Meeting Abstract
Filtration is ubiquitous in nature and in engineered systems alike. Almost all filters suffer from varying degrees of particle clogging at the filter pore; however, mantas and devil rays appear to have solved this problem, allowing the animals to continuously filter particles from large volumes of water without clogging. Previously we showed that manta filters develop hydrocyclonic nets produced at the opening of the filter pore; presumably to separate particles smaller than the pore size of the filter through centrifugal forces. Our goal for this study was to document particle filtration at the hydrocyclonic nets and to estimate filtration efficiency over a wide range of plankton particle sizes (30-300micron) and two densities (1.05g cm-1 ; 2.0g cm-1). We suspended biomimetic mobulid filters inside a flow tank and filmed particle filtration (particles were 5x smaller than the pore size) at the filter pores. We used dye streams to verify that the hydrocyclonic nets were acting as the primary mechanism of filtration. Dye streams also enabled us to visualize how changes to the filter (filter orientation, angle of filter, changes to the surface microstructure) and fluid velocity affect particle motion at the pore. Unexpectedly, the hydrocyclonic nets filtered particles using two distinct mechanisms. As expected, small particles became entrained within the cyclonic flow at the filter and were returned to the pharyngeal flow via centrifugal forces. However particles that interacted with the leading edge of the hydrocyclonic nets were accelerated toward the esophagus, never becoming entrained in the cyclonic flow. Filtering efficiencies for less dense particles ranged between 44-72% depending on the orientation and surface structure and particle size. Increased particle density resulted in decreased particle efficiency (36-57%).
