Effects of rib spacing and height on particle deposition in ribbed duct air flows

In this study, the influences of rib spacing and height on particle deposition in ribbed duct air flows were numerically investigated. The turbulent air flow was resolved using the Reynolds stresses model (RSM) with turbulent fluctuation correction, while the particle phase was tracked by the discrete particle model (DPM). The ratios of rib spacing to rib height p/e were 2, 4, 6, 8 and 10 while the ratios of rib height to duct diameter e/D were 0.05, 0.1 and 0.2. The air flow velocity profiles for both smooth and ribbed ducts as well as particle deposition velocity in a smooth duct obtained in the simulation agree well with previous related study data. It is found that particle deposition velocity is significantly enhanced by the surface ribs for several orders of magnitude, especially for small particles (τp+<1). Particle deposition enhancement increases with the decreasing rib spacing, while no significant difference is found for different rib heights. The mechanisms of particle deposition enhancement were analyzed and discussed in relation to different rib spacings and heights. Moreover, an efficiency ratio has been defined to evaluate the particle deposition enhancement ratio together with the increase of flow drag. The maximum efficiency ratio can reach about 1000 for small particles (τp+<1) and about 100 for large particles (τp+>1) when p/e = 2 and e/D = 0.1. Therefore, a reasonable arrangement of surface ribs is an efficient and effective choice for enhancing particle deposition, and could be adopted in air filtration devices.