Budget and Forecasts Project of Enclosure Fire Dynamics - Assignment Example

Name : xxxxxx Tutor : xxxxxx Topic : Budget and Forecasts project Course : xxxxxx Institution : xxxxxx @ 2010 T1. Thermal explosion A thermal explosion occurs when the heat generated by the walls of a vessel is greater than the surrounding heat. Thermal explosion is therefore minimal in cold-walled vessels and especially the vessels which are fitted with ice as an insulating material especially because the walls act as an insulating material which reduces thermal conductivity (James G. Quintiere, R. L. Alpert, R. A. Altenkirch, 1983). The cold walls of the vessel prevent the leakage of heat from the surrounding into the cold walls. When the amount of heat leakage is reduced, the amount of ice that melts from the cold walls is reduced and the icing process in the vessel is increased and hence minimal chances of thermal explosion. Insulating the vessel using cold walls or ice walls reduces the amount of heat that may enter the vessel from the surrounding hence keeping the vessel cool (Björn Karlsson, James G. Quintiere 2000). Self- accelerating reaction mechanisms in vessels make them to generate a lot of heat from their engines during the induction period. During this period high temperatures are generated due to the increasing velocity of the vessel. As a result a lot of heat is generated from the surrounding environment or from within the vessel. The cold wall prevents the heat transmission from the engine room from leaking into the walls. Cold walls in vessels keep the vessel cool hence reducing thermal explosion. Semenov diagrams are used to explain and demonstrate the critical temperature which is used for cooling. In a cold walled vessel. Exothermal reactions are minimal since the cold walls maintain heat balance in the vessel and hence giving no room for critical conditions for thermal explosion. Due too the heat balance existing between the cold walls of the vessel and the surrounding environment, there is minimal or no heat transfer between the two environments. By use of Semenov diagrams then it is clear that there is no effect of heat transfer on a thermal heat balance in cold walled vessels (Björn Karlsson, James G. Quintiere 2000). Pre-explosion heating causes a lot of heat on the surrounding environment and there is a high rate of heat transfer into the walls and as a result there is a disturbance in the heat balance. By use of Semenov diagrams a critical temperature is required to cool the vessel so as to maintain its heat balance and avoid explosions. Figure 1. Semenov Diagram T3. Explosion, deflagration and detonation Explosion is the explosion or the chemical action which leads to a sudden formation of a huge volume of expanded gas. It can also be defined to the type of bursting which takes place with violence and loud noise resulting from an internal pressure. Many scholars had divergent views on the definition of explosion narrowing it to the sudden and violent release of chemical, mechanical and nuclear energy which is accompanied by a release of gases and a high temperature generation due to an internal pressure. Deflation can be defined as the subsonic combustion which is propagated by thermo conductivity that exists between hot burning materials and cold materials (Björn Karlsson, James G. Quintiere 2000). Detonation on the other hand is the propensity of fuels to pre-ignite in the combustion chamber of an engine. The ignition causes a shock wave in the chamber and the burning and expanding fuel air mixture then collides with the piston which is travelling to the top-dead-center causing the a knock of pistons slamming against the chamber walls. Detonation has both qualitative and quantitative features and they include: the process of combustion takes place behind a shock which is responsible for inducing chemical decomposition; it has a high velocity and pressure, its length is highly correlated with the energy released and they have specific dynamical features resulting from hydrodynamics-chemical kinetics interplay. The development of detonation has been examined on the basis wave dynamic analysis of schlieren photographs which were obtained by Steinicke and Neubert. Present results of detonation are similar to those observed in the Seventh Combustion Symposium with a similar pre-ignition and characteristics hence concluding that process must have been attained in the development process (James G. Quintiere, R. L. Alpert, R. A. Altenkirch, 1983). There have been some advances in the development of detonation which has intensified the use of technology where new methods of making plasma detonation with deposits of coatings and which issue a permanent delivery of gases into the combustion chamber. The reason for this development is to increase the velocity of the detonators. T4. Diffusion Combustion The following are some of the features of a diffusion combustion:, the speed of the fame is determined by the rate of diffusion, flames burn in a low rate due to lack of enough oxidizer and the soot produced is incandescent from the heat and an it is orange in color. There are two types of diffusion flames: momentum and buoyancy dominated fires (James G. Quintiere, R. L. Alpert, R. A. Altenkirch, 1983). Momentum dominated has a jet with high velocity such that the height of the jet is proportional to the orifices diameter and it is independent of the flow rate for as long as the flow rate is enough to sustain the turbulence. Increase in velocity promotes the mixing of air and hence the independence of height of flame on the flow rate. Buoyancy dominate flame has a height which is correlated to the rate of heat release of the flame and they are relatively turbulent. The upward flow of the flame is driven by buoyancy. The suggestions of Froude modeling are that the ratio of inertia to buoyant forces is the key to stimulating the fluid dynamic aspects of pool fires. Froude number is therefore defined to as the ratio of inertia to buoyant forces. For example momentum dominated fires have a Froude number of greater than 1(Fr>1) while buoyancy dominated fires have a Froude number of less than 1(Fr Read More