Genii V. Kuznetsov

Numerical Investigation of Water Droplets Shape Influence on Mathematical Modeling Results of Its Evaporation in Motion through a High-Temperature Gas

The numerical investigation of influence of a single water droplet shape on the mathematical modeling results of its evaporation in motion through high-temperature gases (combustion products of a typical condensed substance) has been executed. Values of evaporation time, motion velocity, and distance passed by various droplet shapes (cylinder, sphere, hemisphere, cone, and ellipsoid) in a high-temperature gases medium were analyzed. Conditions have been defined when a droplet surface configuration affects the integrated characteristics of its evaporation, besides temperature and combustion products concentration in a droplet trace, insignificantly. Experimental investigations for the verification of theoretical results have been carried out with using of optical diagnostic methods for two-phase gas-vapor-liquid flows.

Numerical and Experimental Research of Heat and Mass Transfer at the Heterogeneous System Ignition by Local Energy Source with Limited Heat Content

Numerical and experimental investigations were executed for determination of macroscopic regularities of heat and mass transfer processes under the conditions of the phase transformations and chemical reaction at the ignition of vapors coming from fabrics impregnated by combustible liquid into oxidant area at the local power supply. It was established that initial temperature of local energy source and volume fraction of combustible liquid vapors in fabric are necessary for realization of ignition conditions in a system “fabric—combustible liquid—oxidant.”. Thus three ignition modes are possible for such system. The most widespread mode is an arrangement of ignition zone near the lateral side of local energy source. Also we obtained approximating expressions of ignition delay time on initial temperature and characteristic size of a local energy source for fabrics impregnated by some kinds of combustible liquids (gasoline, kerosene, and diesel fuel). Its dependences may be useful at engineering calculations of fire danger for processes of single hot particles interaction with liquid combustible substances.

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.

Research of Macroscopic Regularities of Heat and Mass Transfer at the Ignition Condition of a Liquid High-Energy Material by an Immersed Source with a Limited Energy Capacity:

We carried out a numerical and experimental investigation of heat and mass transfer at the ignition condition of a liquid high-energy material by a typical immersed source with a limited energy capacity, being a small, intensely heated metallic particle. The numerical research is made on the basis of a model taking into account a group of interrelated physicochemical processes (thermal conductivity, diffusion, convection, mixing, and radiative heat transfer) with phase transitions (evaporation of the liquid and crystallization of the particles material). We established such terminal conditions for the immersion energy source that prevent inflammation of the high-energy material.

Thermal conditions for stopping pyrolysis of forest combustible material and applications to firefighting

Five models describing heat transfer during evaporation of the water sprayed over the forest to stop fires and to cool down the pyrolysis of the bio- top layer are established and investigated by a parametric approach. It aims to improve the understanding of the behaviour and the properties of the forest combustible material. A mathematical description of forest combustible material surfaces (needles of pine and fir-tree, leaves of birch) is established. The characteristic time, td, to cool down the forest combustible material layer below the temperature of the onset of the pyrolysis is the important parameter investigated in the present work. The effective conditions were determined allowing to reach the shortest td and the lowest consumption of e. g. water to be dropped.

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.

Numerical Analysis of Effective Conditions of Chemical Reaction Suppression during Typical Forest Fuel Material Combustion

Three typical solution schemes of adjoint problems of heat transfer, phase transformations and chemical reaction at the forest fuel material surface were analyzed in this work. Characteristic times of thermal decomposition reaction suppression of forest fuel materials (needles of pine and fir-tree, leaves of birch) were presented for concerned heat transfer models. Effective heat exchange conditions which are characterized by minimal times of chemical reaction suppression in forest fuel materials and minimal extinguishing agents expenditure were established.

The Conditions and Characteristics of Wood Particles Ignition in the Stream of the High Temperature Gases

ABSTRACT The results of the experimental and theoretical studies of the ignition processes of the single woody biomass particles have been given. The experiments have been carried out on the setup, providing the closest conditions to the combustion space of the boiler units. The main parameters of heat transfer (the ambient temperature Tg) and the main characteristic of the process—the ignition delay time (tign) have been registered. The equipment has been used in the experiments providing with high precision the determination of the main conditions and characteristics of ignition. According to the results of the experiments, the mathematical model has been formulated describing the heating and thermal decomposition of the wood taking into account the formation of the gaseous and solid products. The model also describes the moisture evaporation, the thermochemical interaction of water vapor and carbon coke, and oxidation of the pyrolysis products with oxygen in the gas area. The nature of the relations of the heat exchange conditions, the temperature field of the particle, and ignition dynamics has been determined. It has been shown that the determining factor is not only the content of the volatiles and moisture of wood, but also the distribution of moisture in the particle. The record of the distribution of moisture content across the thickness of the layer results in the change of moisture from 0% to 60% to increase the time delay of the ignition 2–3 times. The relation has been determined between the particle size, the moisture content, and the ignition delay time.

Numerical Analysis of Integral Characteristics for the Condenser Setups of Independent Power-Supply Sources with the Closed-Looped Thermodynamic Cycle

The mathematical model of heat and mass transfer processes with phase transition is developed. It allows analysis of integral characteristics for the condenser setup of independent power-supply plant with the organic Rankine cycle. Different kinds of organic liquids can be used as a coolant and working substance. The temperatures of the working liquid at the condenser outlet under different values of outside air temperature are determined. The comparative analysis of the utilization efficiency of different cooling systems and organic coolants is carried out.