Analysis of ultralow flow resistance heat exchangers on cooled cooling air and precooling technology

Abstract

In line with increases in aircraft engines’ performance, cooled cooling air technology (CCA technology) has been put forward to address thermal management issues. It mainly utilizes bypass air to cool the compressor bleed air for turbine cooling by the application of a heat exchanger. However, the current serpentine-tube CCA heat exchanger results in significant pressure losses, which have a detrimental effect on both the engine’s total thrust and fuel consumption. Therefore, two novel heat exchangers with ultralow flow resistance characteristics are proposed, and their thermal and hydraulic performances are experimentally tested. Besides, a multidimensional evaluation method is established by simulation work which integrates the heat exchanger itself with the whole engine system performances (including total thrust and specific fuel consumption). In regard to versatility, this work also explores the superiority of these novel types of heat exchangers in precooling technology. Our findings prove that the two novel heat exchangers take an over 50 % lower pressure drop compared to the traditional serpentine-tube type under the same heat transfer conditions. When they are applied to CCA or precooling technology, the enhancement in total thrust FN and reduction in specific fuel consumption sfc have been observed under different flight missions. When using the unilateral plate-fin heat exchanger, the maximum increment in total thrust is approximately 51.5 %, and the decrease in sfc is approximately 33.4 %. And those for the longitudinal flow tube bundle heat exchanger are 38.1 % and 27.2% respectively. Further analyses reveal that the superiority is mainly caused by the increase in mass flow rate and exhaust gas pressure. To sum up, the present study provides a theoretical and experimental basis for the design of advanced heat exchangers in the aerospace field, and further optimization work is still needed to enhance their heat transfer performance.