Thermophysics and Aeromechanics最新文献

The paper presents the results of an experimental study on coolant flow patterns at the inlet section of a fuel assembly (FA) in the cartridge core of a reactor for a RITM small nuclear power plant. The objective was a study on influence of different inlet elements on the coolant axial velocity distribution. This task was performed by a series of experiments on a scale-up experimental model covering the inlet section components from the calibration washer up to the attachment unit between fuel rods and the diffuser. The model also covers the section of the fuel-element bundle between the absorbing grid and the spacer grid. This study is based on the pneumometric method for several critical cross sections over the model length. The allocation of measuring points covers the entire cross section of the model. The coolant flow features are visualized using digital maps for the working medium flow axial velocity in the fuel rod bundle cross section. The experimental modeling can be useful for optimizing the hydraulic profiling of the components at the inlet of the fuel rod assembly. The set of test data can be applied for validation of the LOGOS CFD software and for adjusting the technique of heat and fluid computations for the core zones under a cell approximation.

Various approaches to oil film visualization of the flow on the cylinder surface aligned transversely in a supersonic flow in a pulsed wind tunnel are compared. Two types of fine-particle coloring pigments Al₂O₃ and TiO₂ are considered. Two methods of pigment application are used: sprinkling onto the model surface pre-coated with an oil film and applying a mixture of the pigment and oil onto the model surface. The mass fraction of the pigment in the mixture for oil film visualization is varied from 10 to 20 %. Photographs of the dynamics of variation of the oil film coating on the model surface are presented, which are taken immediately after application, during the experiment, and upon its completion.

Based on the results of the present study, recommendations are formulated on using surface flow oil film visualization with due allowance for specific features of application of this method for experiments in pulsed supersonic wind tunnels.

The flows of a viscous liquid film along the outer surface of a vertical cylinder are considered. The study employs a model nonlinear evolutionary equation for film thickness deviation from the undisturbed level. It is valid for describing long-wave perturbations in the case of small fluid flows and large cylinder radii. The branching of spatial wave regimes from the undisturbed flow regime is investigated. Particular attention is paid to special cases when the values of the radii of the cylinders lie in the vicinity of some specific critical points. To study such cases, a model system of equations is obtained from the initial equation. Several solutions of this system are given.

The study presents the numerical simulation results for a process of the ash liquid phase zone generation in the aircraft engine combustion chamber. The simulation was performed for three operation modes: the aircraft enters an ash cloud while cruise flight, the aircraft exits the ash cloud during climb-out; the aircraft exits the cloud during the flight idle mode (recommended by ICAO). This study was conducted for the case of a dual-flow turbojet engine PD-14 (the mainline aircraft MS-21) under the impact from the Sheveluch volcanic ash in the air. Our simulations revealed that there are significant zones inside the PD-14 engine combustion chamber where the gas temperatures are above the meting point for volcanic ash. The high temperatures zones (creating a risk of volcanic ash melting inside the engine) account for over 54 % of the flame tube volume. Additionally, for the nominal flight mode (climb-out), the volume of ash melt zone exceeds 81 % of the total volume, and the flight idle mode provides only 25.3 % of the volume.

The paper presents an updated physical-mathematical model for a stationary flow of a water-oil flow through the porous space of a rock core (this space is described as an array of capillary clusters). Here we consider an isothermal statement of problem: the temperature is the key parameters for fluid properties and for the value of pressure drop caused by interaction between the fluid phases. The developed model ensures calculating the relative permeability at different temperatures; this approach is based on standard laboratory data for core testing and on experimental data for single-phase filtration of the fluid at different temperatures (or substituted with appropriate formulas). This model was applied for calculating the relative phase permeabilities at different temperatures for the case of weakly-cemented rock formation. This sample was taken from one of Siberian oil fields with a high viscosity oil. The numerical study was conducted on the effect of temperature on the flow pattern in a variable cross-section capillary channel. Simulation was conducted using the OpenFOAM platform. The temperature-caused change in fluid properties alleviates the intensity of a train flow and promotes the transition of the train flow to the droplet flow.

The paper considers experimental data of superfluid helium dynamics in a U-shaped cylindrical channel filled with a backfill of metal balls. An experimental cell is presented and the results of study are shown in the form of a time dependence for the position of vapor–liquid interface. The differences between the oscillations in a free channel and in confined conditions are discussed. For a channel with a finely dispersed porous structure, the oscillation amplitude significantly reduces and a stationary state of the interfacial surface is possible.

The paper presents the results of the experimental study of the structure of a liquid microlayer at the base of vapor bubbles during water pool boiling using the method of light-emitting diode (LED) interferometry and a transparent design of the heating surface. Microlayer profiles were obtained at different time moments and the effect of heat flux density on its characteristics was analyzed. It is shown that the applied technique with a fairly simple optical scheme allows obtaining of up-to-date information on the structure and dynamics of the microlayer under bubbles during boiling.

The present study deals with the optical and thermophysical properties of nanofluids based on spherical carbon nanoparticles stabilized in water by sodium dodecyl sulfate. Nanoparticles with a mean diameter of 11 nm are synthesized using electric arc sputtering in helium at a pressure of 3 Torr. For a concentration of carbon nanoparticles in the nanofluid equal to 0.01 %, the extinction coefficient varies from 400 to 200 m⁻¹ in the wavelength range of 180–1100 nm. For mass fractions of nanoparticles within 0–0.04%, the viscosity is not found to depend on the concentration. With an increase in concentration, the thermal conductivity of nanofluids in the same range of concentrations is found to be lower than the thermal conductivity of water by up to 4%.

The results of an experimental study of the normal integral emissivity (NIE) of lithium, sodium, and potassium during melting and in the liquid state are presented. The research is realized by the radiation method. The experimental results are compared with the theoretical calculation of the NIE from the Foot approximation and analyzed. The behavior of the main thermophysical properties of metals in the melting point region is generalized for the position of alkali metals in the Periodic Table.

In the regimes of mixed convection, the Czochralski method investigates numerically the effect of a melt layer height on hydrodynamics and convective heat transfer in the range of relative heights of the heptadecane layer 0.1 ≤ ≤ H/R_C ≤ 2.0 with a step of 0.1. Calculations were performed using the finite difference method at a fixed rate of crystal rotation corresponding to the Reynolds number Re = 95, with the Grashof, Marangoni and Prandtl numbers Gr = = 1215, Ma = 2930, Pr = 40.35 for the ratio of crucible radius to crystal radius R_C /R_S = 1.94. In this range of parameters, the flow has a laminar, steady and axisymmetric character. The evolution of the spatial flow shape, velocity and temperature fields, radial distributions of local heat fluxes, and integral heat transfer is studied depending on the relative heights of the heptadecane layer.