1. One of the oldest membrane materials used for dialysis is porous cellophane, a thin transparent sheet made of regenerated cellulose. Typical values of parameters for commercial cellophane membranes are as follows: thickness = 80 m, porosity = 0.45, tortuosity = 5.0, and pore diameter = 40 (Seader and Henley, 2006).
   1. Estimate the effective diffusivity of urea through this membrane at 298 K. The diffusivity of urea in dilute aqueous solution at this temperature is 1.38 105 cm2/s. The molecular diameter of urea is 5.28 .
   2. The artificial kidney of Example 1.3 uses a cellophane membrane. If the urea concentration difference across the membrane is 25 mg/dL, estimate the membrane area required.

Note: I am lost on how to calculate the area without the mass flow rate.

DAB,eff=DAB DAB,eff=5.00.45(1.38105)=1.24106scm2 DAB,eff=1.24106Scm2 DA1=1dL25mg1L10dL1,000mg1g1,000g1kg=2.50104m3kg jA=DAB,effzA A=(1.241010)(80106)(0(2.50104))=3.881010m2skg A=jAm=(3.881010)m A=(3.881010)m(skg)m2 DAB,eff=DAB DAB,eff=5.00.45(1.38105)=1.24106scm2 DAB,eff=1.24106Scm2 DA1=1dL25mg1L10dL1,000mg1g1,000g1kg=2.50104m3kg jA=DAB,effzA A=(1.241010)(80106)(0(2.50104))=3.881010m2skg A=jAm=(3.881010)m A=(3.881010)m(skg)m2