2.

A tank of still water has an initial concentration of dissolved oxygen of 3 ppm at a

temperature of 20°C. For time t>0 the water surface is exposed to air at 20°.

a) Determine the time to required for the oxygen concentration at a point 50 cm below the

surface to increase to 6 ppm. The saturation concentration for oxygen in water is 9.3 ppm

at that temperature. (That is the concentration of the water surface for t>0.) 5 pts

b) Find an expression for the flux of oxygen across the water surface as a function of time.

What is the flux (per unit area) at t₁. 5 pts

c) Solve this problem numerically and compare to the analytical solution. Use Finite

difference technique for solving governing equation. Estimate the flux (as is part b)

numerically and compare to result in part b. 5 pts