Exergy Approach to Decision-Based Design of Integrated Aircraft Thermal Systems

The concept of using an exergy-based approach as a thermal design methodology tool for integrated aircraft thermal systems is introduced. An exergy-based approach was applied to the design of an environmental control system (ECS) of an advanced aircraft. Concurrently, a traditional energy-based approach was applied to the same system. Simplified analytical models of the ECS were developed for each method and compared to assess the ability of each method to suggest optimal design paths. The study identified some roadblocks to assessing the value of using an exergy-based approach: Energy and exergy methods seek answers to different questions, making direct comparisons awkward, and high-entropy generating devices can dominate the design objective of the exergy approach. Nonetheless, exergy methods do approach design differently, providing a ready estimate for efficiency on a component and system basis. Multiobjective optimization tradeoff studies between design weight and entropy generated were used to determine optimal design points. The results from the two analyses provide similar but different decision solutions. The methodology and its implementation are illustrated.