Suppose a porous solid $($e$)$ saturated with a certain fluid. The aim is to remove this fluid from this solid by keeping it immersed in a solvent. Develop a mathematical model that describes this process. The solvent is expensive, so it will be reused and its initial concentration is not zero. For a container of volume $V_c$ of solvent, the initial concentration of the fluid to be extracted will be $C_0.$ Your model will describe both the concentration of the fluid in the solid and in the solvent. Consider cylindrical geometry for the solid.