Thermal evaluation of flow boiling in a non-uniformly distributed pin-fin heat sink under transiently varying inlet temperatures

Markal B., Öksüz Ö., Evcimen A.

INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER, cilt.180, ss.1-19, 2026 (SCI-Expanded, Scopus)

Özet

In real-world cooling applications, systems experience unsteady startup periods where evolving inlet tempera­ tures significantly impact thermal management. Addressing this gap, this study is the first to experimentally investigate saturated flow boiling within a novel double-pool micro pin-finned heat sink (DP-HS) under tran­ siently varying inlet temperatures. Time-dependent data and high-speed visualization (2000 fps) were recorded for inlet temperatures rising approximately from 37.5 ◦C to 77 ◦C, tested across heating powers of 180–270 W and mass fluxes of 189–265 kg m- 2 s- 1. Results reveal that lower inlet temperatures enhance two-phase heat transfer coefficient, which drops by a maximum of 57.2% (at 180 W, 265 kg m- 2 s- 1) upon reaching steady-state. Under present conditions, a marked transition in the influence of mass flux was noted when mass flux increased from 189 to 227 kg m- 2 s- 1, after which further improvements diminished. Moreover, forward-acting inertial forces and unbalanced surface tension force (unique to DP-HS) overcome resistive evaporation momentum, ensuring continuous surface rewetting. Furthermore, the DP-HS geometry efficiently manages high thermal loads, limiting the average wall superheat increase to 2.3 ◦C when heating power rises from 180 W to 270 W. Optimizing inlet temperature and exceeding this mass flux threshold are essential for maximizing flow boiling performance.