Vol 55, No 1 (2017)

By means of the flat one-sided probe, the electron velocity distribution function is investigated along with plasma parameters distribution and electrokinetic characteristics in short (without positive column) low-voltage beam discharge in helium, neon, and argon. With the pressure increase, the discharge voltage obtains the value of the excitation potential of the metastable level of the filling gas, U_m. The results of the probe measurements of the electron velocity distribution function make it possible to calculate the generation functions of the inelastic process and to make the conclusion that, at attaining the critical pressure, P_cr, when the processes of atom stepwise ionization begin to dominate over the direct ionization, the discharge burning voltage drops below the ionization potential, U_ion. Based on the performed studies, a technique and a device are proposed to stabilize the voltage within the range of 9–50 V by filling the interelectrode gap with inert gases of different excitation and ionization potentials.

The thermodynamic properties of α-phase and liquid uranium have been investigated by the method of quantum molecular dynamics. The isotherms and equilibrium properties (pressure, temperature, and internal energy) along isochores and isotherms have been calculated for densities of 16.5–41.1 g/cm³ and temperatures up to 60000 K. The dependence of the thermal pressure on temperature and internal energy is analyzed. The melting boundary of α-phase uranium is estimated. The shock adiabat is calculated for pressures up to 1.5 TPa based on the equation of state derived here. The results obtained are in good agreement with the published experimental data and the results of calculations according to different theoretical models.

The embedded atom model (EAM) potentials are proposed, enabling the description of liquid gallium and tin under conditions typical to shock compression. The potentials reported earlier to describe metals under pressures close to normal and the experimental data on shock compression are used. Series of models are constructed 2000 or 2048 atoms in size in a basic cube at compression ratios Z up to 0.5 of the initial volume under pressures up to 385 GPa and temperatures up to 32000 K. These potentials give a satisfactory description of liquid gallium and tin under shock compression. The thermodynamic properties of the metals at compression ratios up to 0.5 and temperatures up to 20000 K are calculated and given in tabular form. In the case of gallium, a small compression of models with normal density decreases the total energy at 300, 500, 15000, and 20000 K, and, for tin, this effect is observed only at 20000 K. The energy and pressure of the FCC metal models are markedly lower than those of noncrystalline models. The cold pressure for the states at temperatures between 0 and 298 K is evaluated. The EAM potential of tin leads to a lowering of the cold pressure of an FCC lattice with respect to the amorphous phase at Z < 0.75.

The problems of the humid biofuel application in the distributed energy engineering facilities are considered. Use of drying (and thermal proceeding) in energy saving makes it possible to perform efficient biofuel gasification, compensating for, in many cases, the negative influence of the moisture on the efficiency of the energy facilities. The complicated functional connection between the drying and the gasification processes as well as of the gasification product purification are analyzed. The cold purification, taken as the basic technology, reduces the efficiency of the gasification versions with the temperature above the level of the liquid slag removal; yet, if the temperature is not higher than the ash softening beginning, then this influence is insufficient. When compared, the efficiency of the STIG steam-gas facility on the humid fuel tends to be just a little lower than the dry fuel and reaches 45–49%. The calculations show that, at the low gasification temperature, we should not remove all the fuel moisture if the humidity is below 40%. The oxygen blast application in the gasifier reduces the efficiency to some extent but oxygen is necessary to accumulate the highenergy synthetic gas, in particular, for the peak or the exterior application.

The paper presents a mathematical model of power-engineering complex implementing a combined technology of production of power, heat, and solid biofuels, namely, torrefied pellets. Torrefaction of fuel pellets is carried out in a thermochemical reactor by heat from exhaust gases of a gas piston power plant. The results of testing the model by experimental data and the results of calculations of the main characteristics of torrefaction, the mass and energy flows are given. The analysis results of efficiency of the power plant with a build-on thermochemical reactor are reported.

Characteristic gas-thermodynamic parameters of interaction of mono- and polydisperse jets with solids under pressures p₀ up to 2 MPa and at stagnation temperatures T₀ = 288–1750 K are investigated. The dependence of the velocity of collision of particles with the flowed solid on their material, size, and initial mass fraction in a settling chamber is taken into account. The regions of absolutely inelastic (erosion) and elastic (with a rebound) interactions of particles with the solid is studied. The semiempirical coefficient providing agreement between the theoretical and experimental densities of the heat flow, brought by particles to the solid in the mode of erosion interaction, is found for the case of a hot jet.

The heat transfer in multiple plate sandwiches of spacecraft’s screen-vacuum heat insulation is simulated for determining the characteristics of heat shielding against long-term solar heat flux. To choose optimal characteristics of heat shielding, it is necessary to determine precisely the number of plates and their peculiarities. The new, absolutely stable method for solving numerically heat transfer problems is presented. We obtain results showing that the screen-vacuum insulation is characterized by low heating-up inertance that is unacceptable. To remove this effect, the inertial heat shielding is used on the internal surface of the heat shielding and its state is examined.

Differential equations of heat conductance of solid body are presented, a result of Fourier, Cattaneo–Vernotte, and two-phase delay hypotheses. The experimental set-up and automated measuring system is described for the study of transient thermal processes in solid. The solution of the boundary problem of the third kind is given with differential equations of heat conductance of parabolic and hyperbolic types. The results of experimental and theoretical study of transient thermal processes in the plate center are given in the sudden immersion into a hot environment. Based on the comparison of theoretical transient processes with recorded automated measuring system, the adequacy of hypotheses and corresponding differential equations of heat conductance are concluded with respect to short-term transient processes. Thermal relaxation and temperature damping constants for polymethyl methacrylate are measured.

In present study the influence of temperature-dependent viscosity, i.e. thermoviscosity on the pressure-driven flow in inhomogeneous temperature field has been recalled. Such viscous stratification impacts on the velocity profile asymmetry, significantly increases the entry length, and causes the velocity inflection point to appear. In certain cases, particularly under high temperature differences of channel walls, the thermoviscosity generates instability that in a view of high local Reynolds numbers can create turbulent zones.

It is demonstrated that free concentrated fire whirls can be physically modeled if the outer circulation is absent. Vortex structures were generated when hexamethylenetetramine pellets, located axially on a substrate (aluminum sheet) burned. The first data on specific features of fire whirl formation and some integral parameters (the lifetime, height, and diameter) were obtained using video shooting.

The dependence of beryllium, magnesium, and praseodymium additives on the temperature dependences of the Zn–55Al alloy thermophysical properties and thermodynamic functions is investigated. With the increase in the alloying additive, the values of the studied properties increase with the temperature increase whereas the Gibbs energies decrease.

Experimental results are presented for the impact on blockage by airflow exhausted from a highpressure vessel and containing micron-sized solid particles. The static and the dynamic pressures on the blockage at different initial jet parameters are determined. The degree of the pressure increase on the blockage depending on the initial pressure in the vessel and the solid phase concentration is determined. The pressure of the flow with the powder on the blockage may be up to three times as much as the same in pure gas.