Understanding pulsed jet impingement cooling by instantaneous heat flux matching at solid-liquid interfaces

In recent decades, jet impingement cooling has gained significant attention due to its ability to remove large thermal loads from local heating zones. This study demonstrates the performance of pulsed jet impingement cooling on a Ti-coated glass window. Infrared (IR) thermography data are analyzed to generate heat transfer coefficient (HTC) maps for a range of heat fluxes (q '' approximate to 20-60 W/cm(2)) and jet pulsation frequencies (f(p) approximate to 7-25 Hz). Heat transfer coefficients are observed to scale as h proportional to root 2f(p) with local maximum values at the center of the jet stagnation zone. For reference, h(max) approximate to kW/m(2)K is found for q '' approximate to 60 W/cm(2) and f(p) approximate to 25 Hz. Moreover, a jet pulsation frequency of f(p) approximate to 15 Hz matches well with both the bubble release rate and dry-out occurrence rate within 50 and 80 ms, respectively, at q '' = 60 W/cm(2). At heat fluxes >40 W/cm(2), boiling regimes were captured in terms of cyclic events of bubble growth, bubble collapse, dry-out, partial rewetting, and full rewetting. Finally, a theoretical model is proposed based on both the HTC expected for a steady jet and HTC augmentation due instantaneous heat flux matching for a pulsed jet at the jet-wall interface. The correlation between experiments and theory are reasonable, yet there are still unresolved complexities associated with thermofluid instabilities, decoupling the transient latent heat and sensible heat transfer mechanisms, and first-principles modeling of the spatiotemporal surface temperature and flow-field oscillations induced by a pulsed jet.