Critical heat flux of water in vertical annular channel with a short heated rod under low pressure and low flow conditions

An experimental study on critical heat flux (CHF) has been conducted in a vertical annulus channel with a short heated rod at low pressure and low flow conditions. The heated rod of the test section was made of Inconel-625 with a diameter of 37.2 mm and a heated length of 390 mm. The pressure, inlet temperature and mass flux were varied in the range of 103-170 kPa, 63 - 90celciusand 59.6-131.9 kg m2 s- 1. The CHF phenomenon was observed through the transparent quartz glass. It was found that the CHF positions firstly appeared in a small zone on the heated rod wall and the dry-out area would further expand if the power was not cut off immediately. The experimental results showed that most of CHF data were firstly detected at the upper thermocouple position near the outlet, while CHFs data were observed at lower positions with low mass flux. And based on Mishima and Ishii's flow regime map, the analysis of experimental flow regime indicated that most of the CHF occurred in slug-churn and churn-annular flow regimes. Finally, the measured CHF data were compared with the results predicted by four commonly used correlations and the method of CHF look-up table, and a new correlation was developed. It was found that the new correlation can be better predicting experimental data with an error within +/- 15%.

Automated summary

An experimental study on critical heat flux (CHF) in a vertical annulus channel revealed that CHF initially occurs in a small zone on the heated rod wall, and the dry-out area expands if power is not immediately cut off. The study also found that CHF is predominantly observed at the upper thermocouple position near the outlet, with lower CHFs observed at lower positions during low mass flux conditions.