Host Tuned Luminescence Lifetime Thermometers for Imaging Boiling Thermal Dynamics Through Bubbles

Phase changes are ubiquitous in critical thermal processes (wing icing, boiling, spray cooling). In this study, luminescence thermometry is used to shed new light on the surface thermal dynamics of a boiling flow. To minimize the impact of the transient optical perturbations caused by the multiphase flow and provide sufficient temperature resolution, luminescence lifetime thermometers with microsecond decay time such as the phosphor ScVO 4 :Bi 3 + are needed. Such a lifetime thermometer with optimal temperature resolution at the water boiling point at atmospheric pressure, 100 °C is developed by forming solid solutions of bismuth‐doped YVO 4 and ScVO 4 . A Fivefold improvement in signal level is obtained with respect to ScVO 4 :Bi 3 + , together with a high temperature sensitivity (>2 %/°C) and a short decay time (≈2 µs). This modified phosphor allowed us to implement lifetime temperature imaging of temperature transients below a rapidly‐evolving boiling flow, and to reveal the fine thermal signature of single bubble growths as well as dry‐out phenomena. This method can readily be applied to understand boiling on micro‐structured surfaces, and therefore enable significant gains in cooling efficiency. Tuning the host composition of bismuth‐doped orthovanadates enables robust, precise 2D thermometry to investigate fast thermal processes within desired temperature ranges.