Hotspot Cooling Performance of Two-Phase Confined Jet Impingement Cooling at the Stagnation Zone

Jet impingement can be particularly effective for removing high heat fluxes from local hotspots. Two-phase jet impingement cooling combines the advantages of both the nucleate boiling heat transfer with the single-phase sensible cooling. This study investigates two-phase confined jet impingement cooling of local, laser-generated hotspots in a 100 nm thick Hafnium (Hf) thin film on glass. The jet/nozzle diameter is ∼1.2 mm and the normal distance between the nozzle outlet and the heated surface is ∼3.2 mm. The jet coolants studied are FC 72, Novec 7200, and Ethanol with jet nozzle outlet Reynolds numbers ranging from 250 to 5000. The hotspot area is ∼0.06 mm 2 and the applied hotspot-to-jet heat fluxes range from 20 W/cm 2 to 350 W/cm 2 . This heat flux range facilitates studies of both the single-phase and two-phase heat transport mechanisms for heat fluxes up to critical heat flux (CHF). The temporal evolution of the temperature distribution of the laser-heated surface is measured using infrared (IR) thermometry. This study focuses on the stagnation point heat transfer - i.e., the jet potential core is co-aligned with the hotspot center. For ethanol, the CHF is ∼315 W/cm 2 at Re ∼1338 with a corresponding heat transfer coefficient of h ∼102 kW/m 2 K. For FC 72, the CHF is ∼94 W/cm 2 at Re∼ 5000 with• a corresponding h∼ 56 kW/m 2 .K. And for Novec 7200, the CHF is ∼108 W/cm 2 at Re∼ 4600 with a corresponding h ∼ 50 kW/m 2 •K.