Heat transfer characteristics of warm water flow with cool immiscible droplets in a vertical pipe

We have conducted measurement for the temperature distribution of warm water flow with cool immiscible droplets of hydrofluoroether in a vertical transparent pipe with the laser-induced fluorescence method. The droplets descend in the upward laminar water flow due to the high specific weight of the liquid. The local temperature is evaluated from the local fluorescence intensity with the calibration curve. We have also conducted flow visualization with tracer particles for the water flow with the droplets. A particle tracking velocimetry method has been applied for the captured images with the scattered light from the particles. The defect of temperature distribution is found in the core of wake flow region of the descending droplets. The thermal wake region is smaller than the wake flow region with the Ω-shaped vortex tube. The Strouhal number for the droplet wobbling motion can be estimated from the empirical equation of rising bubbles. This Strouhal number is lower than the Strouhal number of vortex shedding from a solid sphere.