Three-Dimensional Numerical Analysis of Enhanced Forced Convection of Air in Offset and Offset Slotted Wavy Plate-Fin Cores

Periodically fully developed airflow (Pr ≈ 0.71, 100 ≤ Re ≤ 4000) through offset wavy and offset slotted wavy plate-fin cores is investigated using a well-validated steady-state three-dimensional numerical model. Streamlines, pressure, and normalized temperature contours are presented for four offset wavy fin geometries (sinusoidal, cosinusoidal, S-shaped, and C-shaped fins) to characterize the altered flow structures due to the offsets. The flow structures reveal the location of high-pressure drag created due to the flow impingement, separation, and recirculation. Introducing slots at such locations can promote cross-channel mixing, disrupt boundary layers, and modify local flow recirculation zones. Because the S-shaped and C-shaped fins inherently have 50% less surface area compared to sinusoidal and cosinusoidal offset wavy fins, only the sinusoidal and cosinusoidal offset wavy fins are considered for placement of slots. The computed isothermal fanning friction factor f, Colburn factor j, shows an enhancement in heat transfer performance in both offset and offset slotted wavy fins, along with an increase in the pressure drop penalty when compared to conventional wavy fins. An appropriate performance evaluation criterion is employed to determine which offset and offset slotted wavy fin geometry will require less heat transfer surface area to provide the same heat load as that of conventional wavy fins under the constraint of constant pressure drop. Remarkably, among all the fin configurations considered, one of the offset slotted wavy fin geometry needed 71% less surface area relative to the conventional wavy fins.