Environmental engineering students were given the task to measure the fluxes of 2 compounds of their choice. Bilge chose i) chloride and ii) octanol for this question. i) chloride across the freshwater-saltwater interface in an estuary, she calculated that the concentration drops from 20 ppt to 2 ppt (parts per thousand) at 5 m. Molecular diffusion coefficient of chloride in water at 25 C is 10-5 cm2 /s. ii) n-octane vapor in a tank 2 m tall that is open at the top and contains a thin layer of liquid n-octane at the bottom. Molecular diffusion coefficient of n-octane vapor in air at 25 C is 0.2 cm2 /s and vapor pressure of octane at 25 C is 0.019 atm. Any possible turbulence can be neglected. It is also known that compounds are inert and advective transport can be neglected.

a) Draw the conceptual model for chloride and n-octane.

b) Write mass balance equation for the concentration for chloride.

c) Solve mass balance equation for chloride. Please show all steps. Assume steady diffusion. Do not forget to determine the integration constants and identify the BCs.

d) By using the concentration expression you found in part c, calculate diffusive flux of chloride.

e) Calculate the n-octane flux at a height 1 meter above the bottom of the tank

f) Plot i) Concentration vs Height and ii) Flux vs Height graphs (2 plots in the same graph) for n-octane