(653c) Agglomerate Number: Experimental Validation of the Energy-Based Dimensionless Group in Entrainment of Cohesive Particles
Cohesion significantly impacts entrainment behavior, and predicting entrainment rates for cohesive particles has been problematic for decades. Understanding the macroscopic (many-particle) cohesive behavior via the microscopic (particle-level) interactions is critical for improved predictive capabilities. For systems dominated by brief contacts (e.g., dilute systems), the Agglomerate number (Ag) is the relevant dimensionless group. Ag is defined as the ratio of the critical kinetic energy required for agglomeration to occur to the characteristic (fluctuation) kinetic energy available to overcome agglomeration. Previously, the appropriateness of Ag in collision-dominated (relatively dilute) systems has been shown theoretically for a myriad of systems, including risers, via collapse of the fraction of agglomerates versus Ag. In this work, a comprehensive set of agglomeration measurements of mildly cohesive particles in a dilute riser is compared to Ag for the first time. These local, in situ, non-intrusive measurements include mean particle and agglomerate velocities, relative velocity of particles and agglomerates, agglomerate diameters, fraction of agglomerates, and solids volume fraction. Experiments were designed to test a wide range of Ag values by varying the degree of cohesion via relative humidity (numerator of Ag) and different sized particles (denominator of Ag). Although not all dimensionless groups in the system could be controlled, e.g., the ratio of riser diameter to particle diameter, decent collapse of dimensionless measurements and Ag is observed. Overall, the presented results demonstrate increased agglomeration at high Ag and decreased agglomeration at low Ag.