Temperature imaging of sub-millimeter-thick water using a near-infrared camera

This paper presents a method of imaging temperature distributions of sub-millimeter-thick water using a near-infrared camera and optical narrow-bandpass filter. The principle is based on the temperature dependence of the ν1 + ν3 absorption band of water. Temperature images are constructed by measuring the absorbance of water at the wavelength of 1412 nm through the filter for all pixels of the camera. From calibration measurements on 0.5-mm thick water at temperatures from 26.0 °C to 40.0 °C, the temperature coefficient was 6.3 × 10−4 K−1 and the standard deviation of absorbance was 1.9 × 10−4. Thermal diffusion in 0.5-mm thick water caused by a thin heating wire was visualized with this method. The obtained images were verified against temperature distributions calculated by solving a two-dimensional thermal conduction model. This method would be useful for temperature measurement applications and control of aqueous solutions in microchips.