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Los Alamos National Laboratory
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Los Alamos-developed heat pipes ease space flight
LOS ALAMOS, N.M., April 26, 2000 — A pencil-sized metal tube that moves heat from one end to the other without a pump some day may offer air passengers a two-hour flight between New York and Tokyo, or allow astronauts to travel to Mars and beyond.
A utilitarian yet elegant piece of technology called a heat pipe, first developed nearly 40 years ago at the Department of Energy’s Los Alamos National Laboratory, efficiently transfers large quantities of heat with almost no change in temperature.
A small amount of fluid within the heat pipe vaporizes at the hot end, condenses as it reaches the other, slightly cooler end, and returns to the hot end through a capillary wick, to repeat the process.
"There is a lot going on inside here," says Bob Reid, as he holds up one of his products, a small heat pipe being refined for NASA space flight. "It’s like a little laboratory in a tube."
Reid, a mechanical engineer in Los Alamos’ Engineering Science and Applications Division, works with a team of four in seminal research funded by the Department of Energy, National Aeronautics and Space Administration, and Los Alamos’ internal Laboratory-Directed Research and Development Fund.
Other team members are Tom Sena, a liquid-metals experimentalist; Adam Martinez, a mechanical technician; and Mike Merrigan, a retired Laboratory engineer who is consulting part-time on the heat-pipe project.
"Much of the pioneering and theoretical work on heat pipes was done at Los Alamos. A Los Alamos engineer named George Grover demonstrated the first heat pipe in 1963 inside this building," says Reid, gesturing to the 40-year-old facility that houses his Energy and Process Engineering Group. Heat-pipe technology, destined to be an integral part of space-age travel, was borrowed from rudimentary heat-conducting pipes used by English bakers 100 years ago. Modern applications of this technology include miniature heat pipes that cool the chips inside most laptop computers.
Early Los Alamos heat pipes contained water or sodium. Now they also use lithium, a soft silver-white chemical element that is the lightest known metal. The lithium is inside a molybdenum pipe, which can operate at white-hot temperatures approaching 2,200 degrees Fahrenheit.
"The lithium vaporizes and carries energy down the length of the heat pipe," says Reid. "A lithium heat pipe developed at Los Alamos in the mid-1980s transferred heat energy at a power density of 23 kilowatts per square centimeter. To put this figure in perspective, heat is emitted from the sun’s surface at a mere six kilowatts per square centimeter. We now routinely build heat pipes with similar capability."
Heat pipes now vary greatly in size, depending upon their particular use. Some are the size of hypodermic needles, while larger versions stretch to 24 feet. Groups of heat pipes a half-inch in diameter and nearly five feet long will be used in NASA spacecraft.
NASA’s Marshall Space Flight Center in Huntsville, Ala., is working with Los Alamos to develop heat pipes for use in nuclear reactors to produce propulsion and generate electricity for spacecraft journeying to the solar system’s outer limits.
Los Alamos also recently worked with NASA Langley Research Center in Hampton, Va., in the design of a futuristic hypersonic aerospace plane, a 10,000-mile-an-hour aircraft that would take off from a runway like a jet, but then complete most of its flight in low-Earth orbit. Heat pipes cooling the leading edges of the wings and engine ducts of such a plane could open the door to two-hour New York-to-Tokyo flights.
"In 1996, three Los Alamos heat pipes, prototypes of liquid-metal heat pipes to be used in advanced spacecraft, were flown and tested aboard the space shuttle Endeavor. They operated at temperatures exceeding 900 degrees Fahrenheit and performed flawlessly," says Reid.
"Heat pipes work well in a zero-gravity environment," he says. Commercially developed heat pipes operating near room temperature are now routinely used on geostationary communications satellites."
Now Reid and his co-workers are developing heat pipes for other applications as well. "We are interested in taking this research to the next level," he says. "We are in frequent contact with potential collaborators with problems that can be solved using this technology."
Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy.