CFD investigating flow and heat transfer characteristics in a natural circulation loop

Natural circulation is the most important heat removal mechanism for passive safety systems in new-design nuclear power plants. It is important to investigate the flow and heat transfer characteristics related to the natural circulation mechanism. In this paper, a compressible three-dimensional (3-D) CFD model is proposed to investigate these phenomena in a natural circulation loop. The flow and heat transfer behaviors in a loop can be reasonably captured by the present model, which includes the secondary flow within the elbow and the thermal stratification in the horizontal pipe, etc. This model is also validated with the existing experimental data. Compared with the measured results including time histories of local maximum fluid temperature and temperature difference across the heater, and the relationship between Ress and Grm/NG, the present predicted results show good agreement. These comparisons reveal that the present CFD methodology can be applied in simulating the thermal–hydraulic characteristics related to the natural circulation mechanism in confidence.

► Natural circulation is an essential heat removal mechanism for nuclear power plants.
► A compressible 3-D CFD model is proposed to study a natural circulation loop.
► This CFD model is validated with the existing experimental data.
► Measured data include time histories of Tmax and temperature difference across the heater.
► Prediction of Ress vs Gr/NG show good agreement with measurement.