Introduction to Combustion and Fire - Assignment Example

Leading header: Introduction to Combustion and Fire   Your name   Course name    Professors’ name Date Q1. What are the different states of matter and what is the molecular difference between them? State of matter is divided into three: solid, liquid and gas. Solid properties: a substance which is in solid state/phase is relative rigid, and it usually has definite volume and shape, this is because the atoms or molecules that makes a solid are close together and are not compressible when you compare to other state of matter. As a result of thermal energy in solid, the atoms that are found in solid do vibrate but their movement is very small and very rapid, but cannot be seen with naked eyes (Petrov 1999, p.21). Liquid properties: it has a definite volume, but liquid as the ability of changing it shape when flowing. Particles which makes liquid are able to move around when you compare to solid particles. Since the molecules that makes liquid are randomly moving, they usually take the shape of the container which the liquid is stored (Petrov 1999, p.21). Gas properties: it volume and shape is not definite as compared to liquid and solid, the molecules that makes gases will spread out indefinitely, but if they are confined they will take the shape of their container, this is as a result; gases have enough energy that is able to overcome attractive forces. The particles which make gases are well separated resulting in a very low density (Petrov 1999, p.21). Q2.What is free radicals? What is their relevance to fires? Free radical contains an unpaired electron but is neither positively nor negatively charged in atoms or molecule. These electrons are usually very reactive and unstable (Brown 2000, p.42). Free radical electrons are ‘electron-hungry’ compounds and due to its reactive in nature, they can cause severe damage to human being biological tissues during the occurrence of fire. For example smoke from a fire is loaded with free radicals that can cause lung cancer. Q3. Define the term “Heat of Combustion?” Heat of combustion (ΔHc0), this is the energy which is released as heat when any compound undergoes combustion with oxygen, and it must be under standard conditions. The reaction that takes place in combustion is typically a hydrocarbon reacting with oxygen, and the end result is carbon dioxide, water and heat (Brady, 1996, p.23). Q4. Convert the following temperatures into Kelvin: i. Celsius to Kelvin (K) =C+273.15 46.5+273.15= 319.65K ii. Fahrenheit to Kelvin K = 5/9 (° F - 32) + 273 5/9 (174 - 32) + 273= 351.89K iii. 705+273.15= 978.15K iv. 5/9 (212 - 32) + 273= 373K Q5. Balance the following equations: a. H3PO4 + KOH => K3PO4 + H2O H3PO4 + 3KOH => K3PO4 + 3H2O b. H3PO4 + Mg(OH)2 => 2Mg3(PO4)2 + H2O, 2H3PO4 + 3Mg(OH)2 => 3Mg3(PO4)2 + 6H2O c. C2H6 + O2 => CO2 + H2O=> C2H6 + O2 => CO2 + H2O 2C2H6 + 7O2 => 4CO2 + 6H2O d. Ca3(PO4)2 + SiO2 + C => CaSiO3 + CO + P2Ca3(PO4)2 +3SiO2 + 5C => 3CaSiO3 + 5CO + 2P Q6.The upward movement of flames and gases can be affected and altered by a number of factors. What are the most common? Pressure, density and volume Q7. Q = cp m dT         where Q = amount of heat (kJ),cp = specific heat capacity (kJ/kg.K),m = mass (kg), and dT = temperature difference between hot and cold side (K) When Cp=1.09 dT= 180-30=150+273.15=423.15 Q= 1.09x423.15x1=461.23kJ Q8. According to Boyle’s Law (PV = constant); at constant temperature, pressure and volume of gases are inversely related, when you decrease the volume of a gas, the pressure of gas increases. Likewise, when the volume of the gas is reduced, the pressure of gases will increase; meaning faster reaction (Brown 2000, p.52). Q9. Heat can be defined as the amount of energy in a body/system, heat in a body can be transferred through radiation, conduction and convection. Joules is the SI unit for heat. While, Temperature is the measure of the average molecular motions in a body/system, the SI unit for temperature is degree Celsius/Kelvin Q10. n=MM/empirical formula mass n= 98.96/25 ClCH2= 17+ 6+ 2= 25 n=3.95 Q11. Draw and explain a Semenov diagram for thermal explosions.  Thermal flux against Temperature Curve A: the reactant will enter into the system at lower temperature; the heat production curve is lying above heat loss curve in the diagram, it will continue to heat up until the temperature in a system get to Tstable temperature. If it reaches Tstable , the temperature will be constant and no heating will continue. Curve B: the 3 curves: Tstable, Tcritical, and Tignition are at the same temperature, the heat loss curve is tangential to the heat gain curve in the system. The temperature in a system will rise slowly until it reaches critical temperature; raphid acceleration of temperature will be experienced which will result in thermal explosion. Curve C: in this curve the gain flux will exceed the heat loss flux, this means whatever the temperature the reactants will be in the system and thermal explosion in the system will take place. Q12.  Q/t= 0.48 x 0.32(675-32)/0.042= 2351.54 Q13. What are the different types of fire extinguisher and on what can they be used? There are four types of fire extinguishers which are widely known: Water fire extinguisher, Foam Fire extinguisher, Dry powder Fire extinguisher and Carbon dioxide Fire extinguisher (Diamantes 2006, p.18). Water fire extinguisher: cheapest and widely used it mostly used to extinguish Class A (solid such as paper, wood, plastic) fires, but it is not suitable to extinguish Class B (flammable liquids such as paraffin, petrol, oil etc) fires (Diamantes 2006, p.18). Form fire extinguisher: it is more expensive when you compare it to water fire extinguisher, it is widely used to extinguish Classes A (solid such as paper, wood, plastic) and B (flammable liquids such as paraffin, petrol, oil etc) fires, but it is not recommended to be used in to extinguish Class E (Fires involving electrical apparatus) fires (Diamantes 2006, p.18). Dry Powder Fire Extinguishers: it a multipurpose fire extinguisher, can be used to extinguish Class A. Class B and Class C (flammable gases such as propane, butane, methane etc) fires, but special powders are available for Class D (metals such as aluminum, magnesium, titanium etc) fires (Diamantes 2006, p.18). Carbon dioxide Fire Extinguishers: it ideal to be to extinguish Class B fires but (Diamantes 2006, p.18). Q14. What are the differences between a premixed and a diffusion flame? What are the temperature profiles of each type of flame? Premixed flame: this is a flame which the oxidizer has been mixed with fuel before it reaches the flame front; this will create tiny flame fronts and the reactant will be widely available in the flame. While, a diffusion flame is when an oxidizer will combine with fuel through diffusion process, the flame speed is limited by the rate of diffusion in the combustion. Diffusion flames are slower in nature and they produce a lot of soot when you compare them with premixed flames because they are sufficient oxidized for the reaction to go to completion (Williams 1994, p.45). Q15. What kinds of materials can undergo smoldering combustion? This is a slow, low temperature, flameless form of combustion and is usually sustained by the heat which has been evolved as a result of oxygen attacking directly the surface of condensed-phase fuel/materials. Such materials that can sustain smoldering reaction are: coal, cellulose, wood and tobacco (Williams 1994, p.24). Q16. What is the basic mechanism of fire spread? convention radiation and conduction. Q17. Why is turbulence important in combustion? In the combustion process is dependent on time, temperature and turbulence, time is important because if fuel is not given enough time to burn, significant amount of energy will be unburned and too much time given to fuel to burn will produce long flames (Crew 1990, p.23). So in any combustion of fuel there must be correct balance of time and mixing of fuel so that a proper combustion of fuel must take place and this will also minimize flame impingement and will provide highest combustion efficiency and return it will reduce emission of harmful gases into the environment. Q18. What is the burning velocity of a gas mixture? Under what circumstances can a flame move through a mixture faster than its burning velocity? Burning velocity in combustion can be defined as the velocity of the combustion wave normal to itself and relative to the un-burnt gases in the combustion or volume of the gases which have not used in combustion given per unit time, divided by the volume of used gases in the combustion. Flame will move faster through a mixture than its burning velocity if there is a lot of oxygen used in the combustion (Brown, 2000, p34). Q19. Give three reasons why the thermal radiation from a flame is of importance in fire safety? It will help in protecting those things or materials from being destroyed by fire. Q20. What is a detonation? How is this different from a deflagration? Detonation/ spark knock this is an erratic form of combustion which can cause the gasket to fail as well as other engine parts; detonation will occur when excessive heat and pressure is found in combustion chamber of the engine, caused by air or fuel mixture to auto-ignite. Q21. Fires can generally be classified in to three general categories. What are they? Class A (solid such as paper, wood, plastic) fires, Class B (flammable liquids such as paraffin, petrol, oil etc) fires. Class C (flammable gases such as propane, butane, methane etc) fires Q22. Under each of the three conditions outline in question 21, what toxic species would be produced under each of these conditions? Toxic produced in Class A fires may include nitrogen oxides, sulfur dioxide, heavy metals and dioxin. Toxic produced in Class B fires may include carbon, carbon dioxide, heavy metals. And toxic that is produced in Class C fires may include methane, carbon and carbon dioxide (Diamantes 2006, p.34). Q23. What factors affect oxygen depletion rates during a fire n a compartment? The amount of carbon produced in the fire this is because carbon will mix with oxygen to form carbon dioxide. Q24. Identify the sequence of occurrence of fire hazards, to the occupants within a compartment fire. Overload of electrical systems which result in hot wiring or failed components. Combustible areas used in storage don’t have enough protections. Candle left unattended Smoking Flammable liquids stored inside the house. Q25. Draw and label a diagram showing the standard fire curve. Reference List Brown, T. (2000). Chemistry: the central science. London, Prentice Hall Publisher Crew, H. (1990). General physics: an elementary text-book for colleges, London, Macmillan Publisher. Diamantes, D. (2006). Fire prevention: inspection and code enforcement. London, Thomson Delmar Learning Publisher. Petrov, A. (1999). The lyotropic state of matter: molecular physics and living matter physics. New York, Breach Science Publishers. Serway, R. (1975). Concepts, problems, and solutions in general physics: a study guide for students of engineering and science. London, Saunders Publisher. Williams, F. (1994). Combustion theory: the fundamental theory of chemically reacting flow systems. 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Q4. Convert the following temperatures into Kelvin: i. Celsius to Kelvin (K) =C+273.15 46.5+273.15= 319.65K ii. Fahrenheit to Kelvin K = 5/9 (° F - 32) + 273 5/9 (174 - 32) + 273= 351.89K iii. 705+273.15= 978.15K iv. 5/9 (212 - 32) + 273= 373K Q5. Balance the following equations: a. H3PO4 + KOH => K3PO4 + H2O H3PO4 + 3KOH => K3PO4 + 3H2O b. H3PO4 + Mg(OH)2 => 2Mg3(PO4)2 + H2O, 2H3PO4 + 3Mg(OH)2 => 3Mg3(PO4)2 + 6H2O c. C2H6 + O2 => CO2 + H2O=> C2H6 + O2 => CO2 + H2O 2C2H6 + 7O2 => 4CO2 + 6H2O d. Ca3(PO4)2 + SiO2 + C => CaSiO3 + CO + P2Ca3(PO4)2 +3SiO2 + 5C => 3CaSiO3 + 5CO + 2P Q6.

The upward movement of flames and gases can be affected and altered by a number of factors. What are the most common? Pressure, density and volume Q7. Q = cp m dT         where Q = amount of heat (kJ),cp = specific heat capacity (kJ/kg.K),m = mass (kg), and dT = temperature difference between hot and cold side (K) When Cp=1.09 dT= 180-30=150+273.15=423.15 Q= 1.09x423.15x1=461.23kJ Q8. According to Boyle’s Law (PV = constant); at constant temperature, pressure and volume of gases are inversely related, when you decrease the volume of a gas, the pressure of gas increases.

Likewise, when the volume of the gas is reduced, the pressure of gases will increase; meaning faster reaction (Brown 2000, p.52). Q9. Heat can be defined as the amount of energy in a body/system, heat in a body can be transferred through radiation, conduction and convection. Joules is the SI unit for heat. While, Temperature is the measure of the average molecular motions in a body/system, the SI unit for temperature is degree Celsius/Kelvin Q10. n=MM/empirical formula mass n= 98.96/25 ClCH2= 17+ 6+ 2= 25 n=3.95 Q11. Draw and explain a Semenov diagram for thermal explosions.

 Thermal flux against Temperature Curve A: the reactant will enter into the system at lower temperature; the heat production curve is lying above heat loss curve in the diagram, it will continue to heat up until the temperature in a system get to Tstable temperature. If it reaches Tstable , the temperature will be constant and no heating will continue. Curve B: the 3 curves: Tstable, Tcritical, and Tignition are at the same temperature, the heat loss curve is tangential to the heat gain curve in the system.

The temperature in a system will rise slowly until it reaches critical temperature; raphid acceleration of temperature will be experienced which will result in thermal explosion. Curve C: in this curve the gain flux will exceed the heat loss flux, this means whatever the temperature the reactants will be in the system and thermal explosion in the system will take place. Q12.  Q/t= 0.48 x 0.32(675-32)/0.042= 2351.54 Q13. What are the different types of fire extinguisher and on what can they be used?

There are four types of fire extinguishers which are widely known: Water fire extinguisher, Foam Fire extinguisher, Dry powder Fire extinguisher and Carbon dioxide Fire extinguisher (Diamantes 2006, p.18). Water fire extinguisher: cheapest and widely used it mostly used to extinguish Class A (solid such as paper, wood, plastic) fires, but it is not suitable to extinguish Class B (flammable liquids such as paraffin, petrol, oil etc) fires (Diamantes 2006, p.18). Form fire extinguisher: it is more expensive when you compare it to water fire extinguisher, it is widely used to extinguish Classes A (solid such as paper, wood, plastic) and B (flammable liquids such as paraffin, petrol, oil etc) fires, but it is not recommended to be used in to extinguish Class E (Fires involving electrical apparatus) fires (Diamantes 2006, p.18). Dry Powder Fire Extinguishers: it a multipurpose fire extinguisher, can be used to extinguish Class A.

Class B and Class C (flammable gases such as propane, butane, methane etc) fires, but special powders are available for Class D (metals such as aluminum, magnesium, titanium etc) fires (Diamantes 2006, p.18). Carbon dioxide Fire Extinguishers: it ideal to be to extinguish Class B fires but (Diamantes 2006, p.18). Q14.

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