Integration of Circular Fins into Exhaust Gas Recuperators for Innovative Propulsion Concepts in Aviation

Waste Heat Recovery (WHR) could be a key enabler for future propulsion technologies to meet the defined emission goals by 2050. The recovery of waste heat requires the integration of heat exchanger into the aero engine’s flow path under consideration of several constraints such as mass, compactness and transferred heat. The concept of the Water-Enhanced Turbofan (WET), for example, integrates an evaporator into the exhaust flow of the engine to recover exhaust heat by evaporating liquid water. Despite the fact that the WET concept has been deprioritized by the industry, it still demonstrates the potential of waste heat recovery and provides an ideal platform for the development of appropriate heat exchanger models considering the interdependencies between the engine’s components and the heat exchanger itself. In the evaporator of the WET concept, the thermal resistance of the exhaust side is the limiting factor for the heat transfer capability of this component. In order to reduce the thermal resistance of the exhaust side, an annular finned tube bundle setup for the evaporator of the WET concept is analyzed. Based on 3D Computational Fluid Dynamics Analysis of the finned configuration local heat transfer and flow behaviour of the finned tube bundle arrangement are computed. It is found that the present finned tube bundle setup leads to an overall fin effectiveness of 10 significantly increasing the amount of transferred heat in the heat exchanger compared to an non-finned tube bundle setup.