Analysis, prediction and multi-objective optimization of helically coiled tube-in-tube heat exchanger with double cooling source using RSM

Abstract

A novel technical solution about helically coiled tube-in-tube (HCTT) heat exchanger with double cooling source is proposed to obtain regeneratively cooled air for advance aeroengine. 54 simulation runs are performed according the Box-Behnken design table, in which the effect of geometrical and operating parameters on performance of heat exchanger are well considered. Grid independence was carefully carried out referring to ASME V&V 20–2009. The simulation model is validated based on comparison with available experimental data and analysis of flow pattern. The performance of the HCTT heat exchanger i.e. entropy generation number Ne, absorption heat ratio of the inner tube η, and out temperature of the regeneratively cooled air Ta,out were evaluated using Response Surface Methodology. The significance of each term in regression model has been checked by analysis of variance. The results shows that all the design variables are significant for predicting Ne, η, and Ta,out, except non-dimensional coil pitch λ for finding η; the regression models have a good prediction performance; outer tube curvature ratio (δo) is the most significant structure parameter affecting Ne and Ta,out, while inner tube curvature ratio (δi) is the most significant linear term for predicting η, indicating that δo and δi are key structure parameters. It also shows that heat transfer characteristics of the HCTT heat exchanger are complicated engineering problem subjected to multi factors interaction. For instance, total number of terms in model for predicting η reaches to 18, including 5 linear terms, 10 interaction terms along with 3 square terms. The influences of all interaction terms on Ne, η, and Ta,out were displayed using 3D surface graph, the effect rule of interaction terms were discussed in details. Desirability function approach was employed to conduct multi-objective optimization for goals of Ta,out = 630 K, and minimum Ne and η. The optimum values of design variable were obtained. This method possesses practical significances for prediction and optimization of HCTT heat exchanger.