Engineering Design Practice - Article Example

Author name] [Instructor] [Date] Engineering Design Practice Combustion is a process in which a substance reacts with oxygen to give heat and light. Combustion is a method of burning due to that chemical change, mainly oxidation, accompanied by the production of heat and light. Here heating the fuel higher than its ignition temperature in the presence of oxygen. Due to a lot of heat, the chemical bonds of the fuel are split. If complete combustion occurs, the elements carbon (C), hydrogen (H) and sulphur (S) react with the oxygen content of the air to form carbon dioxide CO2, water vapour H2O and sulphur dioxide SO2 and, to a lesser degree, sulphur trioxide SO3. If enough oxygen is not present or the fuel mixture is inadequate then the burning gases are somewhat cooled below the ignition temperature, and the combustion process stays incomplete. Still fuel gases have components which are burnable mainly carbon monoxide CO, carbon C (soot) and various hydrocarbons CxHy. As all above mentioned components are with NOx, pollutants which damage our environment, measures must have taken to prevent the formation of them. For complete combustion, there must be providing at a certain extent of excess air. Advantage of Combustion optimization saves money. The Fire safeties in buildings depend upon achieving two fundamental objectives: a. To decrease the loss of life or in the neighborhood of, building fires so that not a lot harm. b. Also to decrease the financial loss or in the neighborhood of, building fires. In the mostly countries, to achieve these objects depend upon between government and civic authorities, who have responsibility for life safety through building regulations measures , and insurance companies should be in contact who are concerned with property loss through their fire insurance policies and loss reduce. Mostly, the two objectives are thought to be irreconcilable, even occasionally conflicting. Like sprinklers and automatic detection shows protectors instead of life protectors and insurance companies will usually offer substantial premium discounts. But all this not rate highly in a lot national building regulations, still evidence that is approachable points that they are exceptionally effective in preserving life. In fact the measures required to achieve life and property preservations are very analogous (A. A. Putnam, 1953). Five functional requirements of approved document B are; Requirement B1 requires that satisfactory escape routes be provided to facilitate the occupants to arrive at a safe location outside of the building. Suitable means of giving warning of a fire are also essential. Requirement B2 requires that materials used as wall and ceiling linings do not prop up rapid fire spread or excessively add to the heat produced by a fire. Requirement B3 requires that suitable actions be taken to ensure that: the structural steadiness of the building will be maintained; a wall between two buildings will defy fire spread among the buildings; buildings are subdivided into compartments to confine the size of a fire; Concealed voids are subdivided to inhibit hidden fire spread. These objectives are generally achieved by providing fire resisting constructions. Requirement B4 is principally planned to avoid the spread of fire from one building to another as a consequence of heat radiation or airborne blazing brands. This is generally achieved by: controlling external surfaces of walls and roofs; Providing fire resisting external walls when appropriate. Requirement B5 requires that rational facilities are offered to assist fire appliances to gain admittance to the building and to enable fire fighters to protect life. "Means of escape from fire" can be defined as; "Means of Escape is a structural means, whereby a safe route is provided for persons to escape in case of fire, from any point in a building to a place of safety, clear of the building, without outside assistance". Here Approved Document B can be considerable which shows an affluence of information on both areas protections of structure, also along adjacent buildings and, also mentions means of escape from buildings that may be on fire. Building Control authorities has the basic and very crucial responsibility to make sure all new buildings are provided with necessary means of escape (Nazaroff and R. Harley, 2007). Before taking these satisfactory means of escape from fire its necessary to design of new buildings and to the alteration, also change of use or extension of existing buildings so that more and more precautionary measures have to be taken. It is critical that means of escape are measured at the most basic stage of a project as mistakes are very expensive to correct later in the design. There is a large compact of legislation on means of escape design and control, but this is spread throughout a large numeral of statutes, regulations and guidance credentials. Several buildings need to be licensed and/or registered, as well as require certification and Building Regulation compliance. Following information is required to be known when designing a means of escape from fire in a premises or building, Time of evacuation Travel distances Number of Occupants Calculation of Exit Widths Calculation of Minimum Number of Exits By Appling all these methods, still it is not so clear that their importance will vary according to the circumstances. Sometimes one, sometimes another, will presume greater importance in your assessments and subsequent solution. It is important to perform fire tests because they determine whether or not fire protection products meet minimum performance criteria. The criteria demands building code of applicable and desirable legislation. The question, " " is normally asked by end users of the fire protection products. To answer this question fire tests are performed in order to ensure the credibility and effectiveness of the product in applicable situations and hence meet the specified standards. Fire testing mostly falls under two categories: first tests to measure ignition and the spread of flames from one part to other part, second category tests to measure fire resistance. Fire resistance tests measure a material's ability to continue to serve its structural role during a fire (Heitor, 1996). All products should be tested in a way to ensure ease of use and broad and economical applications as per the applicable legislation and compliance standards. Flammability and fire testing services also conclude spread of heat, smoke and flame in relating different varying internal environmental conditions of houses, commercial kitchens (e.g., a lot insist on stove hoods), and automobiles. The actual fire conditions are very different from the lab conditions based on variety of factors like amount, nature, and distribution of available fuel, ventilation, size configuration and vice versa. Therefore more than one experiment is carried out to check same parameter for different values and in different conditions, so as to ensure and test the maximum number of possibilities (Howell and Buckius, 1984). The trench effect is a grouping of conditions that can cause a fire to climb swiftly up an inclined surface. It depends on two well-understood but separate ideas: the Coandă effect from fluid dynamics and the flashover concept from fire dynamics. The Coandă effect showing tendency moving towards fast-moving stream of air so that to deflect towards nearby surfaces. The fast-moving stream shows the experience as decrease in static pressure, and due to that method creates a pressure difference between those areas which are far away from the wall and the wall itself. This makes sure that the fast-moving stream bends towards the surface and try to keep it attached to that surface. Flashover is a sudden widespread spreading of fire, which happens under the conditions when the majority of surfaces in a space are heated to point at which they give off flammable gases enough hot so that to ignite themselves. Before flashover, flammable gases can be given off but may not hot enough so to ignite themselves. The trench effect happens under a condition when a fire burns next to a steeply-inclined surface. The flames lie down along the surface, clearly as same as the Coandă effect. The flames heat the material more: This emit gases, comes to their auto-ignition temperature and then suddenly start burning, similar like flashover theory. The flames from these parts are themselves shows subject to the Coandă effect blow a jet of flame till at the end of the inclined surface. This jet remains sustained until the fuel taken to be exhausted (Costanza, 1997). Apply generally to vapors and are defined as the concentration range in which a flammable substance can produce a fire or explosion when an ignition source (such as a spark or open flame) is present. The concentration is generally expressed as percent fuel by volume. Above the upper flammable limit (UFL) the mixture of substance and air is too rich in fuel (deficient in oxygen) to burn. This can be called the upper explosive limit (UEL). Below the lower flammable limit (LFL) the mixture of substance and air lacks sufficient fuel (substance) to burn. Similarly like upper explosive limit this can be called the lower explosive limit (LEL). Here extreme cautions require because any concentration between these limits can ignite or explode. It is not safe as being above the upper limit, either. The vapor will be diluted and concentration can drop into range of flammable limit if a mentioned space is above from the upper flammable. There are basically five points which will affect the development of fire growth within a compartment. They can be divided into two categories; those that are concerned with the compartment itself and those which are concerned with the fuel. Please name four of these. c. Fire load type, density and distribution d. Combustion behavior of the fire load e. Compartment size and geometry f. Ventilation conditions of the compartment g. Thermal properties of the compartment boundary Different stages involves for Fire development within a compartment: Growth Stage: Here involves the period when ignition starts until all combustible materials in the compartment are involved in fire. Flashover: When flaming rapidly extends throughout (essentially) the whole compartment the sudden transition between the Growth and Fully Developed stages. Fully Developed Stage: Oxygen start to diminish and temperatures begin to drop as the stage from when all combustibles within compartment are burning. Decay Stage: The stage arises when oxygen start to diminish available fuel and temperatures start to drop suddenly until the fire burns out (or more fuel/oxygen become available). Combustion and flammable fuels fall into five categories: liquid, heat, gases, flame, and smoke. If exposed to a temperature below 100° Fahrenheit a flammable liquid is one which can ignite. The temperature at that point when flammable liquid will ignite is called its “flashpoint.” By looking in depth the liquid does not as ignite, but instead of, gives off vapors that burn when exposed to the air and an ignition source. Heat can be described as a form of energy characterized by vibration of molecules and include a lot resource of initiating and also supporting chemical changes. Gases are such substance that contains no volume of their own and will expand so to take the shape and volume of the space which they occupy. Carbon monoxide, hydrogen cyanide, ammonia, hydrogen chloride, and acrolein all includes in fire gases. Flame which include in the essential luminous portion of burning of vapors. Products of incomplete combustion, suspended in gases, vapors, or solid or liquid aerosols Smoke is the airborne (Tribus, 1961). Name four parameters you can determine using the cone calorimeter. To study the fire behavior of small samples of various materials in condensed phase a cone calorimeter is a modern device to use. It collects data regarding the ignition time mass loss combustion products heat release rate and other parameters associated with its burning properties Explain what is meant by "ignitability" of a material? A solid waste will show the property of ignitability if a representative sample of the waste has any of the following properties: It has flash point less than 60 °C (140 °F) if it is a liquid, other than an aqueous solution containing less than 24 percent alcohol by volume. When ignited burns so vigorously that it creates hazard as It is not a liquid and is capable, under standard temperature and pressure, of causing fire through friction, absorption of moisture or spontaneous chemical changes and, It is an ignitable compressed gas . It is an oxidizer. Fire departments may use fans to pressurize a structure prior to suppressing a fire or ventilation blowers. This positive pressure ventilation (PPV) phenomina can help in the venting of high temperature and smoke combustion products and make them attacking the fire easier than without PPV. Also this phenomina gives additional oxygen to the fire and can help to increase the rate of heat and energy being released (HVAC Systems and Equipment volume of the ASHRAE Handbook,2004). Heat is thermal energy. Temperature can be use as the measurement of average kinetic energy of particles which cpmrise of matter being tested. The temperature of the material can rise, or there may be a change in state (such as from liquid to vapor) When heat flows into a material. . Heat is an extensive property while Temperature is an intensive property and intensive property explains that the amount of substance present will not change the specific trait.Like, the boiling point of water is 100 degrees. 15 liters of water boils at 100 degreesas one liter of water boils at 100 degrees the same as An extensive property shows that does rely on amount present. The amount of heat produced by one liter of boiling water will differ from the fireworks sparklers show a good comparison of heat and temperature. The temperatures of these sparks can reach up to 3000 degrees C as sparks that come off of the sparkler are ejected particles of metal. But one thing should be noticed that these sparks will not burn you as they land on you, even though the temperature is very high. Because the sparks do not have enough mass and also cannot comprise of enough heat. The amount of heat (thermal energy) they contain is very small though the sparks have high temperature. It is important to know the causes of fires, because in our daily life we may be performing certain actions which can cause fire and destruction. If the causes of fire are known by every person the he/she can be careful while performing fire causing activities. Most people do not understand and thinks they can survive fire is a powerful and destructive force. Now a days Fires have become the most leading cause of accidental death, but still there a lot depend that what are the steps fire prevention personnel can do to prevent fires.. The most important to avide fire prevention is awareness to tranasfer basics to all people, by letting them know how fires start and what are the steps they can do to eliminate them. Now a days the leading cause of death from fires is careless smoking, but prblem is still only few smokers now it is still a large problem. If you are drowsy, taking certain medications or drinking alcohol postpones that cigarette until you are alert. Another important area in case of home fires is the kitchen. Also cooking another way cause of fire deaths in the home. When someone leaves to answer the telephone or to check on something else in the home many kitchen fires start. In a Diffusion Flame the oxidizer and the fuel in start are separated. Diffusion flames are represented by candle flames, wood fires and forest fires. Whereas a Premixed flame is any flame in which the fuel and the oxidizer are initially mixed. For Example; a uniform combustible mixture contained inside a tube that is ignited by a spark creating a flame spreading along the tube. The major difference between two is that in Diffusion flame, the fuel-oxidizer ratio varies throughout the flame whereas in premixed flame, it is constant everywhere in the flame (Odum 1995). Flash Point defined as the temperature at which vapour is given off which will ignite when an external flame is applied under standardised conditions. Flash point defining basic aim is to reduce fire risk during normal storage and handling. Many land-nased instalations is 60°C as the minimum flash point for fuel in the machinery space of merchant ships.When residual fuels are even at a below temperature than their measured flash point, still they are enough capable of producing light hydrocarbons in the tank headspace due to which the vapour composition to be within, the flammable range. An actual value is quoted when the temperature is below this value. A very low flash point gives the hint of fuel contamination by a more volatile product. Vapors are very essential to the burning process as they help in ignition process. Proportiobning and Mixing are reactions that should be continuous so that for fire remains to continue to propagate. The oxegen and fuel vapors should be mixed in the correct proportions and proper order. This mixture of fuel vapors and oxygen should be remain within the explosive limits. Flammable limits are expressed in the percentage of fuel vapors in air. A mixture which has too high a concentration of fuel vapors is too rich while a mixture which contains fuel vapors in an amount less than necessary for ignition to occur is too lean (H.W. Jackson 1959). The limiting oxygen index (LOI) is the minimum concentration of oxygen, expressed as a percentage, that will support combustion of a polymer. It is measured by passing a mixture of oxygen and nitrogen over a burning specimen, and reducing the oxygen level until a critical level is reached. The critical oxygen index (COI) also called as limiting oxygen index (LOI), or oxygen index, which is defined as: LOI = [O2, cr] Eq. (1), ------------- [O2, cr] + [N2] where [N2] and [O2,cr] are the minimum oxygen percentage or concentration in the inflow gases required to pass the ``minimum burning length'' criterion and the nitrogen concentration in the inflow gasesas orderwise. Since air comprises about 20.95% oxygen with respect to volume, so any material which have limiting oxygen index less than this will burn a lot easily in air. Similarly the tendency and burning behavior to move flame for a polymer keeping limiting oxygen index greater than 20.95 so that will be zero or reduced after removal of the igniting source. Self-sustaining combustion is not possible if LOI>100, such values are not physically meaningful (Chen 2006). Following are the limitations of LOI test; h. It doesn’t characterize the burning behavior of the polymer. i. Absence of energy feedback in the specimen, since most of the energy is carried away by convection. Piloted ignition is the process of initiation and flame propagation in premixed fuel systems. The minimum condition for the piloted ignition occurs at the lower flammable limit which is the concentration of a fuel at that allows propagation with a small spark. Auto ignition occurs without any spark or flame source. Both of these occur in an identical manner for the evaporated or decomposed fuel gases of liquid and solid fuels respectively. Range, mean, standard deviation and uncertainty. a. Range: Largest No-Smallest No Range= 45.10-41.62=3.48 b. Mean: Sum of numbers/total numbers Mean=435.45/10= 43.545 c. Standard Deviation: Formula: Standard Deviation       Where Σ = Sum of               X = Individual score               M or Mean of all scores               N = Sample size (Number of scores) X M X-M (X-M)2 44.80 43.545 1.255 1.575 42.15 43.545 -1.395 1.946 42.97 43.545 -0.575 0.3306 43.60 43.545 0.055 0.003 43.88 43.545 0.335 0.1122 44.80 43.545 1.255 1.575 42.79 43.545 -0.755 0.57 45.10 43.545 1.555 2.418 41.62 43.545 -1.925 3.705 43.74 43.545 0.195 0.038 Step 2: Find the sum of (X-M) 2. SUM=12.3028 Step 3: N = 10, the total number of values. Find N-1. N-1=9 Step 4: finding Standard Deviation.             √12.3028/√9 = 3.5075/3= 1.169 d. Uncertainty Standard Deviation/Mean*100%= (1.169/43.545)*100%=2.684% 25. Fuel Acetone Test1 Test2 Test3 Test4 Test5 Test6 Test7 Test8 Number of Drops 2 6 10 12 14 16 18 20 Height attained by lid(cms) 0 20 40 80 120 150 110 190 Big Bang Experiment Results Graph: Figure 1: Big Bang Experiment Results Graph- No of Drops vs. Height Attained by Lid (cms) Refernces A. A. Putnam (1953) "Organ-pipe oscillations in a flame-filled tube," Fourth Symposium (International) on Combustion, The Combustion Institute, pages 566-574. M. V. Heitor, (1996),“Unsteady flames and the Rayleigh criterion” page 4. Available on-line at:http://books.google.com/books?id=Je_hG6UfnogC&printsec=copyright&dq=rayleigh+thermoacoustic+&ie=ISO-8859-1&source=gbs_toc_s&cad=1#PPA4,M1 Nazaroff and R. Harley, (2007), Air Quality Engineering, University of California Berkeley, Howell and Buckius, (1984), Fundamentals of Engineering Thermodynamics, McGraw-Hill, New York. HVAC Systems and Equipment volume of the ASHRAE Handbook,(2004), ASHRAE, Inc., Atlanta, GA, USA. H.W. Jackson (1959) Introduction to Electronic Circuits, Prentice-Hall. G.Q. Chen (2006) 'Scarcity of exergy and ecological evaluation based on embodied exergy', Communications in Nonlinear Science and Numerical Simulation, Volume 11, Issue 4, July, Pages 531-552 H.T.Odum (1995) 'Self-Organization and Maximum Empower', in C.A.S.Hall (ed.) Maximum Power: The Ideas and Applications of H.T.Odum, Colorado University Press, Colorado. M.Tribus (1961) Generalized Treatment of Linear Systems Used for Power Production', Thermostatics and Thermodynamics, Van Nostrand, University Series in Basic Engineering, p. 619. R.Costanza, (1997), An Introduction to Ecological Economics, CRC Press - St. Lucie Press, First Edition. Read More