Numerical investigations on effects of gravity and heat sink temperature on dynamic behaviour and stability of single-phase natural circulation loop

This numerical study aims at resolution of flow pattern and stability in single-phase natural circulation in rectangular loops of different inclination and varying heat sink temperatures and comparison of these simulation results with those of experiments performed on L-2 facility at Genoa. Two sizes of NCL were experimentally analyzed at Genoa: large-scale and mini-scale loops. The experimental apparatus (Loop-2, 'L2') consists of a rectangular loop where the heater is placed at the bottom and the cooler on the top of the loop. The Loop-2 is the third NCL realized at DIPTEM labs. The study on the large-scale loop (Loop-2, 'L2') was focused on the effect of the cooler temperature and loop inclination on the stability of the loop. The loop inclination was investigated with the purpose of simulating reduced gravity by decreasing the height between the top and the bottom of the loop, and consequently the buoyancy forces acting on the fluid. The objective of this study is to simulate Genoa L-2 loop using numerical code RELAP5/ MOD3.2 and analyse the effect of three independent parameters; power, heat sink temperature and loop inclination angle on the stability and dynamic behaviour of natural circulation loop. The simulation results from this study are compared with experimental results and behaviour of the loop is tabulated with regard to stable and unstable behaviour. This analysis reveals that the simulation results are in good agreement with experimental results at low heat sink temperature and at lower power while deviates slightly from the same at higher power or high heat sink temperature. (author)