Since the 1960s, researchers have attempted to realize a novel form of maritime propulsion involving no moving parts and providing propulsion through the water using magnets and electricity.
Over the decades, developers have had some success demonstrating magnetohydrodynamic (MHD) drive technology on a small scale. However, it has been inefficient and impractical for full-scale systems due to a couple of big tech hurdles, such as the inability to generate powerful enough magnetic fields and the lack of electrode materials that can withstand corrosion, hydrolysis, and erosion. In recent years, there have been huge strides in the development of magnets, but the electrode materials problem remains.
To overcome this, the Defense Advanced Research Projects Agency (DARPA) announced the 42-month Principles of Undersea Magnetohydrodynamic Pumps (PUMP) program that seeks to create novel electrode materials suitable for a militarily significant MHD drive. The program will assemble and validate multi-physics modeling and simulation tools, including hydrodynamics, electrochemistry, and magnetics, for scaling MHD designs.
“The best efficiency demonstrated in a magnetohydrodynamic drive to date was 1992 on the Yamato-1, a 30m vessel that achieved 6.6 knots with an efficiency of around 30% using a magnetic field strength of approximately 4 Tesla,” said Susan Swithenbank, PUMP program manager in DARPA’s Defense Sciences Office. “In the last couple of years, the commercial fusion industry has made advances in rare-earth barium copper oxide (REBCO) magnets that have demonstrated large-scale magnetic fields as high as 20 Tesla that could potentially yield 90% efficiency in a magnetohydrodynamic drive, which is worth pursuing. Now that the glass ceiling in high magnetic field generation has been broken, PUMP aims to achieve a breakthrough to solve the electrode materials challenge.”
When electric current, magnetic field, and saltwater interact, the major obstacle is the formation of gas bubbles over the electrode surfaces. The bubbles reduce efficiency and can collapse and erode the electrode surfaces. Also, the program will enable the modeling of interactions between the magnetic field, the hydrodynamic, and the electrochemical reactions, which all happen on different time and length scales.
“We’re hoping to leverage insights into novel material coatings from the fuel cell and battery industries since they deal with the same bubble generation problem,” Swithenbank said. “We’re looking for expertise across all fields covering hydrodynamics, electrochemistry, and magnetics to form teams to help us finally realize a militarily relevant scale magnetohydrodynamic drive.”