Multi-objective optimization of fuel–air tube-in-tube helical coil heat exchangers for cooled cooling air system applied in aeroengines

Abstract

In fuel–air heat exchangers used in cooled cooling air (CCA) systems, the power-to-weight ratio (G) has to be as high as possible and the air-side pressure drop (Δpair) as low as possible. In this study, a numerical model of a fuel–air tube-in-tube helical coil heat exchanger used in CCA systems was developed. Multi-objective optimization of the heat exchanger was performed to resolve the conflict between G and Δpair by combining response surface methodology and multi-objective genetic algorithm. Finally, an optimal combination of structural parameters was selected using the Pareto-optimal points captured by Non-dominated Sorting Genetic Algorithm-II. The results indicate that the realizable k−ε turbulence model makes the best prediction of thermal and hydraulic characteristics of the heat exchanger. The analysis of variance showed that the most significant parameter affecting G as well as Δpair was the hydraulic diameter of the heat exchanger annulus side (dh), followed by the inner diameter of the heat exchanger inner tube (di,i). The optimized structural parameters were di,i = 1 mm, dh = 2.3 mm, and number of turns = 4.5, and the corresponding values of G and Δpair were 27.6 kW/kg and 255.7 kPa, respectively. In the optimized heat exchanger, G had increased by 5.34% and Δpair reduced by 50.8%.