Numerical simulation of heat and mass transfer under the conditions of phase transitions and chemical reaction during ignition of condensed substances by single hot particles

Physical and mathematical models of heat and mass transfer under the conditions of phase transitions and chemical reactions have been developed for the numerical analysis of condensed substances ignition by a single particle (size from 0.5 mm to 5 mm) heated up to high temperature (above 800 K). Liquid, solid and gel fuels were considered as condensed substances. Metal and non-metal particles were used as ignition sources. A heat and mass transfer mathematical model is presented as a system of nonlinear non-stationary differential equations in the private derivatives corresponding to the basic provisions of the general theory of heat transfer in chemical kinetics and free convection. An algorithm for solving differential equations with the corresponding initial and boundary conditions is based on the finite- difference method. The locally one-dimensional method was used to solve difference analogous of differential equations. One-dimensional difference equations were solved using an implicit four-point difference scheme. Nonlinear equations were solved by the iteration method. Mathematical model verification and the assessment of numerical research results reliability was executed by its comparison with experimental results. Also the verification of the law of conservation of energy in the solution area of the ignition problem was performed. Besides, testing of applied numerical methods and the developed silving algorithm on the example of a group of less complex challenges of thermal conduction and thermal convection was held. The minimum parameters of hot particles (temperature, size) and the ignition delay time of condensed substances were determined for local heat sources with different shapes. The influence of thermal conduction, convection and radiative heat transfer mechanisms in the “particle – condensed substance” system was established on the ignition characteristics

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 study of heat and mass transfer during ignition of thermal decomposition products of a coal particle

A numerical research was executed for macroscopic regularities determination of heat and mass transfer processes under the conditions of phase transformation and chemical reaction at the ignition of vapour coming from fabrics impregnated by typical combustible liquid into oxidant area at the local power supply. Limit conditions of heterogeneous system “fabric – combustible liquid – oxidant” ignition at the heating of single metal particle was established. Dependences of ignition delay time on temperature and rates of local power source were obtained

Transient Heat and Mass Transfer of Liquid Droplet Ignition at the Spreading over the Heated Substrate

The processes of heat and mass transfer accompanied by phase changes and chemical reactions are numerically modeled for the ignition of a liquid droplet formed from a condensed substance hitting the surface of a high-temperature metallic plate (substrate). The time delay of a droplet ignition is determined as well as the influence scope of a substrate, droplet, and oxidizer temperature, together with sizes and speed of droplet spreading on the ignition response. Conditions are revealed when spreading and deformation of a liquid droplet dominate during the ignition process

Information measuring subsystem oil pumping station “Parabel”

Information-measurement subsystem oil pumping station (OPS) “Parabel”, located on the site of the main pipeline “Alexandrov-Anzhero” (OJSC “AK” Transneft "”. Developed on the basis of a modern microprocessor equipment, automation, as well as high-speed digital data channels. The simple solution to meet the requirements set out in the guidance document "Automation and remote control of trunk pipelines. «General provisions» (RD-35.240.0000-KTN-207-08)

Mathematical Modeling of Heat and Mass Transfer Processes with Chemical Reaction at Polymeric Material Ignition by Several Small-Size Hot Particles

Numerical research of interconnected heat and mass transfer processes in the “two hot particles—polymeric material—air” system was executed. The joint effect of several local heat sources on the main integrated characteristic of ignition process (ignition delay time) was established. Two ignition models characterized by the relative positioning of hot particles on a polymeric material surface were revealed. Besides, there were established characteristics of local heat sources and the distance between them (700  K<Tp<1150 K and L>1.5 or Tp>1150 K and 0.25<L<1.5) when regularities of heat and mass transfer processes in the “two hot particles—polymeric material—air” system are similar to regularities of heat and mass transfer processes in the “single hot particle—polymeric material—air” system

Ignition of a coal particle at the low temperature of gas flow

Regularities of physical and chemical processes occurring during the heating of the coal dust particles by low-temperature air flow are investigated by means of thermogravimetric analyzer TA SDT Q600 and experimental setup of optical diagnostics of multiphase flows based on PIV method. Qualitative and quantitative characteristics were established for the processes of the coal particle inert heating, moisture evaporation, thermal decomposition, combustible gas mixture formation, oxidation of volatiles and carbon. It was revealed that the temperature of the oxidizer required for the coal particle ignition is higher than 500 ∘C. The experimental data can be used to develop predictive mathematical models of technological processes fire hazard in pulverized coal systems of thermal power plants

Comparative Analysis of Partially Renewable Composite Fuels Based on Peat, Lignite and Plant Oil

The inevitable depletion of exploited fossil fuel deposits motivates the investigation of every possibility of saving them. One of the ways to do that is to combine fossil fuels with renewable plant-derived fuels. This paper studies the specific aspects of the thermochemical conversion of composite fuels consisting of peat or lignite with rapeseed oil. It was shown that mixtures of peat or lignite with rapeseed oil can be successfully gasified when the temperature is higher than 700–800 °C. The self-sustaining combustion of these fuels does not support such high temperatures, and thus the process requires external heating. The obtained optimal component ratio for peat-oil and lignite-oil compositions is about 1:2 and 3:2, respectively. Such mixtures allow the most efficient usage of the oxidation heat during conversion. The high calorific value of such fuels is very close to that of rapeseed oil (38.5 MJ/kg), even for the lignite-oil composition with 40 wt% lignite. Lower overall prices of fossil fuels compared to pure renewable plant-derived fuels help reduce costs and save valuable fossil fuels

Hot Surface Ignition of A Composite Fuel Droplet

The present study examines the characteristics of conductive heating (up to ignition temperature) of a composite fuel droplet based on coal, liquid petroleum products, and water. In this paper, we have established the difference between heat transfer from a heat source to a fuel droplet in case of conductive (hot surface) and convective (hot gas) heat supply. The Leidenfrost effect influences on heat transfer characteristics significantly due to the gas gap between a composite fuel droplet and a hot surface

Assessment of the Stability of Condensed Solid Substance Ignition by a Hot Particle

The paper presents a numerical simulation of composite fuel ignition by a disc-shaped hot metal particle. The study establishes the temperature and the source size limits, which are necessary and sufficient for condensed substance ignition. A diagram with coordinates “a heat flow the amplitude – ignition delay time” has been presented. The diagram shows the area of the sustainable initiate combustion of composite solid fuel at local heating by the source with limited energy capacity