Inclusion of H2 increases the electrical conductivity of. CO2 in the range 3000 to 6000 K because CHO molecules produced in this temperature range emit more ...
Electrical Engineering in Japan, Vol. 163, No. 4, 2008 Translated from Denki Gakkai Ronbunshi, Vol. 126-B, No. 1, January 2006, pp. 80–90
Thermodynamic and Transport Properties of CO2, CO2–O2, and CO2–H2 Mixtures at Temperatures of 300 to 30,000 K and Pressures of 0.1 to 10 MPa YASUNORI TANAKA,1 NOBUHIKO YAMACHI,2 SHINJI MATSUMOTO,3 SHUHEI KANEKO,4 SHIGEMITSU OKABE,4 and MASATOYO SHIBUYA5 1
Kanazawa University, Japan Electric Power Co., Japan Shikoku Electric Power Co., Japan 4 Tokyo Electric Power Co., Japan 5 Central Research Institute of Electric Power Industry, Japan 2 Hokuriku 3
SUMMARY
1. Introduction
This paper provides the theoretical calculation results of thermodynamic and transport properties of CO2, CO2– O2 mixture, CO2–H2 mixture under thermal equilibrium condition at temperatures of 300 to 30,000 K and at pressures of 0.1 to 10 MPa. The gas CO2 is one of the candidates for the environmentally benign arc-quenching medium in a circuit breaker. Furthermore, the effect of additional gases O2 and H2 on the thermodynamic and transport properties of CO2 was also investigated in this paper. The hydrogen atom included CO2 is similar to the polymer ablated vapor in switching devices. First, equilibrium compositions of CO2, CO2–O2 mixture, CO2–H2 mixture were calculated through the Gibbs free energy minimization method. Second, thermodynamic properties were computed using the calculated composition. Finally, transport properties were calculated by the first-order approximation of Chapman– Enskog method using the collision integrals between species. Inclusion of H2 increases the electrical conductivity of CO2 in the range 3000 to 6000 K because CHO molecules produced in this temperature range emit more electrons due to the lower ionization potential of CHO. It also increases the thermal conductivity of CO2 especially due to dissociation reactions of H2 around 3900 K and ionization of H around 15,000 K. These properties provided here can be used for CO2 thermal plasma simulation. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(4): 18–29, 2008; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.20467
SF6 is widely used as an arc quenching medium for high-voltage circuit breakers due to properties such as chemical stability and nontoxicity, with an arc quenching performance about 100 times that of air. However, the third Session of the Conference of the Parties to the Framework Convention on Climate Change recognized SF6 as a greenhouse gas subject to emissions reduction. Recently Russia ratified the Convention, and the prevention of global warming has become a major problem for mankind. From the standpoint of prevention of global warming, more environment-friendly arc quenching media are needed for circuit breakers, and studies of SF6 alternatives are in progress. For example, N2 [1], air [2], CO2 [2–6], and other non-fluorinecontaining high-pressure gases are being considered. In particular, CO2 has started to attract attention as an arc quenching medium, and full-scale 72-kV prototype circuit breakers using CO2 have been manufactured [8]. In these prototype devices, the arc quenching performance is improved by the pressure increase inside the chamber due to ablation of polymer materials. Many polymer materials used for this purpose, such as POM (polyoxymethylene) and PMMA (polymethylmethacrylate), include C, H, O, and other elements. Distribution circuit breakers using ablation of PMMA have also been developed [9]. When such carbon-containing gases or vapors are exposed to an arc, deposition of solid carbon is a problem for the insulation. There have been theoretical thermodynamic studies of such carbon deposition [10]. On the other hand, in the field of plasma materials chemistry, there has been research on CO generation and quenching positions in the case of CO2 dissociation [11], and on high-temperature techniques for welding arcs using
Key words: alternatives for SF6; greenhouse effect; carbon dioxide; environmentally benign arc quenching medium; thermodynamic and transport properties.
© 2008 Wiley Periodicals, Inc. 18
tion, P is the pressure (Pa), and P0 is the standard pressure (here 101,325 Pa). µ0j is the chemical potential of particle j (J/mol) calculated as follows:
CO2 [12]. However, regarding CO2 arc quenching, the available fundamental data required for development of thermal plasma processes are not sufficient. In particular, data on the thermodynamic and transport properties are absolutely necessary for numerical thermo-fluid analysis of arcs and thermal plasmas. In this study, aiming at the most fundamental data, we explore the particle composition and the thermodynamic and transport properties of gaseous CO2 and its mixtures with O2 and H2 in terms of atomic–molecular theory and statistical thermodynamics. Here we deal with a very wide range of temperatures and pressures, namely, 300 to 30,000 K and 0.1 to 10 MPa. The thermodynamic and transport properties of gases in the vicinity of 10,000 K are closely related to phenomena occurring in the central part of the arc, and the properties in the range of 3000 to 5000 K are closely related to arc behavior in the breaking process. Thus, the gas properties must be examined in such wide temperature ranges. In particular, CO2–H2 mixtures include atoms of C, H, and O, and their properties are similar to those of the ablation gases produced by polymer materials. Hence, the influences of ablation gases on thermal plasma can be examined separately. In addition, when H2 is added to CO2, we may expect improvement of arc quenching performance due to changes of the thermodynamic and transport properties, especially increased thermal conductivity. Such data would be very important for theoretical studies of CO2 arcs and thermal plasmas, and for the design of arc devices.
(2) Here mj is the mass of particle j (kg), k is the Boltzmann constant (= 1.38 × 10–23 J/K), h is the Prandtl number (= 6.63 × 10–34 J⋅s), Zint j is the internal state sum of particle j, and ∆Hfj is the standard enthalpy of formation (J/mol). The atomic and molecular constants required to calculate Zint j were taken from Refs. 14, 15, and JANAF [16] was used for ∆Hfj. The species considered in our calculations are listed in Table 1. A total of 23 species were involved in the calculation of the particle composition of CO2 and CO2–O2 mixtures (22 species including C, O plus electrons). As regards the particle composition of CO2–H2 mixtures, 23 species including H were added to the 23 types, so that the total number of particles was 46. Solid and liquid phases were not considered in the calculations. For simplicity, the Debye–Hückel pressure correction was also disregarded. The error caused by such approximation is, for example, about +5% for the enthalpy at temperatures over 15,000 K [17]. The temperature range was set to 300 to 30,000 K, and the pressure range to 0.1 to 10 MPa. The particle composition of CO2 at a pressure of 0.1 MPa is shown in Fig. 1. In the temperature range of 300 to 3000 K, CO2 molecules dominate. In the range from 3000 to 5000 K, CO2 molecules decompose, thus producing CO, O2, C, O, C2O, and other species. In this temperature range, electrons are produced mainly by ionization of O2. Above 5000 K, monatomic particles and ions as well as electrons become dominant. The particle composition of 50% CO2 + 50% O2 at a pressure of 0.1 MPa is shown in Fig. 2. Here the admixture ratio is defined as the mole fraction at normal temperature. In the temperature range of 300 to 3000 K, CO2 and O2 molecules exist at high density. O2 begins thermal dissociation at about 3000 K, and the density of O atoms reaches 1024 m–3 at 4000 K. In the range of 3000 to 6000 K, electrons are generated mainly by ionization of O2. At higher temperatures, ionization of C and O becomes the main factor in electron production. The particle composition of 50% CO2 + 50% H2 at a pressure of 0.1 MPa is shown in Fig. 3. Various hydrogencontaining molecules are formed due to the addition of H2. In the temperature range of 300 to 3000 K, CO2, H2O, CH4, and H2 particles are dominant. This indicates that some CO2 and H2 molecules mixed at normal temperature enter into the reaction CO2 + 4H2 → 2 H2O + CH4. At the arc temperature, CO2 and H2 are ionized to the atomic state. As
2. Equilibrium Particle Composition of High-Temperature CO2, CO2–O2, and CO2–H2 Mixtures In a high-pressure steady-state arc or thermal plasma, the temperature in the central part reaches about 10,000 K, accompanied by a high frequency of heavy particle–electron collisions and a mild temperature gradient. Therefore, the analysis is carried out under the assumption of local near-equilibrium. In this study, the particle composition of CO2, CO2–O2, and CO2–H2 mixtures in the thermal equilibrium state is calculated by minimization of the Gibbs free energy [13]. The system’s Gibbs free energy G is expressed as
(1)
Here yj is the number of moles of particle j (mol), Run is the universal gas constant (= 8.31 J/mol/K), T is the temperature (K), L is the number of particle types under considera-
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Table 1. Particles considered in calculation
the atoms are cooled, the original mixture of CO2 and H2 is not restored; instead some of the atoms form energetically stable H2O and CH4. In the range of 3000 to 13,000 K, CO, H, C, and O exist at high density. When the temperature exceeds 13,000 K, ions become the main particles. In the range from 3000 to 6000 K, electrons are generated mainly by ionization of CHO. This is because CHO molecules have a smaller ionization potential than other particles. Figure 4 shows the temperature dependence of the electron density at various H2 contents. In the temperature range of 3000 to 6000 K, the electron density increases with the H2 content. This is because of the increasing molecular density of CHO, with a low ionization potential. As the pressure is increased, the electron density increases proportionally. In addition, we confirmed that the commencement of dissociation and ionization shifts to a higher temperature. This is because the degree of dissociation and ionization at equal temperature is reduced according to Le Chatelier’s law.
Fig. 1. Equilibrium composition of CO2 at pressure of 0.1 MPa.
3. Thermodynamic Properties Using the particle composition data described in the previous section, we examined the thermodynamic properties of CO2 and CO2–H2 mixtures, in particular, the mass Fig. 2. Equilibrium composition of 50% CO2 + 50% O2 at pressure of 0.1 MPa.
Fig. 3. Equilibrium composition of 50% CO2 + 50% H2 at pressure of 0.1 MPa.
Fig. 4. Electron density of CO2 + H2 mixtures at pressure of 0.1 MPa and various temperatures.
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density ρ, enthalpy h, isobaric specific heat Cp, gas constant R, specific heat ratio γ, and sound velocity vs. 3.1 Mass density and gas constant The mass density ρ (kg/m–3) and gas constant R (J/kg⋅K) were calculated by means of the following expressions: (3) (4)
Fig. 6. Gas constant of CO2 in pressure range of 0.1 to 10 MPa.
Here nj is the number density of particle j (m–3). Thus, ρ and R can be calculated from each other. The calculated ρ of CO2 in the pressure range of 0.1 to 10 MPa is shown in Fig. 5. If it were not for dissociation, ionization, and other reactions, the mass density ρ would vary in inverse proportion to temperature. For example, at a pressure of 0.1 MPa, ρ decreases proportionally to the temperature increase below 4000 K. At higher temperatures, ρ decreases more strongly. This is because CO2 dissociates into CO and O. An even more intense decrease at a temperature of about 7000 K is explained by the dissociation of CO into C and O. On the other hand, ρ varies almost directly with pressure. The calculated results for the gas constant of CO2 in the pressure range of 0.1 to 10 MPa are shown in Fig. 6. The gas constant is a very important factor of the state equations in compressed fluid analysis. As is evident from
the diagram, at temperatures below 4000 K, R is almost unchanged at 189 J/kg⋅K regardless of the pressure. When the temperature exceeds 4000 K, the gas constant increases sharply. For example, R = 596 J/kg⋅K at a pressure of 0.1 MPa and a temperature of 10,000 K. Such growth of R at temperatures higher than 4000 K is explained by the fact that CO2 begins dissociation around this temperature, while ρ decreases abruptly. As the temperature exceeds 12,000 K, the gas constant increases even more. This is due to the generation of light electrons via the ionization of C, O, and other species. In addition, the diagram indicates that above 4000 K, R decreases as the pressure increases. The reason is that as the pressure increases, dissociation and ionization at equal temperature is suppressed according to Le Chatelier’s law. Figure 7 shows R for CO2 and its 50% mixtures with H2 and O2; here the admixture ratio is defined as the mole
Fig. 7. Gas constant of CO2, 50% CO2 + 50% H2, and 50% CO2 + 50% O2 at pressure of 0.1 MPa.
Fig. 5. Mass density of CO2 in pressure range of 0.1 to 10 MPa.
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fraction. The gas constant increases as H2 is added. This is because H2 has a smaller mass than the other species, and ρ decreases at a high H2 content. In the case of 50% O2 mixture, the effect is not as pronounced as with H2. 3.2 Enthalpy and specific heat The enthalpy h and isobaric specific heat Cp can be calculated as follows: (5) (6) Fig. 9. Specific heat of CO2, 50% CO2 + 50% H2, and 50% CO2 + 50% O2 at pressure of 0.1 MPa.
As an example, Fig. 8 shows calculated results for the isobaric specific heat of CO2, with the pressure treated as a parameter. With increasing temperature, Cp tends to increase. The temperature dependence of Cp shows several characteristic peaks; in particular, at a pressure of 0.1 MPa, there are maxima at 4700, 7100, and 15,200 K. These maxima represent, respectively, CO2 dissociation, CO dissociation, and the ionization of C and O. Since the particle density increases with pressure, the temperature of these maxima increases according to Le Chatelier’s law. In addition, as the pressure increases, the variation of the degree of dissociation or ionization with temperature becomes gentler, and the maximum values of Cp become smaller. The specific heat Cp of 50% mixtures of CO2 with H2 and O2 is shown in Fig. 9. When O2 is added, Cp shows a peak near 3900 K, which is related to the dissociation of O2. In addition, the maximum values decrease at temperatures of 4700 and 7100 K; this is because the particle densities of CO2 and CO become relatively smaller at a high
content of O2. On the other hand, when H2 is added, Cp increases at temperatures of 300 to 30,000 K. This is because the number of particles per unit mass increases due to the light hydrogen species. In addition, there are maxima of the specific heat at temperatures of 800 and 3900 K, caused by dissociation of CH4 and H2. 3.3 Specific heat ratio and sound velocity The specific heat ratio γ and the sound velocity vs are parameters that characterize a compressed fluid. We used the following expressions for calculation: (7) (8) The specific heat ratio γ of CO2 in the pressure range of 0.1 to 10 MPa is shown in Fig. 10. The ratio is 1.0 to 1.3 at all temperatures and pressures, and shows several characteristic minima versus temperature. For example, at a pressure of 0.1 MPa, minima exist at 4700, 7100, and 15,200 K, corresponding to CO2 dissociation, CO dissociation, and the ionization of C and O, although the effect is not very strong. The specific heats of 50% mixtures with H2 and O2 are shown in Fig. 11. In either case, γ is 1.0 to 1.3, and hence adding H2 and O2 has little effect. The velocity vs of sound in CO2 in the pressure range of 0.1 to 10 MPa is shown in Fig. 12. The sound velocity expresses the pressure propagation speed, an extremely important property when studying the gas flow rate in the throat of circuit breakers and shock wave generation. As is evident from the diagram, vs increases with temperature. In the range of 300 to 4000 K, the sound velocity depends only
Fig. 8. Specific heat at constant pressure of CO2 in pressure range of 0.1 to 10 MPa.
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Fig. 10. Specific heat ratio of CO2 in pressure range of 0.1 to 10 MPa.
Fig. 13. Sound velocity of CO2, 50% CO2 + 50% H2, and 50% CO2 + 50% O2 at pressure of 0.1 MPa.
on the temperature and is almost independent of pressure. This is because dissociation of CO2 does not take place below 4000 K, and the gas consists mainly of CO2 molecules. At temperature higher than 4000 K, vs increases with decreasing pressure. At equal temperature, dissociation advances at lower pressure, so that light molecules and atoms are produced. As a result, vs increases. The sound velocity of 50% mixtures with H2 and O2 at a pressure of 0.1 MPa is shown in Fig. 13. Since H2 is lighter than CO2, vs increases as hydrogen is added. On the other hand, O2 has a molecular weight of 32, which is not too different from the molecular weight (44) of CO2, and atomic oxygen produced by association is included in the dissociation products of CO2. Therefore, the mass density is almost the same.
Fig. 11. Specific heat ratio of CO2, 50% CO2 + 50% H2, and 50% CO2 + 50% O2 at pressure of 0.1 MPa.
4. Transport Properties The transport properties, that is, electrical conductivity σ, thermal conductivity κ, and viscosity coefficient η, were calculated from the particle composition and collision cross-section data. 4.1 Collision integral To find the first-order Chapman–Enskog solution for the transport__properties, the momentum transfer col(1,1) and the viscosity collision integral lision __ integral πΩij (2,2) πΩij are required [18]. These were obtained as explained below. (1) Neutral-particle collision __ __ integrals We used the Ω(2,2) π and for H2 with H2, H collision integrals πΩ(1,1) ij ij with H as proposed by Yos [19]. As regards with H, and H __ __2 (2,2) Ω πΩ(1,1) π and for C–C and O–O collisions, we calcuij ij
Fig. 12. Sound velocity of CO2 in pressure range of 0.1 to 10 MPa.
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lated the integrals using the interparticle potentials proposed by Abrahamson [20],_and __ _ the table of Monchik [21]. (2,2) Ω π and for collisions between Then, using πΩ(1,1) ij ij homogeneous neutral particles such as C2H4O–C2H4O, CH2O–CH2O, or CH2–CH2, we estimated the molecular radii and applied the hard-sphere model. The collision integrals for other combinations of neutral species were found by the empirical combining rule [22]. (2) Ion–neutral particle collision integrals __ Regarding for such the momentum transfer collision integral πΩ(1,1) ij heterogeneous ion–neutral particle combinations as CHO– CHO+, CH–CH+, C2–C−2, O2–O+2 , O2–O−2 , H2–H+2, H2–H−2, OH–OH+, OH–OH–, C–C+, C–C–, O–O+, O–O–, H–H+, and H–H–, calculations were performed using the resonant charge exchange cross section [19, 23]. The resonant charge exchange cross section was estimated as a function of the ionization potential from data by Rapp. On the other hand, the viscosity collision integral was considered equal to that of the neutral particles because charge exchange has no effect. (3) Ion–neutral particle collision __ __ integrals We used and πΩ(2,2) for e–H2, e–H, the collision integrals πΩ(1,1) ij ij e–O2, e–O, etc., as proposed by Yos [19]. The collision integrals for e–C were calculated from the collision cross section [24]. The integrals for collisions between electrons and other particles were estimated using the hard sphere model. (4) Charged-particle collision integrals As regards collisions between charged particles, the integrals were calculated by the Gvosdover cross section for Coulomb potential [19].
Fig. 14. Electrical conductivity of CO2 in pressure range of 0.1 to 10 MPa.
comes smaller. In the range above 15,000 K, in contrast, σ increases with pressure. This is because the density of the ionized electrons increases eventually with pressure. Figure 15 shows the electrical conductivity of 50% mixtures of CO2 with O2 and H2 at a pressure of 0.1 MPa. At temperatures below 6000 K, σ increases when hydrogen and oxygen are added. In pure CO2 and its 50% mixture with O2, electrons are supplied mainly due to ionization of oxygen. At higher O2 content, the electron supply increases and the electrical conductivity increases. When hydrogen is added, ionization of CHO molecules is the main source of electrons at temperatures below 6000 K. Because of hydrogen, the proportion of CHO molecules increases, and σ increases due to the increased supply of electrons.
4.2 Electrical conductivity According to the first-order Chapman–Enskog approximation, the electrical conductivity of a thermal plasma is as follows: (9)
(10) Here e is the elementary charge. The calculated results for the electrical conductivity are shown in Fig. 14. In the temperature range of 4000 to 6000 K, the electrical conductivity σ increases fast with temperature. As the temperature increases, the electrical conductivity reaches about 6000 S/m at 15,000 K, and about 10,000 S/m at 30,000 K. As regards pressure dependence, σ decreases as the pressure increases at temperatures below 15,000 K. At higher pressures, the ionization temperature increases, while at equal temperature, the ionization degree decreases and σ be-
Fig. 15. Electrical conductivity of CO2, 50% CO2 + 50% H2, and 50% CO2 + 50% O2 at pressure of 0.1 MPa.
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Table 2. Reactions considered in calculation of thermal conductivity
4.3 Thermal conductivity The thermal conductivity κ of a thermal plasma can be calculated by the following equations [19]: (11) (12)
(13)
(14) (15) (16)
(17) Here κtr, κint, and κre are the contact thermal conductivity, the internal thermal conductivity, and reactive thermal conductivity, respectively, Cpi is the isobaric specific heat of species i, βli is the stoichiometric coefficient, and ∆Hl is the heat of reaction l. The stoichiometric coefficients were determined while referring to the 42 reactions listed in Table 2. The electrical conductivity of CO2 in the pressure range of 0.1 to 10 MPa is shown in Fig. 16. The thermal conductivity increases with temperature. If nonelastic collisions caused by reactions and excitation do not occur, κ includes only κtr, varying with the 1/2 power of the temperature. Actually, however, nonelastic collisions take place, and the temperature dependence is very complicated. As is evident from the diagram, at a pressure of 0.1 MPa, there are characteristic peaks of κ at 4700 and 6900 K. These peaks are caused by increases of the reactive thermal conductivity due to dissociation of CO2 and CO, respectively. As the pressure increases, the peaks shift to higher temperatures for the same reason as in the case of Cp. Figure 17 shows the thermal conductivity of 50% mixtures of CO2 with O2 and H2 at a pressure of 0.1 MPa. When oxygen is added, a maximum appears at about 3800 K, which is explained by an increase of the reactive conductivity κre due to O2 dissociation. On the other hand, the addition of hydrogen causes an increase in κ at any temperature. The main reasons are that H2 and H have small masses, thus assuring good contact conductivity, and that CH4 is produced when hydrogen is added. At about 3900
K, this CH4 dissociates, thus contributing to the reactive thermal conductivity κre. 4.4 Viscosity coefficient The viscosity coefficient η was calculated as follows: (18)
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Fig. 19. Viscosity of CO2, 50% CO2 + 50% H2, and 50% CO2 + 50% O2 at pressure of 0.1 MPa.
Fig. 16. Thermal conductivity of CO2 in pressure range of 0.1 to 10 MPa.
The viscosity coefficient η of CO2 in the pressure range of 0.1 to 10 MPa is shown in Fig. 18. For example, at a pressure of 0.1 MPa, η increases with temperature until about 11,000 K. The viscosity coefficient is a measure of momentum flow, which basically increases with temperature. On the other hand, at temperatures above 12,000 K, η decreases. The reason is that ions are the main charged particles in this temperature range, and thus are the instrument of momentum transfer. However, ion–ion collisions are Coulomb collisions, resulting in a large collision cross section. In addition, as the pressure is increased, η increases at temperatures above 10,000 K. This is explained by the fact that at equal temperature, the degree of ionization decreases with higher pressure, and the ion fraction becomes smaller. Since ion–ion collisions are Coulomb collisions with greater cross sections than neutral-particle collisions, η is assumed to increase as the degree of ionization decreases. Figure 19 shows η of 50% mixtures of CO2 with O2 and H2 at a pressure of 0.1 MPa. As is evident from the diagram, the influence of additive gases on η is small for admixture ratios of up to 50%.
Fig. 17. Thermal conductivity of CO2, 50% CO2 + 50% H2, and 50% CO2 + 50% O2 at pressure of 0.1 MPa.
5. Adequacy of Obtained Thermodynamic and Transport Properties There are few if any published data, either calculated or experimental, on the thermodynamic and transport properties of CO2 and its mixtures with H2 and O2. Thus, it is difficult to judge the validity of the obtained properties. However, the calculation methods, as well as internal state sums, collision cross sections, and other data used in this study have much in common with previous research in this field [19]. Furthermore, the thermodynamic and transport properties of H2 and O2 have been published. A comparison
Fig. 18. Viscosity of CO2 in pressure range of 0.1 to 10 MPa.
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Table 3. Comparison of calculated results with published results in terms of specific heat of O2 and H2
(3) As regards the isobaric specific heat, marked peaks appear in the vicinity of 800 and 3900 K at a pressure of 0.1 MPa when H2 is added to a CO2 thermal plasma. These peaks represent the dissociation of CH4 and H2. When O2 is added, a peak appears at about 3900 K, which represents the dissociation of O2. Similarly, these dissociation reactions contribute to the reactive thermal conductivity at the same temperatures. (4) The viscosity coefficient does not change significantly, even at H2 and O2 concentrations as high as 50%.
of these published data with the results obtained in this study for the isobaric specific heats of H2 and O2 is shown in Table 3. As indicated by the table, the difference between the data is within 10%. On the other hand, some authors of this study performed an experimental study and electrohydrodynamic fluid analysis to examine how the temperature of an induced thermal plasma (Ar at 0.1 MPa) varied with the addition of various gases [2, 5, 6]. The electrohydrodynamic fluid analysis was performed using the thermodynamic and transport properties of CO2, O2, H2 calculated in the same way as in the present study. As a result, good agreement was achieved with experimental data on the temperature decrease of an induced thermal plasma. Since electrohydrodynamic fluid analysis is governed by the thermodynamic and transport properties of the additive gases, the validity of the properties was confirmed indirectly. Thus, we may conclude that the thermodynamic and transport properties calculated in this study are reasonably valid.
Acknowledgments We express our deep gratitude to the late Professor T. Sakuta (Kanazawa University) for his valuable advice, and to Kanazawa University postgraduate student K. Okada (now affiliated with Denso Techno Corp.) for his assistance.
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6. Conclusions In this study, we estimated the thermodynamic and transport properties of CO2 from the standpoint of atomic– molecular theory. Wide practical temperature and pressure ranges of 300 to 30,000 K, 0.1 to 10 MPa were considered. In addition, we examined the effect of adding O2 and H2. The following main results were obtained. (1) When H2 is added to a CO2 thermal plasma, various species containing C, H, O are produced. When the temperature is decreased below 1000 K, the dominant particles are CO2, H2O, CH4, and H2. When O2 is added to CO2, no major difference from a pure CO2 thermal plasma is observed. (2) The electron density of the CO2 thermal plasma increases with the addition of H2 in the temperature range of 3000 to 6000 K. This is explained by the generation of CHO groups with a low ionization potential. As a result, electrical conductivity also increases.
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AUTHORS
Yasunori Tanaka (member) served as a JSPS Special Researcher in 1997–98. He completed the doctoral program at Nagoya University in 1998 and joined the faculty of Kanazawa University as a research associate, becoming an associate professor in 2002. His research interests are strong-current arc interruption phenomena, fundamental phenomena of thermal plasmas and their applications. He holds a D.Eng. degree.
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AUTHORS (continued) (from left to right)
Nobuhiko Yamachi (member) completed the M.E. program at Toyama University in 1995 and joined Hokuriku Electric Power Co. His research interests are protection of power stations and transformer equipment. Shinji Matsumoto (member) graduated from Okayama University in 1979 and joined Shikoku Electric Power Co. His research interests are planning and operation of transmission networks, power substations. Shuhei Kaneko (member) completed the M.E. program at Keio University in 2000 and joined Tokyo Electric Power Co. His research interests are gas-insulated switches. Shigemitsu Okabe (member) completed the doctoral program at the University of Tokyo in 1986 and joined Tokyo Electric Power Co. He was a visiting researcher at Technical University of Munich in 1992. He holds a D.Eng. degree, and is a member of IEEE. Masatoyo Shibuya (member) graduated from Kanto Gakuin University in 1968. He joined CRIEPI in 1964. He was a contract researcher at Nagoya University in 1983–84. From 1997 to 2000 he was affiliated with the Association for Studies of Superconducting Generators and Materials Science. His research interests are strong-current arc phenomena and applications, hazardous material disposal, superconducting devices and materials. He received a 1995 Paper Award and 1999 Progress Award. He holds a D.Eng. degree, and is a member of CSJ and JSWME.
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