Thermal Conductivity Of Argon Research Articles

An Investigation on Thermal Conductivity of Fluid in a Nanochannel by Nonequilibrium Molecular Dynamics Simulations

Abstract In this paper, molecular dynamics simulation is used to investigate the effect of copper and argon nanochannels size on the thermal conductivity of argon. Thermal conductivity is calculated by nonequilibrium molecular dynamics (NEMD) simulation. Simulations are performed for different distances between the walls. Results for both copper and argon walls are investigated individually. Results show that the existence of argon walls has little effect on the thermal conductivity. However, the amount of it for the argon confined between the copper walls is affected by the distance between the two walls. In the same way, the effect of wall roughness on the thermal conductivity is investigated, which shows that roughness is effective only for low distances between the walls. Also, the thermal conductivity of argon under Poiseuille flow in a nanochannel is studied. The results indicate that by increasing the driving force, the thermal conductivity increases and the increase ratio is higher for larger forces.

Thermal conductivity of argon: Modeling and comparison with experimental data

The thermal conductivity of argon in solid state phase is modeled by studying the physics property of atom vibrations given by different potentials in crystalline networks at temperature less than 80 [K], in the canonical ensemble where volume, mass and temperature are held constant. Mfolecular dynamics simulations are carried out taking into account the Verlet algorithm and the Green-Kubo formalism. We consider some interatomic interactions as Lennard-Jones, Mie and Kihara potential to obtain results that we compare to experimental data. We show that the present modeling based on the Kihara potential is the best, showing a precision (8.8%), which is not found in recent literature.

A molecular dynamics simulation on the effect of different parameters on thermal resistance of graphene-argon interface

Molecular dynamics simulations of argon molecules confined between two parallel graphene sheets are carried out to investigate the parameters affecting heat transfer and thermal properties. These parameters include wall–fluid interaction strength, fluid density and wall temperature. For constant wall temperature simulations, we show that the first two parameters have influence on near-wall fluid density. As a result, the heat transfer at wall–fluid interfaces and thus through argon molecules across the domain will change. Also, we demonstrate that variations in wall temperature rarely affects the density profiles of argon molecules next to the walls. Therefore, in these cases, the variations in thermal resistance at the interface is most dominantly due to wall temperature itself. To analyse the results, the density and temperature profiles and also other parameters including heat flux and temperature gradient of bulk of argon molecules, Kapitza length and argon thermal conductivity are considered. The Kapitza length describes thermal resistance at liquid–solid interface. According to the results, increasing wall–fluid interaction strength leads to greater molecular aggregation of argon molecules near the walls and, consequently, decreasing the Kapitza length. Furthermore, higher fluid density leads to greater thermal resistance at wall–fluid interactions and therefore greater temperature jumps are observed in temperature profiles.

Prediction of thermo-physical properties of argon at cryogenic conditions using modified Benedict-Webb-Rubin equation of state

The present work aims to determine thermo-physical properties such as mass density, specific heat capacity, viscosity, enthalpy and thermal conductivity of argon at cryogenic temperatures and high pressures up to 20 MPa. The deviations from the ideal gas law led to development of many empirical models based on equation of state (EOS) such as van der Waals EOS, Benedict-Webb-Rubin (BWR) EOS, Peng-Robinson EOS, Soave-Redlich- Kwong, etc. to predict the properties of pure substances. The present paper describes the development of a simple computer program in MATLAB for prediction of the properties using Modified Benedict-Webb-Rubin (MBWR) equation of state.

Thermal conductivity of argon at high pressure from first principles calculations

We present calculations of the thermal conductivity of fcc Argon at high pressures (pressure range is 10–150 GPa, temperatures range is 400–1200 K) from first principles in the framework of density functional theory and solution of the Boltzmann Transport Equation. Local density approximation (LDA) and generalized gradient approximation (GGA) produce similar thermal conductivities, with differences accounted by the known overbinding and underbinding of the LDA and GGA, correspondingly. Thermal conductivities at all considered pressures and temperatures are found to be consistent with the results of previous molecular dynamics simulations based on classical 2-body potentials. However, they are not consistent with recent experimental findings. Possible reasons for this disagreement are discussed. In addition, in light of our calculations, we critically examine analytically tractable approximations for thermal conductivity as applied to solid argon.

Argon used as dry suit insulation gas for cold-water diving

BackgroundCold-water diving requires good thermal insulation because hypothermia is a serious risk. Water conducts heat more efficiently compared to air. To stay warm during a dive, the choice of thermal protection should be based on physical activity, the temperature of the water, and the duration of exposure. A dry suit, a diving suit filled with gas, is the most common diving suit in cold water. Air is the traditional dry suit inflation gas, whereas the thermal conductivity of argon is approximately 32% lower compared to that of air. This study evaluates the benefits of argon, compared to air, as a thermal insulation gas for a dry suit during a 1-h cold-water dive by divers of the Royal Netherlands Navy.MethodsSeven male Special Forces divers made (in total) 19 dives in a diving basin with water at 13°C at a depth of 3 m for 1 h in upright position. A rubber dry suit and woollen undergarment were used with either argon (n = 13) or air (n = 6) (blinded to the divers) as suit inflation gas. Core temperature was measured with a radio pill during the dive. Before, halfway, and after the dive, subjective thermal comfort was recorded using a thermal comfort score.ResultsNo diver had to abort the test due to cold. No differences in core temperature and thermal comfort score were found between the two groups. Core temperature remained unchanged during the dives. Thermal comfort score showed a significant decrease in both groups after a 60-min dive compared to baseline.ConclusionsIn these tests the combination of the dry suit and undergarment was sufficient to maintain core temperature and thermal comfort for a dive of 1 h in water at 13°C. The use of argon as a suit inflation gas had no added value for thermal insulation compared to air for these dives.

Thermal conductivity of argon at high pressures and high temperatures

Knowledge of the thermal conductivity of Ar under conditions of high pressures and temperatures (P-T) is important for model calculations of heat transfer in the laser heated diamond anvil cell (DAC) as it is commonly used as a pressure transmitting medium and for thermal insulation. We used a modified transient heating technique utilizing microsecond laser pulses in a symmetric DAC to determine the P-T dependent thermal conductivity of solid Ar up to 50 GPa and 2500 K. The temperature dependent thermal conductivity of Ar was obtained by fitting the results of finite element calculations to the experimentally determined time dependent temperature of a thin Ir foil surrounded by Ar. Our data for the thermal conductivity of Ar are larger than that theoretically calculated using the Green-Kubo formalism, but they agree well with those based on kinetic theory. These results are important for ongoing studies of the thermal transport properties of minerals at pressures and temperatures native to the mantle and core.

Molecular dynamics simulation of thermal conductivity of an argon liquid layer confined in nanospace

Molecular dynamics simulations were used to study the thermal conductivity of liquid argon ultra thin films confined between two plates spaced several nanometres apart. The research focused on the dependence of the liquid argon thermal conductivity on the liquid layer thickness and the interaction between liquid and solid. The results show that the thermal conductivity of liquid argon ultra thin films confined between two plates depends on the distance between the two plates and the existence of solid-like liquid layering at the liquid–solid interface and the average migration frequency of all liquid molecules. Stronger interactions between the liquid and the solid resulted in a larger number of atoms in the solid-like liquid layer along the surface and hence smaller thermal resistance between the liquid and the solid. However, as the strength of the interaction with the solid increased, the thermal conductivity was reduced due to fewer atoms near the hot solid boundary and less molecular migration.

Determination of potential energy functions of argon, krypton, and xenon via the inversion of reduced-viscosity collision integrals at zero pressure

The pair potential energy functions of argon, krypton, and xenon have been determined via the inversion of reduced-viscosity collision integrals at zero pressure. A comparison of the potentials with the previously determined potentials are included. The viscosity and thermal conductivity of argon, krypton, and xenon at different temperatures and pressures have been calculated and compared with experimental values. The present potentials for argon, krypton, and xenon provide a good overall account of the experimental properties of these compounds, considering the stated uncertainty in the measurements.Key words: potential energy function, collision integral, viscosity, thermal conductivity.

Contributions of the Van der Waals Laboratory to the Knowledge of Transport Properties of Fluids

After the presentation of Enskog's theory of the transport phenomena at high densities in 1922, one of the aims of the Van der Waals Laboratory was to check this theory with accurate experimental results. As early as 1931, Michels and Gibson published data on the viscosity of nitrogen taken by means of the Van der Waals vertical-capillary viscometer. In 1952, Michels and Botzen presented thermal-conductivity measurements on nitrogen taken by means of the parallel-plate heat-conductivity apparatus. Finally, in 1968 Trappeniers and Oosting presented data on the self-diffusion coefficient of methane obtained with a nuclear magnetic resonance spin-echo spectrometer. In all of these cases agreement with either the Enskog theory or the modified Enskog theory was not obtained. In 1973 Trappeniers and J. Michels showed that the self-diffusion coefficient of krypton obtained with a tracer method deviates from Enskog theory due to the formation of clusters. Measurements of the thermal conductivity of argon in 1955 motivated a study of transport phenomena of fluids in the critical region. This resulted, in 1962, in the first proof of the existence of a rather strong divergence in the thermal conductivity of carbon dioxide, by Michels, Sengers, and Van der Gulik. In 1978 Offringa showed that the viscosity has only a small critical anomaly, while Oosting showed as early as 1968 that, for selfdiffusion, such an anomaly could not be detected. In 1991 Mostert, and in 1996 Sakonidou, showed that the anomaly in the thermal conductivity is finite in mixtures near the vapor–liquid critical line. In the 1970s a vibrating-wire viscometer suited for measuring the viscosity near the melting line of simple gases was developed to check predictions by computer simulations of the viscosity of hard spheres. From the comparisons, it could be concluded that in the density range from the critical density up to twice this density, a special version of the hard-sphere Enskog theory describes the measurements within the experimental accuracy. With this result it was possible to describe the viscosity in the low-density range, up to the critical density, by a model of a gradual transition from intercluster transport described by the Chapman–Enskog theory to intracluster transport described by the hard-sphere Enskog theory, a model inspired by J. Michels' conclusion that the formation of clusters influences the transport properties.

The thermal conductivity of argon, carbon dioxide and nitrous oxide

The paper presents new, absolute measurements of the thermal conductivity of three gases: argon (Ar), carbon dioxide (CO 2) and nitrous oxide (N 2O). The measurements have been carried out with a transient hot-wire instrument in the temperature range 308 to 430 K and at pressures up to 11 MPa. For most of the range of thermodynamic states covered by the measurements it is estimated that the accuracy of the thermal conductivity data is one of ±0.3%. However, for carbon dioxide and nitrous oxide near their critical conditions the accuracy is degraded and the uncertainty may be as much as ±2%. The new experimental data for argon confirm the accuracy claimed for the thermal conductivity in the limit of zero-density. The thermal conductivity of the polyatomic gases in the limit of zero-density is used in conjunction with information on other transport cross-sections for the same systems, to extract a consistent set of cross-sections sensitive to the anisotropy of the intermolecular pair potential for use in the testing of proposed potential surfaces. Cross-sections for both of the available formulations of the thermal conductivity of a polyatomic gas due to Wang Chang and Uhlenbeck and Thijsse et al. are derived. For both gases it is shown that the Mason-Monchick approximation breaks down in either formulation. However, the effect of the failure on the formulation of Thijsse et al. is smaller and it is possible to represent the data with the aid of a single cross-section which has a very simple temperature dependence. The analysis also demonstrates that all available high-temperature thermal conductivity data for carbon dioxide are in substantial error. In the moderately dense gas the concept of a temperature-independent excess thermal conductivity is confirmed to a high degree of precision for carbon dioxide and argon when due allowance is made for the critical enhancement. A generalized correlation of the temperature dependence of the first density coefficient of thermal conductivity is broadly confirmed.

Accurate thermal conductivity coefficients for argon based on a state-of-the-art interatomic potential

An accurate interatomic potential was constructed by fitting a realistic function, constrained by theory, to a set of judiciously selected macroscopic and microscopic properties but not including thermal conductivity. Using this potential, accurate values of thermal conductivity of argon are obtained for the temperature range 100 to 6600 K. These are presented in tabular form as well as in terms of a correlation function.

Thermal conductivity of argon in the temperature range 107 to 423 K

The thermal conductivity of argon between 107 and 425 K has been measured in a transient hot-wire instrument. The results in the limit zero density have been employed to assess the accuracy of the instrument using exact kinetic theory expressions and has been found to be better than ±0.5%. The data at elevated densities are employed to examine the applicability of the modified Enskog theory in the gaseous phase and the hard-sphere theory in the liquid phase.

Thermal conductivity of argon, nitrogen and carbon dioxide at elevated temperatures and pressures

The transient hot-wire technique has been used to measure the thermal conductivity of argon at 427 and 470 K, nitrogen at 430 K and carbon dioxide at 380, 430 and 470 K at various pressures, the maximum being 30 MPa. The argon results served to test the apparatus, which has been adapted to operate at these higher temperatures. The low-density limits for the argon thermal conductivities were found to be consistent with published viscosity values. The density dependence of the thermal conductivity of argon was found at both temperatures to be equal, within experimental uncertainties, to that observed at lower temperatures. The results for nitrogen were compared with earlier results and the low-density limit gave an Eucken factor consistent with previous trends. The results for carbon dioxide are compared with previous measurements made at low densities by other techniques and with a theoretically predicted surface for the thermal conductivity of carbon dioxide in the region of the critical point.

The effects of thermal diffusion of nitrogen gas on silicon nitridation rate

Recently Mangels [1] has reported that a more complete nitridation and generally higher nitriding rate were obtained by using the variable atmosphere in the nitrogen-demand nitriding runs and explained this behaviour with improved nitridation by decreasing nitrogen partial pressure, which was noted earlier by Atkinson et al. [2] who found that, using an isothermal nitriding run, a more complete nitridation was obtained with reduced nitrogen partial pressures. Present attention is drawn with these results to the higher nitriding rates and more complete nitridation obtained by using helium compared with those obtained by using other gases as the variable atmosphere. For example, the variable helium atmosphere (4% H2, 50% He, balance N 2 in the final gas composition) had the highest nitriding rate (34.6 g Si per hour) and this nitriding rate is higher than that (27 g Si per hour) of the variable argon atmosphere (4% H2, 50% Ar, balance N2 in final gas composition), moreover, even the constant helium atmosphere (7% He/N2) had the nitriding rate (28.69g Si per hour) surprisingly higher than only that (17.6 g Si per hour) of the variable hydrogen (25% H2/N2 in final composition) and also higher than that of the variable argon atmospheres. Since the higher the reaction temperature the higher the reaction rate becomes, the presence of low thermal conductivity gases in the nitriding atmosphere increases the reaction rate more than the presence of high thermal conductivity gases do due to the retardation of heat dissipation generated by the exothermic reaction. However, argon's thermal conductivity is less than nitrogen's and that of hydrogen and helium are greater than that of nitrogen and helinm which are slightly less than hydrogen's. Therefore, these can explain the formation of RBSN with a uniform microstructure but cannot explain the reason for an increase in the nitridation rates by using helium. Moreover, hydrogen has the function of aiding the removal of the reaction-inhibiting silica film but helium has not. On the other hand, this can be explained if more reduced partial pressure of nitrogen around the silicon compact is obtained with additions of helium as compared with other gases. In order to solve this question, we are studying the effect that the thermal segregations by the Soret effect [3]; inside a nitriding furnace containing the various binary gas mixtures, have on the nitridation rate and some brief preliminary results are described here . Diffusion is most frequently associated with a nonuniform ~ composition, but it can also arise from a nonuniform temperature. Enskog and Chapman [4], independently developed the kinetic theory of gases in nonuniform states, and showed that in general a temperature gradient should cause diffusion. Therefore, because of thermal diffusion known as Soret effect, when a temperature gradient is set up in a mixture which is initially uniform in composition, a concentration gradient develops, and this increses until the separating effect of thermal diffusion is balanced by the diffusion which tends to equalize composition. In gas mixtures at normal temperatures, the heavier molecules usually diffuse down the temperature gradient, leading to a higher concentration in the colder region rather than the warmer one. Accordingly, when the nitridation of silicon is performed in a closed tube or cold wall furnace which contains the nitriding atmosphere of the binary gas mixture, in N2-H2 and N2-He mixtures, the nitrogen gas migrates to the cold region and hydrogen or helium gas to the hot region, leading to a lower concentration of nitrogen gas in the hot region than the cold region, whereas in N2-Ar mixtures the nitrogen gas migrates to the hot region and argon gas to the cold region, leading to a higher concentration of nitrogen gas in the hot region than in the cold region.

ChemInform Abstract: THERMAL CONDUCTIVITIES OF ARGON, NITROGEN, AND HYDROGEN BETWEEN 300 AND 400 K AND UP TO 25 MPA

AbstractMessungen der Wärmeleitfähigkeiten mit Hilfe einer Hitzdraht‐Transientmethode bei 3 Temp. zwischen 300 und 400 K und einer Reihe von Drücken bis 17 MPa für Ar und bis 25 MPa für N, und H, liefern akkurate Werte für die Niederdruckgrenze der Wärmeleitfähigkeit, die mit theoretischen Bestimmungen verglichen werden.

Thermal conductivities of argon, nitrogen and hydrogen between 300 and 400 K and up to 25 MPa

The thermal conductivities of argon, nitrogen and hydrogen have been measured using an apparatus of the transient hot-wire type at three temperatures between 300 and 400 K and at a number of pressures up to 17 MPa for argon and 25 MPa for nitrogen and hydrogen. The results give accurate values for the low-pressure limit of the thermal conductivity and these are compared with theoretical estimates. For argon they are close to the values predicted by rigorous kinetic theory and for hydrogen close to the values predicted by the modified Eucken equation. For nitrogen the new experimental values are below those predicted by the Mason–Monchick equation and well below those predicted by the equation of Viehland, Mason and Sandler, which takes spin polarisation into account. The experimental results also show that the variation of thermal conductivity with density of a particular gas shows very little change with temperature over the range studied.

Isochoric thermal conductivity of argon, krypton, xenon, and nitrogen as a function of the triple points up to 300?330�K at pressures of up to 3000 atm

We investigate the isochoric thermal conductivity of Ar, Kr, Xe, and N2, and, in the critical region, we estimate the critical indicators of thermal conductivity. The experimental results are compared with conclusions drawn from the kinetic theory.

Thermal conductivity of argon, krypton and their mixtures at low temperatures (90-270 k)

Experimental thermal conductivity values of argon, krypton and their mixtures have been measured at 1 atm (101.325 kN/m 2) in a specially designed hot-wire cell in the temperature range 90-270 K. These values are compared with the recommended values based on available data for pure systems, and with the predictions of kinetic theory based on L-J (12-6), exp-six and (11-6-8) potentials. Combination rules for predicting the interaction parameters for unlike molecules from the knowledge of parameters for like molecules have been derived for (11-6-8) potential. Two variants of the procedures based on Sutherland-Wassiljewa expressions have also been examined for mixtures.

Thermal conductivity of argon and argon-neon mixtures at high temperature

The thermal conductivity of neon and argon-neon mixtures is studied in the temperature range 400–1500°K. This is the first recording of such data above 793°K.