Issue link: https://www.e-digitaleditions.com/i/1212417
March 2020 / 19 Dilute-phase flow. In dilute- phase (stream) flow, shown in Fig- ure 1, the material must be accel- erated above the saltation velocity (point at which particles begin to fall out of suspension) in the accel- eration zone, which is the convey- ing line section after the feedpoint. Because the material has little or no velocity at the feedpoint, the material must be accelerated by the conveying gas drag. To achieve this, we must follow certain design criteria in the con- veying line acceleration zone: 1. The conveying gas velocity must be above the saltation veloc- ity so the drag can accelerate the material above the saltation veloc- ity. To shorten the acceleration zone or accelerate the material more quickly, the conveying line diameter prior to the feedpoint can be reduced. However, conveying through a smaller line diameter will require a little more energy (horsepower), particularly if the conveying line direction changes near the feedpoint. 2. The acceleration zone's length is a function of the material being conveyed and the conveying gas velocity. Accelerating a large, heavy material (such as lead shot) requires a longer acceleration zone than accelerating a fine, light material (such as talc powder). The acceleration zone length is typically 15 to 20 times the pipe diameter. Formulas for calculating this length are available in several pneumatic conveying books. FIGURE 1 Dilute-phase flow IMPERIAL. NORTH AMERICA'S BEST SELLING WELDED SILOS AND TANKS FOR OVER YEARS. 38 1-800-558-2945 | imperialind.com Imperial Industries is the trusted choice for welded tank design and fabrication, proudly family-owned and operated for more than 38 years.