With the rapid advancement of aviation technology， airborne electronic devices have been increasingly integrated， making traditional single-phase cooling technologies insufficient to meet the increasingly demanding heat dissipation requirements. To address this problem， this study proposes a new and efficient cooling technology that couples microchannel heat sinks with a spray cooling module. A high-power open flash evaporation experimental system simulating high-altitude low-pressure environments was built to explore the effects of the inlet superheat of the hot-side fluid and the type of working fluid on heat transfer performance. The results indicate that reducing environmental pressure and increasing the inlet temperature of the hot-side fluid can both increase the inlet superheat of the hot-side fluid， thereby enhancing heat transfer and improving working fluid utilization. However， the mechanisms of these effects differ. The physical properties of the working fluid are crucial factors affecting flow and heat transfer characteristics. When water is used as the hot-side fluid， the heat transfer rate can reach up to 3 326 W， with a vaporization ratio of 30.84% and a power consumption ratio of 456. In contrast， when 65# coolant is used as the hot-side fluid， the heat transfer performance significantly decreases， with the heat transfer rate and vaporization ratio both reducing by about 18% and the power consumption ratio reducing by around 53%， compared to the case of water. The main reason for this is that 65# coolant has a higher dynamic viscosity and a lower thermal conductivity， leading to characteristics of deteriorated flow and heat transfer. This study can provide a theoretical basis for the design and performance optimization of efficient thermal management systems for high-power airborne electronic devices.