CFD-Based Numerical Assessment of Pin-Fin Height Optimization for Enhanced Thermal Performance in MWCNT Nanofluid Microchannel Heat Sinks

Abstract

Microchannel heat sinks are often redesigned with taller pin fins under the assumption that larger surface area inherently yields better cooling. However, this study reveals a counterintuitive yet significant finding that the shortest pin fin (6.2 µm) consistently outperforms all taller configurations across the full range of operating conditions. A three-dimensional CFD model developed in ANSYS Fluent evaluates a plain channel and four pin-fin heights (6.2, 18.6, 31.0, and 43.4 µm) over Reynolds numbers 55 - 225, using water and MWCNT nanofluids at 1, 2 & 3% concentrations. The thermo-hydraulic behavior is assessed through Nusselt number, friction factor, pressure drop, and thermal performance factor (TPF). Although taller fins enhance heat transfer, they impose substantial pressure and pumping penalties, diminishing overall system efficiency. In contrast, the 6.2 µm geometry demonstrates a TPF consistently above unity with a strong increase at higher Reynolds numbers, indicating an efficient flow-mixing mechanism achieved with minimal hydraulic cost. In microscale cooling, shorter and compact pin fins rather than taller ones unlock superior thermal performance. This unexpected dominance of the smallest configuration highlights an important design insight. A supporting data-driven heat-map visualization is also employed to interpret multi-parameter trends, reinforcing the identification of the 6.2 µm pin height with 3% MWCNT as the most efficient case. Overall, the study provides clear guidance for next-generation microchannel heat-sink optimization and challenges conventional assumptions about fin geometry in miniaturized cooling systems.