Integrative Thermodynamic Optimization of the Crossflow Heat Exchanger for an Aircraft Environmental Control System

This paper documents the process of determining the internal geometric configuration of a component by optimizing the global performance of the installation that uses the component. The example chosen is the crossflow heat exchanger used in the environmental control system of a modern aircraft. The optimization of global performance is achieved by minimizing the total entropy generation rate of the installation. There are three degrees of freedom in the heat exchanger configuration (the length-to-width and height-to-width aspect ratios, and the separator plate spacing ratio), which is subjected to two global constraints: total component volume, and total wall material volume (or weight/density) of wall material. Numerical results show how the optimal configuration responds to changes in specified external parameters such as volume, weight, Mach number, diffuser inlet cross-sectional area, and the pressure at which the cabin air is initially bled from the engine compressor. It is shown that the optimal configuration is robust and that major features such as the ratios of channel spacings and flow lengths are relatively insensitive to changes in some of the external parameters. It is also shown that the optimal heat exchanger geometry is insensitive to the thermodynamic irreversibility caused by discharging the used ram air into the ambient.