09 April 2004

The Curious Eye: Magnetohydrodynamics

Dianna Hrabovsky

Magnetohydrodynamics. Immediately upon reading this word, it caught my eye. The most interesting components of the word are magnet and hydro, which is normally associated with water. The whole word makes me think of magnets moving water, but water isn't magnetic.

What could magnets have to do with water movement? First, a dictionary definition might help to move me along this strange river of thought.

Definition of Magnetohydrodynamics

The first stop was Merriam-Webster Online at http://www.meriamwebster.com¹ or www.merriamwebster.com to see what this word meant.

The definition there had to do with the interaction of magnetic fields with electrically conductive, moving fluids and plasmas. The definition collectively described this as a "phenomena," a type of word that always makes it fun to find out more, especially since the dictionary definition was rather vague. There was a link to Britannica on the definition page, so that seemed like a good place to check out next. So I visited www.britannica.com.

While glancing down the list of articles about magnetohydrodynamics, which is shortened to the initials MHD, the ideas of "modern concepts" of plasma physics and "elegantly simple" underlying principles put the fear of calculus into me. There has to be a Non-Theoretical Physicist (NTP) understanding of this topic out there.

My NTP Understanding of MHD

It became obvious almost immediately that the scope of MHD is huge. Applications and studies of MHD include such diverse fields as plasma containment, solar flares, thermonuclear fusion, the relationship of Earth's magnetic field to its liquid core, and many other interesting areas.

I did find a simple explanation of how MHD is used to ionize materials in water.

Magnetic water softeners are a controversial application of MHD. The ideas that I originally thought were valid regarding the application of MHD to water softener technology were explained as incorrect. While MHD, along with other processes, can play a role, it does not work like it is presented in many articles trying to sell water treatment devices based on MHD technology.

Some manufacturers of MHD water treatment systems claim that certain solids dissolved in water can be influenced by a magnetic field. Dissolved limestone (calcium carbonate), for example, is supposedly kept from being deposited as scale in water pipes within a magnetic field.

The formation of scale can be observed when hard water is boiled in a pan. A white film will form on the side of the pan as the water boils away. Scale deposits can eventually become so thick that they impede the flow of water through a pipe.

MHD supposedly keeps dissolved minerals from being deposited as scale when water is flowed through the fields of a series of very strong magnets. As dissolved minerals flow through the fields of such magnets, they remain suspended in the water.

The reason this process does not appear to work in the water softener industry is that the water must be constantly moving past the magnets at a fast rate. Otherwise the process is very inefficient. One university study confirmed that the process occurs, but only to a very small degree.

This is only a brief, simplified example of one form of MHD. You can find many articles about this topic by searching on various key words at any of the Internet search engines. The way plasma containment fields work, and how the motion of Earth's molten core affects Earth's magnetic field, seem much out of the NTP, or Non-Theoretical Physics, realm for now.

Closing Thoughts

An interesting part of this research was learning about ceramic magnets. These magnets include a substance, usually a ferrite, that, once magnetized, retains its magnetic field over time. However, heating these magnets to around 850 degrees or so causes them to lose their magnetic properties.

I had never heard of ceramic magnets before, yet they are all over the place. They are in car speakers, dc motors, Magnetic Resonance Imaging (MRI) scanners, and many other common, everyday devices.

These applications for magnets and MHD are all very interesting subjects and are by no means out of the Curious Eye's mind. Perhaps in the future I will delve into plasma containment and ceramic magnets and how they work. It all sounds extremely interesting, and it's great fun to see where a seemingly simple word, object, or idea can take you.

"May we never lose our curious eye."Di Hrabovsky.

1: It appears that both addresses will get you to the Merriam-Webster Online dictionary page. It is an amusing idea that they provide dictionary and spelling help and also provide access to their online page, whether or not you can spell Merriam correctly.