Thermal Fluid Assessment of Cylinders with Multiple Slots in Aligned Flow

Abstract

The hydrodynamic and thermal performance of a circular cylinder with slots of different configurations in transverse flow is investigated. The first configuration consists of a cylinder with two slots, one aligned with the flow and the other in a perpendicular arrangement (two orthogonal slots). Each slot has a normalized slot width s/D = 0.2, where D is the cylinder diameter. The second configuration consists of a cylinder with two parallel slots aligned to the transverse free stream flow. The two slots are sized at s/D = 0.1 and are symmetrically placed on both sides of the cylinder centerline. The slots introduce additional heat transfer surface area between ~77% and ~109% for the orthogonal-slots and parallel-slots, respectively. Two-dimensional incompressible airflow for Reynolds numbers between 100 and 1000 is numerically simulated. The slotted cylinders are found to have a total drag force reduction up to ~30%, compared to a solid cylinder despite the additional viscous drag force of the slots. Convection heat transfer rate is enhanced up to ~81% and ~100% for the orthogonal-slot and the parallel-slot cylinders, respectively. Combining the hydrodynamic and thermal changes associated with the slotted cylinders, the performance index, defined as the ratio of the normalized heat rate to the normalized drag force, increases up to maximum of ~2.4 and ~2.8 for the orthogonal-slot and the parallel-slot cylinders, respectively, indicating better overall thermal-fluid performance. This enhancement is due in part to the additional heat transfer surface area and the reduced pressure drag from increased downstream external pressure caused by the interaction of the slot exhaust with the flow in the wake region. The easily fabricated, slotted cylindrical fins are capable of enhanced overall performance for cooling applications, such as electronic component heat dissipation.