CHEMICAL ENGINEERING TRANSACTIONS

Small minimum temperature approach, large surface area per volume, high heat transfer efficiency and possibility of handling several streams of multi-stream plate-fin heat exchangers lead to more heat recovery and smaller heat exchanger size. Therefore, plate-fin heat exchangers have been applied extensively in sub-ambient processes. However, one major difficulty in optimising the design of plate-fin heat exchangers is the large number of discrete combinations of standardised fin parts and types involved in the thermal design. A new approach is proposed to systematically optimise fin selection and thermal design of plate-fin heat exchangers simultaneously. Continuous correlations are developed between basic fin geometry parameters and thermal performance of plate-fin heat exchangers based on published data. Validation study shows a good agreement between published results and prediction from the developed correlations. Such correlations can then be incorporated into an overall design procedure, in which the problem is solved as a continuous NLP problem. Compared with previous published design results, 20% heat exchanger volume could be saved with the new design method. Furthermore, the minimum temperature approach optimisation is also integrated into the design model to minimise the total cost for better trade-offs between energy cost and capital cost.