A process that has a series of similar steps or devices having the same function. Each step or device may not provide sufficient chemical, biochemical, or physical change so further devices are therefore required to bring about a measurable or desirable change. For example, in the enrichment of the isotope uranium-235, the separation of uranium-235 from the heavier uranium-238 in the form of uranium hexafluoride (UF6) gas in a single centrifugal separator is very low. Natural uranium contains 0.7 per cent of the uranium-235 isotope with the remainder being uranium-238. To achieve the sufficient level of enrichment consequently takes place in a cascade process involving many centrifugal separators operated in series in which the enriched gas forms the feed to the next separation.
Another example of a cascade process is where the conversion of a chemical reaction in a continuous stirred-tank reactor (CSTR) is very low such that the continuous overflow from one can be fed into another reactor for further reaction and conversion. Where there are many CSTRs in series, the operation approximates to that of a plug flow reactor.