for the World Bank Project “The Knowledge City (2001-2002) as Project Study Director. His research interests are in the synthesis and characterization of polymers, thermophysics of refrigerants and high temperature thermal properties of molten materials, focusing structure-thermophysical property relationships. Awards - Colorado School of Mines, Dean's List 1992-1997, Outstanding Graduating Senior 1992, Institute of Engineers, India National Paper Contest Winner 1991. Member of the American Institute of Chemical Engineers, American Chemical Society and the Materials Research Society, USA.

Carlos A. Nieto de Castro was born in Lisbon, Portugal in 1949. He received the Chemical Engineering degree from the Instituto Superior Técnico, in Lisbon, Portugal in 1971, the Ph.D. degree from the Instituto Superior Técnico, in Lisbon, Portugal in 1977. He has been since 1979 full professor of Chemical Physics of Fluids at the Faculdade de Ciências da Universidade de Lisboa, were he has been Head of Department for several years, President of the

Scientific Council (1990-1993), being currently Director of the Center for Molecular Sciences and Materials and Coordinator of the Technological Chemistry degree. Guest scientist of NIST (USA). Current memberships include the Royal Society of Chemistry (Member), the Portuguese Chemistry and Physics Societies, Ordem dos Engenheiros, the chartered Professional Organization of Engineers in Portugal (Senior Member) and the Portuguese Society of Metrology. Expert in the field of Thermophysical Properties of Gases and Liquids, extended his research work to materials science and metrology. Actual research interests also include ionic liquids and thermophysics of nanomaterials, including thin films. In 2005 he was awarded the Portuguese Excellence Prize for Research.

Umesh V. Mardolcar was born in Goa, India in 1955. He received the Mechanical Engineering degree from Instituto Superior Técnico, in Lisbon, Portugal in 1978 and the Ph.D. degree in physics from the same University, in 1988. He has been an assistant professor in this University since that time. He is a member of the Department of Physics of this University and the Center for Molecular Sciences and Materials. He is responsible for some projects in the area of

thermal diffusivity of solids by the laser flash method, at high temperatures (up to 2500 K). Other area of interest is concerned with dielectric properties of fluids.

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Dielectric properties of alternative refrigerants