The Elysian E9X, a 90-seat battery-electric aircraft with an 800 km range, offers potential to reduce aviation-sector CO₂ emissions by up to 14%, with future range extensions targeting a segment responsible for 43% of emissions. Achieving this requires an efficient thermal management system (TMS), as battery-electric aircraft rely on active cooling that may introduce significant weight and drag penalties. This thesis presents a systematic methodology to optimize condenser and radiator heat exchangers arranged in series within the E9X ram air ducts. The work comprises three components: development of a multi-point optimization framework using reduced-order models (ROM), implementation of a computational fluid dynamics (CFD) methodology using porous media modeling (PMM), and application of these models to assess the impact of heat exchanger design parameters on overall TMS performance.

A multi-objective optimization framework is developed using the in-house finite-volume heat exchanger code HeXacode coupled with the NSGA-II genetic algorithm. The optimization minimizes both heat exchanger mass and weighted air-side pressure drop across eight operating points spanning the E9X mission profile. Air-side pressure drop is converted to equivalent battery mass through its impact on ram air duct drag, enabling system-level optimization that balances structural mass with aerodynamic penalties.

A 2D RANS CFD approach is implemented in Ansys Fluent using PMM with calibrated momentum and energy source terms. Key methodological contributions include wall temperature correlations enabling off-design heat transfer prediction and improved momentum source term calibration that addresses consistent pressure drop deviations observed in earlier studies. ROM and CFD predictions agree within 1–5% for system-level metrics.

The methodology is applied in three studies. First, offset strip fins (OSF) consistently outperform louvered fins (LF), reducing total equivalent system mass by approximately 100 kg. Second, heat exchanger inclination from 0° to 60° is systematically evaluated. Inclination increases effective frontal area, reducing inlet velocity and enabling denser fin configurations. CFD simulations reveal inclination introduces additional pressure losses due to flow turning (15% increase at 60°). A correction factor correlation is developed and incorporated into the ROM. Despite this penalty, 60° inclination reduces total equivalent system mass by 60 kg. Third, two TMS architectures are compared: a series configuration with eight ram air ducts each containing both condenser and radiator, and a separate-duct configuration with 16 total ducts (eight for condensers, eight for radiators). Despite suboptimal radiator performance due to preheated air, the series configuration reduces total equivalent system mass by 213 kg by having only half the number of ram air ducts and thereby reducing frontal area and external drag.

Combined effects yield cumulative savings of approximately 326 kg, corresponding to a 10 km (+1%) range increase, demonstrating the significant influence of TMS design on battery-electric aircraft performance. The methodology can be extended to alternative architectures, operating conditions, and 3D CFD analysis.