Methods for the Preliminary Design of Heat Exchanger in Aircraft Engines

Abstract

The Water-Enhanced Turbofan (WET) is a promising approach to increase engine efficiency and to reduce emissions. For this concept, a Heat Recovery Steam Generator (HRSG) is required to evaporate and superheat liquid water before injecting it into the combustor. However, the integration of a HRSG into an aero engine has not been investigated in detail yet and the design specifications as well as metrics differ from state of the art, ground-based HRSG applications. Therefore, this paper presents methods and correlations that are combined to build a preliminary design tool for heat exchangers with evaporation. The resulting model is verified by a comparison to experimental heat exchanger studies. Finally, the model is used to assess a HRSG located downstream of the turbine section of a generic aero engine evaporating different water mass flows. The large differences in exhaust temperature and mass flow between cruise and take-off conditions outline the difficulty in finding a well balanced HRSG design.