Thermo-Hydraulic Behavior of Inverted Two-Phase Flow

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Inverted two-phase flow was investigated experimentally in vertical and horizontal flow channels with various diameters using Freon 113 as a test fluid.The folloving are clarified:(1) Inverted two-phase flow has three flow regimes, which are inverted annularflow, liquid slug flow and superheated dispersed flow.(2) Inverted annular flow appears in the region where thermally equilibrium quality is less than zero, liquid slug flow occurs in the region where it is between zero and 0.1, and superheated despersed flow is formed in the region where it is more than 0.1.(3) Superheated dispersed flow is the same as the one under post-dryout conditions.(4) Nusselt number of liquid slug flow coincides the one of inverted annular flow at zero quality, increases linearly as increasing the thermally equilibrium quality and is proportion to the square of Reynolds number.The thermo-hydraulic behavior under thermally non-equilibrium conditions has never been understood in the constitute equations for n … More umerical analysis of transient two-phase flow, which is important for safety analysis of light water reactors. Inverted annular flow has thermally large non-equilibrium state in the same flow cross section where subcooled liquid and superheated vapor exit. Therefore, inverted annular flow was taken up secondly to produce the fundamental data base on the thermo-hydraulic behavior under thermally non-equilibrium conditions and to model it.From these results, the following are clarified:(5) Nusselt number of inverted annular flow is proportion to 0.35th of Reynolds number for the horizontal flow but is independent of it for the vertical flow.(6) Nusselt number of the horizontal flow decreases exponentialy as increasing wall superheating and thermally equilibrium quality. As increasing the flow diameter, the absolute values of the power concerning superheating increases but the one concerning thermally equilibrium quality decreases.(7) The fundamental data base on vapor film thickness is produced, which is very important for modeling mass, energy and momentum transfer from the interface. The empirical correlation of the thickness is proposed.(8) The frictional multiplier of inverted annular flow to liquid single phase flow is not correlated by the ratio of the vapor film thickness to the flow diameter but by the thickness. The multiplier is less than 1 lor the thickness less than 0.4mm. Less