A 3D-printed sheathed elutriator for size resolved collection of microparticles and droplets

A low cost, easy-to-manufacture particle classification device for coarse mode, supermicrometer particles and droplets remains important for a variety of industries and environmental measurements, including agricultural sprays, pharmaceutical powders, spray drying processes, precipitation, and dust storms. While optical techniques can typically be used to analyze particle sizes in this range (20 μm–100 μm), there are few instruments available for size-segregated particle collection. Here, we demonstrate that a horizontal, parallel-plate sheathed elutriator can be designed and 3D printed, enabling modest-to-high resolution size segregated particle and droplet collection in the supermicrometer size range. In such elutriators, gravitational settling drives sampled particles vertically down the device (between two plates), while a clean sheath flow drives motion orthogonally; the net result is aerodynamic diameter-specific particle and droplet trajectories. In designing a sheathed elutriator, we develop both an analytical deposition location distribution function, similar to the transfer function of sheath mobility analyzers, as well as a 3D computational fluid dynamics model of a prototype instrument. The prototype is built solely from 3D printed parts (and PVC sheath lines) without any high voltage sources or high power pumps required. The performance of the prototype is tested by examining the deposition location distribution of monodisperse uranine-doped oleic acid droplets in the 26 μm–81 μm size range. Uranine signal intensity was determined using both traditional fluorometric analysis and via yellow-color intensity analysis from a digital camera, with both measurements in good agreement with one another. Overall excellent agreement is observed between the analytical model, computational fluid dynamics simulations, and experimental measurements, demonstrating that inexpensive elutriators provide a means to collect coarse-mode particles in a size selective manner, and further suggesting that they can be designed for aerodynamically monodisperse particle selection.