Quantification of local heat transfer during bubble growth on a holed fin structure using LIF thermometry

We present a quantitative study of localized heat transfer during subcooled nucleate boiling on a holed-fin surface using two-color laser-induced fluorescence (LIF) thermometry. The holed-fin geometry enables evaluation of transient heat transfer during bubble growth by generating a large bubble in response to heat input. The heat transfer characteristics are investigated through transient temperature measurements using two temperature-sensitive tracers. Fluorescein and sulforhodamine B dyes are excited at 514 nm, and their emission intensities are recorded simultaneously by two high-speed cameras to obtain emission-intensity ratios, thereby improving measurement accuracy. The intensity ratios are then converted to temperature using calibration, with a temporal resolution of 0.04 s and a spatial resolution of 10 μm per pixel. From the temperature fields, we estimated the local heat flux and integrated it over the axisymmetric bubble surface to obtainthe heat transfer rate near the bubble-liquid interface. Experiments conducted at bulk liquid temperatures of 80 ◦ C and 90 ◦ C reveal steep temperature gradients near the bubble base, with peak near-interface heat transfer occurring at bubble departure. At the departure stage, the near-interface heat transfer converged to approximately an 45–49% of the input heat transfer rate at the departure moment. These results provide a first-order experimental estimate of near-interface heat transfer and offer a new benchmark for heat-transfer models of nucleate boiling.