IR thermographic investigation of nucleate pool boiling at high heat flux

• Pool boiling at high-heat flux was investigated using high-speed IR thermography.
• Hot spots are likely to occur in the middle of so-called “irregular” bubble sites.
• The temperature of the hot spot significantly exceeds the average heater temperature.
• The spots remain present on the boiling surface even after the bubble departure.
• The calculations based on 3-D IHCP showed decreased local heat flux at the spots.

Nucleate water pool boiling at high heat flux was investigated on the 25 µm titanium and stainless-steel heaters at atmospheric pressure. A high-speed IR thermographic camera was applied to measure the rapidly changing transient temperature field, which served as input data for calculating the transient local heat flux distributions by solving a 3-dimensional (3-D) inverse heat conduction problem (IHCP). A phenomenon of hot spot was observed at the irregular active bubble site characterized by a longer waiting time and a higher activation temperature compared to a regular active nucleation site. The results show that the temperature of the hot spot can significantly exceed the temperature of the heater in its surroundings and remains present on the boiling surface even after the bubble departure. The calculations have shown a strong reduction of the local heat flux at the spot, which represented a potential for the beginning of the boiling crisis.