Erratum to “Experimental study on the air/water counter-current flow limitation in a model of the hot leg of a pressurized water reactor”

This paper replaces the paper published in the journal by Deendarlianto et al. (2008). Because of an error in the implementation of the air flow meter some of the data given by Deendarlianto et al. (2008) are wrong. They are corrected within the present paper. The general results and conclusions remain unchanged.An experimental investigation on the air/water counter-current two-phase flow in a horizontal rectangular channel connected to an inclined riser has been conducted. This test-section representing a model of the hot leg of a pressurized water reactor is mounted between two separators in a pressurized experimental vessel. The cross-section and length of the horizontal part of the test-section are (0.25 m × 0.05 m) and 2.59 m, respectively, whereas the inclination angle of the riser is 50°. The flow was captured by a high speed camera in the bended region of the hot leg, delivering a detailed view of the stratified interface as well as of dispersed structures like bubbles and droplets. Counter-current flow limitation (CCFL), or the onset of flooding, was found by analyzing the water levels measured in the separators. The counter-current flow limitation is defined as the maximum air mass flow rate at which the discharged water mass flow rate is equal to the inlet water mass flow rate.From the high-speed observations it was found that the initiation of flooding coincides with the formation of slug flow. Furthermore, a slight hysteresis was noticed between flooding and deflooding. The CCFL data was compared with similar experiments and empirical correlations available in the literature. Therefore, the Wallis-parameter was calculated for the rectangular cross-sections by using the channel height as length, instead of the diameter. The agreement of the CCFL curve is good, but the zero liquid penetration was found at lower values of the Wallis parameter than in most of the previous work. This deviation can be attributed to the special rectangular geometry of the hot leg model of HZDR, since the other investigations were done for pipes.     

CFD studies on the phenomena around counter-current flow limitations of gas/liquid two-phase flow in a model of a PWR hot leg

In order to improve the understanding of counter-current two-phase flow and to validate new physical models, CFD simulations of a 1/3rd scale model of the hot leg of a German Konvoi pressurized water reactor (PWR) with rectangular cross section were performed. Selected counter-current flow limitation (CCFL) experiments conducted at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) were calculated with ANSYS CFX using the multi-fluid Euler–Euler modelling approach. The transient calculations were carried out using a gas/liquid inhomogeneous multiphase flow model coupled with a shear stress transport (SST) turbulence model.In the simulation, the drag law was approached by a newly developed correlation of the drag coefficient (Höhne and Vallée, 2010) in the Algebraic Interfacial Area Density (AIAD) model. The model can distinguish the bubbles, droplets and the free surface using the local liquid phase volume fraction value. A comparison with the high-speed video observations shows a good qualitative agreement. The results indicate also a quantitative agreement between calculations and experimental data for the CCFL characteristics and the water level inside the hot leg channel.     

Investigation of liquid film behavior at the onset of flooding during adiabatic counter-current air–water two-phase flow in an inclined pipe

The liquid film characteristics at the onset of flooding in an inclined pipe (16 mm i.d. and 2.2 m in length) have been investigated experimentally. A constant electric current method and visual observation were utilized to elucidate the flow mechanisms at the onset of flooding. Two mechanisms are clarified to control the flooding in lower flooding and upper flooding, respectively. The lower flooding occurred at lower liquid flow rate and high pipe inclination angle. In this mechanism, the liquid film does not block the pipe cross-section. On the other hand, the upper flooding occurred at higher liquid flow rate and low pipe inclination angle. In this case, blocking of the pipe cross-section by large wave and entrainment plays an important role. The experimental data indicated that there was no reversal motion of liquid film at the onset of flooding during the operation of both lower flooding and upper flooding. The effects of pipe inclination angle on the onset of flooding are also discussed.     

Prediction of flooding gas velocity in gas–liquid counter-current two-phase flow in inclined pipes

The purpose of the experimental study is to investigate the effects of pipe inclination, pipe length, pipe diameter and surface tension of the working liquid on the onset of flooding of gas–liquid adiabatic counter-current two-phase flow in inclined pipes. Flooding in inclined pipes were observed by using the combination of visual observation, measurement of discharged liquid flow rate and time variation of liquid hold-up. And it was defined as the maximum air flow rate at which the discharged liquid flow rate is equal to the inlet liquid flow rate. As a result we proposed a correlation to predict the flooding gas velocity in inclined pipes under a given liquid flow rate, and the predictions agreed well with the experimental observations.     

Experimental study on the air/water counter-current flow limitation in a model of the hot leg of a pressurized water reactor

An experimental investigation on the air/water counter-current two-phase flow in a horizontal rectangular channel connected to an inclined riser has been conducted. This test-section representing a model of the hot leg of a pressurized water reactor is mounted between two separators in a pressurized experimental vessel. The cross-section and length of the horizontal part of the test-section are (0.25 m × 0.05 m) and 2.59 m, respectively, whereas the inclination angle of the riser is 50°. The flow was captured by a high-speed camera in the bended region of the hot leg, delivering a detailed view of the stratified interface as well as of dispersed structures like bubbles and droplets. Countercurrent flow limitation (CCFL), or the onset of flooding, was found by analyzing the water levels measured in the separators. The counter-current flow limitation is defined as the maximum air mass flow rate at which the discharged water mass flow rate is equal to the inlet water mass flow rate.From the high-speed observations it was found that the initiation of flooding coincides with the formation of slug flow. Furthermore, a hysteresis was noticed between flooding and deflooding. The CCFL data was compared with similar experiments and empirical correlations available in the literature. Therefore, the Wallis-parameter was calculated for the rectangular cross-sections by using the channel height as length, instead of the diameter. The agreement of the CCFL curve is good, but the zero liquid penetration was found at lower values of the Wallis parameter than in most of the previous work. This deviation can be attributed to the special rectangular geometry of the hot leg model of FZD, since the other investigations were done for pipes.