Transport phenomena lecture: deadline $03/06/2024$

$\frac{20}{05}\frac{?}{2024}$

Problem statement $10$

Imagine a closed container with a thin layer of water molecules adsorbed on a dry desiccant surface $($silica gel$).$ When the container is evacuated $($pressure reduced$),$ the water molecules desorb from the desiccant and begin to fill the container space.

Conditions:

a$)$ The water molecules interact with the desiccant surface through adsorption forces.

b$)$ When the pressure is reduced, the equilibrium between adsorbed and desorbed molecules shifts towards desorption. More water molecules leave the surface and enter the gas phase.

c$)$ The desorbed water molecules then diffuse throughout the container due to a concentration gradient $($higher concentration near the surface, lower concentration further away$).$

Problem:

a$)$ Distinguish between unimolecular desorption $($UMD$)$ and equimolar counterdiffusion $($EMD$).$

b$)$ Explain the role of pressure in the water desorption process.

c$)$ Sketch a qualitative concentration profile of water vapor within the container after some desorption has occurred. Label the axes.