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This study focusses on investigating the effect of flow orientation on global and local two-phase flow parameters under two-phase flow conditions. Flow visualization, pressure measurement, and conductivity probe measurements are performed in a test facility made of 50.8 mm inner diameter acrylic pipes with flow visualization, pressure measurement, and conductivity probe measurement. Characteristics of flow regimes and interfacial structures, and frictional pressure drop prediction in the vertical upward and vertical downward two-phase flows are compared and analyzed. The results show that unique coring phenomenon and slug bubbles with off-centered noses appear in the vertical downward flow. The flow regime transition boundaries shift to the lower gas superficial velocities in the vertical downward flow compared to that in the vertical upward flow. Furthermore, the distribution and one-dimensional transport of the void fraction, interfacial area concentration, bubble velocity, bubble Sauter-mean diameter, and bubble frequency are acquired and compared to study the effect of flow orientation on interfacial structures. The interfacial structure and its development are found to be mainly affected by the lift force and the turbulence related bubble interactions. The frictional pressure drop is acquired and modeled by the Lockhart–Martinelli correlation. The frictional pressure drop is found to be larger in the vertical upward flow than that in the vertical downward flow. The recommended C value for both vertical upward and vertical downward flows are proposed.

The Standard model in ANSI/ANS-58.2 (1988) has been widely employed in the design and safety analysis of nuclear power plants for jet impingement under postulated pipe rupture accidents. However, the potential non-conservatisms presented in Standard Review Plan (2015) need to be addressed when evaluating this model. The current work aims to improve the model on jet prediction including jet geometry and stagnation pressure, as well as to address the potential non-conservatisms. Based on the model evaluation results in Part I, new correlations for the jet core length and stagnation pressure in subcooled water and saturated water/two-phase jets are implemented to replace the existing correlations in the Standard model. It is shown that the revised code with the newly developed correlations predicts the stagnation pressure generally higher or conservatively for all conditions investigated. On the potential blast wave effect, the current work develops an approach to quantify the over-static and reflected pressures using the equivalent weight of TNT approach in literature. To employ this approach, the released energy in the equivalent of TNT needs to be determined from jet impingement. This energy is calculated using the vessel burst energy concept with conservative assumptions in the current work. For jet geometry, dynamic models to predict the jet spreading angle for saturated steam jets are compared with the Prandtl-Meyer angle for under-expanded supersonic jets. It is found that the jet spreading angle for saturated steam jets in the Standard model generally agrees with the dynamic model in literature for a wide range of initial vessel stagnation pressure conditions. Regarding the pressure distribution within jets, it is confirmed that edge-peaking pressure profiles can be observed for saturated steam jets at far distances from the break plane (z > 3.3 D); however, the dimensionless pressures at these locations are generally less than 0.07. Regarding the jet dynamic loading effect, the literature review suggests that dynamic amplification and resonance of impinged downstream structures and components might not occur for jet impingement in nuclear power plants.

Under postulated pipe rupture accidents in nuclear power plants (Loss-of-Coolant Accident or LOCA), jet impingement can occur where the high-energy fluid is discharged and cause damage to the surrounding structures, systems, and components (SSCs). As a part of addressing the potential non-conservatisms in the Standard model ANSI/ANS-58.2 (1988), the current work investigates characteristics of jet impingement in high energy piping systems as in nuclear power plants including pressure distribution within jets, pressure on target, and critical mass flux and performs model evaluation. The pressure prediction using ANSI/ANS-58.2 (1988) as well as critical mass flux models are evaluated using the experimental data available in literature. An organized experimental database with different inlet fluid conditions including subcooled water, saturated water/two-phase (0 ≤ x 3.3) can be underestimated, the dimensionless pressures at these axial locations are below 0.07. For saturated water/two-phase jets, the stagnation pressure can be predicted well using the Standard model for the large-scale test data (D > 0.28 m) but are underestimated at some axial locations for the medium- and small-scale test data (D