Turbulence in liquid phase and its influence on aeration and pressure surge in intermittent type two-phase flow

Abstract

Nuclear industry considers intermittent type of two-phase flow as a complex flow pattern due to its intricate hydrodynamics. Turbulence causes aeration inside the liquid slug leading to sudden surge in pressure and large Reynolds stresses near the wall. This result in high mechanical impact associated with structural vibration and erosion-corrosion in the pipeline. Fast accelerated corrosion associated with high momentum of slug and aeration in the slug body leads to cracks in the pipeline. In order to avoid hazardous accidents in nuclear industry associated with leakages from these cracks, a detailed analysis of the phenomena of aeration in the liquid slug is vital. The present work reports how turbulence in the liquid phase leads to aeration and its augmentation in the slug. In the first part of the present article, flow visualization analysis is presented depicting that at low level of turbulence, aeration is absent in plug flow regime. Increase in level of turbulence in liquid phase causes aeration and its augmentation in slug. The second part deals with analysis of the measured instantaneous averaged velocity variations in the liquid phase using Laser Doppler Velocimetry (LDV). The turbulence characteristics in the liquid phase measured using LDV is used to depict the cause of aeration in slug and its consequences on the pressure fluctuations. Instantaneous pressure signals and the pressure drop per unit length are measured in plug, less aerated slug (LAS) and high aerated slug (HAS) regime and correlated to the turbulence characteristics. At the end, the consequence of turbulence and pressure surge on pipe failure are depicted.