Numerical performance simulation of a wetted wall bioaerosol sampling cyclone

Computational fluid dynamics techniques are used to study the performance of an axial flow bioaerosol sampling cyclone that continuously collects particles onto a flowing liquid film. A special shell-volume concept was developed to study formation and development of the liquid film on the inner wall of the cyclone. For a previous version of the cyclone, simulations demonstrated the presence of a ring of liquid in the region just upstream of the liquid skimmer that was suspected of causing liquid carryover into the exhaust air stream and degradation in aerosol collection efficiency. This ring was eliminated by re-design of the cyclone. For the upgraded version of the cyclone, CFD was used to successfully predict aerosol collection efficiency and cyclone pressure drop. The simulations reveal a complex flow evolution inside the cyclone. Stream-tubes are used to describe a significant narrowing of the width of the airflow as it enters the cyclone and an inward displacement of the flow as it travels in the axial direction. The particle deposition occurs primarily in a region that is subtended approximately by the length of the rectangular entrance slot and the first half turn of the flow in the cyclone. Cutpoint Stokes number is about 0.05 and the cut-point particle size is about 1 mu m aerodynamic diameter. At a flow rate of 1250 L/min, the pressure drop across the cyclone is 5.6 kPa (22 inches of water).