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  • Characterization of diabatic two-phase flows in microchannels : flow parameter results for R-134a in a 0.5mm channel
    Revellin, Rémi ...
    An optical measurement method for two-phase flow pattern characterization in microtubes has been utilized to determine the frequency of bubbles generated in a microevaporator, the coalescence rates ... of these bubbles and their length distribution as well as their mean velocity. The tests were run in a 0.5 mm glass channel using saturated R-134a at 30 °C (7.7 bar). The optical techniqueuses two laser diodes and photodiodes to measure these parameters andto also identify the flow regimes and their transitions. Four flow patterns(bubbly flow, slug flow, semi-annular flow and annular flow) with their transitions were detected and observed also by high speed video. It was also possible to characterize bubble coalescence rates, which were observed here to be an important phenomena controlling the flow pattern transition in microchannels. Two types of coalescence occurred depending on the presence of small bubbles or not. The two-phase flow pattern transitions observed did not compare well to a leading macroscale flow map for refrigerants nor to a microscale map for air-water flows. Time averaged cross-sectional void fractions were also calculated indirectly from the mean two-phase vapor velocities and compared reasonably well to homogeneous values.
    Source: International journal of multiphase flow. - ISSN 0301-9322 (Letn. 32, št. 7, 2006, str. 755-774)
    Type of material - article, component part
    Publish date - 2006
    Language - english
    COBISS.SI-ID - 9522203

    Link(s):

    http://dx.doi.org/10.1016/j.ijmultiphaseflow.2006.02.016

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