Home – Home – Jornals – Thermophysics and Aeromechanics 2026 number 2

An experimental and numerical study was conducted to examine the effect of a passive perturbation from a vortex generator on heat transfer in a bubbly flow in a flat channel. Wall temperature measurements were taken using an infrared camera. To describe the flow dynamics and heat and mass transfer in the gas and dispersed phases, unsteady Reynolds-averaged Navier-Stokes equations were used, written taking into account the presence of polydisperse bubbles within the Eulerian approach. The influence of flow velocity, air bubble concentration, and vortex generator height on heat transfer in a two-phase gas-liquid flow was studied. It was found that the thermal pattern of separated two-phase bubbly flow behind an obstacle in the presence of a passive disturbance differs significantly from the dynamic pattern. The results demonstrated an increase in heat transfer in the bubbly flow behind the obstacle. A comparison was made between the obtained experimental and numerical data on heat transfer in a two-phase turbulent bubbly flow in the presence of an obstacle installed on the channel wall, and satisfactory agreement was demonstrated in terms of the characteristics of convective heat transfer.

This paper aims to expand the capabilities of experimental studies of the gas dynamics of supersonic, highly rarefied jets by employing new diagnostic tools for determining flow energy parameters. Known methods for measuring temperature in a rarefied gas flow are considered. A detailed description of the chosen methodology and equipment for measuring transverse molecular beam density (or intensity) profiles and determining the perpendicular velocity ratio from them is provided. A comparison of a large array of experimental data with known theoretical models confirms the reliability of the obtained information. The possibilities and conditions for calculating the translational (perpendicular) temperature are considered. The error and range of reliability of the obtained results, the influence of concomitant processes of skimmer interaction and penetration of background gas into the jet on the recorded parameters, as well as the possibility of expanding the range of research using this method are discussed.

A numerical model for multiphase immiscible flows in porous media is presented. It is based on the lattice Boltzmann (LBM) method using a color gradient. An algorithm for specifying arbitrary wetting angles at interfaces with a solid surface is implemented. The model is verified using Laplace's law and liquid lens geometry for two- and three-phase systems. Numerical modeling, applied to oil displacement experiments in a digital core model obtained from micro-computed tomography data, allowed us to obtain a physically correct saturation distribution, including the effects of capillary locking and breakthrough channels. The developed approach can be used to analyze and optimize oil production processes, study residual saturation and storage of carbon dioxide in geological reservoirs.

The segregation in melts of the Li-K-Pb system in the temperature range of 941-1187 K has been studied using the gamma-ray attenuation technique. It has been shown that the addition of 28.6 at.% Pb to the liquid Li-K system is insufficient to exit the immiscibility region, the boundaries of which remain unknown. The gamma-ray linear attenuation coefficient profiles in liquid alloys Li₄KPb₂ and Li₁₆K₃Pb₇ have been studied at two temperatures. It has been shown that during the cooling process homogeneous melts of Li₄KPb₂ and Li₁₆K₃Pb₇ reach the immiscibility region at temperatures of about 1045 and 1063 K, respectively.

The article presents the results of an experimental study of the efficiency of controlling a supersonic turbulent boundary layer on a flat surface using distributed positive air mass transfer through a finely perforated wall. The experiments were performed at a Mach number of 2 and a unit Reynolds number of 12.5 x 106 m^-1. The mass transfer rate varied from 0 to 0.00941. A significant effect of mass transfer on the skin friction coefficient is demonstrated, with the reduction at the end of the active control region reaching more than 80% compared to the baseline value. It was found that with spontaneous mass transfer, achieved through the natural difference between barometric and static pressure in the working section of the wind tunnel, it is also possible to achieve a significant reduction in the skin friction coefficient, down to zero at the end of the control region.

The results of an experimental study of the thermal conductivity (λ), thermal diffusivity ( a ), heat capacity (Cp), density (ρ), and elastic moduli of four polymer composite samples as functions of temperature and pressure are presented. The polymers were synthesized by supercritical dispersion using a CO₂ solution (SEDS). Thermal conductivity measurements were carried out in the temperature range from 293 K to 343 K at a pressure of 0.101 MPa; sample PP2 was studied at a pressure of up to 40 MPa using the stationary flat layer method. The thermal diffusivity coefficient was measured in the temperature range from 293 K to 368 K at atmospheric pressure using a Netzsch LFA 457 (Laser Flash, LFA) device using a non-contact method. The heat capacity of the same samples was measured in the temperature range from 129 K to 363 K using a DSC 204 F1 differential scanning calorimeter. The elastic moduli were obtained by measuring the propagation velocity of longitudinal and transverse ultrasonic waves using the pulsed method.

A study was conducted on the thermal and environmental characteristics of liquid hydrocarbon fuel combustion in a steam-atomizing burner with a gasification chamber under limited air supply to the chamber at various power parameters. It was shown for the first time that limiting the primary air supply to the gasification chamber during steam atomization leads to a narrowing of the device's operating zone and a shift in carbon monoxide emission characteristics compared to a device with free air supply. At the same time, a key advantage is a significant reduction (up to 70%) in nitrogen oxide emissions due to lower peak temperatures in the combustion zone. A comparison of the performance of a device with a forced-air controlled air supply revealed that, with the same amount of air in the gasification chamber, the different supply methods exhibit differences in the distribution of combustion products in the flame, such as CO, H₂, and CH₄, due to the higher temperatures achieved with forced air supply. Consequently, it was established that modifying an atmospheric steam-atomizing burner by limiting the air supply to the gasification chamber allows for a reduction in NOₓ production over a wide power range while maintaining high combustion efficiency.

This paper continues a series of studies devoted to a method for determining the amplitude-frequency response (AFR) of a constant-resistance hot-wire anemometer based on the direct application of a short-duration pulse to the sensor's sensitive element, simulating the effect as a delta function. The pulse is generated by laser radiation. This method is used to study the influence of parameters such as different settings of the constant-resistance hot-wire anemometer and changes in flow velocity on the AFR. Practical recommendations for selecting the laser radiation intensity/power for accurate frequency response assessment have been developed. A practical application of the method for comparing boundary layer pulsation spectra is demonstrated.

This article is devoted to the numerical modeling of the co-combustion of diesel fuel and micro-ground coal dust in a small-scale furnace with a steam-oil burner. A comprehensive mathematical model describing heat and mass transfer processes in burner and furnace devices is presented: diesel fuel evaporation under the influence of a steam jet, turbulent combustion of evaporated diesel fuel, and burnout of coal particles. The simulations demonstrated that the existing combustion chamber with a steam-oil burner allows for the combustion of micro-ground coal dust and operates stably over a wide range of coal dust flow rates. The obtained numerical modeling results can be used in the design of new compact combustion devices for flare combustion of coal dust.

A video recording of the boiling process on biphilic copper surface with arrays of hydrophobic cavities of about 100 μm in size and a pitch of 780 μm was conducted. The departure diameters and frequencies for bubbles were determined depending on the heat flux, and their ascent rates were established depending on the diameter. The dependence of the diameters on the heat flux was compared with theoretical dependencies and with data from other authors. It was shown that common dependencies do not take into account the parameters important for boiling on biphilic surfaces with inhomogeneities in the form of depressions/caverns and are poorly suited for describing the bubble dynamics on them.

The article presents the results of an experimental study of the effect of mechanical vibration on heat transfer and vaporization dynamics during nucleate boiling of saturated water in the pressure range of 10-101.3 kPa. The relevance of the study is determined by the need to improve heat transfer efficiency in power and thermal engineering systems operating under reduced pressure and subject to external mechanical influences. Despite the existence of numerous studies devoted to boiling at atmospheric pressure, the effect of vibrations at reduced pressures remains insufficiently studied. This study demonstrates that applying vibration to a liquid leads to an earlier onset of boiling, a reduction in heating surface superheat, and an increase in heat flux at a fixed superheat. The most pronounced effect is observed at lower pressures, whereas at atmospheric pressure, the influence of vibration is weakened and manifests itself primarily in the region of initial nucleate boiling. Analysis of video data revealed that vibration exposure leads to a decrease in the bubble separation diameter, an increase in the frequency of bubble separation, and an increase in the density of active vaporization sites, especially at low pressures. The obtained results confirm that mechanical vibration is an effective active method for controlling boiling processes and can be used in the development and optimization of thermal engineering systems operating over a wide pressure range.

This work presents an experimental investigation of a water film thickness driven by a turbulent gas flow in a flat minichannel. It was found that the transition from macro- to minichannels can lead to a significant reduction in film thickness at comparable flow parameters. An existing model has been modified to estimate the average thickness of a liquid film under conditions of turbulent gas-driven film flow in a minichannel.

For ethanol, equations have been developed for vapor pressure line, the vapor and liquid density lines, and the "apparent" heat of vaporization, r *, which describe the phase equilibrium line in the temperature range from the triple point and to the critical point. All four equations are consistent in terms of critical parameters, as well as critical indices and exponents of all components of the equations, calculated within the framework of the renormalization group and scaling theory. The coefficients of saturation line, which determine the behavior of the average diameter and the order parameter in a wide vicinity of the critical point, are established based on the correlation between the critical amplitude and the critical index of the saturation line, as well as the renormalization group. The proposed phase equilibrium line model describes the experimental data of the pressure and density of saturated vapor, and the density of saturated liquid of ethanol with less uncertainty than the equations of Bazaev et al (2007), Polikhronidia et al (2007), Ustyuzhanin et al (2013), Schroeder et al (2014).

The influence of the diffuser aperture angle and the flow swirl degree on the characteristics of a turbulent flow and the precessing vortex core forming within it was experimentally studied. Laser Doppler anemometry was used to analyze the flow. It was shown that the effects associated with changes in the diffuser aperture angle depend significantly on swirl. With strong swirl, nonmonotonic behavior of the integral swirl parameter in the far wake was observed, which is interpreted as a change in flow regimes. Increasing the aperture angle enhances velocity fluctuations associated with vortex precession. The results form the basis for validating computational models and optimizing diffusers in power plants.

Measurements of the liquidus temperature in the NaCl - KCl system were carried out in the range of compositions from 0 to 100% mol. KCl on 14 samples using the oscillation method of phase analysis (VFA). The melting temperatures of the components and the minimum composition of this system have been clarified.