Development of a Two-Dye LIF Technique for Measuring Fluid Temperature Fields in Microfluidic Devices

The feasibility of implementing a two-color laser-induced fluorescence (LIF) technique to study thermal transport at the microscale is investigated. A temperature-sensitive fluorescent dye (Rhodamine B) and a temperature-insensitive dye (Nile Red) are used in tandem to determine fluid temperature with high accuracy and low noise using a pulsed Nd: YAG laser as an illumination source. While the fluorescence intensity of the temperature-sensitive dye is proportional to temperature, it can be biased by variations in the illuminating intensity. Therefore, a second, temperature-insensitive dye is required to account for noise associated with variations in illumination intensity. Calibration of the system reveals that the two-color dye mixture in ethanol yields 1.0%/K of temperature sensitivity with volume illumination from the Nd:YAG laser. The feasibility of this methodology is explored by measuring steady-state conduction in a heated micro-reservoir.