Vol 26, No 4 (2019)

The work is devoted to the numerical simulation of a supersonic plane mixing layer of multicomponent gases in the presence of injection of particles at the interface of flows. A. algorithm for solving the system of Navier-Stokes equations for the gas phase and the system of ordinary differential equations for solid particles based on the Eulerian-Lagrangian representation is proposed I. is assumed that the turbulent flow is quasi-two-dimensional and the solution of the an original system is produced by the 2D-DNS approach without using additional closure models of turbulence. A detailed study of the influence of the gas phase on the particles distribution and their capture with coherent structures is performed with the variance of Mach numbers and particles injection locations The enhancing influence of the centrifugal force on the dispersion of particles is obtained with increase in the input Mach number. A quasi-equilibrium state with a gas flow of small particles is established.

The paper presents the experimental data on distribution of static pressure and heat transfer in a separation zone behind a backward-facing step equipped with vortex generators. The size and gaps between generators (tabs) of rec-tangular shape were varied in experiments. Experimental results were compared with two limiting cases: a smooth step (no tabs), and a step with a solid fin. The strongest influence on flow and heat transfer from the set of installed tabs was observed within the recirculation zone just behind the step base. The tabs allocated at the step edge resulted in the displacement of the Nusselt number maximum to the step base that caused the enhancement of a local and ave-rage heat transfer.

In this paper, heat transfer characteristics of new types of perforated fins with cross perforations are investigated using experimental measurement and numerical simulations. Conjugate equations of turbulent flow and conduction heat transfer are solved around fins and within fins using a finite volume code. Solution includes two types of circular and square perforations and Reynolds numbers from 2×10⁴ to 4×10⁴ based on the fin length. From the results of nu-merical simulation, structures of flow field and heat transfer for each configuration are illustrated and discussed. For validation, comparison is made with solid fin as well as perforated fins and reasonable trend for heat transfer is ob-served. For further analysis, a series of measurements is carried out for a model of perforated fins with one streamwise opening and one cross opening. It is shown that among different perforation configurations, a fin with 1 longitudinal perforation and 3 vertical perforations shows the best heat transfer performance. In addition, it is found that the circular perforation is preferred in comparison with square perforation considering both heat transfer performance and pressure drop.

The determination of thermophysical properties of hydrofluorocarbons (HFC_S) is very important, especially the thermal conductivity. The present work investigated the potential of an artificial neural network (ANN) model to correlate the thermal conductivity of (HFC_S) at (169.87-533.02) K, (0.047-68.201) MPa, and (0.0089-0.1984) W/(m·K) temperature, pressure, and thermal conductivity ranges, respectively, of 11 systems from 3 different categories including five pure systems (R32, R125, R134a, R152a, R143a), four binary mixtures systems (R32 + R125, R32 + R134a, R125 + R134a, R125 + R143a), and two ternary mixtures systems (R32 + R125 + R134a, R125 + R134a + R143a). Each one received 1817, 794 and 616 data points, respectively. The application of this model for these 3227 data points of liquid and vapor at several temperatures and pressures allowed to train, validate and test the model. This study showed that ANN models represent a good alternative to estimate the thermal conductivity of different refrigerant systems with a good accuracy. The squared correlation coefficients of thermal conductivity predicted by ANN were R² = 0.998 with an acceptable level of accuracy of RMSE = 0.0035 and AAD = 0.002 %. The results of applying the trained neural network model to the test data indicate that the method has a highly significant prediction capability.

Methods for calculating the motion of a melt along the fuel element surface under the conditions of an accident are presented. The calculation was carried out using semianalytic methods for the shear stress and gravity-driven films. The results of calculations of the motion of a melt under various initial conditions are presented. Particular attention is paid to the influence of surface tension forces on the interface between the melt and a solid surface.

The paper presents experimental results on study of production of force pulses and bubble pulsation near a flat thrust-producing wall with the diameter of 100 mm designed for combustion of stoichiometric propane-oxygen gas mixture. In combustion of the same gas charges for production of thrust, the design of combustion at a flat wall has qualitative and quantitative benefits vs. case of combustion in a cylindrical duct. The force amplitude becomes higher due to the larger contact area between the bubble and thrust wall. The period of bubble pulsation is shorter for this case as compared to bubbles generated in a cylindrical duct; the pulsation period is described by the Rayleigh-Willis law. The shorter bubble pulsation period ensures better conditions for increase in the average thrust generated in pulse-in-cycle mode of combustion of gas charges in water medium.

The article presents the results of an experimental study of the dynamics of vaporization at water boiling at subatmospheric pressures up to 8.8 kPa. The usage of a transparent heater, high-speed video and IR thermography allowed analyzing the effect of pressure on the dynamics of vapor bubbles, the evolution of dry spots as well as the surface superheating corresponding to the onset of boiling. It is shown that the pressure reduction at a given heat flux density leads to a significant increase in the Jacob number at the activation of the nucleation site and the growth rate of vapor bubbles. It has been found that the curve of dry spots growth rate has a nonlinear dependence on the pressure in the range of 8.8-103 kPa. The minimum value of the growth rate of dry spots is observed at a pressure of 42 kPa.