Olga V. Vysokomornaya

Experimental determination of times, amplitudes, and lengths of cycles of water droplet deformation in air

The regularities of deformation of water droplets moving in air at the moderate Weber numbers (We < 7) are experimentally investigated with the use of high-speed cross-correlation recording equipment at frame delays of less than 100 ns. Deformation cycles with characteristic times, amplitude, lengths, and droplet forms are established. The effect of the droplet velocity on the main characteristics of the deformation cycles is determined.

Numerical analysis of heat-mass transfer mechanisms in gas-phase ignition of films of liquid condensed substances by a laser beam

A complex of interrelated processes of heat-mass transfer with phase transitions at the ignition of liquid condensed substance by a low-power laser beam is investigated. Mechanisms of the heat-mass transfer processes are analyzed. The scale of influence of the power and the lasing range radius of the laser beam on the ignition characteristics is found. Critical conditions that do not enable the ignition in a system of liquid condensed substance film-laser beam-gas-vapor mixture are determined.

Investigation of Regularities of Heat and Mass Transfer and Phase Transitions during Water Droplets Motion through High-Temperature Gases

The macroscopic regularities of heat and mass transfer and phase transitions during water droplets motion through high-temperature (more than 1000 K) gases have been investigated numerically and experimentally. Water droplet evaporation rates have been established. Gas and water vapors concentrations and also temperature values of gas-vapor mixture in small neighborhood and water droplet trace have been singled out. Possible mechanisms of droplet coagulation in high-temperature gas area have been determined. Experiments have been carried out with the optical methods of two-phase gas-vapor-droplet mixtures diagnostics (“Particle Image Velocimetry” and “Interferometric Particle Imaging”) usage to assess the adequateness of developed heat and mass transfer models and the results of numerical investigations. The good agreement of numerical and experimental investigation results due to integral characteristics of water droplet evaporation has been received.

Mechanism of heat transfer in heterogeneous droplets of water under intense radiant heating

Thermocouple measurements of temperature have been performed at three main points of heterogeneous water droplet–high-temperature gases system: on the surface and in the depth of a solid inclusion, as well as on the free surface of the water droplet. Investigations have been carried out for water droplets of an initial volume of 5–15 μl with single inclusions of cubic graphite particles of a typical size of 1 mm. The gas temperature varied from 700 K to 1200 K, which corresponds to the main practical applications: thermal purification of water from solid and liquid impurities, fire extinguishing, treatment of heat-loaded surfaces of power equipment, etc. A hypothesis about the dominant role of radiant heat transfer in vaporization within heterogeneous water droplets has been grounded. It has been shown that in a short period (a few seconds), the surface temperature of an opaque solid inclusion within a droplet can reach the boiling point of water. A significant change in the optical properties of water with increasing temperature has been revealed, i.e., water became partially transparent to the infrared radiation. Presence of an opaque heterogeneous inclusion enhances this effect due to intensification of the heating of the water film. The heat and mass transfer characteristics obtained in the experiments were used for designing a model that takes into account the radiative properties of water film and adequately reproduces the results of thermocouplemeasurements. Based on the findings of the investigations, a conclusion has been formulated that models of high-temperature evaporation of water droplets should be developed with due account of changes in the optical properties of water and formation of a vapor buffer layer around inclusions.

Mathematical Simulation of Heat and Mass Transfer Processes at the Ignition of Liquid Fuel by Concentrated Flux of Radiation

The physical and forecasting mathematical models of heat and mass transfer with phase transformations and chemical reactions under heating and following ignition of typical liquid fuel by using concentrated flow of radiation were developed. The influence scales of energy absorption process by means of gas-vapor mixture and liquid on ignition characteristics were established. The ignition delay time dependencies on the concentrated luminous power and radius of its coverage were determined.

Experimental investigation of the influence of the liquid drop size and velocity on the parameters of drop deformation in air

The deformation of water, kerosene, and ethyl alcohol drops traveling a distance of up to 1 m in air with different velocities (1–5 m/s) is recorded by high-speed photography (the frame of the cross-correlation camera is less than 1 µs). It is shown that the shape of the drops varies cyclically. Several tens of “deformation cycles” are found, which have characteristic times, drop size variation amplitudes, and number of shapes. It is found that the velocity and size of the drops influence the parameters of their deformation cycles. Experiments with the drops are conducted in air at moderate Weber numbers (We < 10).

Numerical solution to the plane heat-mass transfer problem in a system of focused radiation flux-liquid condensed substance film-oxidizer

The plane problem of heat and mass transfer in a focused radiation flux-liquid condensed substance film-oxidizer system is numerically solved. Peculiarities of heat and mass transfer at radiation energy absorption by a vapor-gas mixture near the liquid surface are analyzed. The influence of the radiation density distribution in a flux and the liquid and oxidizer parameters on the conditions of heat and mass transfer is assessed.

Modeling the Water Droplet Evaporation Processes with Regard to Convection, Conduction and Thermal Radiation

A predictive model was developed for investigation of high-temperature heating and evaporation of water droplets. The model takes into account the basic interrelated processes of heat transfer and phase transitions. Typical velocity and temperature profiles were found in the high-temperature gas–water droplet system with external gas medium temperature varied from 100 to 800°C. Various formulations of the problem, significantly different in the type of considered processes and factors, are considered.We analyzed temperature conditions of heating and evaporation of water droplets, which allow the use of simplified models and which need consideration of all complex interrelated processes of heat and mass transfer (including convection, conduction and radiant heat transfer in droplets, and also in the surface vapor–gas layer).

Evaporation of aqueous suspension drops with ground admixtures in the region of high-temperature combustion products

The effect of typical admixtures (clay, sand, soil, and silt) on the integral evaporation characteristics of aqueous suspension drops in high-temperature gases (at nearly 1100 K) has been experimentally studied using optical methods and a high-speed video record system (up to 105 fps). The heating and evaporation of suspension drops was established to appreciably intensify with a change in the relative mass fraction of admixtures within γ = 0–0.1 for sand and γ = 0–0.01 for clay, soil, and silt. An essential effect of the preliminary heating of suspensions on the intensity of their evaporation in a flow of high-temperature gases has also been revealed. Some recommendations have been formulated for selecting evaporation parameters for the studied suspensions in contemporary and advanced high-temperature chemical and thermal engineering technologies for the purification of water from admixtures and in the sphere of fire safety.

Experimental investigation of trajectory of motion of water drops in a flow of high-temperature gases

The conditions of slow-downs, hang-ups, and turns when drops of sprayed liquid are in an opposite flow of high-temperature gases (temperature was around 1100 K) using panoramic optical methods of particle image velocimetry, interferometric particle imaging, shadow photography, and Tema Automotive software have been dedicated. The distances passed by the drops until the full slowing down have been measured. Investigations have been carried out on the change in the characteristic dimension (conventional average radii) of drops in the range of 0.05–0.5 mm. The initial velocities of their motion and gases were varied in the range of 0.5–2.5 m/s and 0.5–5 m/s, respectively. The processes of water drops slowing down at the comparable initial velocities with gases in the conditions of intensive evaporation have been studied. The possible directions of improvements of chemical technologies of water and emulsions purification on its basis in the field of energy conservation using the results of experimental investigations carried out have been set.