Prediction of coutercurrent flow limitation in a slightly inclinded pipe with elbows

Sensitivity computations were carried out for hot leg models (ratio of the horizontal pipe length to the diameter, L/D = 8.6) and pressurizer surge line models with and without elbows (ratio of the inclined pipe length to the diameter, L/D = 63) to evaluate suitable wall friction coefficients and pressure loss coefficients of elbows in a one-dimensional model predicting countercurrent flow limitation (CCFL) in a piping system. Computed results were compared with measured values. When the interfacial drag coefficient of fi = 0.03 and wall friction coefficients fwG of single-phase gas flows (i.e. adjustment factor, NwG = 1) were used, the appropriate adjustment factor for wall friction coefficients fwL of single-phase liquid flows was NwL = 6; this gave good fit of the computed CCFL values with the CCFL values measured in piping systems without elbows (L/D = 8.6 and 63). When fi = 0.03, NwG = 1, and NwL = 6 were used, the appropriate adjustment factor for pressure loss coefficients ζe of elbows in single-phase flows was Nde = 10; this gave good fit of the computed CCFL values with the CCFL values measured in the piping system with elbows (L/D = 63).