Non-Newtonian Fluid Cavern and Newtonian Cloud Height Tests to Characterize Pulse Jet Mixer Operation

Pulse jet mixing systems are being developed for use in the Waste Treatment Plant in Washington State. To assist with system development, scaled tests were conducted to obtain experimental measurements of the cloud height for Newtonian slurries and cavern heights for a Non-Newtonian yield stress material. The measurements were required to assess the effective mixing and material mobilization produced during pulse jet mixer operation. The cloud height measurements were obtained for a single steady-state jet directed downward in a spherical-bottom tank. The cloud tests used glass beads in water to evaluate the height of the suspended slurry as a function of jet velocity. Cloud testing revealed that the glass bead material was suspended in the tank quickly and developed a distinctive height for each combination of flow rate and particulate size tested. The solids loading had minimal impact on the cloud height for a given particle size. During all cloud tests, the surface of the tank remained relatively calm, indicating that the slurry was dissipating the mixing energy of the relatively high velocity jet. Cavern tests were conducted to obtain experimental data of non-Newtonian fluid mixing for fluid properties similar to those of certain tank wastes. A transparent material that exhibited a yield stress and shear thinning behavior was used to obtain measurements of steady-state cavern heights as a function of jet velocity. For the non-Newtonian fluid cavern tests, distinct cavern volumes were readily developed for the four velocities tested. A linear relationship was observed to exist between cavern height and nozzle velocity. Since the experimental work detailed in this paper was completed, additional scaled tests have been conducted with pneumatic drive systems and direct drive systems similar to that described for this effort. Data from both types of measurements are shown to be linear; however, effects from the reciprocating drive systems that are not yet incorporated into models may be affecting the ability to collapse this data independent of scale. It is recommended that future efforts to assess performance of PJM operations using scaled tests consider employing direct drive systems to aid in evaluating scaling trends. A test system can be configured to allow testing at both reciprocating and direct drive conditions; thereby allowing direct comparison between them.