An experimental study on heat transfer and pressure drop in a narrow rectangular channel having staggered miniature pin-fins with tip clearance

Abstract

This study focuses on the experimental examination of single-phase forced convection heat transfer and pressure drop during internal flow in a sandwich-like, shallow, rectangular copper channel under top-only, bottom-only and both-side heated conditions. Miniature pin-fin arrays of different shapes were formed on the bottom of the channel. Two different staggered miniature pin-fin geometries, rectangular-shape and knife-edged, were used on interchangeable bottom plates with the fin orientation parallel to the flow direction of the working fluid. The tip clearance of the fins to the opposite surface was precisely adjusted to 100 & micro;m. The working fluid, water, entered the channel as fully developed flow; this was achieved by maintaining a previously calculated length required to obtain fully developed flow for maximum Reynolds numbers in the experiments. Measurements were carried out at varying inlet temperatures (10, 20 and 30 degrees C) and Reynolds numbers (4000, 6000, 8000, 10,000, 12,000, 14,000 and 16,000), while the results were compared to a non-finned surface. The measured results show that higher heat transfer coefficients can be obtained for both the finned surfaces under comparable operating conditions. At 20 degrees C, with a Reynolds number of 16,000, the Nusselt number is about 110 in the non-finned channel, about 175 in the knife-edge finned channel, and about 300 in the rectangular finned channel, but the use of miniature pin fins results in a higher pressure drop through the channel. The rectangular fin exhibits higher Nusselt number and higher pressure losses at all instances. The rectangular fin type has higher FOM (Figure of Merit) values despite greater pressure drops compared to the knife-edge fin type, due to enhanced heat transfer. The FOM value for the rectangular fin at a Reynolds number of 4000 is 1.74 with a water inlet temperature of 20 degrees C, whereas at a Reynolds number of 16,000, this value decreases to 1.28. That of the knife edge fin reduced from 1.4 to 0.91. The performance of the rectangular fin type is better in all heating modes and Prandtl numbers. The findings of this study offer a significant contribution to the design of state-of-the-art thermal management systems. Specifically, the demonstrated superiority of rectangular pin-fins with tip clearance provides a viable pathway for optimizing liquid cooling plates in high-power density applications, such as electric vehicle battery packs.