R. Klemens

Numerical study of dust lifting in a channel with vertical obstacles

Abstract In the paper, several results of numerical computation of multiphase flows in a channel with complex geometry are considered. The objective of the research was to study the dust lifting process from a layer behind a shock wave in a rectangular channel with vertical obstacles in the upper part of the tube. It is to be shown that that kind and also any sort of geometry may crucially change the whole phenomena of dust enhancement and of combustion. This is very important for safety in, for example, coal mines where channels are usually of more sophisticated structure than is usually assumed by most researchers.

Suppression of dust explosions by means of different explosive charges

Abstract The research was aimed at the development and testing of a super fast explosion suppression system using different explosive charges. The experiments were carried out on a prototype device (steel container) of 2 l capacity, closed by means of a membrane. Below the membrane, there was an exhaust connector pipe, at the end of which was a dispersing head. About 1 kg of extinguishing material was located inside the container. The membrane was ruptured by the explosion of a miniature cumulative charge placed on the membrane surface inside the container. In some experiments the explosive charge was located both on the membrane surface and in the upper part of the container—over the extinguishing material. Pentryt, pyrotechnic charge and powder charge were used as the explosive material. In the first case, the container was filled up (above the extinguishing material surface) with nitrogen under pressure in the range of 30–50 bar. In two other cases, there was no overpressure inside the container. The pyrotechnic charge and powder charge were used as gas generators in order to produce the overpressure only after triggering the system by the signal from the protected volume. Standard electric igniters were applied to initiate the explosive material. The main reason for using the explosive materials for membrane perforation was their high combustion velocity, that enabled opening of the membrane within several microseconds. The dust explosion suppression occurred as a result of the activity of extinguishing material blown out of the container by means of compressed gases. The suppressing powders were used as the extinguishing material. The results of the research into optimization of the shape and miniaturization of the explosive charge mass are presented. Also, the process of shaping of the exhaust stream of the extinguishing material was recorded. Finally, the dust explosion suppression process in a 1.25 m 3 chamber, using the developed super fast extinguishing system was studied.

Experimental and theoretical study of ignition of single coal particles at zero gravity

Abstract In the coal combustion process one of the most important problems is the knowledge of chemical reaction principles concerning combustion of single particles and the knowledge of mutual interaction between the burning particles. In this paper theoretical results are presented, which demonstrate the characteristic ways of ignition between coal particles depending both on volatile content in the coal and oxygen content in the atmosphere. The influence of the particles diameter and the distance between them are also discussed. Based on these experiments, a mathematical and physical model of the process have been made. Due to numerical calculation, the radiation and conduction portion in overall balance of heat exchange between the particle and its surrounding in the course of ignition process for various kinds of cool and oxygen contents in the air have been determined. The presented calculation results show an accordance with data results of experiments carried out at zero gravity conditions.

Experimental Studies of Explosions of Methane-Air Mixtures in a Constant Volume Chamber

Results are presented for the variation of flame propagation velocity with rising explosion pressure for methane-air mixtures. The experiments were carried out in an explosion chamber with a volume of 1.25 m3. Photos of the flame propagating during the explosion processes were obtained through a window in the middle of the front cover of the chamber. The influence of the methane concentration on the time delay between the flame front approaching the chamber wall and the moment when the pressure inside the chamber reached its maximum is also discussed.

Hybrid Detonations in Oats Dust Clouds in Methane-Air Mixtures

Detonation waves in oats dust clouds in methane-air mixtures were investigated experimentally. Tests were carried out in a vertical tube 4,5 m long with an 8cm internal diameter. The hybrid mixture was ignited by a shock wave generated by means of the detonation of an oxygen-hydrogen stoichiometric mixture in the driver section. Flame propagation was recorded with the use of a streak camera and pressure profiles were measured at selected tube positions. It was found that hybrid detonations are possible in oats dust clouds in methane-air ixtures for a range of methane concentrations from 8.5% to 14.5%, with oats dust concentrations not greater than 0.1 kg/m3. Moderate concentrations of oats dust were found to promote transition to detonation, but this depends on the composition of the gaseous mixture; higher concentrations act as a suppressant.

On ignition and unsteady flows of dusty gases with combustion reactions

Studying of ignition, combustion and detonation processes in dusty gases is presented. The dusty gas is considered as a two-continuum medium with taking into account transport effects in the phases and non-equilibrium chemical reactions. Two-dimensional problems of ignition and detonation developing in a plane gallery caused by a supersonic inflow stream and heating of the closed end of the gallery are studied with the analytical mediod of catastrophe and two finite-difTerence numerical methods.