Mass Transfer Example

Question:

Think of the last time that you washed the dishes. You placed your first greasy plate into the water, and the dishwater got a thin film of oil on the top of it, didn’t it? Find the flux, J, of oil droplets through the water to the top surface. The sink is 18 cm deep, and the concentration of oil on the plate is 0.1 mol/cm³. Assume that there is no oil at the top of the sink yet.

Answer:

To solve this problem, we will need to apply the mass transfer equation we just learned.

J= -D* D C/D x

where: D = 7 x 10^-7cm²/s

D C = concentration at the top of the sink – the concentration of oil on the plate.

The concentration at the top of the sink = 0

The concentration of oil on the plate = 0.1 mol/cm³

D C = 0 – 0.1 = -0.1 mol/cm³

D x = the depth of the sink = 18 cm

Since we know all of the numbers needed, we can calculate the flux.

J= -D* D C/D x

J = -(7 x 10^-7 cm²/s) * (-0.1 mol/cm³) / (18 cm)

J = 4 x 10^-4 mol / (cm²s)

Good Job!

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This project was funded in part by the National Science Foundation and is advised by Dr. Masel and Dr. Blowers at the University of Illinois.