Whole field measurement of temperature in water using two-color laser induced fluorescence

A technique is described that measures the instantaneous three-dimensional temperature distribution in water using two-color laser-induced fluorescenc e (LIF). Two fluorescent dyes, Rhodamine B and Rhodamine 110, are used as t emperature indicators. A laser light sheet scanned across the entire measur ement volume excites the fluorescent dye, and an optical system involving a color beam splitter gives the intensity distribution of the individual flu orescent dyes on two separate monochrome CCD cameras. The ratio of these fl uorescence intensities at each point of the image is calibrated against the temperature to eliminate the effect of the fluctuation of illuminating lig ht intensity. A stable thermally stratified layer was measured by this syst em to evaluate the total accuracy of the measurement system. The random err or of the measurement was +/-1.4 K with 95% confidence. Measurements of the rmal convection over a heated horizontal surface show temperature iso-surfa ces having typical structures such as plumes, ridges and thermals.