A modified shape normalization, which was successfully used earlier fo
r monoporous pellets, has now been defined for pellets which have a bi
porous structure. Such a normalization consolidates the eta-phi curves
into a single curve. The biporous effectiveness for any arbitrary sha
pe can now be evaluated with a high degree of accuracy using the infin
ite slab effectiveness. With this modification, the spread in the curv
es for various shapes is less than 6%.