A Semi-Empirical Correlation for the Onset of Density Wave Oscillations in a Helical Coil Steam Generator

Abstract

NuScale Power has completed a series of full-length helical coil steam generator tests at SIET Laboratories in Piacenza, Italy. The test program included an investigation of the onset and evolution of density wave oscillations (DWOs). This paper describes the mechanisms leading to the onset of DWOs. A semi-empirical DWO stability correlation was developed from first principles using data from tests performed in the full-height (2015) TF-2 counterflow test facility. This research supports the concept that the onset of DWOs is caused by liquid bridging inside the boiling length of the tubes. A DWO onset correlation is obtained by performing a steady-state momentum balance on the liquid slug created by liquid bridging in annular flow. This yields a momentum balance equation in terms of a set of dimensionless superficial velocities, a corresponding dimensionless pressure drop term, and an average void fraction. Envelope theory is then used to obtain a critical void fraction, which is substituted into the dimensionless momentum balance to obtain a DWO onset correlation similar to the Wallis countercurrent flooding correlation. Predictions using the DWO stability correlation have been compared to DWO experiments from the (2022) TF-2, TF-1, and Polimi. The predictions for the onset and termination of DWOs show excellent agreement with the data.

Keywords:

• Density wave oscillations
• helical coil steam generator
• envelope theory

Acknowledgments

The author gratefully acknowledges the expert testing team at SIET Laboratory in Piacenza, Italy, and the NuScale testing and code assessment experts for their valuable insights.

Disclosure Statement

No potential conflict of interest was reported by the author.

Additional information

Funding

This work was sponsored by NuScale Power.