Deflagrations transition to detonations

The process of flow mixing in rough-walled tubes has a leading role in flame front pre-detonation acceleration [6, 7, 12, 13]. Rough walls are not the only 

Gelfand et al., Thermo-Gas Dynamics of Hydrogen Combustion and Explosion, Shock Wave and High Pressure Phenomena, 

8 Shock-Free and Spontaneous Initiation of Explosive Regimes 

Based on data obtained in [14], Fig. 8.2 illustrates the decrease in pre-detonation zone length with increasing mass concentration of inert 80-pm particles, grains of sand dispersed in the hydrogenous mixture volume. Water steam condensation resulting in water drop suspension in the mixture volume also increases the probability of deflagration-to-detonation transition. 

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Deflagration to Detonation Transition A reaction front that starts out with velocities below the speed of sound and subsequently accelerates to velocities higher than the speed of sound in the unreacted material is said to have undergone a Deflagration to Detonation Transition. The possibility of transition is enhanced by confinement/turbulence generators in the path of the reaction front. 

An in-line detonation flame arrester must be used whenever there is a possibility of a detonation occurring. This is always a strong possibility in vent manifold (vapor collection) systems, where long pipe runs provide sufficient run-up distances for a deflagration-to-detonation transition to occur. Figure 3-3 shows the installation of in-line arresters of the detonation type in a vent manifold system. 

Deflagration-to-Detonation Transition (DDT) The transition phenomenon resulting from the acceleration of a deflagration flame to detonation via flame-generated turbulent flow and compressive heating... 

Although the status of many 3D codes makes it possible to carry out detailed scenario calculations, further work is needed. This is particularly so for 1) development and verification of the porosity/distributed resistance model for explosion propagation in high density obstacle fields 2) improvement of the turbulent combustion model, and 3) development of a model for deflagration to detonation transition. More data are needed to enable verification of the model in high density geometries. This is particularly needed for onshore process plant geometries. 

VI. Preparation VII. Detonation Characteristics VIII. Thermal Decomposition IX. Combustion DDT (deflagration-to-detonation transition) X. References. The major emphasis will be placed on Sections VII, VIII and IX... 

Detonation in SP is initiated by shock or by DDT (deflagration to detonation transition). Let us first examine shock initiation, ie, initiation by in-contact or close-by detonation of HE... 

In 1957, a flame propagating in a long tube under conditions resulting in a deflagration to detonation transition (DDT) was given the name "tulip" by Salamandra et al. [7]. This term was subsequently commonly applied in detonation studies to describe this typical shape [8,9]. Figure 5.3.2 shows a few... 

A deflagration can also evolve into a detonation. This is called a deflagration to detonation transition (DDT). The transition is particularly common in pipes but unlikely in vessels or open spaces. In a piping system energy from a deflagration can feed forward to the pressure wave, resulting in an increase in the adiabatic pressure rise. The pressure builds and results in a full detonation. 

Chatrathi, K. et al., Process Safety Progr., 1996, 15(4), 237 A study of deflagration to detonation transition in pipes, for gas/air and dust mixtures, has been made and reported. Obviously it depends upon the exact mixture, but departures from the straight and narrow generally facilitate this transition from slight to seriously destructive over-pressures. 

Deflagration to Detonation Transition and Shock Interaction is discussed by Cook(1958), pp 183-87... 

Deflagration to detonation transitions for either the composite or HPDB (High-performance double-base) proplnts have not resulted from the use of mild thermal initiation even when strongly confined. It was generally observed that porous beds of material are required to provide compressioned heating that ultimately develops into a self-sustained deton, as was proposed by Andersen ... 

In conclusion of this rept, Gibson, et al state that deflagration to detonation transition seems to be related to the physical characteristics of an explosive or propellant bed Gibson et al (Refs 12a 12b) also conducted at the BurMines a research which was broader than transition from combustion and deflagration to detonation. The prime objective of the reseat ch was to evaluate mechanisms involved in the initiation and growth of detonation in systems that ate capable of rapid exothermal decomposition. 

M.A. Cook et al, PrRoySoc 246A, 281-83 (July 1958) (Deflagration to detonation transition in solid and liquid explosives)... 

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