Boiling instabilities in helical coil steam generator

Abstract

Helically coiled steam generator is an essential part of current generation small modular reactors like NuScale due to its compactness and high heat transfer area. Instabilities due to boiling water inside helically coiled tubes is an important research question due to its importance for the steady-state operation of the plant. This study presents an experimental investigation of two-phase boiling instabilities inside helically coiled tubes. Four experiments were carried out with different thermal power, mass flow rate, and pressure to understand flow behaviour under different system conditions. It is found that thermal oscillation inside the tube increases with the power step and tube length while decreasing with the mass flow rate. The thermal oscillation period also increases with a higher power step. A semi-empirical correlation based on experimental data is developed. The overall heat transfer coefficient is calculated theoretically using the Chen correlation and later compared with the experimental value. Both experimental and theoretical value of the heat transfer coefficient agrees well.