Investigation of heat transfer limits for flow boiling in expanding heat sinks having micro pin fins

Abstract

Critical heat flux (CHF) represents heat transfer limit for a heat sink working under flow boiling conditions. In the literature, for the first time, in micro-pin-fin heat sinks with expanding structure, this paper experimentally focusing on CHF and proposing a correlation for saturated flow boiling at quite low mass velocities. Parallel channel heat sink is evaluated as reference case. Three mass velocities (G = 45, 68, 90 kg m−2 s−1) are studied by beginning from 130 W up to boiling crisis. Test-range falls in the pure saturated boiling conditions, and inlet temperature is approximately kept constant at 60 °C. Flow mechanism is figured out over the flow images. The heat sink with expanding structure (T-2) clearly boosts CHF compared to parallel counterpart (T-1); such that, by successfully manipulating bubble dynamics, T-2 increases the CHF up to 32.9% at the lowest mass velocity (G = 45 kg m−2 s−1). For highest mass velocity (G = 90 kg m−2 s−1), T-2 provides lower wall superheat up to 89.5% against T-1. The CHF ranges from 225 to 443.31 kWm−2, even though quite low mass velocities. Regarding prediction of the experimental data, mean absolute error (MAE) of proposed correlation is 4.7%; and all those of predictions fall in ±12% error bands.