Hydraulic performance and deposition enhancement of ultrafine particles for in-duct twisted tapes under stationary and rotating conditions

Sustainable and energy-efficient air-conditioning systems require high-performance filtration systems with low air resistance. Experimentally, we investigated different diameters of both stationary and rotating twisted tapes (TTs) duct-inserts to characterize their hydraulic performance and level of ultrafine particles (UFP) deposition. It is an innovative study using an active approach (rotating TTs) for particle removal in the ventilation duct. Friction factors and particle deposition velocities were calculated both for empty ducts and for ducts with TT inserts in stationary and rotating conditions under constant pumping power. In addition, the overall particle deposition-hydraulic performance index was established to quantify the effectiveness of TTs under both laminar and turbulent airflows. The results showed a marginal difference in friction factor between stationary and rotating TTs under turbulent flow. The rotating TTs yielded a higher UFP deposition velocity than stationary TTs, peaking at 7.3 times compared to the deposition velocity for empty duct for particles smaller than 20 nm. Moreover, the highest performance index of a rotating TT could reach 6.5 for particles smaller than 20 nm at a Reynolds number of 10,000. Overall, a rotation or an increase in diameter of TTs both could improve the particle deposition performance. Notably, this study is the first to develop a filterless system for the removal of particles in the ventilation duct. Using in-duct rotating TTs would provide a solution for developing high filtration devices at less pressure penalty or smaller fanning energy consumption.