Latent heat storage enables self-sustaining endurance in unmanned underwater vehicles

Unmanned underwater vehicles (UUVs) are critical assets for ocean exploration and marine-resource development. To address the issues of limited endurance, suboptimal manoeuvrability, and restricted payload capacity in existing UUVs, this paper proposes a method to harness ocean thermal energy through a solid–liquid phase change during the cyclical motion of a UUV from the seabed to the sea surface. A power generation system based on the organic Rankine cycle was designed for UUVs. The system transforms ocean thermal energy into electrical energy for driving UUVs. The feasibility and operational characteristics of the system were evaluated by developing a dynamic model for the power generation system. The results of this study indicate that the proposed system can effectively support the self-sustained operations of UUVs. A power generation system equipped with 210 kg of a phase change material required approximately 6000 and 1200 s for energy storage and power generation, respectively. The system achieved a peak power output of 1600 W and a total energy generation of 1920 kJ. During the power generation stage, the ratio of time required for latent heat release to that for sensible heat release was approximately 8:1, with the ratio of corresponding energy outputs being approximately 10:1.