Simultaneous spatiotemporally resolved temperature and velocity field measurements of nucleate boiling*

Boiling is exploited in applications where high heat transfer rates are required, however, our fundamental understanding of the complex underlying thermo-fluid physical processes and their interactions across scales that give rise to this phenomenon remains incomplete. Experiments of nucleate boiling are performed in which the temperature of the heated surface is recorded with an infrared camera simultaneously with the application of laser-based techniques that provide space/time-resolved information on the temperature and velocity fields in the liquid surrounding a bubble during its nucleation, growth and detachment. A laser excites two fluorescent dyes and microparticles introduced into the flow as markers. The fluorescent signals of the dyes are captured individually by two high-speed cameras, and their ratio is used to measure the temperature around the bubble and to identify the corresponding thermal boundary layer, while limiting the effect of interface reflections. At the same time, particle image/tracking velocimetry algorithms are applied to isolated tracer particle images in order to reveal the flow field around the bubbles.