3. A solid A is dissolving in a flowing liquid stream S in a steady-state, isothermal flow system. Assume in accordance with the film model that the surface of A is covered with a stagnant liquid film of thickness & and that the liquid outside the film is well mixed. a) Develop an expression for the rate of dissolution of A into the liquid if the concentration of A in the main stream is negligible. b) Develop a corresponding expression for the dissolution rate if the liquid contains a substance B, which at the plane z=K, reacts instantaneously and irreversibly with A- A+B P. The main liquid stream consists primarily of B and S, with Bamole fraction of xBo. It is necessary to recognize that species A and B both diffuse towards a thin reaction zone as shown in the figure. Well-mixed A diffusing Bdiffusing | stream of B and S AU through S through S 2=0 (reaction plane) (outer edge of stagnant liquid film) You should obtain the following. a)N A,z=0=D CDASX A0 b)N A,z=0D XBcoDBS 1+ X A0DAS