In situ measurement of the temperature of water in microchannels using laser Raman spectroscopy

Abstract For an improved understanding of physical and chemical processes in microreactors and their optimization, it is important to know the temperature distribution within microchannels. For this purpose, laser Raman spectroscopy can be applied. In this work, a 32 mm long microchannel with 0.4 mm width and 0.2 mm depth was used. Its temperature was controlled between 30 °C and 58 °C. The beam of a continuous argon ion laser was coupled into the tube of a microscope and focused through a quartz plate into the microchannel. The scattered Raman light of the molecules was measured with a spectrometer and a CCD camera. For first investigations, pure water was used. The broad vibrational Raman band of the OH stretch is bimodal with peaks at about 3250 cm −1 and 3450 cm −1 and leads to different shapes, which are dependent on temperature. The dependence of the peak intensities on temperature shows a linear course, and the temperature can be determined with an accuracy of ±1.2 °C. Further own investigations with the same Raman system show that the measuring procedure used here has a lateral local resolution of approximately 15 μm and a depth resolution of 25 μm. Therefore, the temperature profile inside microchannels can be determined with this spatial resolution.

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