Impact of pulsating flow on hydro-thermal performance of a Schwartz-D heat sink

The Schwartz-D structure has been considered as a promising heat sink design for advanced liquid cooling and has gained increasing attention in the pursuit of new heat transfer enhancement techniques. Following the knowledge of the authors’ previous work that flow unsteadiness and non-uniformity exert a synergetic effect on heat convection, the present study investigates the thermal performance of a Schwartz-D heat sink in pulsating flow by both numerical simulation and experimental validation. The time-averaged flow Reynolds number is maintained at 222 with a peak value of 1110, and the pulsation Strouhal number is varied from 0.14 to 2.23. The dominant mechanism for heat transfer enhancement is attributed to the alternating inter-unit mixing at the pulse-on stage and the intra-unit mixing at the pulse-off stage in the Schwartz-D structure. A secondary contributor for thermal performance improvement is the consecutive heat entrainment by dynamic vortex evolution over multiple Schwartz-D cross-sections and at different pulsation instants. The complementation of flow mixing and heat entrainment in both spatial and temporal domains results in a maximum Nusselt number increase of 140% and a respective thermal performance factor of 1.58 in comparison to the steady case. The corresponding Strouhal number is 1.4 where the flow convective distance over a pulsation cycle equals the unit length of the Schwartz-D structure. Additionally, the temporal variation of Nusselt number for the pulsating flow decreases to 2.90% as Strouhal number increases while the spatial non-uniformity across the Schwartz-D structure remains constantly 30% lower than the steady case. The current work highlights the remarkable thermal performance of combining mixing-based heat sinks with pulsating flow and proposes a specific criterion for the pulsation design by elucidating the underlying mechanism.