Optical temperature measurements in superheated liquid droplets

Abstract

A new laser-induced fluorescence (LIF) methodology, using a mixture of Kiton Red and Rhodamine 6G dyes (the 2cPLIF method), is developed and applied to the microscale liquid–liquid two-phase systems of oil and water. The results of the measurement of temperature fields for water–oil droplets, using this methodology and dyes with similar fluorescence spectra, are presented. Complex image processing, when dyes with similar emission peaks (585 nm and 550 nm) and threshold filters instead of bandpass filters are used, is required for this methodology. In the temperature range corresponding to the superheated state, the measurement error using this methodology is approximately $1.5°$C, which makes this approach more accurate than those used earlier. For complex objects with curvilinear interfaces (composite droplets), this approach is shown to effectively resolve their internal interfacial boundaries. The methodology, however, cannot properly compensate for the low intensity on the visible contour of the droplet and aberration effects. Potential applications of measurements of the temperature at the fuel/water interface, using the new methodology, could lead to an in-depth understanding of the underlying physics of puffing/micro-explosion in composite fuel/water droplets.