Temperature measurement around multiple boiling bubbles in a confined space using two-color laser-induced fluorescence

Boiling heat transfer has a combination of sensible heat transfer of liquid and latent heat transfer due to vaporization. To examine the sensible heat transfer in boiling, thermometry of liquid in liquid-vapor multiphase flow must play a significant role. Although there are several optical methods proposed for the thermometry of boiling phenomena, it is challenging to directly measure the temperature field of boiling at relatively high heat flux due to many boiling bubbles' interruption of the illumination and observation. This study proposes a novel thermometry method using a confined space, a sandwiched space between two transparency plates, and two-color laser induced fluorescence thermometry to measure the liquid temperature distribution around multiple boiling bubbles. The confined space restricted the fluid motion to make it possible to illuminate and observe the almost whole area of interest. The intensity ratio of the two kinds of fluorescent dye exhibits the local and temporal temperature without any invasion of physical probes. We successfully observed the scavenging of superheated liquid from the heat transfer surface to demonstrate this method's utility. The temporal temperature changes at several positions extracted from experimental data with this method were consistent with the boiling bubble behavior. We also discussed remained issues on the method.