A 0.8 m-diameter pool of ethanol is ignited at floor level in a room with a...

 

 
 
 

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A 0.8 m-diameter pool of ethanol is ignited at floor level in a room with a normal door opening. After a while the smoke layer stabilizes at a height of 1.5 m from the floor. Calculate the CO, concentration in the hot layer. Suggested answer: Using equations and tables from Chapter 3, we find m = 0.0075 kg/s, m, roughly 0.8 kg/s, o = 0.086, yco, = 1.77 g/g (Table 9.2), f = 0.0094, and Yco, = 1.7%. 9.3 A pool of ethanol is ignited in the scenario described in Problem 9.2, but now the door is closed. There is a well-specified leakage opening at floor level. The upper layer is now O00 by CRC Press LLC much hotter and the mass loss rate is measured to be m; = 0.05 kg/s. The mass flow rate in through the leakage opening is measured to be 0.3 kg/s. Estimate the concentration of CO, and O, in the hot layer. Suggested answer: The equivalence ratio is found to be o = 1.51. Table 9.3 gives yo, max = 2.09 and yco, max = 1.91. Therefore yo, = 2.09/1.51 = 1.38 g/g and yco, = 1.26 g/g. Fuel mixture fraction is f= 0.05/(0.05 + 0.3) = 0.143, so Yco, = 1.26 - 0.143 18.0% and Yo, = 1.38 0.143 = 19.7%. = 1.91/1.51 %3D TABLE 9.2 Typical Combustion Product Yields for Various Fuels Ventilation-controlled Well-ventilated (WV) fires (6 < 1) (VC) fires ( >1) D. (kl/g) (m/g) (g/g) Yco, Yco Y. Уна Yco Fuels (g/g) (g/g) (g/g) (k)/g) (g/g) (g/g) 0.005 0.024 Propane Acetylene Ethanol (ethyl alcohol) Heptane Polystyrene Nylon Polyurethane (flexible) PU 2.85 74 76.4 0.16 NA 0.23 0.011 2.6 0.042 0.096 37 48.2 0.32 NA 1.77 0.001 0.008 26 26.8 NA NA 0.22 0.0098 2.85 0.01 0.037 41 44.6 0.19 NA 2.3 0.06 0.16 27 39.2 0.34 NA 2.06 0.038 0.075 27 30.8 0.23 NA 1.5 0.031 0.23 19 27.2 0.33 NA Polymethyl methacrylate 2.1 0.01 0.022 24 25.2 0.109 NA 0.19 0.032 Wood 1.33 0.005 0.015 12 17.7 0.037 NA 0.14 0.0024 Polyvinyl chloride (PVC) 0.46 0.063 0.14 5.4 16.4 0.40 0.5 0.4 Notes: NA = not applicable; -= not measured. Source: From Tewarson, A., "Generation of Heat and Chemical Compounds in Fires," SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, 1995. With permission. TABLE 9.3 Maximum Theoretical Yield of Species Based on Stoichiometry Stoich. fuel/ox Yco,max Yco,mas Ratio, r Youmax (g/g) Fuel (g/g) (g/g) Propane Acetylene Ethanol (ethyl alcohol) Неptane Polystyrene Nylon Polyurethane (flexible) PU Polymethyl methacrylate Wood (pine) Polyvinyl chloride (PVC) 0.276 1.91 3.00 3.64 0.325 2.15 3.39 3.69 0.480 1.22 1.91 2.09 0.284 1.96 3.08 3.52 0.325 2.15 3.38 3.08 0.428 1.48 2.32 2.61 0.580 1.41 2.21 2.05 0.521 1.4 2.2 1.92 0.601 0.89 1.40 1.13 0.710 0.903 1.42 1.42 A 0.8 m-diameter pool of ethanol is ignited at floor level in a room with a normal door opening. After a while the smoke layer stabilizes at a height of 1.5 m from the floor. Calculate the CO, concentration in the hot layer. Suggested answer: Using equations and tables from Chapter 3, we find m = 0.0075 kg/s, m, roughly 0.8 kg/s, o = 0.086, yco, = 1.77 g/g (Table 9.2), f = 0.0094, and Yco, = 1.7%. 9.3 A pool of ethanol is ignited in the scenario described in Problem 9.2, but now the door is closed. There is a well-specified leakage opening at floor level. The upper layer is now O00 by CRC Press LLC much hotter and the mass loss rate is measured to be m; = 0.05 kg/s. The mass flow rate in through the leakage opening is measured to be 0.3 kg/s. Estimate the concentration of CO, and O, in the hot layer. Suggested answer: The equivalence ratio is found to be o = 1.51. Table 9.3 gives yo, max = 2.09 and yco, max = 1.91. Therefore yo, = 2.09/1.51 = 1.38 g/g and yco, = 1.26 g/g. Fuel mixture fraction is f= 0.05/(0.05 + 0.3) = 0.143, so Yco, = 1.26 - 0.143 18.0% and Yo, = 1.38 0.143 = 19.7%. = 1.91/1.51 %3D TABLE 9.2 Typical Combustion Product Yields for Various Fuels Ventilation-controlled Well-ventilated (WV) fires (6 < 1) (VC) fires ( >1) D. (kl/g) (m/g) (g/g) Yco, Yco Y. Уна Yco Fuels (g/g) (g/g) (g/g) (k)/g) (g/g) (g/g) 0.005 0.024 Propane Acetylene Ethanol (ethyl alcohol) Heptane Polystyrene Nylon Polyurethane (flexible) PU 2.85 74 76.4 0.16 NA 0.23 0.011 2.6 0.042 0.096 37 48.2 0.32 NA 1.77 0.001 0.008 26 26.8 NA NA 0.22 0.0098 2.85 0.01 0.037 41 44.6 0.19 NA 2.3 0.06 0.16 27 39.2 0.34 NA 2.06 0.038 0.075 27 30.8 0.23 NA 1.5 0.031 0.23 19 27.2 0.33 NA Polymethyl methacrylate 2.1 0.01 0.022 24 25.2 0.109 NA 0.19 0.032 Wood 1.33 0.005 0.015 12 17.7 0.037 NA 0.14 0.0024 Polyvinyl chloride (PVC) 0.46 0.063 0.14 5.4 16.4 0.40 0.5 0.4 Notes: NA = not applicable; -= not measured. Source: From Tewarson, A., "Generation of Heat and Chemical Compounds in Fires," SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, 1995. With permission. TABLE 9.3 Maximum Theoretical Yield of Species Based on Stoichiometry Stoich. fuel/ox Yco,max Yco,mas Ratio, r Youmax (g/g) Fuel (g/g) (g/g) Propane Acetylene Ethanol (ethyl alcohol) Неptane Polystyrene Nylon Polyurethane (flexible) PU Polymethyl methacrylate Wood (pine) Polyvinyl chloride (PVC) 0.276 1.91 3.00 3.64 0.325 2.15 3.39 3.69 0.480 1.22 1.91 2.09 0.284 1.96 3.08 3.52 0.325 2.15 3.38 3.08 0.428 1.48 2.32 2.61 0.580 1.41 2.21 2.05 0.521 1.4 2.2 1.92 0.601 0.89 1.40 1.13 0.710 0.903 1.42 1.42

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