A generalized flow correlation for two-phase natural circulation loops (original) (raw)
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Use of the Natural Circulation Flow Map for Natural Circulation Systems Evaluation
Science and Technology of Nuclear Installations
The aim of this paper is to collect and resume the work done to build and develop, at the University of Pisa, an engineering tool related to the natural circulation. After a brief description of the different loop flow regimes in single phase and two phase, the derivation of a suitable tool to judge the NC performance in a generic system is presented. Finally, an extensive comparison among the NC performance of various nuclear power plants having different design is done to show a practical application of the NC flow map.
Foundation of Computer Applications, 2019
A simple one dimensional numerical method is presented for the evaluation of the steady state behaviour of a two phase natural circulation loop. This method is applicable for loop consisting of two vertical limbs connected by point heat source and sink. In this work, Thermo-physical properties are considered as per the loop fluid state. The influence of following parameters such as heat input, inlet subcooling at heat source, loop diameter and height on the loop performance is analysed. Results show that mass flow rate increases with heat input. However, with the increase in heat input, mass flow rate increases initially up to a peak value and thereafter decreases. Also, the increase of loop diameter increases the mass flow rate for all heat inputs. However, increase of loop height has peculiar effect.
In this paper, semi-analytical and numerical models developed in our previous works to study the dynamic behaviour of natural convection are assessed against the experimental data obtained by means of the L2 Natural Circulation Loop (NCL) of DIME-Tec Labs (University of Genoa). As for the experimental campaign, reference is made to a set of nine experiments performed using water as working fluid and providing a thermal power of 2 kW. This set of data is firstly adopted for the validation of a semi-analytical linear analysis tool aimed at studying the asymptotic behaviour of NCLs through the definition of dimensionless stability maps. Then, two different numerical models (adopted in our previous work to confirm the linear analysis) are assessed, namely an Object-Oriented (O-O) one-dimensional model and a three-dimensional Computational Fluid Dynamics (CFD) model. In this regard, the O-O model represents a fast tool for the evaluation of the most important quantities, such as the velocity and the temperature fields in the loop along the axial coordinate. On the other hand, the CFD tool, which is intended as a support to the 1D analysis, is characterised by a high computational burden, but allows highlighting interesting 3D spatial effects. The validation of these tools is not secondary with respect to that of the stability maps. Actually, the numerical approach is fundamental to study the time-dependent behaviour of both stable and unstable natural circulation regimes, for which the stability maps do not provide information. As for the achieved results, the developed models are able to catch the behaviour of the experimental data. In particular, this outcome is possible if an accurate modelling of both the heat-exchanger section and the piping thermal inertia is considered.