A new direction for microgravity fires.
In one experiment, an astronaut lit the center of a strip of paper clamped inside a wind tunnel. As a slight breeze blew from the right side of the tunnel, the flame bent into the wind and crept toward the right. "It's almost completely opposite [what happens in] normal gravity," says Takashi Kashiwagi, a fire science researcher with the National Institute of Standards and Technology in Gaithersburg, Md.
Although the phenomenon may strike some people as counterintuitive, Kashiwagi says, it makes sense. In gravity, oxygen flows around the flame, and the airflow determines the direction of the flame's reach. In low gravity, the oxygen downstream becomes depleted, so the flame seeks the most abundant supply of oxygen-the influx of air.
Not all flames in microgravity burn backward, though. In an experiment by Kurt Sacksteder of NASA's Lewis Research Center in Cleveland, the flame traveled in the expected direction. "At first glance, it may seem that our observations disagree, but they don't," Sacksteder says.
In the first experiment, the flame had paper to burn both upstream and downstream. It headed upstream because that side had more oxygen. In the second experiment, the strip of paper was lit at the end closer to the source of the breeze, with all of the fuel downstream. These flames spread much more quickly than the ones heading upstream in the first experiment. Sacksteder's experiment also shows that in a slight breeze, materials are more flammable in space than on Earth.
Kashiwagi's research produced what he calls a "crazy, unexplained smoldering phenomenon." A smoldering fire on Earth spreads outward in expanding rings as the fire burns more fuel.
Not in microgravity. A smoldering fire in space sends out tendrils away from the fire source. Each tendril splits into two, and each new tendril divides as the fuel smolders.
Kashiwagi says smoldering fires in space could prove "extremely dangerous" because they are hard to detect and would fill the air with toxins. Another series of experiments tested how well NASA's smoke detectors work in space. The detectors effectively measured fumes from burning candles, paper, metal wires, and rubber coating, says David L. Urban of NASA's Lewis Research Center.
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|Title Annotation:||experiments on fires in space show the influence of microgravity|
|Article Type:||Brief Article|
|Date:||Feb 22, 1997|
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