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UNIT 1: FIRE DYNAMICS

UNIT 1: FIRE DYNAMICS

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UNIT 1: FIRE DYNAMICS

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  1. UNIT 1:FIRE DYNAMICS

  2. TERMINAL OBJECTIVE • Given a written exam, explain fire development and the effects of room-and-contents geometry, ventilation factors, and different materials on fire growth.

  3. ENABLING OBJECTIVES The student will: • Explain the dynamics of laminar flame formation in a candle. • Discuss the basic principles of physics and chemistry that provide the foundation for understanding fire dynamics and fire modeling.

  4. ENABLING OBJECTIVES (con.) • Articulate how fire grows and progresses. • Identify the effects of geometry and materials on fire growth. • Describe the effect that ventilation has on fire progression.

  5. ENABLING OBJECTIVES (con.) • Explain basic fire behavior chemistry and physics using the following terms as they relate to the built environment: • Flashpoint • Boiling point • Flammable limits • Conduction • Convection • Radiation • Oxidizer • Triple point • Basic research • Applied research • Closed system

  6. ENABLING OBJECTIVES (con.) • Explain the progression of fire from start to extinguishment using the following terms as they relate to the built environment: • Heat flux/transfer • Heat of combustion • Heat-release rate • T2 fire • Flashover • Backdraft • Fire plume • Ceiling jet • Homeostasis

  7. INTERNET REVIEW RESOURCES Physics: • Hyperphysics: • http://hyperphysics.phy-astr.gsu.edu/ hbase/hframe.html • Dolores Gende: Physics Tutorials: • http://apphysicsb.homestead.com/tutorial.html • Physics 2k2: • http://wshs.wtvl.k12.me.us/~physics361/

  8. INTERNET REVIEW RESOURCES (con.) Chemistry: • Chemtutor Home page links will take you to the appropriate content area. • http://www.chemtutor.com

  9. FIRE The study of fire is complex and requires knowledge of: • Heat transfer • Chemistry • Fluid mechanics • Thermodynamics

  10. Wick is lighted with external heat source. Radiated heat from the flame begins to soften and melt the paraffin wax. The melted paraffin wax is drawn up the wick by capillary action. Faraday referred to process as “capillary attraction.” DYNAMICS OF A LAMINAR CANDLE FLAME

  11. Wax exposed to heat of wick flame is vaporized into combustible fuel. Fuel is vaporized in lower part of flame. Rising vapors of paraffin are then consumed by the flame. The combustion gases rise due to effects of buoyancy. DYNAMICS OF A LAMINAR CANDLE FLAME (con.)

  12. Cooler oxygen-rich air is drawn into the flame from below, as the warmer products of the flame’s combustion rise upwards. The entrainment of fresh air from below provides a continuing supply of oxygen, and the flame will burn until the paraffin fuel is exhausted. DYNAMICS OF A LAMINAR CANDLE FLAME (con.)

  13. PRODUCTS OF COMBUSTION • Visible light • Heat • Soot • Carbon dioxide • Water vapor

  14. MICHAEL FARADAY • 1826 began series of Christmas Lectures at Royal Institute, England • 1860 presented The Chemical History of a Candle • Article in your SM, you should read this evening

  15. Slide 1-18

  16. BONUS QUESTION • What makes these candle flames different?

  17. WORK, ENERGY, AND MOMENTUM Work: • Activity involving a force that acts on body in direction of motion, or has component in the direction of motion. • If movement does not occur when force is applied, no work in scientific sense has been done. • Units are joules (Newton-meters) or pound-feet • In everyday life we think of work as an activity requiring mental or muscular exertion. In scientific sense, it has a more restricted definition.

  18. WORK, ENERGY, AND MOMENTUM (con.) Energy: • The ability of a system to do work or supply heat • Common unit--joule, older units are calorie, kilocalorie, and British thermal unit (Btu) • In general, we do not think of finding energy at a particular point of space and time. • Rather, we think about what occurs when we change energy from one form to another.

  19. FORMS OF ENERGY • Kinetic energy • Potential energy • Energy that is stored because of its position • Gravitational potential energy • Elastic potential energy • Electrical potential energy • Energy due to position of electrons • Chemical potential energy • Nuclear potential energy

  20. WORK, ENERGY, AND MOMENTUM (con.) Power: • Power is the rate at which work is done. • Units: • Power (metric) = Newton-meters/second = joules/second = Watts (SI units). • Power (English) = pound-feet/second = ft lb/s = horsepower (hp).

  21. WORK, ENERGY, AND MOMENTUM (con.) System: • A system is a portion of our universe that we are interested in studying. It will have prescribed limits and matter within it. • An isolated system assumes that matter and energy within the system does not interact with the rest of the universe at all.

  22. In our real world… • There are no such systems. The concept serves as a simplifying assumption that enables us to focus on basic principles without the confusion of extraneous factors.

  23. WORK, ENERGY, AND MOMENTUM (con.) • In order to isolate a particular phenomenon that is under consideration, the system is most often considered closed. • A closed system is isolated from the effects of the outside world. • The total matter and energy remain constant within it, but may change form, and the effects of gravity and other energy and matter are assumed to remain constant.

  24. WORK, ENERGY, AND MOMENTUM (con.) • An open system permits exchange of matter and energy between itself and the outside surroundings. • The system can gain and lose energy and/or matter to its surroundings over time. • When the system and its surroundings are combined, they form the thermodynamic universe for the particular process under review.

  25. CLOSED SYSTEM

  26. OPEN SYSTEM

  27. A conservation law always involves an interaction that occurs within a physical system or between a system and its surroundings. CONSERVATION LAWS

  28. CONSERVATION LAWS (con.) • Conservation of mass is illustrated in all chemical reactions, where the total mass of the reactants is always equal to the total mass of all of the products of the reaction.

  29. CONSERVATION LAWS (con.) Conservation of energy: • Energy can never be created or destroyed. Energy may be transformed from one form to another, but the total energy of an isolated system is always constant. • Mechanical energy can be transferred into thermal energy. • From a universal point of view, the total energy of the universe is conserved. If one part of the universe gains energy in some form, another part must lose an equal amount of energy.

  30. TEMPERATURE AND HEAT Temperature: • The concept of temperature comes from our ideas of hot and cold, based on our sense of touch. • To define quantitatively, we must be able to assign numbers to various degrees of hot and cold. • Requires using a material that is sensitive to hotness or coldness (i.e., mercury) and a calibrated scale.

  31. TEMPERATURE AND HEAT (con.) Heat: • Heat is the process of transfer of energy from systems or objects of higher temperature to those of lower temperature. • It is not correct to state that objects or systems possess “heat.” • Objects do not contain heat; they possess thermal (internal) energy. • Objects having higher energy transmit the energy to objects of lower energy.

  32. TEMPERATURE AND HEAT (con.) • Temperature also is related to the motion (average internal kinetic energy) of the molecules in the material. • When an energy transfer takes place solely because of a temperature difference, this is called heat flow. • Energy can also be transferred by doing work on an object to increase the thermal (internal) energy.

  33. PRINCIPLES OF THERMODYNAMICS • A thermodynamic system is a system that can interact with its surroundings in two ways: • By heat transfer • By work done • Heat also can be understood by relating the internal energy to the internal kinetic and potential energies of the molecules.

  34. LAWS OF THERMODYNAMICS First Law • The First Law defines conservation of energy in thermodynamic processes. • Nothing lost, nothing gained

  35. LAWS OF THERMODYNAMICS (con.) Second Law • The Second Law imposes constraints on the direction of heat transfer. • It is easy to convert mechanical work to heat, but is not so easy to convert heat completely to mechanical energy; in fact it has never been done. • It is impossible to extract heat from a warmer reservoir and perform work, without having some of the energy lost to a colder reservoir. • Stated differently, the direction of a process always favors the direction of greater disorder.

  36. CHEMICAL REACTIONS AND EQUATIONS • A chemical reaction occurs when one or more reactants (elements and/or compounds that are going to react) react and form other products (materials that have been produced by the reaction).

  37. CHEMICAL REACTIONS AND EQUATIONS (con.) • A chemical equation describes what happens in a chemical reaction. • Equations are symbols representing elements and compounds. • The symbols representing the reactant materials are placed to the left of an arrow pointing to the right and the symbols representing the products are placed to the right of the arrow.

  38. CHEMICAL REACTIONS AND EQUATIONS (con.) • The Law of Conservation of Mass states that in a chemical reaction no mass is gained or lost. There must be the same total number of atoms of each element on both sides of the equation. • Some chemical reactions are reversible, and this is indicated by a double-headed arrow.

  39. WRITING CHEMICAL EQUATIONS • Write the formulas for all of the materials involved on the proper side of the arrow: • Reactants on the left and products on the right side • The arrow means “produces” or “yields” • To balance the equation, never change the formulas for any of the reactants or products. Only change the coefficients.

  40. WRITING CHEMICAL EQUATIONS (con.) • You must have the same amount of each element on each side of the arrow. • To get this, you add coefficients in front of the formulas in each of the terms to get the same number of atoms of each element on both sides of the equation.

  41. BALANCING BURNING REACTIONS • Most burning reactions are the oxidation of a fuel with oxygen gas. • Complete burning produces carbon dioxide from all the carbon in the fuel, and water from the hydrogen in the fuel. • An example: • Methane burning in air to make carbon dioxide and water

  42. EXAMPLES OF BALANCING CHEMICAL EQUATIONS

  43. SOME COMMON COMBUSTION REACTIONS • PROPANE C3H8 + 5 O2 > 3 CO2 + 4 H20 • WOODC6H10O5 + 6 O2 > 6 CO2 + 5 H20 • BUTANE2 C4H10 + 13 O2 > 8 CO2 + 10 H2O • METHANE2 CH3OH + 3 O2 > 2 CO2 + 4 H20

  44. COMBUSTION OF A WAX CANDLE • C15H31CO2C30H61 + 68O2 = 46 CO2 + 46 H2O • C15H31CO2C30H61 + 45O2 = 46 CO + 46 H2O

  45. THE GAS LAWS - EXPERIMENT AND THEORY • Theories are used to describe the behavior of the universe. The descriptions are good if they fit known facts and can be used to predict what will happen in particular situations. • If the explanations and predictions made by theory agree with experimental behavior, this builds confidence that the theory is a valid representation of what is occurring.

  46. THE GAS LAWS - EXPERIMENT AND THEORY (con.) • If there is no agreement it means that there is an error in the primary assumptions. We then have a choice of modifying our ideas and assumptions to fit the newly discovered circumstance, or using an entirely different approach.

  47. THE GAS LAWS - EXPERIMENT AND THEORY (con.) Observed (experimental) behavior of gases • Qualitative properties • High mobility • Low density • Exert pressure • Diffusion • Quantitative • Boyle’s law (1662) • Charles’ law (1787 • Gay-Lussac’s law (1802) • Ideal Gas Law

  48. THE GAS LAWS - EXPERIMENT AND THEORY (con.) • By applying conservation laws and making assumptions, scientists were able to get theoretical results that were in agreement with the experimental results.

  49. THE GAS LAWS - EXPERIMENT AND THEORY (con.) Assumptions of theory: • Particles of gases are infinitely small. • Particles are in constant, random motion. • Gases don't experience intermolecular forces. • Average kinetic energy of gas molecules is directly proportional to their temperature in Kelvin. • Gas molecules undergo perfectly elastic collisions.