Exergy-based Analysis and Optimization of Complex Aircraft Thermal Management Systems

Design and optimization of aircraft thermal management systems (TMS) is typically conducted at steady-state conditions using performance metrics such as bleed air flow rate, fuel burn flow rate, or total system mass. However, when trying to increase the overall performance of a legacy system or analyzing new system architectures, it can be difficult to identify how individual component or subsystem changes will propagate throughout the overall TMS. To address this problem, we investigate the relationship between exergy destruction minimization and conventional design metrics such as bleed air flow rate or system mass. This is motivated by the fact that exergy destruction is a quantity that can be calculated for any subsystem or component, regardless of energy domain or function. A notional system architecture is proposed and modeled using steady-state thermodynamic relationships that captures coupling between individual subsystems of a TMS. We show that exergy destruction is not only sensitive to individual component parameters in a manner consistent with conventional performance metrics, but that due to its generalizability, it also captures how changes in one subsystem propagate throughout the overall TMS. Specifically, through a design case study, we show that minimizing system-wide exergy destruction rate (without an engine model) yields a similar engine fuel burn rate as when fuel burn is minimized directly, but also results in a significantly lower system mass.