This work presents a noncontact laser-based thermoreflectance technique to measure changes in temperature or concentration at a liquid surface. Changes in temperature and, for multi-component liquid mixtures, concentration result in a change in the liquid index of refraction, which alters the reflectivity of the liquid surface. An intensity-stabilized diode laser and silicon photodiode are used to monitor the surface reflectivity. Temperature variations in 1-propanol, methanol, ethanol, and water are measured with uncertainties of 0.5, 0.7, 0.7, and 3.7°C, respectively. For binary mixtures, the concentration of a methanol-propanol mixture is measured with an uncertainty of 0.3 percent. The experimental configuration is noninvasive, simple in design, and inexpensive. The technique can be used over a wide range of time scales, ranging from micro-seconds to minutes, and can achieve high spatial resolution by focusing the probe laser beam to a small spot size on the liquid surface. [S0022-1481(00)02803-6]

Issue Section:
Microscale Heat Transfer
Keywords:
Heat Transfer, Laser, Liquid, Measurement Techniques, Temperature and Concentration, thermoreflectance, liquid mixtures, spectral methods of temperature measurement, spectrochemical analysis, measurement by laser beam
Topics:
Lasers, Temperature, Temperature measurement, Water, Methanol, Ethanol
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