Heat Exchangers Modeling and Calibration for Complete ECS Architectures Simulations
Creators: name:  C. OLIET 
name:   S. TORRAS 
name:   N. ABLANQUE 
name:   J. RIGOLA 
name:   A. OLIVA 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: ADVANCED PERFORMANCE ENGINEERING
FLUID
THERMAL

description: The interest of the European aeronautical industry in the development of more efficient and environmentally friendly aircrafts is at the core of the CleanSky2 European research program. Among the most promising actions to reduce the aircraft carbon dioxide footprint the implementation of the More Electric Aircraft (MEA) concept stands out. This approach considers a significant reduction - or complete elimination - of bleed air from the engines in order to reduce the fuel consumption and to enhance the aircraft overall energy efficiency. The aim is to free the engines from producing compressed air for secondary needs such as the Environmental Control System (ECS) and to supply the energy demand in form of electricity. In this sense new ECS configurations based on more complex interactions with the electrical system are necessary. Both the ECS optimal design and its efficient operation are critical to attain the expected global efficiency improvements as, after propulsion, the ECS is the largest energy consumer in relatively large aircrafts. The analysis of an e-ECS based on numerical simulations is particularly complex due to the large number of subsystems involved and their different physical phenomena, namely, thermal, electrical, pneumatic and mechanical. Heat exchangers are arguably the most challenging components to model within the thermal architecture of novel aircraft ECSs based on the MEA approach. In particular, besides the air-to-air heat exchangers that make up the Air Cycle Machine (ACM), these new ECS systems include Vapor Compression Systems (VCSs) with both condensers and evaporators. The complexity of the phenomena occurring in those heat exchangers (e.g. multi-phase characteristics, evaporation and condensation), together with the numerical difficulties when simulating closed refrigeration loops (VCSs), and the need for low time consuming simulations of the full ECS make the modeling of these specific components crucial for the correct ECS simulation. In other words, the heat exchangers models to be developed need to be fast in terms of computational time, robust regarding the numerical resolution, and accurate to correctly represent their real behavior. The aim of this work is to present a detailed overview of heat exchangers models that have been developed to fulfil the aforementioned purpose. The heat exchanger models are based on a Switching Moving Boundary approach (SMB) where the fluid main phase zones are considered (i.e. gas, liquid and two-phase) but only three control volumes are used. This approach offers a good balance between time consumption and physical representativeness. The traditional SMB model approach has some particular numerical limitations and instabilities, therefore, it has been subjected to additional simplifications to attain the expected numerical performance. In addition to the model structure, a comprehensive calibration process based on heat transfer/pressure drop correlations fitting and global corrections has been conducted. The main features of the numerical model and the calibration procedure are presented in this work. Illustrative results in terms of robustness, speed and accuracy are also shown herein.