Numerical study of forced convection over phase change material capsules in a traditional spherical shape and a biomimetic shape

The use of biomimetic red blood cell (RBC) shaped capsules for latent heat thermal storage is a novel concept. The RBC shape provides a much higher heat transfer rate than that of other shapes. However, the heat transfer characteristics of external flows around RBC-shaped capsules and the optimal attack angle are unknown. In the present work, forced convection of external flows over an RBC-shaped PCM capsule was numerically studied in a steady-state laminar flow region with Reynolds number in the range of 20–200, and compared to that of a conventional spherical capsule. Moreover, the local Nusselt number, surface-average Nusselt number and drag coefficient at various Reynolds numbers and attack angles of RBC-shaped capsules were investigated. The surface-average Nusselt number of the RBC-shaped capsule was found slightly smaller than that of the spherical capsule with a maximum disparity of 12.04%. The drag coefficient of the RBC and spherical capsule both decreased with the increase of Reynolds number, and the disparity between them was very small. 0° attack angle was recommended for the RBC-shaped capsule layout, as it had the lowest drag force with a relatively high average Nusselt number.