An Engine with Nothing Inside? Building a Magnetohydrodynamic Drive

Overview

Objectives/Goals To investigate magnetohydrodynamic (MHD) thrust, an intriguing force that can quietly power a boat without moving parts. To design, test and improve a series of MHD engines made from readily available materials. To see if an MHD engine could power a small toy boat. Methods/Materials -Understand the Lorentz force that creates MHD thrust and determine how to measure the thrust. -Test magnets (NdFeB and ceramic) and metal electrodes (Al, Cu, Mo, Ti, Ta, Sn, 304 stainless steel, brass, galvanized steel, Haynes 214) for building MHD engines. -Build prototypes (using rectangular plastic tubing, electrical tape, duct tape and an adjustable power supply), optimizing magnets, tube dimensions, electrode sizes, and wire-to-electrode contacts. -Measure the thrust of the engines by suspending them from a pendulum (fishing line) in salt water (with salinity of seawater) and calculating thrust from deflection. -Select the engine with the best thrust/weight ratio. -Determine whether thrust vs. current is linear. -Create and test MHD demos that propel small plastic spheres and a toy boat. Results -Thrust was proportional to current, but lower than predicted. -The best electrodes were aluminum, because they corroded least. -Making the electrodes shorter than the magnets produced more thrust by forcing the current through the highest magnetic field. -Keeping the weight low is especially important due to low thrust. -The engine produced "gunk" and gas bubbles. -We could power a toy boat, but not very quickly. Conclusions/Discussion -A simple equation really did generally predict thrust as it should have: Thrust = (current) x (engine width) x (magnetic field) -Narrowing the electrodes to keep current flowing in the region with the strongest magnetic field significantly improved our results. -It is exciting to see water propelled through a seemingly empty tube. -MHD engines do work, but even with ideal performance, the thrust is limited with our power supply and magnets. We could power a small toy boat, but it did not move very quickly.

Awards (1)

• First Place

Competition history

• CSEF 2008 Aerodynamics/ Hydrodynamics (Junior Division Only) · Entry J0125

Resources

• CSEF project summary ↗

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