In order to determine the Counter-Current Flow Limitation (CCFL) in hot legs of PWRs, CCFL characteristics of air-water and saturated steam-water flow were experimentally investigated in a modeled flow path of a horizontal tube connected to an inclined riser. The ranges of dimensions of experimental tubes were as follows : diameter D 0.0260, 076 m, length of horizontal tube H 0.010.4 m, length of inclined riser I 0.0380.6 m and inclination angle of inclined riser θ 40°or 45°.Wallis-type correlation (Jg*1/2+mJl*1/2=C) was applicable to the data during a steady separated flow. An analysis based on envelope theory showed that the constant C should be a function of H/D and I. A function of C with those parameters was empirically determined by using data obtained in this study. The developed function correlated well with the results of Richter el al. (D=0.203m, H=1.26 m, I=0.5 m and θ=45°). The constant m in the Wallis-type correlation was almost constant 0.75. The problems were discussed, which should be made clear to apply the correlation obtained in this study to an actual PWR hot leg.
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