You want to measure the effectiveness of a porous solid desiccant. To do so, you attach a slab of the desiccant 0.5 × 20 × 20 cm to a thin wire. You then attach the wire to an analytical balance and suspend the slab in a chamber at 45°C and twenty percent relative humidity. You find that the slab weight varies with time as follows:

Find the permeability of water vapor in this desiccant. You will find that the data fit neither a finite slab nor an infinite slab. One good alternative model is to postulate pores in the slab.
 

Time(min) 0 10 20 30 40 50 60 Slab weight(g) 166.25 167.03 167.59 168.07 168.48 168.88 169.25