Research on Temperature/Velocity Measurement Technique Utilizing Laser-Doppler Velocimetory with Fluorescent Seed Particles

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In order to examine the mechanism of heat transfer in heterogeneous heat transfer media, e.g.gas-solid two-phase flow, from microscopic view point, it is keenly required to develop the technique for simultaneous measurement of temperature and velocity of the media in local basis. In this research project, the concept of a temperature/velocity measurement technique utilizing Laser-Doppler Velocimetory (LDV) with fluorescent seed particles was proposed, and its feasibility was experimentally examined. To examine the feasibility of the technique, an optical setup of LDV was constructed by using an Ar^+ ion laser (visible light) or a He-Cd gas laser (UV light), and the fluorescent seed particles dispersed in the heat transfer medium enable us to measure the fluorescent light, from which the temperature of medium was evaluated, as well as the scattered light for the velocity measurement. Obtained results can be summarized as follows :1. In the simultaneous measurement for the temperature and velocity of the same seed particle, fluorescent light and scattered light can be effectively separated by using a monochromator. The measurement of fluorescent light through the monochromator would improve the accuracy of temperature measurement, since the lifetime of fluorescence depends upon the wavelength of the fluorescent light.2. The fluorescent particles developed for the fluorescent lamps and/or CRT display are suitable as the seed particles, since the particles emit relatively strong fluorescent light in visible wavelength range. However the decay of fluorescence of these particles after the excitation is quite slower than the rising, and thus the temperature dependence of fluorescent lifetime of these particles can be observed not as the phase shift but as the change of smoothing effect on the Doppler burst signal.