Optimization of a commercial aircraft environmental control system

In this work, two optimization criteria, minimum weight and minimum entropy generation are simultaneously applied to deduce the main geometric characteristics of the two finned cross-flow heat exchangers that the environmental control system (ECS) of commercial aircraft normally incorporate. The performance of this system, described and modelled in this paper, is optimized as a whole instead of considering the optimal operation of isolated devices. The ECS is based on Brayton inverse cycle, where two air streams are involved, one to be conditioned or the main stream and a coolant one. The whole evolution of the two streams is analyzed. The main stream is studied starting from ambient conditions, before entering the aircraft engine, following with the bleed process until the turbine exit where the required temperature and pressure conditions are achieved. The coolant ram air stream is also considered from ambient conditions to the nozzle exit from where it is rejected. The heat exchanger surfaces have been selected using a compactness criterion but taking into account that compactness increases pressure losses. Once the parameters and variables are identified, the optimization task would lead to an optimum geometry by means of a trade-off solution. The numerical results found in this case illustrate the adequacy of this kind of optimization to study complex thermal systems. (C) 2002 Elsevier Science Ltd. All rights reserved.