| A Heat Exchanger Networks (HEN) is a configuration of heat exchangers designed to transfer heat between three or more streams. HENs are present in a wide variety of applications wherever thermal management is required. The range in size and complexity is limitless. HEN optimization is a high stakes game where initial construction/implementation costs are weighed against the long-term operating costs of the network. Much has been published on optimization methods and strategies. The Second Law of Thermodynamics provides the guiding principles for most ideal processes. Several authors have argued that the Second Law be incorporated into HEN design. They have described how to approach the optimization challenge from a Second Law point-of-view and demonstrated how straight-forward principles can be used to improvements (sometimes drastic improvements) to pre-existing networks. Unfortunately, the infinite variety of possible network combinations has made the identification of the clear, ideal network difficult to pin down. Engineers are familiar with ideal cycles where the processes take place in a reversible fashion. This does not apply to heat exchanger networks. Whenever we are dealing with a network where the inlet and target temperatures of the individual streams are established, the total amount of entropy generation is fixed. Reducing this entropy is not only pointless, it's impossible. Furthermore, since the purpose of a heat exchanger is to exchange heat across a finite temperature difference, entropy production is fundamentally necessary and should be encouraged. The question then becomes "How do we best configure a network to make maximum use of this entropy production?" This paper will define the optimum HEN configuration for a basic network where one hot stream is paired with two cold streams. The findings and methodology presented in this work can be added to the arsenal of the engineer, providing him or her with yet another tool to fine-tune their HEN design. |
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