Analysis of Grashof Number in Large-Scale Passive Cooling Systems Based on Temperature Changes

This study investigates the Grashof number calculation in large-scale passive cooling systems, focusing on temperature-induced changes. The research utilizes the FASSIP-02 test loop, a second-generation facility for passive cooling systems, to analyze natural circulation flow. Experiments were conducted by heating a Water Heating Tank (WHT) to various temperatures (50-90°C) and maintaining steady-state conditions for five hours. Flow rates and Reynolds numbers were measured and calculated, revealing a turbulent flow regime across all temperature settings. The Grashof number was then calculated and correlated with the Reynolds number to establish a relationship specific to the FASSIP-02 test loop. Results showed Grashof numbers ranging from 4.93 x 1012 to 1.64 x 1013, confirming turbulent flow. The correlation between Reynolds and Grashof numbers was determined to be Re = 0.1356(Grm/NG) 0.31, with R² = 0.9952. This correlation closely aligns with previous research on turbulent flow in natural circulation systems, with slight variations attributed to differences in measurement precision. The study contributes to understanding passive cooling system behavior in nuclear reactors, particularly for residual heat removal during accidents or shutdowns.