ESM222ps4_2008

# ESM222ps4_2008 - Spring 2008 ESM 222 Fate and Transport of...

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Spring 2008 1 ESM 222 Fate and Transport of Pollutants Assignment #4 Due: Wednesday 05/21/08 (in class) 1) Rate-limited Mass Transfer a) Gasoline evaporating from a spill on the ground (18 points) After you top-off your car’s gas tank, you end up spilling 0.15 L of gasoline on the floor… Let’s try to calculate how fast it will evaporate. Assume that the gasoline spreads out to form a thin film on the floor about 1 mm thick. ¾ Calculate the area available for contact (only the top surface is in contact with air) ¾ The saturation concentration of gasoline in air, C sat a , at 20 o C is 1.9 kg/m 3 ; lets assume that at the gasoline/air interface the concentration C a/gasoline = C sat a , and that the air around the gas station is at least 100 times less concentrated, C a (bulk) = 0.01 C sat a . The diffusivity of gasoline in air, D a , is about 1 x 10 –5 m 2 /s. The thickness of the boundary layer above the gasoline, z a , is about 5 mm. Calculate the flux (kg/m 2 s) ¾ Calculate the rate at which mass evaporates (kg/s) ¾ The density of gasoline is ~ 730 kg/m

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ESM222ps4_2008 - Spring 2008 ESM 222 Fate and Transport of...

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