12 At the end of a manufacturing process, a flat slab of a polymeric material contains water that must be removed before the material can be used. The initial water concentration in the slab is 3.2104mol/L and the slab has a total thickness of 3cm. The slab is exposed on both sides to fast-flowing, well-mixed air that contains water with a partial pressure Pw. The air is at 80C and 1atm. Under these conditions, water equilibrium between the air and the polymer is given by Pw(atm)=12.5cws(mol/L) where cws is the concentration of water in the polymeric material. The diffusivity of water in the polymeric material is 1.5105cm2/s. a. Determine how long it would take to remove 95% of the water from the material if it were exposed to air that is completely dry (Pw=0). b. It is found that drying the slab so fast produces cracks in the material. For this reason, we wish to increase the drying time calculated in part (a). This will be achieved by increasing the air moisture. Calculate the value that Pw must have to remove 95% of the water from the material in a time that is twice as long as that calculated in part (a)