Countercurrent flow limitation in slightly inclined pipes with elbows

One-dimensional (1D) sensitivity computations were carried out for air-water countercurrent flows in a 1/15-scale model of the hot leg and a 1/10-scale model of the pressurizer surge line in a pressurized water reactor to generalize the prediction method for countercurrent flow limitation (CCFL) characteristics in slightly inclined pipes with elbows. In the 1D model, the wall friction coefficient fwG of single-phase gas flows was used. The interfacial drag coefficient of fi = 0.03, an appropriate adjustment factor of NwL = 6 for the wall friction coefficient fwL of single-phase liquid flows (NwG = 1 for fwG of single-phase gas flows) and an appropriate adjustment factor of Nde = 6 for the pressure loss coefficient ζe of elbows in single-phase flows were determined to give good agreement between the computed and measured CCFL characteristics. The adjusted factors were used to compute and then discuss effects of the inclination angle and diameter on CCFL characteristics.