Unit 4 Assignment: Case Study: Heat Flux
Review the case study file and write a 2-page paper that explains heat flux and its implications in the danger of fire heat transfer. After reviewing the pictures in the case study file of the two- sided, three-sided, and four-sided work stations, do the following:
•Prepare a brief listing of the arrangement and composition of fuels present in each office cubicle.
•Compare the amounts of fuel in each cubicle and determine if they are the same or different.
•Explain which fire develops faster.
•Describe why each fire develops faster in terms of heat flux and heat transfer by looking at the time in seconds and mega-watts being produced. In other words, if each fire set is the same, then why did the fire in one of the three cubicles develop faster than the other two and release more heat energy?Heat Transfer Case Study Assignment Heat Transfer • Major factor in the ignition, growth, spread, decay and extinction of a fire. • Heat energy transferred to an object increases the object’s temperature • Heat energy transferred from an object decreases the object’s temperature • Heat is always transferred from the hotter object to the colder object. Mechanisms of Heat Transfer • Conduction – heat transfer within solids or between contacting solids • Convection – heat transfer by the movement of liquids or gasses • Radiation – heat transfer by electromagnetic waves Radiative vs Convective HRR • Most fuels release the majority of their heat via convection and followed by radiation. • 60 to 75 % Convective • 25 to 40 % Radiative Fuel • Organic Fuels – typically contain carbon, hydrogen, oxygen – wood, plastics, gasoline, natural gas • Inorganic Fuels – typically contain no carbon – magnesium, sodium Forms of Fuel • Gaseous – Methane • Liquid – gasoline or LP • Solid – Wood • What is actually burning? Heat Release Rate • Heat release rate from an object is controlled by: – the chemical and physical properties of the fuel – geometry of fuel and containment – ventilation – surrounding fuels Heat Release Rate • The heat release rate of an object or a room is important to understanding how the energy released from that item would change the thermal conditions in a room or how it might ignite other nearby fuels via heat transfer. Geometry of Fuel • Liquids – Spray vs Spill • Solids – Thin vs Thick – Low density vs high density – Flat, convex vs concave Pool Evaporation vs Spray Pool fire vs Spray Fire Thermally Thin vs Thick Low Density vs High Density Flat vs Convex vs Concave Work Station Arrangements 2 -sided 3 -sided 4 -sided 30 sec 100 kW 180 sec 350 kW 300 sec 1.4 MW 360 sec 2.2 MW 420 sec 3.0 MW 2-Sided Workstation 60 sec 90 kW 180 sec 280 kW 330 sec 1.7 MW 360 sec 2.3 MW 480 sec 3.8 MW 3-Sided Workstation 60 sec 140 kW 150 sec 400 kW 180 sec 700 kW 240 sec 1.5 MW 360 sec 6.9 MW 4-Sided Workstation