Dynamic analysis of the bubble's spatiotemporal evolution on a microheater under microsecond pulse heating

Transient heating of liquids upon a microheater surface manifests an exceedingly rapid temperature escalation, inducing a pronounced superheating at the onset of nucleation. Rare study focuses on the spatiotemporal behavior of subcooled boiling bubbles on a thin-film microheater surface. The present study experimentally explores the subcooled pool boiling heat transfer process on a platinum thin-film microheater with dimensions of 1000 μm × 1000 μm under microsecond pulse heating conditions. The visualized results indicate that three typical heat transfer regimes related to various heating scenarios can be identified, including the single-phase, nucleate boiling and film boiling heat transfer regimes. Consequently, the boiling incipience moment and the corresponding average microheater temperature are meticulously discussed and compared with analogous scholarly contributions. Moreover, the rapid bubble lifecycle involving nucleation, growth, coalescence and collapse within approximate 130 μs under microsecond pulse heating is captured and detailly analyzed. At lower heat flux, the boiling process is distinctly classified into five phases: (I) single-phase heat transfer, (II) isolated bubbles nucleation, growth and coalescence, (III) formation and growth of vapor blanket, (IV) shrinkage and collapse of vapor blanket, followed by (V) microbubbles condensation. As the vapor blanket nearly envelops the microheater completely, the temperature dramatically surges, with the increase rate markedly surpassing that observed during phase II. When further raising the heat flux, the regrowth of main bubble locating at the central area can be observed. Meanwhile, the nucleation and growth of numerous microbubbles in the peripheral zones after the collapse of vapor blanket are identified.