Conductivity Of Carbon Dioxide Research Articles

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.

Acid-base and respiratory responses to hypoxia in the grasshopper Schistocerca americana.

How do quiescent insects maintain constant rates of oxygen consumption at ambient PO2 values as low as 2-5 kPa? To address this question, we examined the response of the American locust Schistocerca americana to hypoxia by measuring the effect of decreasing ambient PO2 on haemolymph acid-base status, tracheal PCO2 and CO2 emission. We also tested the effect of hypoxia on convective ventilation using a new optical technique which measured the changes in abdominal volume during ventilation. Hypoxia caused a progressive increase in haemolymph pH and a decrease in haemolymph PCO2. A Davenport analysis suggests that hypoxia is accompanied by a net transfer of base to the haemolymph, perhaps as a result of intracellular pH regulation. Hypoxia caused a progressive increase in convective ventilation which was mostly attributable to a rise in ventilatory frequency. Carbon dioxide conductance ( micromol h-1 kPa-1) across the spiracles increased more than threefold, while conductance between the haemolymph and primary trachea nearly doubled in 2 kPa O2 relative to room air. The rise in trans-spiracular conductance is completely attributable to the elevations in convective ventilation. The rise in tracheal conductance in response to hypoxia may reflect the removal of fluid from the tracheoles described by Wigglesworth. The low critical PO2 of quiescent insects can be attributed (1) to their relatively low resting metabolic rates, (2) to the possession of tracheal systems adapted for the exchange of gases at much higher rates during activity and (3) to the ability of insects to rapidly modulate tracheal conductance.

Ab initio Calculation of Transport Properties of Supercritical Carbon Dioxide

Self diffusion, shear viscosity and thermal conductivity of carbon dioxide are determined fully ab initio using two different intermolecular potential energy surfaces. These properties are calculated using the time-correlation formalism in classical equilibrium molecular dynamics simulations. The self diffusion constant is in addition determined from the Einstein relation. For the shear viscosity we use two different models of momentum localization: at the center of mass of the molecules, or at each atom. For the thermal conductivity we apply the formulae for rigid and flexible molecules assuming energy localization at the center of mass of the molecules. The results obtained are in good agreement with experiment. A fully ab initio calculation of transport properties allows for a prediction of these quantities even at state points where experiments are hardly possible.

Nonequilibrium molecular dynamics study of molecular contributions to the thermal conductivity of carbon dioxide

We calculate the thermal conductivity of supercritical and liquid carbon dioxide using a recently developed nonequilibrium molecular dynamics (NEMD) algorithm for molecular fluids. We evaluate the translational, rotational, potential energy and force contributions to the heat flux separately. We find that at high density both the rotational contribution for a nonspherical molecule and the contribution from the total force acting on the molecule are important for predicting the thermal conductivity accurately. The NEMD results for the thermal conductivity agree well with experimental data. At a near critical state point, we observed a phase separation induced by the fictitious external field. The contribution to the thermal conductivity from the Lennard-Jones potential energy becomes important at this state point.

Thermal conductivity and effective diffusion coefficient for vibrational energy: carbon dioxide (350-2000K)

The thermal conductivity of carbon dioxide is measured from continuum heat transfer measurements in a carefully designed column in the temperature range 350 to 2000K and with an estimated maximum uncertainty of about 2%. The data are correlated with the following cubic polynomial in temperature, T: k(T)=-10.280+0.0942T-0.1937*10-4T2+0.2619 *10-8T3. Here k is in mW m-1K-1 and T in K. The conductivity values are compared with the other available data and with the predictions of various theories developed for polyatomic gas systems. The conductivity data are also employed in conjunction with theory to compute the effective diffusion coefficient for the transport of vibrational energy as a function of temperature.