Jet Impingement Boiling in Micro-domains

Liquid jet impingement is one the most effective methods to remove heat from local hotspots in microelectronics. Due to its normal incident flow-field, jet impingement cooling can achieve heat transfer coefficients (HTCS) up to l MW/ml/K due to its ability to thin the local thermal boundary layer in the stagnation region. This work investigated the HTC for water jet impingement cooling of a Hafnium (Hf) coated glass surface heated by both a steady and pulsed laser diode heating source. The laser induced local hotspots have areas ranging within 0.04 mm2 to 0.2 mm2 and hotspot heat fluxes up to 3.5 MW/m2/K. A submerged jet impingement configuration was pursued with an inlet jet diameter of 1.2 mm, jet nozzle to heated surface distance of 3.175 mm, and a jet Reynolds Number of Re :2 2004. The spatiotemporal wall temperature and corresponding heat transfer coefficients were characterized using infrared thermography. The investigation focused on mainly i) how the HTC is influenced by changes in the modulation frequency of the wall heat flux, ii) the how the HTC is influenced by changes in the offset between impinging jet and the center of the laser-induced hot-spot. At zero offset (ie, a jet focused on the center of the hot-spot), the HTC was measured as #2600 kW/m2/K for steady (unmodulated) laser heating and #470 kW/m2/K for modulated laser heating. Thus, reduced cooling performance is observed when the local hot-spot heat source is temporally unsteady.