Calculation of thermophysical properties for CO2 gas using an ab initio potential model

The density, isochoric heat capacity, shear viscosity and thermal conductivity of CO₂ gas in the pressure range of 1–50 atm and 300 K are calculated based on a five-centre potential model obtained from ab initio calculations of the intermolecular potential of a CO₂ dimer. The quantum effects of the intramolecular motion are included in a model by the Monte Carlo (MC) Method. Without using any experimental data, the present model achieves excellent agreements between the calculated thermophysical properties and experimental data for all simulated CO₂ densities except the highest one at 135 kg/m³ (3 mol/L). The contributions of potential to the thermophysical properties of the moderate dense CO₂ gas and their dependence on density are investigated in detail.     

Thermodynamics properties and thermal conductivity of Mg2Pb at high pressure

The thermodynamics properties and thermal conductivity of Mg2Pb at high pressures have been calculated by first-principles.The enthalpy of formation and heat capacity obtained at 0 GPa are in good agreement with the experiments and other theoretical results.The thermal conductivity and coefficient of thermal expansion of Mg2 Pb at high pressure were evaluated.The thermal conductivity presents a second-order polynomial with pressure.The calculated thermal conductivity of Mg2Pb indicates that it is suitable to be used as thermal conductor at 0 K.     

Transport properties of a binary mixture of CO2ben N2 from the pair potential energy functions based on a semi-empirical inversion method

The potential energy surface of a CO₂-N₂ mixture is determined by using an inversion method, together with a new collision integral correlation [J. Phys. Chem. Ref. Data 19 1179 (1990)]. With the new invert potential, the transport properties of CO₂-N₂ mixture are presented in a temperature range from 273.15 K to 3273.15 K at low density by employing the Chapman-Enskog scheme and the Wang Chang-Uhlenbeck-de Boer theory, consisting of a viscosity coefficient, a thermal conductivity coefficient, a binary diffusion coefficient, and a thermal diffusion factor. The accuracy of the predicted results is estimated to be 2% for viscosity, 5% for thermal conductivity, and 10% for binary diffusion coefficient.     

Vibrational Raman scattering temperature measurements

Experimental data and analyses are presented for the determination of gas temperature by measurements of vibrational Raman scattering intensity ratios of Stokes Q-branch fundamental bands. The method is demonstrated for two thermal equilibrium experiments: (1) CO₂ (a gas well-suited for use in multi-component mixtures near ambient temperatures) in a test cell, and (2) N₂ (a gas well-suited for use at elevated temperatures) in a flame. This method of temperature measurement is of particular value for non-thermal equilibrium conditions, for which vibrational excitation temperatures can be assigned to each pair of vibrational level corresponding to observable Raman bands.     

Interferometric determination of the dispersion of vibrational polarizability and the integrated intensities of fundamental bands of 32, 34SF6 and NF3 molecules

The refractivity of gaseous SF₆ and NH₃ in the region of the intense absorption bands of these compounds was measured by two-beam, two-color interferometry using a He-Ne laser and a CO₂ laser tunable throughout its emission lines. Quantitative data on the profiles of the absorption bands of these gases were also obtained by IR Fourier spectroscopy. By using the joint processing of the results of refractometric and spectral measurements on the basis of the Kramers-Krönig formalism, the dispersion dependences of the vibrational polarizabilities of the given molecules were calculated and the integrated intensities of their fundamental vibrational bands were refined. A table of values of total and vibrational polarizabilities at the emission frequencies of the CO₂ laser was compiled.     

Kinetic modelling of electrooptically Q-switched CO2 laser

In this paper, a six-temperature model for CO₂ lasers is used to describe the process of the dynamic emission in the electrooptically Q-switched laser. The dissociation of CO₂ molecules, the electron excitation and the energy-transfer of vibrational levels and the rotational relaxation of rotational levels are involved. The calculated pulse waveforms are in good agreement with the experiment.     

Thermal conductivity of fluids with steeply repulsive potentials

We consider the thermal conductivity of steeply repulsive inverse power fluids (SRP) in which the particles interact with a pair potential, φ(r) = ε(σ/r)ⁿ. The time correlation function for the heat flux, C_λ(t), and the time average, C_λ(0) are calculated numerically by molecular dynamics simulations, and accurate expressions for these are also derived for the SRP fluid. We show, by molecular dynamics simulations, that close to the hard-sphere limit this time correlation function has the same analytic form as for the shear and pressure correlation functions for the shear and bulk viscosity, i.e. C_λ(t)/C_λ(0) = 1 ?T* (nt*)² + 0((nt*)⁴), where T* = k _B T/ε, is the reduced temperature, k _B is Boltzmann's constant and t* = (ε/σ²)^1/2 t is the reduced time. The thermal conductivity for the limiting case of hard spheres is numerically very close to that given by the traditional Enskog relation. At low densities the normalized relaxation times are typically largest for the thermal conductivity, followed by shear and then bulk viscosity. Close to the maximum fluid density, the latter two increase rapidly with density (especially for the shear) but continue a monotonic decline for the thermal conductivity. This reflects the relative insensitivity of the thermal conductivity to the approach to the fluid-solid phase boundary.     

Electron Energy Distribution Functions in CO2 Laser Mixture: The Effects of Second Kind Collisions from Metastable Electronic States

Electron energy distribution functions (eedf) in CO₂ laser discharge (He—CO₂—N₂—CO mixture) have been calculated by solving the Boltzmann equation in the presence of given concentrations of excited (vibrational and electronic) states. The results show a well structured eedf as a result of second kind collisions coming from metastable electronic states of N₂ and He as well as a strong dependence of rate coefficients for CO₂ dissociation and for the ionization of the different species.     

Prediction of the thermal properties of CO2, CO, and Xe laser media

Approximation functions describing the experimental data of thermal conductivity and viscosity of chosen gases (CO₂, N₂, He, Xe, CO, O₂, Ar) are given in the paper. Introduced formulas allow to predict thermal conductivity and temperature distribution of typical high-power laser gas mixture. Examples of temperature distribution in RF excited CO₂, CO, and Xe laser media are shown. Knowledge of the temperature distribution in the laser cavity can be useful for predicting the general properties of laser.     

Quenching of infrared emission from CO2 by near-resonant vibrational interactions with SF6, BCl3, and PF5

The transfer of substantial amounts of vibrational energy from CO₂ to specific complex molecules has been observed in flow-tube experiments by monitoring the spectra from the 4·3 μm fundamental bands and the 2·7 μm mixed-mode Fermi-resonance bands of CO₂. Small amounts of SF₆, BCl₃, and PF₅ were found to reduce the intensities of these emissions significantly. Quenching cross-sections were calculated using a non-equilibrium analysis.     

An accurate expression of the CO2 refractivity from the radiofrequencies to the visible region

The refractivity around an absorption band is related to the strength of the band absorption. In this work this relation is used to derive the CO₂ vibrational band strengths from the accurate measurements of the refractivity and to accurately represent with a simple expression the refractivity behaviour of CO₂ from the visible to the microwave region.     

Thermal blooming in gases

The absorption of light and subsequent thermalisation of the absorbed energy can be significantly affected by the presence of non-equilibrium population distributions in gases. The phenomenon of thermal blooming in gases is discussed from this standpoint. It is shown that a transient phenomenon of absorption cooling can occur, leading to a focusing rather than defocusing of an incident laser beam. Flux densities causing saturation in air and pure CO₂ are calculated. For vibrational saturation in air, I > 3.66 kw/cm², for pure CO₂, I > 4.58 kw/cm². For rotational saturation, in either gas, I > 840 kw/cm².     

Efficiencies of third bodies in the reaction H + O2 + M = HO2 + M

Vibrational transition probabilities have been calculated by the Schwartz, Slawsky and Herzfeld method [3] for the deactivation of HO₂* in collision with H₂, O₂ and CO₂. The relative efficiencies of H₂, O₂ and CO₂ are compared with their third-body efficiencies found experimentally and it is concluded that the transfer of large vibrational quanta from HO₂* is unlikely to play an important part in determining the position of the second explosion limit of the H₂/O₂ reaction. This conclusion is at variance with the explanation put forward by Walsh [1] of the ‘anomalous’ third-body efficiencies of H₂O and CO₂ in this reaction.     

A numerical simulation of machining glass by dual CO2-laser beams

In the flat panel display (FPD) industry, lasers may be used to cut glass plates. In order to reduce the possibility of fracture in the process of cutting glass by lasers, the thermal stress has to be less than the critical rupture strength. In this paper, a dual-laser-beam method is proposed, where an off-focus CO₂-laser beam was used to preheat the glass sample to reduce the thermal gradients and a focused CO₂-laser beam was used to machine the glass. The distribution of the thermal stress and the temperature was simulated by using finite element analysis software, Ansys. The thermal stress was studied both when the glass sample was machined by a single CO₂-laser beam and by dual CO₂-laser beams. It was concluded that the thermal stress can be reduced by means of the dual-laser-beam method.     

Concentration-dependent depolarized Raman spectra of HCl and DCl in solution in liquid carbon dioxide

The depolarized component of Paman scattering by pure liquid HCl and DCl and of solutions of these acid halides in liquid CO₂ are reported. At room temperature the band contours show no S branch intensity in pure acid halide liquid, but in solution in liquid CO₂ and S branch is increasingly evident with increasing CO₂ concentration. The frequency shifts are a function of the dielectric constant and refractive index of the solution. Reorientational correlation functions calculated from the anisotropic scattering decay more slowly in the first few tens of femtoseconds than predicted for monomeric acid halides, suggesting contribution to the composite correlation function by species of larger moments of inertia but vibrational frequencies identical with those of the monomers.     

Heat transfer in the high-temperature phase of solid SF<Subscript>6</Subscript>

The temperature dependences of the thermal conductivity are calculated for solid SF₆ and Xe. The influence of thermal pressure in a crystal on the isochoric thermal conductivity is investigated. The contributions of the phonon-phonon and phonon-rotation interactions to the total thermal resistance of solid SF₆ are calculated using a modified method of reduced coordinates. The temperature dependence of the isochoric thermal conductivity of SF₆ is explained by a combined effect of thermal pressure and phonon-rotation interaction.     

Vibrational kinetics of the active media of CW CO<Subscript>2</Subscript> lasers

The vibrational kinetics of CW CO₂ lasers has been analyzed within the framework of a temperature model. The necessity of taking into account the coupling of the vibrational modes of the CO₂ molecule in determining the occupation numbers and the store of vibrational energy in individual modes is shown. Expressions that connect vibrational temperatures with the rates of excitation and relaxation of the lower vibrational levels of modes have been obtained. The ratios between the vibrational temperatures on selective excitation of the 00° 1 level and on excitation of CO₂ molecules in an electric discharge as well as the character of the dependences of vibrational temperatures on the pumping-energy value are discussed.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 72–79, January–February, 2005.     

Electronic structure,optical properties,and phonon transport in Janus monolayer PtSSe via first-principles study

Motivated by the synthesis of a Janus monolayer, the new PtSSe transition-metal dichalcogenide (TMD) have attracted remarkable attention due to their characteristic properties. In this work, we calculated the electronic structure, optical properties, and the thermal conductivity of the PtSSe monolayers, and performed a detailed comparison with other TMDs (monolayer PtS₂ and PtSe₂) using first-principles calculations. The calculated band gaps of the PtS₂, PtSSe, and PtSe₂ monolayers were 1.76, 1.38, and 1.21?eV, respectively, which are in good agreement with experimental data. At the same time, we observed a larger spin-orbit splitting in the electronic structure of PtSSe monolayers. The optical properties were also calculated and a significant red shift was observed from the PtS₂ to PtSSe to PtSe₂ monolayers. The lattice thermal conductivity of the PtSSe monolayer at room temperature (36.19?W/mK) is significantly lower than that of the PtS₂ monolayer (54.25?W/mK) and higher than that of the PtSe₂ monolayer (18.07?W/mK). Our results show that the PtSSe monolayer breaks structural symmetry and has the same ability to reduce the thermal conductivity as MoSSe and ZrSSe monolayers due to the shorter group velocity and the lower converged phonon scattering rate. These results may stimulate further studies on the electronic structure, optical properties, and thermal conductivity of the PtSSe monolayer in both experimental synthesis and theoretical efforts.     

Simulation of characteristics of optical gas sensors based on diode optopairs operating in the mid-IR spectral range

An analytic model is proposed for an optical gas sensor based on diode optopairs, which takes into account the line spectral structure of gases being analyzed, as well as peculiarities of spectral characteristics of immersion-type light-emitting diodes and photodiodes operating in the mid-IR spectral range. The model makes it possible to calculate the transfer characteristic of the sensor and to estimate the measurement error for gas analyzers operating on the basis of these sensors. The experiments demonstrate bright prospects of application of sensors based on immersion-type diode optopairs in small-size gas analyzers; the expected values of the threshold sensitivity of a CO₂ sensor at a level of 10 ppm and the absolute error of measurements below 0.1% (reduced error is 1%) in a range of up to 10 vol % at a speed of up to 10 counts per second exceed the parameters of available portable CO₂ gas analyzers. The validity of the model is confirmed by conformity between the calculated data and the experimental results obtained on a prototype of a CO₂ diode sensor.     

Relating phase transition heat capacity to thermal conductivity and effusivity in Cu2Se

Accurate measurement of thermal conductivity is essential to determine the thermoelectric figure‐of‐merit, zT. Near the phase transition of Cu₂Se at 410 K, the transport properties change rapidly with temperature, and there is a concurrent peak in measured heat capacity from differential scanning calorimetry (DSC). Interpreting the origin as a broad increase in heat capacity or as a transient resulted in a three‐fold difference in the reported zT in two recent publications. To resolve this discrepancy, thermal effusivity was deduced from thermal conductivity and diffusivity measurements via the transient plane source (TPS) method and compared with that calculated from thermal diffusivity and the two interpretations of the DSC data for heat capacity. The comparison shows that the DSC measurement gave the heat capacity relevant for calculation of the thermal conductivity of Cu₂Se. The thermal conductivity calculated this way follows the electronic contribution to thermal conductivity closely, and hence the main cause of the zT peak is concluded to be the enhanced Seebeck coefficient. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)