Hierarchical thermal management of multi-functional UAVs using a vapor compression/thermoelectric hybrid refrigeration system

The deployment of multifunctional unmanned aerial vehicles (UAVs) imposes stringent thermal-management demands on airborne electronics, including multiple heat sources, multiple temperature levels, high local heat fluxes, and different temperature-control accuracies. Conventional single-mode cooling strategies are limited in satisfying these demands over a large temperature span. To address this issue, this study proposes a quasi-two-stage vapor-compression/thermoelectric hybrid refrigeration system for hierarchical UAV thermal management. In this system, the medium-temperature evaporator provides background cooling, while the low-temperature evaporator maintains the hot-side temperature of thermoelectric modules (TEMs) for local precision cooling. A thermodynamic vapor-compression refrigeration system (VCRS) model is coupled with a temperature-dependent TEM model to compare four configurations, namely, the basic vapor-injection cycle (BVIC), single-stage TEM-coupled cycle (BCST), two-stage TEM-coupled cycle (BCTT), and ejector-assisted BCTT (MCTT). The effects of key operating parameters are analyzed to reveal the performance-improvement mechanisms, feasible operating boundaries, and flight-envelope-based condensing-temperature response. The results show that TEM coupling redistributes the large temperature lift between the vapor-compression and thermoelectric branches, thereby reducing compressor pressure ratio, discharge temperature, and the operating penalty of direct deep vapor-compression cooling. Under the baseline condition of t _jc = −40 °C and t _c = 50 °C, replacing the single-stage TEM with the two-stage TEM increases the system COP and exergy efficiency by 2.46%–2.54% and 3.38%–3.47%, respectively. Further ejector integration enhances the COP and exergy efficiency by 10.51%–46.17% and 8.18%–33.12% by recovering throttling-related pressure energy between the two evaporating levels. Component-level exergy analysis shows that, although TEMs introduce additional electrical power consumption, the reduction in vapor-compression irreversibility is more dominant; after ejector integration, the system exergy efficiency is further improved by 20.08%. The module-number analysis indicates that the optimal TEM scale results from the trade-off between high-current Joule irreversibility at low module numbers and weakened single-module cooling contribution at excessive module numbers. Under the severe t _jc = −70 °C condition, the MCTT increases the COP and exergy efficiency by 50.44% and 37.76% compared with the BCST. The first-order flight-envelope assessment further shows that the system COP remains above 2.39, while the compressor, ejector, and TEMs operate within stable ranges. These results demonstrate the potential of the proposed hybrid system for hierarchical thermal management of heterogeneous UAV airborne loads.