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WATER JET CONFERENCE - Waterjet Technology Association

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FIGURE 9. INNER CORE OF PERCUSSIVE <strong>JET</strong> DISCHARGED AT 500 PSIG.<br />

Using this infrared photography technique, the mist surrounding the central core of a<br />

high-speed jet can be penetrated. In this photograph, the bunches have formed and are<br />

about 2 1/2 times the diameter of the original jet (1/2-inch). Surrounding the central core<br />

is a sheath which is the mist which has been illuminated by scattered light. The Jet is<br />

travelling at about 330 feet/second and the modulation frequency is 300 cycles per<br />

second. Therefore the wavelength or distance between bunches in this photograph is<br />

about 12 inches. The exposure time was 3 microseconds.<br />

NAME: Gerald Zink<br />

COMPANY: Stoneage, Inc.<br />

DISCUSSION<br />

QUESTION: "The slide of a 'water pik' jet backlighted by 750 nm infrared light<br />

appeared to show absorption in the thinner edges of drops and transmission through the<br />

thicker center. Why is this?"<br />

ANSWER: The "water pike slides were chosen to show how absorption in the<br />

main body of the water drop increased with increasing wavelength of light as predicted<br />

by the absorption spectrum of water. At the edges of the drop, some light is scattered or<br />

bent away from the camera and appears dark. As a result, using single drops to simulate a<br />

turbulent water jet has some limitations as you noted. However, the main point is well<br />

illustrated.<br />

97

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