New Thermal Buoyancy Engine Design Proposed for Underwater Gliders

Researchers from University of Strathclyde, Tianjin University, and the Jiangsu University of Science and Technology have proposed a new thermal buoyancy engine design for underwater gliders used in oceanographic research.

These gliders have engines that work by changing the buoyancy of the glider. The engine uses a phase change material to harvest thermal energy as the temperature of seawater drops from surface temperatures of around 20 to 30 °C to around 4 °C below 650 feet.

The aim of the researchers' work was to achieve a higher energy yield than existing thermal buoyancy engines and therefore enhance the energy efficiency of gliders. To maximize the power output, they designed their thermal engine to have a higher ballast capacity that could therefore provide a large driving force for the glider.

This was achieved by fully using the pressure that the engine's phase change material can generate. This amplified the ballast capacity of the glider without increasing the mass of phase change material so it provided more kinetic energy to the glider’s rear-mounted foldable turbine.

The researchers explain: “When the glider is in power-generation mode, the thermal buoyancy engine uses the thermal energy to change its buoyancy and drive the glider vertically with the assistance of an attitude adjustment unit. During the ascend and descend, the foldable turbine behind the hull opens and harvests energy.” When gliding, the turbine is folded behind the hull of the glider.

In future work, the researchers plan to study the hydrodynamic interaction between the hull and the turbine using CFD simulation and to explore opportunities for realizing the technology.

The study was published in Ocean Engineering.