Synchronous and Sequential Strategies in the Process Design of Cascade Equipment

Cascade or multistage equipment is characterized by the repetition of similar equipment elements in series. Process design, resulting into the main geometric and kinematic dimensions of the equipment, makes use of different strategies. These strategies, based on a process description, the (equality- and inequality) constraints and the number of degrees of freedom of the mathematical system, which describes the process, can be divided in synchronous- and sequential procedures. In a synchronous strategy no a priori requirements are made as to the distribution of a given process variable over the stages, so that the equipment dimensions are obtained simultaneously. In contrast to this a sequential strategy makes use of a priori statements resulting into stage-to-stage calculations and a decreasing number of degrees of freedom. The general theory presented with detailed information on process description, constraints and degrees of freedom, has been applied to the process design of a multi-stage centrifugal compressor.