Computational Fluid Dynamics Modeling of Additively Manufactured Extreme Environment Heat Exchangers for Waste Heat Recuperation

Advanced Brayton cycle-based waste heat recovery (WHR) system for a targeted energy efficiency of 20-50% and gravimetric power densities of 1.6-1.9 kW/kg are attractive propositions for future airplane designs. One of the critical challenges for the maturation of these technologies is the need to achieve highly compact heat exchangers (HX) capable of operation under extreme pressure and temperature environments. The current work presents computational fluid dynamics (CFD) modeling strategies for the design and development of additively manufactured extreme environment heat exchangers (EEHX). Modeling and simulation-driven design improvements to the HX are implemented to achieve a power density of 15 kW/kg under the extreme environment of 800 degrees C inlet temperature and 80 bar pressure with supercritical CO2 as the working fluid. Various CFD-based modeling methods are described, starting from selecting, rating, and sizing heat transfer (HT) surfaces, followed by detailed core modeling through periodic and end-section models. Further, a novel porous media-based modeling approach with a high-fidelity manifold model is implemented to generate optimal manifold profiles while minimizing flow maldistribution through the core. Comprehensive physical testing of the additively manufactured heat exchanger prototypes has been used to validate the developed numerical models within 5-10% of pressure drop and heat transfer predictions.