Effects of fluid properties on interfacial and wall friction factors under counter-current flow limitation in a vertical pipe with sharp-edged lower end

Abstract

A gas–liquid counter current flow may possibly occur in the U-tubes of the steam generator in a PWR due to loss of the residual heat removal during mid-loop operation. For safety analysis based on the one-dimensional multi-fluid simulation, correlations of the interfacial and wall friction factors are required. Experiments on air-glycerol water solution counter-current annular flows in a circular vertical pipe of 20 mm in diameter and 400 mm in length with a sharp-edged lower end, hence, were carried out to investigate the effect of the liquid viscosity on the flow structure and the interfacial and wall friction factors. The liquid flow rate, the pressure gradient and the liquid volume fraction were measured to evaluate the friction factors. The time-strip flow visualization technique was applied to flow images in the pipe for detailed observation. The obtained conclusions are as follows: (1) the flows under CCFL condition in the present study can be classified into two regimes, i.e. the rough film with disturbance waves forming at the lower pipe end (RF-I) and the disturbance waves flowing upward with dissipation and regeneration (RF-II), (2) the interfacial friction factor is independent of the liquid viscosity and mainly determined by the balance between the inertial and buoyant forces. The gas Froude number, JG*, is the primal dimensionless group in correlating the interfacial friction factor, (3) the wall friction factor can be correlated in terms of the liquid Froude number JL*, the liquid Reynolds number ReL and the dimensionless pipe diameter D*, and (4) the correlations of the friction factors were proposed. The applicable ranges of the correlations are 0.58 ≤ JG*1/2 ≤ 0.78, 0.01 ≤ JL*1/2 ≤ 0.10, 0.15 ≤ ReL ≤ 178 and 7.28 ≤ D* ≤ 17.79.