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

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 degrees 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.