Effects of fluid properties on CCFL characteristics at a vertical pipe lower end

The purpose of this study is to derive a counter-current flow limitation (CCFL) correlation and evaluate its uncertainty for steam generator (SG) U-tubes in a pressurized water reactor (PWR). Experiments were conducted to evaluate effects of the liquid viscosity on CCFL characteristics using air-40 wt% or air-60 wt% glycerol water solution and saturated steam-water at atmospheric pressure with vertical pipes simulating the lower part of the SG U-tubes. The steam-water experiments confirmed that CCFL characteristics could be expressed in terms of the Wallis parameters (J G * and J L *) for the pipe diameters of D = 14, 20, and 27 mm. A CCFL correlation was derived using the ratio μ G /μ L of the viscosities of the gas and liquid phases, μ G and μ L , as a correction term representing effects of fluid properties, where J G *1/2 (μ G /μ L ) −0.07 was expressed by a cubic function of J L *1/2 (μ G /μ L ) 0.1 . In the correlation, the constant C indicating the value of J G *1/2 (μ G /μ L ) −0.07 at J L * = 0 was (1.04 ± 0.05), and this uncertainty of ±0.05 would cover most of the previous experimental data including the ROSA-IV/LSTF data at 1, 3, and 7 MPa.