Alloy-Enhanced Fans Maintain Fresh Air in Tunnels

The Partnership for Next Gen eration Vehicles (PNGV) is not a NASA initiative to develop powerful new rockets and spacecraft, even though it may sound like one. PNGV was a partnership established by the Clinton Administration between the federal government and the U.S. Council for Automotive Research to develop technologies that improve fuel efficiency and reduce emissions from cars and trucks.

In support of this effort, Jonathan Lee, a materials engineer at NASA’s Marshall Space Flight Center in Alabama, worked with a major automobile manufacturer in 1995 to develop a strong aluminum alloy for high-temperature applications. The aim was to use the alloy for manufacturing parts for an internal combustion engine, as well as for NASA’s propulsion applications. When funding from PNGV ended, Marshall continued to support the alloy’s development. Together with PoShou Chen, a scientist with Morgan Research Corp., Lee invented a high-strength aluminum alloy called MSFC-398 that, when tested, was three to four times stronger than conventional aluminum alloys at high temperatures.

By the late 1990s, NASA scientists had successfully developed and patented this technology, which has great potential applications not for just automotive, but also for aerospace, marine, and commercial applications.

The most recent success of this technology was in 2010. Twin City Fan Companies Ltd. in Minneapolis, MN, lic ensed the alloy to make impellers (blades and hubs) for safety ventilation fans in rail and road tunnels. They wanted a high-temperature alloy that would have the strength and properties needed for safety fan impellers at very high temperatures. The division of Twin City Fan Companies that is marketing the first fans made with the NASA aluminum alloy is Clarage, based in Pulaski, TN.

Twin City Fan licensed the NASA alloy with a specific application in mind: tunnel safety fans for the European market, where fans must be able to operate in 752 °F for two hours. The reason for the high-temperature requirement is the fan must be able to operate successfully when there is a fire in a road or rail tunnel. When spinning in one direction, the fan provides clean air to the people inside; when spinning in the other direction, it removes the smoke and gasses from the fire.

Before the NASA alloy, there were two ways to meet these temperature requirements. One was to use existing aluminum to make a bigger fan that spins more slowly. The drawback to this approach was that a bigger fan requires more space. Using the NASA alloy, the fan is smaller relative to the competition, and the tunnel can be smaller as well. In addition, the properties of the material allowed the fans to run hotter, leading to safety smoke exhaust at temperatures beyond what tunnel designers anticipated.

The other solution was to make the fan blades out of steel, but this required a specialized motor to turn and reverse the fan. Steel weighs roughly three times more than aluminum. If it is three times as heavy on the rotating parts, the bearings are heavier, the shaft is heavier, and the motor is heavier.

While Twin City Fan has purchased the tools to produce three sizes of the fan, it plans to manufacture 12 different sizes in total. In 2011, Clarage sold the first of its fans made with the NASA alloy to a company testing the fans to certify them to European standards.

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