scholarly journals Studies on the Effects of Interphase Heat Exchange during Thermal Explosion in a Combustible Dusty Gas with General Arrhenius Reaction-Rate Laws

2012 ◽  
Vol 2012 ◽  
pp. 1-15 ◽  
Author(s):  
K. S. Adegbie ◽  
F. I. Alao
Keyword(s):  
Heat Exchange ◽  
Thermal Explosion ◽  
Reaction Rate ◽  
Numerical Solutions ◽  
Combustion Process ◽  
Solid Particles ◽  
Dusty Gas ◽  
Rate Laws ◽  
Fuel Droplets ◽  
Interphase Heat Exchange

A mathematical model for thermal explosion in a combustible dusty gas containing fuel droplets with general Arrhenius reaction-rate laws, convective and radiative heat losses, and interphase heat exchange between gas and inert solid particles is investigated. The objective of the study is to examine the effects of interphase heat exchange between the gas and solid particles on (i) ignition of reacting gas, (ii) accumulation of heat by the solid particles during combustion process (iii) evaporation of the liquid fuel droplets, and (iv) consumption of reacting gas concentration. The equations governing the physical model with realistic assumptions are stated and nondimensionalised leading to an intractable system of first-order coupled nonlinear differential equations, which is not amenable to exact methods of solution. Therefore, we present numerical solutions as well as different qualitative effects of varying interphase heat exchange parameter. Graphs and Table feature prominently to explain the results obtained.

Thermal explosion characteristics of a combustible gas containing fuel droplets

2021 ◽  
Vol 13 (2-3) ◽  
pp. 124-145
Author(s):  
Saad A. El-Sayed
Keyword(s):  
Thermal Explosion ◽  
Numerical Solutions ◽  
Exothermic Reaction ◽  
Single Step ◽  
Critical Conditions ◽  
Phase System ◽  
Characteristic Parameters ◽  
Fuel Droplets ◽  
Spray System ◽  
Combustible Gas

This paper investigated the critical ignition conditions of combustible gas containing liquid fuel droplets. The analysis is done based on the criteria of the thermal explosion theory. It includes analytical and numerical solutions of modeling equations of fuel droplets heating and evaporation by convection and radiation from the surrounding reactive hot gas. The exothermic reaction is usually modeled as a single-step reaction obeying an Arrhenius temperature dependence. The thermal conductivity of the fuel droplet is dependent on temperature. The analytical solution produced relations between the main critical characteristic parameters in all planes of the solution. The results obtained from investigating the effect of the characteristic parameters on the explosion behavior of gas and fuel droplets and the thermal radiation proved that both of them are significant. The study proved that the criticality definitions of the thermal explosion of a single-phase system can be used effectively and efficiently to determine the critical conditions of a multi-phase system. Finally, the application of the numerical solutions of the modeling equations was used to analyze the explosion characteristics of a diesel fuel spray system.

scholarly journals Gelfand-type problem for two-phase porous media

2014 ◽  
Vol 470 (2163) ◽  
pp. 20130573 ◽  
Author(s):  
Peter V. Gordon ◽  
Vitaly Moroz
Keyword(s):  
Porous Media ◽  
Heat Exchange ◽  
Thermal Explosion ◽  
Natural Extension ◽  
Type Problem ◽  
Two Phase ◽  
Single Temperature ◽  
Different Temperatures ◽  
Gelfand Problem ◽  
Interphase Heat Exchange

We consider a generalization of the Gelfand problem arising in Frank-Kamenetskii theory of thermal explosion. This generalization is a natural extension of the Gelfand problem to two-phase materials, where, in contrast to the classical Gelfand problem which uses a single temperature approach, the state of the system is described by two different temperatures. We show that similar to the classical Gelfand problem the thermal explosion occurs exclusively owing to the absence of stationary temperature distribution. We also show that the presence of interphase heat exchange delays a thermal explosion. Moreover, we prove that in the limit of infinite heat exchange between phases the problem of thermal explosion in two-phase porous media reduces to the classical Gelfand problem with renormalized constants.

THERMAL CONTROL OF MECHANOCHEMICAL REACTION

2021 ◽  
pp. 3-10
Author(s):  
Yu. Tolchinsky ◽  
V. Ved ◽  
I. Rofe-Beketova
Keyword(s):  
Heat Exchange ◽  
Block Diagram ◽  
Mechanical Energy ◽  
Thermal Control ◽  
Solid Particles ◽  
Mechanochemical Reaction ◽  
Flow Mode ◽  
Stress Concentrations ◽  
Reaction Heat ◽  
Crushed Material

Mechanochemistry studies and explains the processes of chemical and physicochemical transformations that are generated by mechanical action on a substance. When carrying out deep mechanochemical transformations, as a rule, it is necessary to transfer to solid reagents a portion of energy comparable to the energy of interatomic bonds. For this, various machines and apparatus are used, such as extruders, in which mechanical energy is constantly transferred to the crushed material. The article discusses the interaction of two reagents in a simple chemical reaction in the state of a mixture of particles of two types, which occurs during compression of particles having a rough irregular shape, and colliding with each other, forming areas of contact. Significant stress concentrations and heating of the substance with the formation of a new phase arise in these regions. Thermal control of the mechanochemical reaction is to maintain an optimal balance of dissipative heat and heat from the coolant in the worm reactor so that the rate of flow and the final product of the reaction meet the specified specifications. The formulas provided in the article for calculating the coefficient of the rate of mechanochemical reaction, heat transfer between worm reactor and jacket channel, heat exchange between jacket and environment allows to calculate the balance conditions for thermal management. The block diagram of the technological line, which is presented in the article, is more economical in comparison with carrying out the same reaction in a solvent. The economic benefit lies in the elimination of the steps of introducing and removing the solvent from the reaction product. At the end, it is indicated that the mechanochemical reaction of the transformation of a mixture of two dispersed materials consisting of solid particles into a liquid can be realized in continuous conditions in a flow mode in a worm machine. And thermal control of the course of a mechanochemical reaction can be carried out using controlled heat exchange with a coolant in a jacket under conditions of turn-around spatial dispersion.

Study on Preparation of Ti Powder by Self-Propagating High-Temperature Synthesis (SHS) with Magnesiothermit Reductive Process

2008 ◽  
Vol 575-578 ◽  
pp. 1086-1092
Author(s):  
Peng Lin Zhang ◽  
Tian Dong Xia ◽  
Guo Dong Zhang ◽  
Li Jing Yan
Keyword(s):  
Reaction Rate ◽  
Combustion Temperature ◽  
Combustion Process ◽  
Green Compact ◽  
Reaction Products ◽  
Technological Parameters ◽  
Solid Reaction ◽  
Temperature Synthesis ◽  
High Temperature Synthesis ◽  
Ti Powder

The combustion process of Mg-TiO2 system was preliminarily investigated from three aspects of thermodynamics, reaction kinetics and the technological parameters. The result indicates that the adiabatic temperature of Mg-TiO2 system is between 2060K and 2140K because the major existent modalities of TiO2 is the rutile and anatase, this meets the empirical criterion that the SHS reaction will be self-sustaining; The solid-solid reaction occurs at about 767K; Ti powders can be produced only when the ratio between Mg and TiO2 arrives at 2.9:1; The higher the vacuum, the more complete the reaction; The combustion temperature arrives at its peak when the pressure of green compact arrives at 250MPa; the velocity of the combustion wave increases with the augmentation of the pressure of green compact. So the proper control of the technological parameters can change the reaction temperature, reaction rate and the components of reaction products.

Heat and Mass Transfer of Temperature-Dependent Viscosity Models in a Pipe: Effects of Thermal Radiation and Heat Generation

2020 ◽  
Vol 75 (3) ◽  
pp. 225-239 ◽  
Author(s):  
Fayyaz Ahmad ◽  
Mubbashar Nazeer ◽  
Mubashara Saeed ◽  
Adila Saleem ◽  
Waqas Ali
Keyword(s):  
Thermal Radiation ◽  
Heat Generation ◽  
Numerical Solutions ◽  
Physical Property ◽  
Solid Particles ◽  
Temperature Fields ◽  
Fluid Temperature ◽  
Temperature Dependent Viscosity ◽  
Dependent Viscosity ◽  
Increasing Trends

AbstractIn this paper, a study of the flow of Eyring-Powell (EP) fluid in an infinite circular long pipe under the consideration of heat generation and thermal radiation is considered. It is assumed that the viscosity of the fluid is an exponential function of the temperature of the fluid. The flow of fluid depends on many variables, such as the physical property of each phase and shape of solid particles. To convert the given governing equations into dimensionless form, the dimensionless quantities have been used and the resultant boundary value problem is solved for the calculation of velocity and temperature fields. The analytical solutions of velocity and temperature are calculated with the help of the perturbation method. The effects of the fluidic parameters on velocity and temperature are discussed in detail. Finite difference method is employed to find the numerical solutions and compared with the analytical solution. The magnitude error in velocity and temperature is obtained in each case of the viscosity model and plotted against the radius of the pipe. Graphs are plotted to describe the influence of various parameter EP parameters, heat generation parameter and thermal radiation parameters against velocity and temperature profiles. The fluid temperature has decreasing and increasing trends with respect to radiation and heat generations parameters, respectively.

Chemical-looping combustion — a thermodynamic study

2008 ◽  
Vol 222 (6) ◽  
pp. 1005-1019 ◽  
Author(s):  
N R McGlashan
Keyword(s):  
Heat Exchange ◽  
Redox Reactions ◽  
Oxygen Carrier ◽  
Combustion Process ◽  
Reduction Process ◽  
Equilibrium Temperature ◽  
Working Fluid ◽  
Chemical Looping Combustion ◽  
Chemical Looping ◽  
Ic Engine

The poor performance of internal combustion (IC) engines can be attributed to the departure from equilibrium in the combustion process. This departure is expressed numerically, as the difference between the working fluid's temperature and an ideal ‘combustion temperature’, calculated using a simple expression. It is shown that for combustion of hydrocarbons to be performed reversibly in a single reaction, impractically high working fluid temperatures are required — typically at least 3500 K. Chemical-looping combustion (CLC) is an alternative to traditional, single-stage combustion that performs the oxidation of fuels using two reactions, in separate vessels: the oxidizer and reducer. An additional species circulates between the oxidizer and reducer carrying oxygen atoms. Careful selection of this oxygen carrier can reduce the equilibrium temperature of the two redox reactions to below current metallurgical limits. Consequently, using CLC it is theoretically possible to approach a reversible IC engine without resorting to impractical temperatures. CLC also lends itself to carbon capture, as at no point is N2 from the air allowed to mix with the CO2 produced in the reduction process and therefore a post-combustion scrubbing plant is not required. Two thermodynamic criteria for selecting the oxygen carrier are established: the equilibrium temperature of both redox reactions should lie below present metallurgical limits. Equally, both reactions must be sufficiently hot to ensure that their reaction velocity is high. The key parameter determining the two reaction temperatures is the change in standard state entropy for each reaction. An analysis is conducted for an irreversible CLC system using two Rankine cycles to produce shaft work, giving an overall efficiency of 86.5 per cent. The analysis allows for irreversibilites in turbine, boiler, and condensers, but assumes reactions take place at equilibrium. However, using Rankine cycles in a CLC system is considered impractical because of the need for high-temperature, indirect heat exchange. An alternative arrangement, avoiding indirect heat exchange, is discussed briefly.

Effect of interphase heat exchange on the kinetics of condensation relaxation of supersaturated vapor

2009 ◽  
Vol 54 (11) ◽  
pp. 483-487
Author(s):  
N. M. Kortsenshteyn ◽  
E. V. Samuĭlov ◽  
A. K. Yastrebov
Keyword(s):  
Heat Exchange ◽  
Supersaturated Vapor ◽  
Kinetics Of ◽  
Interphase Heat Exchange

Thermal radiation effect on thermal explosion in gas containing fuel droplets

1999 ◽  
Vol 3 (4) ◽  
pp. 769-787 ◽  
Author(s):  
Igor Goldfarb ◽  
Vladimir Gol'dshtein ◽  
Grigory Kuzmenko ◽  
Sergei Sazhin
Keyword(s):  
Thermal Radiation ◽  
Thermal Explosion ◽  
Radiation Effect ◽  
Fuel Droplets ◽  
Thermal Radiation Effect
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