A Heuristic-Numerical Advisory System for the Choice of Reactors in Process Design. Since it has become apparent that neither expert systems nor numerical calculations alone satisfy requirements placed on them in the search for the most suitable industrial reactor, a new type of system,viz. the heuristic-numerical advisory system, was developed. It utilises both knowledge-based techniques (production rules and/or frames) and the wide range of calculation tools available in chemical reaction engineering, which are addressed via interfaces. In this way it has become possible to obtain very early reliable information about the later design of an appropriate industrial reactor.