A comprehensive understanding of the transient heat- and mass-transfer processes on the submicron scale requires the development of novel, non-invasive, temperature-measurement techniques. This work presents the development of a high-resolution fluorescence imaging technique for a non-invasive characterization of the transient temperature fields on the submicron scale using a temperature-sensitive co-doped transparent fluoride glass and co-doped glass-ceramic. These inorganic materials are more stable in the scope of degradation and photobleaching compared to the usually used organic dyes. The heat-conduction and boiling experiments were performed on an Er:GPF1Yb0.5Er glass-ceramic and an 6 % Er:ZBLALiP fluoride glass, which were also simultaneously used as a temperature sensor. Transient temperature measurements were made by analyzing the spectral variations of the fluorescence emission. Imaging of the transient temperature fields was performed by utilizing high-resolution, fluorescence microscopy, which enabled diffraction-limited spatial resolution at submicron scale. Furthermore, optical sectioning has been applied for the reconstruction of the wall-temperature distributions. The high-speed visualization at several hundred frames per second ensured sampling of individual bubble-nucleation event during saturated boiling of water. The proposed technique enables reliable transient temperature measurements at a spatial resolution that is almost two orders of magnitude better compared to the results published in studies with infrared thermography. Consequently, the development of this technique could provide new insights for a better understanding of the nucleate boiling process and the nature of the prevailing surface heat transfer mechanisms. This technique could also have applications in the numerous physical, biological and electrochemical processes, which are closely dependent on the solid-liquid interfaces, as it allows the visualization of temperature variations on the submicron scale.
|
