2007 Volume 24 Issue 4 Pages 389-399
Adiabatic vertically upward and downward air-water two-phase flow characteristics in a commercial plate heat exchanger were investigated based on visualization experiments by a neutron radiography method. From the visualized results of gas-liquid two-phase flows in a single channel, large difference in the flow pattern between the upward and downward flows was observed at lower gas volumetric flux less than about 2 m/s. In this case, the flow pattern for the upward and downward flow was an intermittent flow and separate flow, respectively. For high gas volumetric flux above 13 m/s, liquid distribution in the heat exchanger seemed to be homogenous for the both flow directions. In spite of the difference in flow pattern for low gas volumetric flux, the effect of the flow direction on the average void fraction was little over the experimental range. On the other hand, liquid distributions into 18 parallel channels were evaluated from the measured results of liquid volumetric fractions in each channel. It was shown that the liquid distribution strongly depended on the inlet flow condition and configuration of the header.
