Investigating the Dynamic Behavior of Loosely Supported Parallel Triangular Arrays Subjected to Two-Phase Flow

Abstract Flat-bar supports have long been employed to control transverse fluidelastic instability (FEI) in steam generators. While they might be effective for transverse vibration suppression, large displacements in the streamwise direction may occur due to the presence of support clearances. The incident at the San Onofre Nuclear Generating Station (SONGS) illustrated that excessive streamwise tube motion can occur, leading to tube failures even with flat-bar supports in place. An investigation was conducted to assess the impact of varying support clearance on the mechanisms of FEI in a densely packed parallel triangular tube array (P/D = 1.27). The tubes were subjected to both single-phase and two-phase flow of refrigerant R123, allowing for phase-change and yielding mass-to-density ratios closer to real values found in operating steam generators. A tube/support gap of 1.5 mm was tested under mass fluxes ranging from 50 to 500 kg/m2s. Tube responses were monitored in both the transverse and streamwise directions. Capacitance sensors were used to perform real-time void fraction measurements, offering good estimation of flow density of the two-phase mixture. The nonlinear dynamic behavior of the loosely supported array was investigated under various cross-flow conditions. Results demonstrated that the tube array’s stability is highly sensitive to support clearance, shedding some light on a critical factor that influences streamwise FEI in heat exchangers and steam generators.