Spray-immersion cooling at low ambient pressure: Enabling lightweight applications

Effective energy management in advanced aircraft demands a careful balance between high-efficiency heat transfer and lightweight system design. In this study, we develop a system weight model and build a water-based open-loop cooling system to simulate the heat dissipation of high-power airborne loads. Experimental tests are conducted on three modules under an ambient pressure of 7.5 kPa and a hot-side fluid inlet temperature of 53 °C. The results reveal that the vaporization ratio, a critical factor for lightweight cooling, is strongly influenced by the interaction between droplets, liquid films and surfaces during the spray process. At low flowrates, the spray produces sparse, low-velocity droplets that enhance heat absorption and vaporization, thereby increasing the vaporization ratio. However, this occurs at the cost of reduced heat transfer power. To address this, multi-scale structures are introduced on the outer surface of the heat sink to reorganize liquid film flow and expand wetting area, which simultaneously improves heat transfer and vaporization efficiency. These enhancements yield a record-high vaporization ratio of 42.7 % without external power consumption. In addition, to further enhance water utilization, a spray-immersion coupled cooling system is proposed. This system achieves a maximum vaporization ratio of 58.6 % and a 28.1 % reduction in system weight, demonstrating strong potential for lightweight thermal management in next-generation aircraft applications.