Cylindrical particles with internal voids are frequently used in packed tubes both to decrease pressure drop and to increase available surface area. For the simulation of particle behavior and for packed tube design it is important to have reliable correlations for transport from the particle to the flowing fluid, in particular for the drag coefficient C_D and the heat and mass transfer Nusselt numbers. Correlation formulas are available for arbitrary shaped particles at various angles of inclination to the flowing fluid (e.g. Hölzer and Sommerfeld, Powder Technology Vol. 184 (2008) pp. 361-365 for C_D). Our work presents the results of CFD simulations of flow around single equilateral hollow cylinder particles for Re between 1000 and 10000. Verification of the mesh was performed over a range of inclination angles by both grid adaption based on curvature of the velocity magnitude, and conventional mesh doubling.

The results of the simulations show the complex nature of the microscale flow around such particles. At a zero incidence angle, the flat end of the particle causes instant separation of the flow and a large wake region is formed, while a jet-like flow results through the hole in the center of the particle. These strong flows give rise to a pattern of vortices behind the particle, with reverse flow along almost the entire particle length. These features are then distorted as the angle of incidence increases, with a boundary-layer formation on the upstream side of the particle and a complex pattern of vortices on the downstream. The flow through the particle hole decreases with incidence angle.

Macroscale drag coefficients and particle surface heat and mass transfer coefficients are determined and used to evaluate literature correlations such as the one mentioned above for use with these types of particle. The microscale features of the flow shed light upon the agreement between CFD simulation results and the empirical correlations, or the lack of it.