Scale-up in Chemical Engineering (Repost)

A chemical engineer is generally concerned with the industrial implementation of processes in which chemical or microbiological conversion of material takes place in conjunction with the transfer of mass, heat, and momentum. The characteristics of these processes depend on their scale.
They include heterogeneous chemical reactions and unit operations. Understandably, chemical engineers have always wanted to find ways of simulating these processes to gain insights assising them while designing new industrial plants or trying to optimize existing plants.
Irrespective of whether the model involved represents a or a , certain important questions always apply: How small can the model be? Is one model sufficient or should tests be carried out in models of different sizes? When must or when can physical properties differ? When must the measurements be carried out on the model with the original system of materials? Which rules govern the adaptation of the process parameters in the model measurements to those of the full-scale plant? Is it possible to achieve complete similarity between the processes in the model and those in its full-scale counterpart? If not: how should one proceed?