Experimental Study on the Vibration Characteristics of Two-Phase Flow Post Dryout in Helical Coiled Tube

Abstract Boiling two-phase flow after drying is one of the main flow forms in spiral tubes. Exploring the flow-induced vibration response law caused by it is of great significance to the safety analysis and design of steam generators. Leveraging laser Doppler vibration measurement, this study yields crucial experimental data encompassing post-dryout flow rates, wall and fluid temperatures, and vibration displacements. Post-dryout, the root mean square (RMS) of vibration displacement follows a distinctive trend, initially escalating and subsequently diminishing with the upswing in outlet thermal equilibrium steam content. Pre-dryout, the RMS of vibration hovers around 238 μm, spiking dramatically to 1298 μm post-dryout, eventually stabilizing at approximately 200 μm. Significantly, a robust correlation manifests between the vibration frequency of helical coiled tube and the thermal equilibrium steam content. Specifically, at a steam content of 0.70 (pre-dryout), the vibration frequency registers around 0.2 Hz; at 0.85, it diminishes to 0.1 Hz, and surpassing 1.0, it sharply rises to 7.4 Hz. Methodically analyzing experimental data through statistical, time domain, and spectral approaches elucidates the intricate relationship between vibration response characteristics and two-phase boiling flow within the tube. These insights offer valuable references for refining the thermal design and optimizing vibration suppression in helical coiled tube Once-through steam, enhancing their practical applicability and operational stability.