Physical modelling to minimise air entrainment over an industrial weir and into a discharge pipeline

Physical modelling was used to simulate cooling water flow entering a chamber over an industrial weir and exiting through long discharge pipelines. The weir was required to maintain a backwater for condensers, but also resulted in significant aeration of the flow. The objectives were to minimise the air entrained to the discharge pipeline and to ensure de-aeration of any air within the pipeline was fully effective. Physical modelling was selected as the most reliable means of investigation as the complex air entrainment and free surface interactions would require highly complex CFD numerical modelling, with limited confidence in the results. The physical modelling study concentrated on flow patterns, air entrainment and the amount of air released within the chamber, discharge pipes and air release structures. A suite of flow and entrainment characterisations by dimensionless numbers have been assembled from the literature and used to scale the model of this complex system. The study highlights the need for careful consideration of geometry to minimise aeration and how relatively simple changes to flow asymmetry can reduce the air entrainment. The solution is relevant to other entrainment problems.