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March 2020 / 23 to either dilute-phase or two-phase conveying. In fact, material sliding down the incline aids conveying. If your conveying system should be operating in dilute phase but problems are plaguing the operation, it's possible that some section or the entire system is operating below the saltation velocity and is conveying in two- phase flow. If the conveying line includes an inclined section, the problem could be serious. A simple test can show if mate- rial is accumulating or if refluxing is occurring in the conveying line. To ensure the material is conveyed above the saltation velocity in the test, the material should move at about the same velocity as the conveying gas. For example, if the conveying line is 400 feet long and gas velocity is 4,000 fpm, the gas will pass through the entire line in 6 seconds (0.1 minute). If we assume the material is traveling at 50 percent of the gas velocity, the material will pass through the sys- tem in 12 seconds. Listen to the material passing through the conveying line near the end of the system. Have some- one turn off the material feeder and time the material flow after the feed stops. If you can hear material still flowing after 12 seconds, the material was accumulating in the line and, thus, was below saltation velocity. If you can hear material flowing for more than 40 seconds, refluxing is occurring. What about an inclined conveying line in a dense-phase system? You may think that a dense-phase con- veying line's orientation shouldn't be critical because the material travels in a slug, and saltation doesn't have any effect on the system, but that's wrong. Tests have shown that as a slug is pushed through an upwardly inclined conveying line, the slug tends to break or shear on a vertical plane. The break occurs at an angle MORE THAN JUST A MAGNET COMPANY 231.582.3100 • WWW.MAGNETICS.COM INDUSTRIAL MAGNETICS, INC. • Industry leading process & product protection • Highest strength Rare Earth magnet material commercially available • line of magnet tubes optimized for the application • Certified food safe processing equipment • Multiple cleaning options Gravity Feed Metal Separation Products Pneumatic Feed Metal Separation Products Testing Equipment, Certifications & Services MORE THAN JUST A MAGNET