A NOTE ON THE MINIMUM NUMBER OF UNITS FOR HEAT EXCHANGER NETWORK SYNTHESIS

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Abstract
Although graph theory shows that the minimum number of exchangers (Umin) in a network is usually one less than the number of streams (N - 1), examples have been published, which demonstrate that this limiting case cannot always be achieved. Some of these examples contain a pinch point, for which it is advocated that the ‘N - 1 target’ should be applied on both sides of the pinch. However, by using a novel arrangement of stream splitting, mixing and by-passes, some of the literature examples can be designed to conform to the N - 1 target. For networks with similar total areas, those having fewer units will usually be cheaper, so Umin networks often have lower capital costs. Although the networks discussed here have somewhat larger total areas, possible applications are discussed where they may be economically attractive.