Enclosure Fire Dynamics - Assignment Example

Enclosures Enclosures Student University 1). Thiazole (C3H3NS) A chemical reaction can be represented by a chemical equation. To write an equation that accurately represents the reaction; you must correctly perform three steps. Determine the reactants and the products C3H3NS+O2 Assemble the parts of the chemical equation. Write the formulas for the reactants on one side of the equation, usually on the left, and connect them with plus signs. Write the formulas for the products on the right side of equation. Connect the two sides using an arrow to show the direction of the reaction C3H3NS+ O2 CO2 + H2S+ N2+H2O Balance the equation balancing means showing an equal number of atoms for each element on both sides of the equation. In chemical reactions, no mass is lost or gained. The same amount of matter is present before and after the reactions. So, the same number and kinds of atoms must be present on both sides of an equation. The equation below is not balanced The balanced reaction 4C3H3NS+13O2 12CO2 + 4H2S+2N2+2H2O the RMM of thiazole C3H3NS 12 X3+(1X3)+14+32 = 85 the fuel-air mass ratio Air – fuel ratio = Air – fuel ratio = = 1.22 fuel-air mass ratio = fuel-air mass ratio = = 0.817 the oxygen depletion This occurs when oxygen is dissolved in water and its amount is reduced in the environment leading loss of some creatures like in the lakes. When pollution takes place in the lakes the amount of oxygen is reduced the yield of CO2 = = 67.2% the yield of H2O= = 20% the yield of N2 = = 8.2% the yield of carbon-monoxide = = 32.94% 2). Burns There are three types of burns in the human body. The three types of burns are superficial which is first degree burn, partial thickness which is second degree bums and full thickness burns which is the third degree burn. Superficial- this where is where the skin epidermis is affected but blisters does not form Partial-thickness - burn is where the skin epidermis and dermis are affected and this type of burn is deep. Blisters are formed are formed in this partial degrees burns which takes between two to three weeks to heal. When treating these types of burns, surgery is not required. Full thickness burns - Full thickness burn is a severe form of burn where the skin is affected completely including the muscles in this type of burn; surgery is required to correct the damages. The diagram below shows various types of burns in the human body. From the above diagram it can be noted that even the bones can be affected. These type of burns usually occurs in severe fire where the fitting was exposed to fire for along period. in the Lund-Browder chart, severe burns eschar will appear as follows the significance of ‘eschar’ Eschar is very important because it helps shade out dead tissues on a burn thus leaving a empty skin. Eschar can be brown, black or crusty which is shed off,. Eschar usually helps the body heal. If the body does not form eschar it will not heal. Eschar appear on a Lund-Browder chart From the diagram above it can be noted that for children under the age of 10 with 15% total body burns will require surgery while in others it is 25%. 3). zone and field models Zone models Zone modelling is where enclosures are split into different zones before the fire modelling is done. A room can be divided into two zones, the upper zone and the lower zone and the combustion materials are pressed in the lower zone before fire is lit. The main aim in this zoning is to have the ability to predict the temperature changes, spread of smoke in both zones. The models are based on the simple calculation techniques. the compartments are control zone models being divided into two smaller control volumes, where all conditions and properties are considered homogenous. One division takes the smoke and the other utilises fresh air, and the volumes do not resolve flow, temperature and species. However, it is possible for mass and energy to be transferred between the two control volumes. In using the extinction model, the occurrence of the reaction is instantaneous when there is the mixing of oxygen and fuel in the cells when the combining of the gas and oxygen fall in Burn zone and shown in the figure. On the other hand if the combining of the gas and oxygen happen to fall in the “No Burn” zone there will be mixing of fuel and oxygen but no reaction will occur. The occurrence of such a situation is described as a null reaction. In the instantaneous reaction models products that are produced may include CO2 H2O, CO and soot through the combustion process which is in proportion with the rate at which the fuels are being consumed. It is thus appropriate to give the yields of the products bearing in mind the mass of the fuel that has been consumed. Field models Field modelling is called computational fluid dynamics models where boxes are used as enclosures and they are divided into small cells for analysis. This model works based on the principle of momentum conservation, mass and imaging. Field models are composed Reynolds Averaged Navier-Stokes (RANS) models, Direct Numerical Simulations (DNS) models and Large Eddy Simulations (LES) models. In context, DNS simulations possess various problems in respect to modelling an environment with the computational resources currently available. This calls for highly fine grid resolution. In situations where there is the use of grid resolutions that is fine enough it is possible to model the turbulent flow with no necessity for a sub-grid approximation. The sub-grid approximation finds its application exclusively in compartment fire application in also in research situation owing to its computational cost. A large eddy simulation has the capability of fully simulating all the fluctuations which are large than the mesh size. When an estimation is being made for smaller eddies there is little uncertainties due to the fact that the eddies are of a uniform character In experimenting and FDS modelling of fire the design of compartment was done is such a way that it is possible to determine the effect of the size of the fuel which is being used in the process. Understanding of compartmental fire behaviour is of importance as it enables the deriving of straight predictions over the impact it has on the structural elements. There has been little which has been done on fuel properties, ventilation and configuration and this remains a setback that need to be solved. The issue of regions with limited ventilations has been discussed in great length by authors Takede and Akita. In there research it was found that increasing the opening area of compartment resulted in a change in the regimes including: stable laminar burning, extinction, unstable oscillation and stable burning that included a possibility of oscillation (Yang and Hu, 2010). It has been discovered from fire field models there is limited ability to have access to accurately predict thermal conditions and chemical species in ventilated compartment fires. Further, in formal ventilation progress it has shown that if a well ventilated compartment is accessed, with the exception of grunge, field models have been found to perform well in the prediction of temperatures and in proper species if the experiment uncertainties is well accounted for. With the availability of an inaccurate prediction of an incomplete burning levels thud impacts the calculations derived from radioactive heat transfer and burning rates which are estimated by human tenability’s. High quality which comes in with quantified uncertainty and relatively low temperatures provides measurements of fires gas species from the interior of the under ventilated compartment fires that are needed for guiding the development and also for validation of improved fire fields models. A computer is used in this modelling these models has many advantages and disadvantage 4). rate of heat transfer from the smoky layer to the floor Useful figures & formulae: (1) (2) Where and X= 9/2.15 Figure 1. Parallel plates Where and X= 9/2.15 = 4.186 Y= 14/2.15 = 6.512 ) ) Q=2,2,948,549.67 5). This material can not be igited at within ten minutes if exposed to 10 kW m-2? Useful formulae: = 4.24 X 10-6Wm-2/J W = J / s 0.82 W m-1 K-1 X 824 J kg-1 K-1X 2300 kg m-3 1,554,064 m-4 K-2S-1 = = 20.38 minutes This material can not be igited within ten minutes if exposed to 10 kW m-2 as the time taken to ignite it is 32.26minutes at thick side and 20.38 minutes for thin. References Doty, S & Turner, CW 2009, Energy management handbook, Fairmont press Inc. Lilburn, GA- USA. Holhorn. P.G.. Bishop. S.R.. Drysdale. D.D. and Beard. A.N.. Experimental and tha)retical models ctf flashover. Fire SLifkty Jourtiul (in press). Hume, B, 2009) The Use of CFD Computer Models for Fire Safety Design in buildings Available: http://www.communities.gov.uk/documents/fire/pdf/381249.pdf Last accessed 17th April, 2015 Kreith, F, Manglik, RM & bohn, SM 2011, Principles of heat transfer, Cengage Learning, Stanford UK Novozhilov, V (2001) Computational fluid dynamics modelling of compartment fires. Progress in energy and combustion science. 27 () p611-666 Rangwala AS. (2002). Mathematical modeling of low ventilation small-scale compartment fires. MS Thesis,Department of Fire Protection Engineering, University of Maryland, College Park, MD. Rawlins, CA & Phillips, HR 2001, Reduction of in mine heat load 7th. International mine ventilation congress, pp. 381-389. Ringwelski BA (2001). Low ventilation small-scale compartment fire phenomena: wall vents. MS Thesis,Department of Fire Protection Engineering, University of Maryland, College Park, MD,. Tewarson A. (1973). Some observations on experimental fires in enclosures, part II—ethyl alcohol and paraffin oil. Combust Flame Thomas PH. (1981). Fire modelling and fire behaviour in rooms. 18th Symposium (int.) on combustion, The Combustion Institute, Yang, D & Hu, L (2010) Comparison on FDS predictions by different combustion models with measured data for enclosure fires. Fire Safety journal. 45. Read More