The following illustrated spherical capsule is used for long-term, sustained drug release. A saturated liquid solution containing the dissolved drug (solute A) is encapsulated within a rigid gel-like...

The following illustrated spherical capsule is used for long-term, sustained drug release. A saturated liquid solution containing the dissolved drug (solute A) is encapsulated within a rigid gel-like shell. The saturated solution contains a lump of solid A, which keeps the dissolved concentration of A saturated within the liquid core of the capsule. Solute A then diffuses through the gel-like shell (the gel phase) to the surroundings. Eventually, the source for A is depleted, and the amount of solute A within the liquid core goes down with time. However, as long as the lump of solid A exists within the core, the source solution is saturated in A and the concentration c_A
is constant. The diffusion coefficient of solute A in the gel phase B is
 The concentrations of solute A in the gel phase at the boundaries of the shell are

a. State the differential forms of the flux equation and the differential equation for mass transfer for this diffusion process.

b. Develop the final analytical, integrated equation to determine the total rate of drug release, W_A, from the capsule under the condition where the concentration of A within the liquid core of the capsule remains constant.

c. What is the maximum possible rate of drug release from the capsule, in units of gram moles of A per hour?