In the present paper, we established the conditions and the main characteristics of the stable boiling and subsequent explosive disintegration of emulsion droplets based on water and oil products under high-temperature (from 350 to 1100 K) heating using high-speed video recording (up to 105 frames per second). The studies were carried out under various conditions of energy supply to the droplet: on a massive substrate, in contact with a heated rod (local heating), and in a heated air flow. The times of heating up the emulsion droplets before the explosive decay are determined. The scale of the effect of the ambient temperature (up to 1100 K), the heat flux density (up to 104 kW/m2), and the oil product concentration (up to 70%) in the emulsion on these characteristics is established. Using high-speed video tracking, the main characteristics of the emulsion droplet decay are determined: the duration, surface transformation stages, and the number of liquid fragments formed (up to 300) and their total area (7–8 times higher than the initial one). The conditions for the emulsion drop decay both before and after its ignition were studied.

An experimental study has been performed to investigate the integral characteristics of the processes of heat and mass transfer and phase transformations during interaction of a droplet flow with the combustion front of a highly porous condensed material. The macroscopic regularities of the suppression of flaming combustion and thermal decomposition of typical forest fuel material due to the removal of heat as a result of its absorption during vaporization and convective cooling were studied. Three modes of interaction of a droplet aerosol with the burning forest fuel materials were considered. The time of combustion termination and the time of thermal decomposition of forest fuel materials were determined. The mechanisms of the main physicochemical processes occurring during interaction of droplet flow with the combustion front of typical forest fuel materials were established.

The results of experimental studies of hydrodynamics and heat transfer in a swirl air flow (Pr = 0.7) and a helium-xenon mixture (Pr = 0.2) in heated circular channels with original screw inserts in a wide range of Reynolds numbers are presented. The efficiency analysis of heated channels with a swirl of the flow is compared with the efficiency analysis of the channels without swirling the flow using the energy necessary for pumping the gas through the heated channel.

Investigation results on heat transfer in low-Prandtl helium-xenon gas mixture and air, flowing in a small diameter tube, are presented. New experimental data on the heat transfer coefficient in the flow of helium-xenon mixture are obtained; results of numerical simulation are compared with the experimental data and known empirical correlations. Based on the simulation data it is shown that in a heated tube an increase in the Reynolds number due to an increase in the flow rate intensifies the heat transfer, and it may be due to the flow acceleration. It is shown that the high flow velocity and significant acceleration have a considerable effect on heat transfer in a tube, and the use of mean-mass stagnation temperatures as the determining one for generalization of data on "heat transfer is insufficient. For the studied conditions, the known correlations give a significant error in determination of the heat transfer coefficient: the lower the Prandtl number and gas density, the higher the error. (C) 2017 Elsevier Ltd. All rights reserved.

Presented are results of experimental studies of the heat transfer processes in suppression of thermal decomposition of typical forest fuels (FFs) (spruce needles, birch leaves, aspen twigs, or amixture thereof) due to the effect of aerosol water flow (drop radii: 0.01–0.12 mm; concentration: 3.8 · 10−5 m3 drop/m3 of gas). The experiments have been carried out with FF samples in the form of cylinders of a thickness of 40–100 mm and a diameter of 20–150 mm. The times required to stop the thermal decomposition of FF have been found, as well as amounts of water necessary to lower in a given time the temperature in a layer of material to the point of decomposition beginning. A dimensionless complex has been derived for prediction of water spraying parameters (amount and time of supply) that ensure sustainable termination of FF decomposition within a specified time interval.

An experimental electrodiffusional technique with eight double probes is used to detect perturbation of the wall shear stress by a single bubble in laminar upward tube flow. Small almost spherical and long Taylor bubbles are tested. The wall shear stress perturbations by bubbles have a complex structure. It is possible to define three components of perturbation caused by a small bubble. The perturbation by Taylor bubble contains only two components due to the main flow symmetry around the bubble. An unexpectedly long shear stress pulsations zone is registered behind the Taylor bubbles.

This paper describes the results of an experimental study of heat transfer in the case of the flow of a helium–xenon mixture with a Prandtl number approximately equal to 0.23 and the flows of pure helium and air in heated tubes of circular or triangular cross sections with a constant density of the heat flow. The region of thermal stability is studied. The law of heat transfer on the stabilized region is compared with known relationships. The approach that helps obtaining an expression for the calculation of heat transfer in heat transfer devices with circular and triangular cross sections, which operate in a mixture heating mode on the initial region, is developed.

The main stages of the formation of a droplet cloud during the disintegration of water masses (with an initial volume of 0.05–1 L) during their free fall from a great height (up to 15 m) have been determined. High-speed (up to 6 × 105 frames per second) video cameras were used to perform 3D video recording of the transformation and destruction of water mass with the formation of a droplet cloud. It is found that the transverse sizes of the newly formed droplet cloud rapidly increase when the mass passes the first few (up to 10) meters from the onset of falling. It is shown that the maximum cross-sectional areas of the water mass change only slightly with an increase in the discharge height at heights above 10 m. A model of limited growth of the transverse sizes of droplet cloud is developed for the first time based on the results of large-scale experiments.

Using a test bench the main part of which is a vortex combustion chamber, characteristics describing the initiation of burning of solitary droplets of a typical organic coal–water fuel (OCWF) are established. The oxidizer temperature varied in the range of 600–850 K. The linear motion velocity of the oxidizer in the vortex chamber was about 3 m/s. The configuration of the chamber and parameters of the air flow provided a stable regime of floating for droplets with a size (radius) of about 0.5 mm. The analysis results show that the intensity of initiation of OCWF combustion under conditions of processes occurring in boiler furnaces is significantly (by a factor of 2–4) higher than for droplets that are immovably fixed or freely float in the heated air flow.

Evaporation rates of water droplets in high-temperature gases were experimentally determined using high-speed video recording cameras and low-inertia thermocouples (for heated air flow as an example). The experiments were carried out for droplets of initial size (radius) 1–3 mm at an air temperature of 500–1000 K. Dependences of the evaporation rate of water droplets on time and gas temperature were obtained for various initial droplet sizes.

Investigation of heat and mass transfer at nonisothermal absorption on the falling liquid film surrounded by pure vapour is presented. The analytical method for entrance region and numerical method for solving the problem are proposed. The analytical solution is obtained for the entry region, where temperature and concentration perturbations are near the interface. Then, the analytical solution is used as an inlet condition for further numerical solution by the finite-difference method. The key dimensionless criteria characterizing heat and mass transfer at absorption on the falling liquid film are defined.

In this paper the mathematical model describing the falling thin liquid film on a vertical wall is considered taking into account heat and mass transfer at the interface in the regime of periodic rolling waves. The families of exact and numerical generalized solutions, where periodic traveling waves conjugate through the strong and weak discontinuities with each other or with the residual thickness, are constructed. Evolution of exact periodic generalized solutions is studied in time.

We investigated heat transfer in a channel with a triangular cross-section. The working medium is a helium–xenon mixture with a low Prandtl number. This channel configuration corresponds to one of possible cases of fuel cells layout in a gas-cooled nuclear reactor. New experimental data on heat transfer in helium–xenon mixtures were obtained. Results of numerical modeling were compared with the experimental data and the known empirical correlations.

The conditions and integral characteristics of stable low-temperature ignition of droplets of suspension organic water–coal fuels are established by using the means of high-speed video-detection. The oxidizer temperature for these conditions varies in the range of 600–900 K (much below the temperatures in furnace chambers of modern power installations exceeding 1200 K). The velocity of the oxidizer-flow motion varies from 0.5 to 5 m/s, and the sizes (conditional radii) of droplets vary from 0.5 to 1.5 mm. The times of initiation of burning under conditions of low-temperature heating and the duration of the complete combustion of droplets of the corresponding compositions of organic water-coal fuels are determined. The necessary and sufficient conditions of stable ignition are singled out for promising organic water–coal fuels.

Helium is widely used in all industries, including power plant engineering. In recent years, helium is used in plants operating by the Brayton cycle, for example, in the nuclear industry. Using helium-xenon mixture in nuclear reactors has a number of advantages, and this area is rapidly developing. The hydrodynamics and mass transfer processes in single tubes with various cross-sections as well as in inter-channel space of heating tube bundle were studied at the Institute of Thermophysics, Siberian Branch of the Russian Academy of Sciences. Currently, there is a strongest shortage in helium production. The main helium production method consists in the liquefaction of the natural gas and subsequent separation of helium from remaining gas with its further purification using membranes.

The results of experimental investigations are presented for the ignition of droplets (particles) of organic coal–water fuels (OCWFs) floating in a flow of an oxidizer using a special combustion chamber from high-temperature quartz glass. The temperature and the velocity of motion of the oxidizer vary in the ranges of 500–900 K and 0.5–3 m/s. The initial sizes (radii) of fuel droplets amounted to 0.3–1.5 mm. As the basic OCWF components, particles (of 80–100 µm in size) of brown coal “B2,” water, mazut, and waste castor and compressor oils are used. With use of the system of high-velocity video registration, the conditions providing for floating of OCWF particles without initiation of burning and with the subsequent steady ignition are established. Four modes of OCWF-droplet ignition with different trajectories of their motion in the combustion chamber are singled out. The times of the OCWF-ignition delay in dependence on the size of fuel particles and oxidizer temperatures are determined. The deviations of the OCWF-ignition-delay times obtained under conditions of suspension of a droplet on the thermocouple junction and while floating in the oxidizer flow are established.