Analysis of natural convection in IPWR type SMR test facility
In advanced and conventional reactors natural circulation plays an important role in cooling of core. This dissertation is based on modeling of a test facility using RELAP5/MOD 4.0. Test facility (TF) comprises of heating core, riser, helical coil heat exchanger, and shell and tube heat exchanger and down comer these components are joined with associate piping and fittings. In the TF, heating core is cooled by natural circulation. In this thesis, analysis of natural circulation depends on geometry and operational parameters. The primary objective of this thesis is to investigate the effects of riser height, riser diameter, Source and sink distance, power and secondary side mass flow rate on primary loop mass flow rate, which is established due to natural convection. Natural circulation loop of TF modeled with the aid of RELAP5/MOD 4.0 thermal hydraulic system code. Riser length=78 inch, Pressure= 1Bar, Pitch to diameter = 1.4, SS Flow rate = 0.45kg/s, ΔH = −5 inch, Riser Diameter = 6 inch and power 37.0kw. Primary loop mass flow rate is 0.17kg/s (612kg/hr), analytical solution mass flow rate is 0.18kg/s, average error is 12.8% in computational solution. This error reduces as power increases with constant intervals. The RELAP5/MOD 4.0 results give good agreement with analytical solution.
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.
Investigations on the role of mixed convection and wall friction factor in single-phase natural circulation loop dynamics
Abstract The objective of the present paper is to present a 1-D model for simulating the startup from rest of water cooled single-phase natural circulation loops having horizontal heaters. The starting point of analysis is the inability of the 1-D codes to account for natural convection in the heater. Present 1-D models are unable to account for axial diffusion in the fluid caused by natural convection. Start-up from rest and many other characteristics cannot be simulated using classical 1-D models because of the inherent tendency of the predicted dynamics to be attracted by zero flow condition. The paper presents an elegant approach for taking into account both natural and forced convection. The enhancement of fluid motion and thermal mixing by natural convection is an important consideration in the design of nuclear reactors. Hence, the model developed is of direct relevance to nuclear reactor thermal hydraulics. The model developed for natural convection has been validated against the CFD simulations. The model developed has been incorporated in a classical 1-D model developed by the authors previously. The application of model to a rectangular single-phase natural circulation loop show that the model can predict the loop behavior from start-up with fidelity. The model reproduces most of the characteristics like unidirectional oscillation, bidirectional oscillations and chaotic switching reasonably well. Finally, model has been used to investigate the phenomenon of hysteresis observed in experimental loop. The paper also brings out the role of constitutive laws for wall friction in predicting the loop dynamics.