Caged Molecular Fluorescence Velocimetry to measure meso-to micro-scale thermal flow fields

Abstract

A caged molecular fluorescence velocimetry (caged MFV) system has been developed to measure velocity profiles of thin meniscus flow fields commonly established in micro-scale thermocapillary devices such as micro heat pipe and capillary pumped loop (CPL). The system utilizes a microscope objective lens, caged molecular fluorescence probes, Nd:YAG laser for UV light source, Ar-ion laser for 488 nm fluorescence pumping, and a color CCD camera to record a series of fluorescent images. Caged fluorescence probes have a specific characteristic that causes them to fluoresce only after they are exposed to UV light. The fluorescent image is seen like a thin thread in a fluid field. The thickness of a fluorescent image depends on the UV beam diameter that is adjusted as small as 20 æm. The flow velocity fields are analyzed using a time-averaged line tracking method. An example application has been made for three-dimensional thermocapillary driven flows, inside a 5-mm diameter pore. The developed MFV technique successfully shows the Lagrangian mapping of complicated flow fields driven by both thermocapillary stress and natural convection.