New measurement techniques for transport phenomena using a UV laser

Continuous-wave (CW) laser light is widely used in thermo-fluid dynamics measurements, e.g., velocity measurement by laser Doppler velocimetry (LDV) and density measurement by interferometry. The high monochromaticity, high coherence and high beam parallelism are the main reasons for using laser light in such measurements. Recently, new laser measurement applications are developing that use high intensity and/or short-pulse laser pulses. Laser induced fluorescence (LIF) is a typical example. In this paper, applications of high-intensity, short-pulse laser radiation to transport phenomena measurements in liquids are discussed. The non-contact nature of laser-based measurements is ideal for measurement at a liquid-gas interface. Recent work involving surface-tension-driven flow (Marangoni convection) caused by the laser heating is investigated for measuring the temperature dependence of the surface tension. A simple analysis to determine the behavior of thermal-based laser-induced flows is found to agree well with experimental data. On the other hand, the mass transfer mechanism in liquids is quite different from that in the gas phase, because of the high Schmidt number of liquids. The diffusion boundary layer is too thin to measure by conventional probe measurements, and convection is the dominant mechanism for mass transfer. The LIF method is applied to measure the concentration of CO₂ in water and the turbulent mass transfer rate is determined.