Excerpts from letter by AW. NASA, Ames

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AW of NASA Ames called to express his satisfaction with the overall performance of the Vicount 5000 smoke machine in the NASA wind tunnel using recycled air.

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A..'s current application is:

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Wind tunnel dimensions: 40 x 80 x 1,000 ft. long - i.e. the total path length for the smoke and the return path is 2,000 ft. The wind tunnel (and probably the laser) are the largest in the world.                                              

Entrance duct dimensions:120 high x 240 ft wide                                

Airflow: Recycled air

Target area:1  x 1.5 ft. :                          

Wind speed: Not known

Application: Particle image velocity  

Placement of generator: The generator was placed on the floor downwind (behind) the target area. From there the smoke would travel through the wind tunnel's return path and into the entrance duct of the wind tunnel through a diffuser. This would ensure that the smoke was thoroughly mixed with the surrounding air - a 'uniform seed'. 

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A.. had found that two Vicount 5000 units running for between 10 and 15 minutes had produced too much smoke at a concentration way beyond what was needed. From this he had surmised that one Vicount 5000 would probably been all that was necessary. Overall, they were VERY happy with its performance.

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A..double-pulse laser burst image is captured by cameras located outside the tunnel walls - approx. 45 ft away from the target viewing area. These large aperture cameras record each 40 millisecond laser pulse 'flash' and operate in tandem for a stereo effect.

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A.. stated that they might welcome a larger particle size (but still less than 1 micron) because the laser(s) and cameras could more easily determine the air flow. (The option of a boost in laser power is very expensive). Also, he assumed that with a larger particle size the number of particles produced per sec would be reduced.

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Note: This is a different application from that used by R.. M... In that application NASA used 6 Vicount 5000's in a straight-thru 80 x 120 ft wind tunnel airflow to examine a 15 x 15 ft target area.

The smoke machines were located upwind (in front) of the target area and raised from the ground by a hydraulic lift. This application of airflow visualization required that there be 'blocks' of smoke streaming towards the target area...

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