Tuesday, September 09, 2008

Magnetohydrodynamic Propulsion

Motors without moving parts

In the 1990 film The Hunt for Red October (based on the Tom Clancy novel of the same name), Sean Connery plays the captain of a Russian submarine. This much I remembered from having seen the film many years ago. I did not recall that the submarine in question—the eponymous “Red October”—used a special high-tech propulsion system that, having no moving parts, was silent. I’m sure my science fiction filter was on, and I just assumed at the time that the top-secret engine was the sort of almost-plausible futuristic contrivance any modern spy movie will have—and not worth taking very seriously. Just a few years later, though, Mitsubishi demonstrated a boat using a propulsion system of roughly the design Clancy described in his novel. And now variations on this technique are being used in electrical generators, nuclear reactors, and even spacecraft design.

Gimme an “M”

The scientific principle in question is known as magnetohydrodynamics, which is a fairly straightforward combination of magneto (as in magnet), hydro (as in water), and dynamics (as in motion). Those in the biz call it MHD for short. And yes: it uses magnetism to cause motion in water (or another fluid). MHD is not by any means a new discovery—academic researchers have been working on this since at least the 1960s, and the Journal Magnetohydrodynamics has been published since 1965 by the University of Latvia. But in recent years, MHD designs have begun to appear more frequently in everything from large-scale commercial operations to high school science fair projects.

The basic concept is simple, even though it relies on some complex math and physics. When a conductive fluid (such as saltwater, liquid metal, or even plasma) is exposed to a magnetic field and an electric current at right angles to each other, their interaction propels the fluid in a direction perpendicular to the other two axes. In other words, the fluid itself functions more or less as the moving part of an electric motor.

You can demonstrate this effect on a small scale if you have a free afternoon, a few tools, and a bathtub. Take a small plastic tube and glue a pair of nice, strong magnets onto the top and bottom (opposite poles facing inward). Then glue strips of metal to the insides of the tube on the left and right; these will be the electrodes. Affix this assembly to the bottom of a small toy boat. Wire the electrodes to a fairly high-power battery (being careful, of course, to keep the battery dry), and float the entire contraption in a saturated solution of salt and water. If the battery is strong enough and the boat is small enough, it will start moving through the water.

The Solid-State Paddlewheel

Of course, if you want to power a boat large enough to hold passengers, the engines will have to be pretty large. You’re going to need some very strong magnets—think helium-cooled superconducting electromagnets—plus an awful lot of electricity to provide current to the electrodes. Even then, you may find (as Mitsubishi did) that the thrust produced is a bit underwhelming. The prototype boats were expected to reach speeds of 200 kilometers per hour, but only got up to 15 km/h. Even though MHD drives have virtually no drag (unlike propellers), the energy conversion efficiency is currently pretty low. (Had they used the same amount of electricity to power conventional motors, the boats would have gone much faster.) Further technological advances are needed to make this a practical propulsion system for marine vessels.

As far as I know, there are no submarines using such drives now, but a Red October is at least more plausible than I’d previously have suspected. However, I should point out that MHD drives are only sort of quiet. By this I mean there’s no noise from an engine or propeller, but the electrodes do produce huge numbers of bubbles—after all, this design amounts to magnetically enhanced electrolysis, and electrolysis separates water molecules into hydrogen and oxygen atoms. So a submarine with an MHD drive would not be quite as stealthy as you might imagine.

Much more promising are designs that use other kinds of fluids that conduct electricity better. For example, plasma-based propulsion systems being studied for long-distance space travel use a variation on MHD. It remains to be seen whether technological innovations will make MHD an efficient and practical means of propulsion (terrestrial or otherwise), but the mere fact that you can induce motion in a fluid without either moving parts or combustion seems incredibly cool to me. As with so many scientific discoveries, truth is much more exciting than fiction. —Joe Kissell

Wireless Powering of LEDs via Resonant Inductive Coupling

Tesla's dream coming true..... I never knew we could do that so easily.. It was always trouble for me when i tried that...

The Big Bang and the CERN

Did you know that the matter in your body is billions of years old?

According to most astrophysicists, all the matter found in the universe today -- including the matter in people, plants, animals, the earth, stars, and galaxies -- was created at the very first moment of time, thought to be about 13 billion years ago.

The universe began, scientists believe, with every speck of its energy jammed into a very tiny point. This extremely dense point exploded with unimaginable force, creating matter and propelling it outward to make the billions of galaxies of our vast universe. Astrophysicists dubbed this titanic explosion the Big Bang.

The Big Bang was like no explosion you might witness on earth today. For instance, a hydrogen bomb explosion, whose center registers approximately 100 million degrees Celsius, moves through the air at about 300 meters per second. In contrast, cosmologists believe the Big Bang flung energy in all directions at the speed of light (300,000,000 meters per second, a hundred thousand times faster than the H-bomb) and estimate that the temperature of the entire universe
was 1000 trillion degrees Celsius at just a tiny fraction of a second after the explosion. Even the cores of the hottest stars in today's universe are much cooler than that.

History of Universe Hubble Deep Field

There's another important quality of the Big Bang that makes it unique. While an explosion of a man-made bomb expands through air, the Big Bang did not expand through anything. That's because there was no space to expand through at the beginning of time. Rather, physicists believe the Big Bang created and stretched space itself, expanding the universe.

A Cooling, Expanding Universe

For a brief moment after the Big Bang, the immense heat created conditions unlike any conditions astrophysicists see in the universe today. While planets and stars today are composed of atoms of elements like hydrogen and silicon, scientists believe the universe back then was too hot for anything other than the most fundamental particles -- such as quarks and photons.

But as the universe quickly expanded, the energy of the Big Bang became more and more "diluted" in space, causing the universe to cool. Popping open a beer bottle results in a roughly similar cooling, expanding effect: gas, once confined in the bottle, spreads into the air, and the temperature of the beer drops.

Rapid cooling allowed for matter as we know it to form in the universe, although physicists are still trying to figure out exactly how this happened. About one ten-thousandth of a second after the Big Bang, protons and neutrons formed, and within a few minutes these particles stuck together to form atomic nuclei, mostly hydrogen and helium. Hundreds of thousands of years later, electrons stuck to the nuclei to make complete atoms.

About a billion years after the Big Bang, gravity caused these atoms to gather in huge clouds of gas, forming collections of stars known as galaxies. Gravity is the force that pulls any objects with mass towards one another -- the same force, for example, that causes a ball thrown in the air to fall to the earth.

Where do planets like earth come from? Over billions of years, stars "cook" hydrogen and helium atoms in their hot cores to make heavier elements like carbon and oxygen. Large stars explode over time, blasting these elements into space. This matter then condenses into the stars, planets, and satellites that make up solar systems like our own.

How do we know the Big Bang happened?

Astrophysicists have uncovered a great deal of compelling evidence over the past hundred years to support the Big Bang theory. Among this evidence is the observation that the universe is expanding. By looking at light emitted by distant galaxies, scientists have found that these galaxies are rapidly moving away from our galaxy, the Milky Way. An explosion like the Big Bang, which sent matter flying outward from a point, explains this observation.

Another critical discovery was the observation of low levels of microwaves throughout space. Astronomers believe these microwaves, whose temperature is about -270 degrees Celsius, are the remnants of the extremely high-temperature radiation produced by the Big Bang.

Interestingly, astronomers can get an idea of how hot the universe used to be by looking at very distant clouds of gas through high-power telescopes. Because light from these clouds can take billions of years to reach our telescopes, we see such bodies as they appeared eons ago. Lo and behold, these ancient clouds of gas seem to be hotter than younger clouds.

Scientists have also been able to uphold the Big Bang theory by measuring the relative amounts of different elements in the universe. They've found that the universe contains about 74 percent hydrogen and 26 percent helium by mass, the two lightest elements. All the other heavier elements -- including elements common on earth, such as carbon and oxygen -- make up just a tiny trace of all matter.

So how does this prove anything about the Big Bang? Scientists have shown, using theoretical calculations, that these abundances could only have been made in a universe that began in a very hot, dense state, and then quickly cooled and expanded. This is exactly the kind of universe that the Big Bang theory predicts.

CERN and the Big Bang

How do experiments at CERN improve our understanding of the early universe? Click the photo above to hear Dr. Alvaro De Rujula explain. You will need the RealPlayer in order to view this video.

In the first few minutes after the Big Bang, the universe was far hotter -- billions of billions of billions of degrees hotter -- than anywhere in the universe today. This heat gave particles of matter in the early universe an extraordinary amount of energy, causing them to behave in a much different way from particles in the universe today. For example, particles moved much faster back then and collided into one another with much greater energy.

If these conditions do not exist anymore, how do scientists study the behavior of matter in the early universe? One of the most powerful tools for such analysis is the particle accelerator. This device allows physicists to recreate conditions just after the Big Bang by making a beam of fast-moving particles and bringing them together in very high-energy collisions.

Researchers at CERN are using an accelerator called the Large Hadron Collider (LHC) to accelerate subatomic particles called protons to close to the speed of light. This is how fast scientists believed these particles moved in the instants after the Big Bang. By looking at the behavior of these protons, CERN physicists hope to better understand how the Big Bang created the universe.

photo: CERN

When completed in 2005, the Large Hadron Collider at CERN will provide new insight into the past, present and future of our universe.

What is the fate of the universe?

The Big Bang theory raises some important questions about the fundamental nature of the universe: Will the expansion of the universe, set in action by the Big Bang, continue forever? Or will gravity stop the expansion and eventually cause all the matter in the universe to contract in a Big Crunch?

Scientists don't yet know the answers to these questions for certain. But particle physics experiments like the accelerator studies at CERN may offer some clues down the road. By probing into what matter is made of and how it behaves, such experiments can help us explore what the matter in our universe--the planets, stars, and galaxies--might be doing billions of years from now.

Courtesy: Exploratorium