Non-invasive measurement of void fraction and liquid temperature in microchannel flow boiling

Past thermometry research for two-phase microfluidic systems made much progress regarding wall temperature distributions, yet the direct measurement of fluid temperature has received little attention. This paper uses a non-invasive two-dye/two-color fluorescent technique to capture fluid temperature along with local liquid fraction in a two-phase microflow generated by injecting air into a heated microchannel. The fluorescent emission of Rhodamine 110 and Rhodamine B, measured with photodiodes, is used to obtain local liquid temperature (±3°C) and void fraction (±2% full-scale) over a temperature range from 45 to 100°C. Arrays of these sensors can significantly expand the set of measurable flow parameters to include bubble/slug frequency, size, velocity, and growth rates in addition to mapping the local liquid temperature and void fraction.