Energy And Exergy Based Impact Of Avionics Thermal Management Systems On Tactical Aircraft Performance
Thermal management systems for tactical aircraft electronics cooling were studied in this work. The systems consisted of an HFC-134a based vapor compression cycle (VCC) and an air-based reversed-Brayton cycle (RBC). The heat loads consisted of aircraft electronics, including avionics. The system models were built using detailed component-level models. The models underwent verification and validation to check mass and energy conservation, as well as ensuring the model’s behavior reflected the actual system’s behavior. Both models were run through a matrix of boundary conditions that represented specific segments of two tactical aircraft missions with next generation thermal loads. These segments included typical tactical aircraft operating conditions: ground idle, cruise, combat, dash, and loiter. The resulting system performance of both models was analyzed using a first law energy-based fuel impact and second law exergy-based irreversibility method to determine their respective impact to the aircraft. Component level irreversibilities were also analyzed.
The VCC cooling system met or exceeded cooling performance goals, while the RBC fell short during some mission segments. The VCC also had a lower fuel impact than the RBC from an energy perspective and lower system and component level irreversibilities from an exergy perspective for most mission segments. The opposite trend was observed during the ground idle segment, where the VCC’s fuel impact was larger but irreversibilities were lower than the RBC’s.
The VCC’s lower fuel impact was due to the engine power take-off having less of an impact on engine fuel flow than the RBC’s bleed air. The VCC’s lower irreversibilities were due to the system’s use of phase change in the heat exchangers, which tended to be more efficient than the single-phase heat transfer in the RBC’s heat exchangers.
Some limitations of the study should be addressed in future work, including electrical power generation losses and an improved air humidity model that operates better at low temperatures and incorporates moisture evaporation. Alternative VCC refrigerants with higher critical temperatures should also be explored to ensure the system does not limit the aircraft operationally. New architectures should be explored that combine RBC cooling and VCC cooling.
Overall, the VCC cooled the thermal load more efficiently with a lower overall impact to the aircraft than the RBC from both energy and exergy based perspectives.