Study On Influence Of Branch Angle On Entrainment Characteristics Of Large T-junction

T-junction structures are widely used in nuclear power plant systems,the fourth-level automatic depressurization systempipeline of AP1000 reactor and the structure formed by the crevasse and main pipeline in reactor loss of coolant accident,etc.In order to ensure the operation safety of nuclear power plants,it is very crucial to correctly predict the entrainment phenomenon in T-junction.Many scholars at home and abroad have done a number of analyses on the entrainment of T-junction,but most of the existing researches take the small-size branch as the research object and the model established can not accurately predict the onset entrainment and steady-state entrainment of largeT-junction.At the same time,there is little research on the entrainment of multi-angle branch pipes,so this thesis mainly focuses on the gas and liquid entrainment process of multi-angle large-size branch pipes to fit the entrainment initiation model of liquid phase and gas phase and the mass gas volume fraction model of branch pipe within a certain branch pipe angle range.It can make up for the deficiency of previous studies,and at the same time enrich the entrainment data of large-size branch pipes,so as to provide theoretical analysis and model reference for nuclear power plant safety analysis and different calculation procedures.In this experiment,adopting air and water two-phase medium,together with d/D is 0.387,the liquid entrainment process of large T-junction between 30° ???60° and the gas entrainment process of large T-junction between-45° ???-900 are studied.By qualitative and quantitative analysis,the entrainment mechanism and regularity of branch pipe angle to large T-junction are studied.It can be seen that the onset liquid entrainment of the inclined branch pipe enters the branch pipe in the form of rising liquid film along the inner wall of the branch pipe.The onset of liquid entrainment is related to branch pipe gas phase Frg,dimensionless air chamber height hb/d and branch pipe angle ?.hb/d decreases as Frg increases,hb/d increases as ?increases,and Frgincreases as ? decreases.There are two typical entrainment flow types in liquid steady-state entrainment,namely,wave flow and intermittent slug flow.Liquid steady-state entrainment is related to branch pipe gas phase Frg,dimensionless gas chamber height h/d,and branch pipe angle ?.As ? gradually decreases,themass quality x of branch pipe also gradually decreases,as Frg increases,x gradually decreases,and as h/d increases,x gradually decreases.The gas entrainment of large branch at different angles enters the branch pipe in the form of whirlpool.The onset of gas entrainment is related to the branch pipe liquid phase Frf,the dimensionless liquid level height hb'/d and the branch pipe angle ?.hb'/d increases as Frfincreases,hb'/d increases as ? increases,and Frf increases as ? decreases.There are two forms of gas steady-state entrainment,namely,rotational entrainment and non-rotational entrainment.Gas steady-state entrainment is related to branch pipe gas phase Frf,dimensionless liquid level height h*/d*,and branch pipe angle ?.As ? gradually decreases,themass qualityx of branch pipe also gradually decreases.As Frfincreases,x also gradually increases As h*/d*increases,x gradually decreases.In this thesis,the onset liquid entrainment and branch pipe mass quality models suitable for 30°,45° and 60° branch pipes and the onset gas entrainment and branch pipe mass quality models suitable for-45°,-60° and-90° branch pipes are obtained according to the experimental data.The maximum errors of onset liquid entrainment and branch pipe mass quality models are ±21%and ±3 7%,respectively,while the maximum errors of onset gas entrainment and branch pipe mass quality models are±28%and±26%,respectively,and the prediction results are basically good.