Pressure drop and nanoparticle deposition characteristics for multiple twisted tape inserts with partitions in turbulent duct flows

Abstract

In this study, the pressure-drop (flow resistance) and nanoparticle deposition characteristics of multiple twisted tapes (MTTs) with partitions were experimentally investigated in turbulent duct flows using air as working fluid. Penetration tests for nano-sized particles and pressure drop measurements were performed in the empty duct and ducts fitted with twisted tapes (TTs), and zones under the same pumping power condition. A co-swirling arrangement was used for MTT inserts. Different nanoparticle diameters (5–100 nm), Reynold numbers (4000–11000), TT twist ratios (3 and 7), number of tapes (1, 2, and 4), and partition schemes were considered in the present investigation. It was found that the penetration efficiency of nanoparticles generally increased with the diameter of nanoparticles and Reynold number. The nanoparticle deposition velocity was always higher in ducts fitted with MTTs than in ducts equipped with a single twisted tape (STT). The results also showed that the ratios of nanoparticle deposition velocities for TT-equipped ducts to the empty duct ranged from 1.8 to 13.7, while the corresponding ratios of friction factor varied from 1.4 to 3.2. Beside, TTs with a smaller twist ratio offered higher particle deposition velocities and flow resistances than TTs with a larger twist ratio. Furthermore, empirical correlations for friction factor, nanoparticle penetration efficiency, and deposition velocity were proposed, respectively. The fouling resistance caused by accumulation of deposited particles was analyzed and the results showed that the maximum resistance decreased with the increasing Reynolds number, but was comparable for particle size between 50 nm and 100 nm.