Introduction to Combustion and Fire - Assignment Example

Running head: Introduction to Combustion and Fire Name Course name Professors’ name Date Questions 1. Different states of matter are: Solids: attractive forces between molecules are greater than energy causing them to move apart. Individual molecules vibrate in a fixed position. When the temperature of solid is increased, vibration subsequently increases but in the same volume and shape. Liquids: Molecules can move away from each other when temperature is raised. Intermolecular forces in liquids pull molecules together and are easily broken. Temperature increases movement of individual molecule. Gases: This exist when energy in the system exceed attractive forces between molecules. In this case, gas molecules have little interaction between each other. Temperature increases movement of individual molecules hence can expand and contract. Plasmas: They are formed under conditions of extremely high energy such that molecules are split apart to leave atoms. The outcome is a gas with high energy charged atoms. Bose-Einstein Condensates: these are gaseous super-fluids cooled to temperatures approaching absolute zero. Atoms can flow without touching each other since they have the same quantum mechanical state. 2. Free Radical is an atom or molecule that has free unpaired electrons but is neither positively nor negatively charged (Tipler, 1995). In a burning building, the smoke has free radicals which are unstable and reactive. Through an oxidation process, free radicals damage cells membrane, enzymes, blood lipoproteins, and even chromosomes and DNA. This illustrates its relevance in fires. 3. Heat of Combustion: This represents energy released after a complete combustion of a compound with oxygen. The condition that this takes place must be standard. Typically, hydrocarbon fuel reacts with oxygen to form carbon dioxide, water and heat. 4. Conversion of temperatures into Kelvin. I. 46.5°C K = C+ 273.15 K = 46.5 + 273.15 K = 319.65 II. 174°F C = 5/9 (F - 32) C = 5/9 (174 - 32) C = 78.89ºc To Kelvin = 78.89 +273.15 352.04 K. III. 705°C K = C+ 273.15 K = 705+273.15 K = 978.15 k IV. 212°F C = 5/9 (F - 32) C = 5/9 (212 - 32) C = 100 To Kelvin is 100+ 273.15 373.15k 5. Balancing equations I. H3PO4 + 3 KOH => K3PO4 + 3 H2O II. 2 H3PO4 + 3 Mg(OH)2 => Mg3(PO4)2 + 6 H2O III. 2 C2H6 + 7 O2 => 4 CO2 + 6 H2O IV. Ca3(PO4)2 + 3 SiO2 + 5 C => 3 CaSiO3 + 5 CO +2 P 6. Upward movement of Flames and gases can be affected by: compartmentation, dilution, air flow, pressurization or buoyancy. 7. E = mc (T1-T2) E = 1kg* 1.09 kJ/kg K* (T1-T2) K = C+ 273.15 K = 423.15 E = 1*1.09*423.15 E = 461.23 KJ 8. When volume is reduced, there is bound to be more collision between the gases. This forms a reason why a mixture of gases would react faster. 9. Temperature simply is a measurement of kinetic energy of particles in a matter under examination. Temperature as a result, is a number that corresponds to type of energy whilst heat is actual energy which is measured in joules. 10. Mass of empirical unit = ( 35.45g + 12.01g+ [2*1.10])= 49.48 g/mol Molecular mass/empirical mass= 98.96/49.48= 2 Multiply the subscripts by 2: (ClCH2)2 Molecular formula is therefore Cl2C2H4 11. Semenov diagram for thermal explosions: The beginning of flashover is induced by thermal effects which are associated with fuel, its configuration, source of ignition, and thermal feedback of the compartment. Semenov diagram illustrate various growth scenarios of fire. Source: (Tipler, 1995) 12. Thickness= 4.2 cm then covert to meters becomes 0.042m Areas= 0.32 square meters Temperature difference (675 - 32) = 643ºC then converting to Kelvin is 643+273.15 = 916.15K Thermal conductivity of gypsum plaster = 0.48 W/mK Q/t = kA (T.hot – T.cold)/d Q/t = 0.48* 0.32 (916.15)/ 0.042 Q/t = 3350.49 W 13. Types of fire extinguishers: Water Fire extinguishers: Used on solids such as paper, wood and plastics Foam Fire Extinguisher: Used on flammable liquids and solids which are under class B and A respectively. Dry powder fire extinguishers: This is often termed as multi-purpose extinguisher since they can be used on classes A, B, and C fires. Class A, B and C are solids, flammable liquid and flammable gases respectively. Carbon Dioxide fire extinguishers: this is used on fires involving electrical apparatus and class B liquid fires. Wet chemicals: specifically used on class F fires e. g cooking oil and fat. For metal fires: used on class D fires such as metal fires sodium, manganese, aluminium and lithium which are in form of turnings. 14. Premixed flame involves mixing the fuel and oxidizer before reaching the flame. The stoichiometry of the combination is controllable through an adjustment made on the ration of fuel and oxidizer and nitrogen as an inert gas is utilized in diluting the reactants and subsequently modify the flame temperature (Gaydon, 1970). The flame is divided into preheat zone where little heat is released and reaction zone where most chemical energy is released. Diffusion flame entails a supply of the fuel to the burner. An oxidizer is supplied from an ambient air such that mixing and reaction takes place. Diffusion fuel burns slower and produces more soot. 15. Smouldering is in fact slow, low temperature flameless form of combustion. In a nutshell, it is an incomplete combustion. Materials that can undergo smouldering combustion include coal, cellulose, wood, cotton, tobacco, peat, synthetic foams, and charring polymers. 16. The basic mechanism of fire spread is through conduction, convection and direct Pyrolysis. 17. Turbulence amplifies the mixing procedure and improves combustion. Momentarily, burning releases heat that affects instability by means of buoyancy consequently improving changeover into turbulence. 18. Burning velocity of gas mixture simply denotes the rate of mixture entrainment which always increases as the stretch rate increases. With increase in fraction of hydrogen, flame can move through a mixture faster than its burning velocity. 19. Importance of thermal radiation from a flame in fire safety: Thermal radiation is responsible for transition into flashover Thermal radiation determines fire extinguisher to be used on a compartmental flame. Thermal radiation is useful in designing fire safety into a building. 20. A detonation is the high spread of combustion by shock compression. Generally, a detonation is a high explosive that generates an abrupt force within a short time. It is observable in both solids and liquid explosive. On the contrary, deflagration is low spread of combustion by thermal conductivity. 21. Fires are classified into the following categories: Class A: fires capture regular burnable materials such as wood Class B: fires takes place in the vapour or air mixture on the surface of flammable and combustible liquids e. g fuel oil Class C: fires entail energized electrical equipment Class D: fires capture combustible metals such as magnesium. 22. Toxins from different types of fires Class A: Carbon monoxide Class B: Hydro carbons Class C: Electrocution Class D: Metal compounds 23. Factors that affect oxygen depletion rates during a fire in a Compartment are: Carbon monoxide, carbon dioxide and smoke. 24. Sequence of occurrence of fire hazards fire hazards within a compartment fire is as follows: For combustion to take place, heat, fuel and oxygen are required. Growth of fire is a function of fuel and oxygen. From such a condition fire will continue to grow consequently leading to high temperatures. Upon substantial generation of heat (500 to 600ºC), the fire becomes fully developed thus engulfing the whole compartment. When the whole fuel or oxygen in a compartment is depleted fire decays. 25. It is necessary that a building does not have many combustible building materials. Instead it should contain fire resistant materials that can delay spread of fire thus providing extra minutes to save life and property. The standard fire curve (ISO 834) is illustrated below. Source: (Williams-Leir, 1973) References Gaydon, A. G., and Wolfhard, H. G., 1970. Flames: Their Structure, Radiation and Temperature. 3rd ed. London: Chapman and Hall. Tipler, P. A., 1995. Physics for Scientists and Engineers. 3rd ed. New York: Worth Publishers. Williams-Leir, G., 1973. Analytic equivalents of standard fire temperature curves. Fire Technology, 9 (2), 132-136. Read More

 

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