Electric power by magnetohydrodynamics

Electric Power by Magnetohydrodynamics

Power to the people

Power generation for the most part involves somehow converting heat into electricity: you generate heat, the heat heat turns water into steam, the steam drives a turbine connected to a dyanamo or alternator to generate electric current.

This basic approach has remained essentially unchanged since the early days of electricity. Development has mainly focussed on finding new ways of generating that heat: coal, gas and oil have conventionally been used, and then the introduction of nuclear power was a big advancement in the 1950s and 1960s.

The trouble is all the mechanical connections and moving parts needed in a conventional generator can reduce the efficiency of the electricity generation, so in the 1960s researchers began to wonder if there was another way of generating electricity without moving mechanical parts.

Cut out the middle man

Researchers in the 1960s began to wonder if something could be done about the process from getting the heat to electricity, which is normally done by a mechanical/magnetic generator. One novel way to achieve this is to remove all mechanical moving parts and replace them with ionised fluid.

The result, discussed in this New Scientist article from 1962, is the magnetohydrodynamic generator. Heat is used to ionise gas which is then passed through a magnetic field. Moving the charged particles through the magnetic field then generates a current in the ionised gas, in similar manner to a conventional generator.

A host of problems

While rather straightforward in concept, the magnetohydrodynamic generator posed many engineering problems including how to achieve sufficiently high conductivity in the ionised gas, how to subject the gas to a sufficiently high magnetic field and even problems of selecting materials for the generator duct itself.

Despite these issues, the article still ventures to speculate on what a full scale  magnetohydrodynamic generator might look like.

Ultimately the issues raised in the article proved too much for the MHD generator, and further developments in conventional power generation meant that comparable efficiencies could be achieved of much less cost.

The MHD Dynamo

The MHD generator may not have succeeded, but its complement, the MHD dynamo, or MHD drive has had some limited success.

In effect an MHD drive is an MHD generator run in reverse, so a stream of ionised fluid is pumped out of the drive, which can be used to generate thrust.

Experimental systems for ship and space propulsion have had slightly more success than generator schemes, but are still dogged the problems of complexity and expense, so are unlikely to completely change the world any time soon.

In the film version of Tom Clancy’s The Hunt for Red October, the silent drive of the Russian submarine is based on MHD principles.

Who knows? Perhaps in another 50 years MHD technology won’t seem quite so science fiction.

New Scientist, 1 Feb 1962