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Detonation Initiation in H2-Air and CH4-Air Mixtures by Incident Shock Wave - One-Dimensional Numerical Simulation

Mitrowski A., Teodorczyk A.

Archivum Combustionis

2005

Vol. 25 nr 1-4

85-104

Detonation processes in gas mixtures for a long time have been an object of interest of many scientists studying combustion processes. This paper is the contribution to expanding growth of numerical investigations in detonation processes and increasing knowledge of physical aspects of this phenomenon. This paper presents detailed analysis of one-dimensional model of shock initiation of detonation wave. Two combustible mixtures hydrogen-air and methane-air were taken under consideration. Hydrogen-air mixture was analyzed with different concentration of hydrogen, from rich to very lean and with two Mach numbers of strong incident shock wave. The analysis of the transition to detonation process was performed for a bursting diaphragm experiment. In the presented simulation, an increase of Mach number of incident shock wave was made by releasing chemical energy in the driver section at the moment of bursting of the diaphragm. The hot gas in the driver section and fuel mixture in the shock tube is separated by inert gas section. The physical model deals with Euler conservation equations, using an ideal gas law. The set of conservation equations was integrated numerically with the FCT method. The heat release mechanism bases on integration of detailed chemical kinetics equation with the use of CHEMKIN package. Results of the investigation include distribution of thermodynamic and flow parameters in respective time sequence from hot spots formation to detonation relaxation, including collision of retonation wave and contact surface. The main events occurring in the shock tube simulation are also presented on position-time diagrams.

Numerical analysis of forced convection heat transfer during fully developed flow in a channel filled with porous medium

Mitrowski A., Furmański P.

Archives of Thermodynamics

1998

Vol. 19, no 3/4

39-57

The paper presents an analysis of heat transfer in a cylindrical duct filled with porous material in the form of a granular medium. The flow through the porous medium is assumed to be hydrodynamically developed and the porous medium is assumed to have properties variable with the duct radius. The momentum and energy equations for the porous medium were solved numerically and the influence of many factors on the fluid velocity and temperature distributions investigated. Finally, the enhancement of heat transfer from the fluid (flowing through the porous medium) to the duct wall was studied by calculating the heat transfer coefficient (Nusselt number) for the thermally fully developed flow. It was found that the presence of the porous medium in the duct may cause an increase in heat transfer rate by even a hundred of times in comparison to the free fluid flow. This effect of enhancement of heat transfer can be achieved by a proper choise of the medium porosity, solid particles diameter to the tube radius and a ratio of particles to fluid thermal conductivity.