The temporal response of inorganic temperature-sensitive phosphor films with different layer thickness and composition

Abstract

The temperature-sensitive paint (TSP), one of the temperature measurement techniques, is useful to evaluate temperature from a cryogenic temperature to a high temperature over 1000°C. An inorganic phosphor TSP was painted on a micro scale indium tin oxide (ITO) heater on a slide glass substrate. The temporal response of TSP to a short heating pulse from the micro-scale heater was estimated by using experimental data and numerical simulation. Measuring the temporal delay using the ITO heater with a micro-scale width and the TSP with a micro-scale thickness necessarily requires data acquisition with high temporal and spatial resolution. In this study, an extremely high spatio-temporal resolution, a temporal resolution of 200 kHz and a spatial resolution of 1.05 μm/pixel, was achieved by using a high-speed camera. We assume that the tendency of temperature at bottom of the TSP which contacts with the ITO is the same as the tendency of the current signal applied to the ITO, and the tendency of surface temperature of the TSP reversely follows the tendency of the phosphorescence signal due to the thermal quenching effect. The time delay was defined as the time difference between the time when the current signal becomes maximum and the time when the phosphorescence signal becomes minimum. Based on the definition of the time delay, the time delay was successfully calculated from the experimental data. The shortest time delay is 30.86 μs which is sufficient to visualize highly dynamic phenomena such as boiling flow. The current signal was employed as a boundary condition for numerical simulation of the one-dimensional heat conduction equation, and the time delay was calculated numerically based on the definition of time delay. The experimentally obtained time delay was compared to the numerically calculated time delay. The results showed that experimentally obtained time delay is longer than expected. Several factors explain the reason why the experimental results are different from expected. The quantitative evaluation of time delay of the fast response TSP for a high temperature measurement was successfully implemented, and the results will play an important role as a first step in understanding the thermo-physical properties of the TSP.