Ordered layers and structured packings are used as internals in numero
us rectification columns. They characteristically exhibit low pressure
drops and high plate numbers per unit length. The relatively high inv
estment costs are frequently offset by small column dimensions and hen
ce lower equipment costs. In packings of industrial dimensions unstabl
e flow states may occur which significantly lower the plate numbers. S
uch instabilities can be detected experimentally by tomographic method
s. Moreover, flow patterns can be predicted theoretically. A theoretic
al description permits the engineer to scale up such columns containin
g packings and to deduce the design features necessary for industrial
scale columns from laboratory experiments.