Single-phase density wave oscillation -A new phenomenon of flow instability in inverted U-Type Steam Generator

Abstract

Due to the symmetric geometry of inverted U-Type Steam Generator (UTSG), gravity pressure drop can play a significant role of the total pressure drop under low flow condition, which makes it possible for single-phase flow instability (FI) to take place. Most existing studies on single-phase FI in UTSG are related with flow reversal, a type of static FI. In this paper, flow instability in a three-U-tube UTSG simulator test section was studied experimentally, and distinct oscillation of different parameters was found under single-phase condition. The oscillation characteristics of different parameters, the oscillation stability boundary and period were researched based on the experiment data. The results showed that the oscillation was a type of inter-tube oscillation dominated by the short tube, and its period has the properties of Density Wave Oscillation (DWO). Effects of different parameters on oscillation characteristics were also studied. It was found that the oscillation stability boundary could be highly influenced by primary inlet temperature, but may be independent on operation process, local loop resistance, and effects of cooling mass flow may be not large, while the oscillation period could be highly related with primary inlet temperature and cooling mass flow. Additionally, two non-dimensional parameters were proposed to predict the stability boundary, and the most data could be well predicted within an error of 10%.