Experimental and theoretical study of magnetohydrodynamic ship models

Abstract

Magnetohydrodynamic (MHD) ships represent a clear demonstration of the Lorentz force in fluids, which explains the number of students practicals or exercises described on the web. However, the related literature is rather specific and no complete comparison between theory and typical small scale experiments is currently available. This work provides, in a self-consistent framework, a detailed presentation of the relevant theoretical equations for small MHD ships and experimental measurements for future benchmarks. Theoretical results of the literature are adapted to these simple battery/magnets powered ships moving on salt water. Comparison between theory and experiments are performed to validate each theoretical step such as the Tafel and the Kohlrausch laws, or the predicted ship speed. A successful agreement is obtained without any adjustable parameter. Finally, based on these results, an optimal design is then deduced from the theory. Therefore this work provides a solid theoretical and experimental ground for small scale MHD ships, by presenting in detail several approximations and how they affect the boat efficiency. Moreover, the theory is general enough to be adapted to other contexts, such as large scale ships or industrial flow measurement techniques.

The effect of magnetic field on the dynamics of gas bubbles in water electrolysis

“…Only a suitable magnetic field direction generates a Lorentz force and enhances the convective phenomenon for water electrolysis. The magnitude of the Lorentz force that acts on the fluid in the duct of MHD system is given as 15 : where F L is the Lorentz force, B eff is the effective field, which depends on the design parameter of the MHD configuration, I is the current, and w is the distance between the electrodes. A magnetic field is added to the electric field to increase the rate of electrolysis because charged particles are forced in a direction that is perpendicular to the magnetic lines as the magnetic equivalent lines and electrical equivalent lines are orthogonal.…”

“…The conductivity between the electrodes is measured to determine the optimal layouts for electrodes and magnetic field that increases the charging performance and the effectiveness of electrolysis. The results in this study are applicable to various fields including energy conversion, biotechnology 26 , 27 , and an MHD thruster used in seawater 15 , 16 .…”

“…The voltage can be further decreased in the presence of a higher magnetic field because of the magnetohydrodynamic (denoted as MHD) effect 13 , 14 . Such MHD effect has been scaled up and widely employed to generate propulsion for a seawater vehicle or thruster 15 , 16 .…”

The Effect of Magnetic Field on the Dynamics of Gas Bubbles in Water Electrolysis

“…Only a suitable magnetic field direction can have the Lorentz force, and enhance the convective phenomenon of the MHD in water electrolysis. The magnitude of Lorentz force imposing on the fluid in the duct of MHD configuration is defined as follows 40 :…”

Design and Control of an Underwater Launch System

“…Another possible method of propulsion would be magnetohydrodynamic (MHD) propulsion. This would essentially be an electromagnetic pump which would induce MHD propulsion by using a voltage source to maintain an electric potential between two oppositely polarized electrodes, inducing a Lorentz force in the water between them [4]. The construction for this method could involve one, or multiple, thrusters in the shape of smooth nozzles, each wrapped in magnetic coils.…”