Vol 56, No 3 (2018)

In this paper, the first and second-law analysis for the thermodynamic air-standard Atkinson cycle with an account for heat transfer is performed using finite-time thermodynamics. In order to have more accurate evaluations, the effects of thermodynamic and design key parameters on the performance characteristics of Atkinson cycle are shown. Further, artificial neural network and imperialist competition algorithm are employed to predict and optimize the net work output value versus the minimum cycle temperature and also the compression ratio. The results obtained show that the heat loss is an effective factor of the performance of the cycle and it should be considered in the analysis and comparison of practical internal combustion engines.

The problem of the determination of sufficient conditions for the existence of the optimal thickness of an anisotropic wall, one of whose surfaces of is exposed to axisymmetric stationary heat flux with the intensity of the Gaussian type, while the other is cooled by the external medium with a constant temperature, was formulated and solved using the two-dimensional exponential integral Fourier transform. The requirement for minimization of the temperature of the most heated point of object of study was used as an optimality criterion. The sufficient condition that was obtained is an inequality that establishes the link between the thermophysical characteristics of the anisotropic material of a wall, the intensity of heat transfer on its cooled surface, and the factor of the concentration of the outer heat flux. These results confirm the well-known effect of the “drift” of the temperature field in an anisotropic material with the common type of anisotropy of its properties.

Experiments on heat transfer in subsonic jets of dissociated nitrogen have been carried out on a IPG-4 induction plasmatron. The heat fluxes to copper, stainless steel, nickel, graphite, and quartz surfaces at the stagnation point of a water-cooled cylindrical flat-faced model 20 mm in diameter and dynamic pressures have been measured at a pressure of 50 hPa in the test chamber and a power of 35–65 kW of the HF generator. The experiments showed the influence of surface catalytic properties on the heat flux in relation to the nitrogen atom recombination. In the conditions of the experiments, a numerical simulation of nitrogen plasma flows in the discharge channel of plasmatron and the subsonic dissociated nitrogen jet flow around the cylindrical model has been carried out. The experimental and calculated data on heat fluxes to cooled copper, stainless steel, nickel, graphite, and quartz surfaces are compared. The quantitative catalyticity scale of the studied materials in relation to the heterogeneous recombination of nitrogen atoms is established.

The effect the flow swirl parameter on heat transfer in a gas-droplet flow is numerically modeled by the Euler approach. The gaseous phase is described by a system of 3D RANS equations with consideration of the back effect of particles on transfer processes in the carrier phase. The gaseous phase turbulence is calculated according to the Reynolds stress transport model with consideration of the dispersed phase effect on the turbulent characteristics. A rapid dispersion of droplets over the pipe cross section is observed in a nonswirling gas-droplet flow downstream of an abrupt pipe expansion. A swirling flow is characterized by a growing concentration of fine particles at the pipe axis due to the accumulation of particles in the zone of flow recirculation and to the turbophoresis force. In a swirling flow, the separated-flow region becomes significantly shorter (by almost a factor of two as compared to that in a nonswirling flow). It is shown that addition of droplets results in a significant growth of heat transfer intensity (by more than a factor of 2.5) in comparison with single-phase swirling flow.

The differential equations of heat conduction of a solid body, which are a consequence of the Fourier, Cattaneo–Vernotte, and Lykov’s equations, are considered. A mathematical model of the transient, three-period process in a circular plate is constructed in the form of a solution to the hyperbolic boundary value problem of heat conduction with boundary conditions of the third kind. The method to determine the Bio numbers in each period of the transition process and the time of thermal relaxation is described by the results of experimental and theoretical studies of transient thermal processes in the center of round plates of different thicknesses made of polymethylmethacrylate upon their sudden immersion in hot water.

The temperature dependence of the specific heat, C_p, is analyzed for different percentages of ruthenium (Ru) content in LiKSO₄ using a power-law formula deduced from Ising model. For this analysis, data observed are taken from the literature and the values of the critical exponent for C_p are extracted in the vicinity of the transition temperature (T_c = 708 K) within the incommensurate phase of Ru doped LiKSO₄. Obtained values of the critical exponent of C_p confirm in most cases above and below C_p the critical exponent value predicted by the 3D Ising model for the doped LiKSO₄. On this basis, the specific heat, C_p, of some other molecular crystals can also be analyzed using the same power-law formula as studied here.

A numerical study is made of the structure of a swirling argon flow with atmospheric pressure in a closed tube duct with an asymmetric gas outlet, a localized heat source simulating gas heating by a longitudinal pulse repetitive HF discharge, and the source of an acoustic field simulating sound generation by discharge pulses. It is shown that, at supercritical amplitudes of the acoustic field, helical gas-dynamic and thermal flows capable of inducing the formation of a discharge channel with a structure that is close to the shape of a helical flow can form. The results are shown to qualitatively agree with the known experimental data.

An electric double layer in gas-discharge plasma in mercury vapor has been studied. The currentvoltage characteristic and electron energy distribution function are measured in anode plasma of an arc discharge in mercury vapor. The distribution function curves of thermal electrons have been obtained. The structure of the layers of space charges has been experimentally studied, and the relationship between the potential distribution and the electron energy distribution function with this structure was established. It is revealed that the potential in collisionless plasma exceeds the equivalent electron temperature by an order of magnitude.

The graphite electrode surface is studied after impact by an electric arc burning in an argon atmosphere at a pressure of 50 kPa. The arc occurred as a result of the local destruction of a graphite rod heated by electric current and preliminarily kept for 2 × 10³ s at a temperature of about 3 kK. After the arc discharge with a current of about 100 A with a duration within 1 s, we found drop-like particles, 0.1–0.3 mm in size, on the graphite electrode surface, which is evidence of the local occurrence of liquid carbon phase at a temperature of about 3.3 kK. With longer arc burning, the melting zone propagated over the entire working surface of the electrodes; the surface became smoothed.

A fluctuation theory is proposed in which both the regular region of the phase diagram and the region in the vicinity of the critical point are described based on the same assumptions. It was shown that the critical indices could be determined more precisely within the fluctuation theory than by the scaling concept; the critical point affects almost the entire regular region of the phase diagram; the critical isotherm is a line of singular points of the statistical sum, etc. The experimental data confirm all of these predictions of the theory.

A general particle distribution function over potential energies has been obtained. It describes well both an equilibrium system and an evaporating liquid. Near the evaporating surface itself, the distribution function is corrected to take into account the particles escape. Using the obtained distribution function over potential energies, the mass and energy fluxes on the surface of the evaporating liquid are calculated. The results of the analytical expressions are compared with numerical simulation; the coincidence is sufficiently good.

Differential-scanning calorimetry is used to study the thermophysical properties of boron carbide irradiated by the ionizing radiation from the ⁶⁰Co source. With increased temperature, the heat capacity and entropy values of nonirradiated and irradiated B₄C specimens increase. At high temperatures (723–1300 K), the character of variation of the enthalpy and the Gibbs’ potential of the irradiated B₄C specimen depends on the presence of oxygen. The values of the thermodynamic functions vary due to the formation of excited atoms, active centers, defects of the B₄C crystal structure, and B₄C oxidation in the presence of the air oxygen after the ampoule opening. Also possible is an increase, at 723–1300 K, in the rate of oxidation of the boron carbide surface (contacting with the air oxygen), where the defects that form upon irradiation are distributed. At temperatures above 723 K, melting of the oxygenated part (B₂O₃) in B⁴C specimens irradiated by the absorbed dose of 194 Gy is observed; that process continued until the transformation of ~26% of crystal structure into the amorphous phase at 1300 K.

The set-up for the measurement of the density of high-temperature melts by means of penetrating gamma-radiation is described. The modern device base, which makes it possible to automatize the work, is the main difference from the earlier existing gamma-densitometers. The key characteristics of the absolute measurements with the use of very exact values of the mass attenuation coefficient for the gamma-quanta beam are described and the accuracy of measurements is estimated. The results of the density measurement of the molten aluminum, cadmium, tin, and bismuth are presented; they confirm the a priori estimate of the error.

This article presents a comparative analysis of the efficiency of six conventional energy technologies for the production of electrical and thermal energy and three original alternative technologies developed at the Joint Institute for High Temperatures, Russian Academy of Sciences, that have been proposed for implementation. The thermal efficiency of all the of the considered options for the ratio of electric and thermal energy production typical of Russia’s average climatic conditions is compared with a unified methodology. The efficiency values of electric power generation based on heat consumption is compared for all the options. It is demonstrated that, when domestic gas turbine units are used, the efficiency of the electric energy generation of the developed technologies can significantly exceed that in the best existing energy technologies with the use of promising, imported, high-power gas turbines. These advantages can be attained not only by increasing the parameters of the working fluid but also by optimizing the structure of the thermodynamic cycle of the energy technology.