Globally optimal basic design of multiple-unit heat exchangers

A novel approach (Complete Set Trimming) to address the globally optimal design of multiple-unit heat exchangers (Shell and Tube, Double Pipe, Plate, etc.) is presented. Three arrangements: Series, Parallel, Series–Parallel, and Parallel–Series, for minimizing area, CAPEX, or total annualized cost are considered. The geometry of all (equal) units is determined together with the number of units and the fluid allocation. The article illustrates the need to minimize CAPEX explicitly instead of using the minimization of Area as its proxy objective function. In addition, the influence of available pressure drop in the final optimal design is also discussed. Finally, the article shows that solutions obtained by minimizing the Total Annualized Cost (TAC) render different solutions than those obtained by minimizing CAPEX, indicating that pumping costs matter, depending on the balance between operational and capital costs.