Improving Nanosilica Fluidization by Premixing with Geldart A and B Particles: A Detailed Region-Wise Study

Ultrafine nanosilica exhibits a strong tendency to form agglomerates, with sizes often several orders of magnitude larger than the primary particles. This agglomeration severely impairs its effectiveness in fluidization and other applications requiring uniform powder dispersion. To address this issue, the present study employed an assisted fluidization technique involving premixing of nanosilica with small amounts of external inert particles. The aim was to disrupt the structural integrity of the agglomerates by altering the inter-agglomerate force equilibrium. Two types of inert silica (SiO₂) particles, representing Geldart groups A (finer) and B (coarser), were individually premixed with the nanosilica in different proportions. This strategy led to a significant reduction in both the minimum fluidization velocity ($U_{mf}$) and fluidization hysteresis. Moreover, a clear vertical segregation pattern emerged within the fluidized bed: the finer Group A particles (S-A) primarily enhanced fluidization in the upper and middle regions, while the coarser Group B particles (S-B) were more effective in the middle and lower regions. Interestingly, even at low premixing proportions, a significant volumetric contraction (up to 40%) of the premixed nanosilica bed was observed, which confirmed the disruption of the inter-agglomerate force balance within the nanosilica, contributing to enhanced fluidization behavior.