Integration of Heat Exchanger Models into the Performance Analysis of Innovative Aero Engine Architectures

Innovative aero engine architectures are needed to tackle the emission reduction goals set. Some of them make use of heat exchangers for heat recovery and thermal management. The Water-Enhanced Turbofan (WET) as one of the innovative and promising concepts incorporates two heat exchangers. An evaporator is one of them and used to preheat, evaporate and superheat liquid water while cooling the turbine exhaust gas. This increases the thermal efficiency of the cycle and increases power density. The evaporator is one of the key components introduced with the WET concept. Heat exchangers suitable for the WET application were not used in aero engines so far and adequate models have to be developed. From a thermodynamic perspective, the evaporator model needs to predict the transferred heat from the exhaust to the water side and has to account for the pressure losses in both fluids. Additionally, the mass and size of the evaporator are relevant to analyze the options for engine integration and to estimate the overall engine mass. To the authors knowledge, there is no method published for an evaporator model used in thermodynamic analysis of aero engines. Therefore, in this paper the following three novel approaches for the thermodynamic analysis of the evaporator introduced in a WET performance model will be investigated and compared: First, the use of a simplified 1D surrogate model in the WET performance model. Second, the iterative integration of a preliminary design tool for heat exchangers into a WET performance model, and third, the direct integration of the same tool into the performance simulation. The comparison will present differences between computational speed, robustness and accuracy of the approaches. Furthermore, the advantages and disadvantages regarding the different modelling options are discussed and shown exemplarily in a design and an offdesign study. In the future, more comprehensive studies of the WET concept are enabled by the use of the presented methods.