Flow Characteristics of Gas-Liquid Two-Phase Flow in a Plate Heat Exchanger

Adiabatic vertically downward air-water two-phase flows in a single channel commercial plate heat exchanger were visualized by a neutron radiography method to clarify the flow characteristics and the differences in liquid distribution from those of vertically upward flows. From the visualized results, it was shown that water fell down without a spreading at a lower gas volumetric flux and tended to flow in the left-side of the shortest pass between the inlet and exit. The liquid distribution was opposite to that of the upward flows in which liquid fraction was higher along the both side of the single channel. In the case of a higher gas volumetric flux above 7 m/s, liquid spread at the enlarged section and the liquid distribution in the main part of the heat exchanger seemed to be homogenous. Measured average void fractions for the air-water downward flows showed almost the same tendency as those for the upward flows, and those were well correlated based on Drift flux model. On the other hand, the frictional pressure loss of the downward flows showed lower values than those of the upward flows at the lower gas volumetric flux less than 13 m/s. The difference was might be caused by the difference in flow pattern. For the higher gas volumetric flux over 13 m/s, the difference in frictional pressure loss was a little. Frictional pressure loss was well correlated by L-M method.