Accurate predictions of steam generator bundles using new heat transfer correlations and flow regime maps

A RELAP5/MOD2 computer code model for a Once Through Steam Generator has been developed. Parametric studies were conducted on aspirator placement, code-allowed junction geometry options, tube heat structure surface area, tube hydraulic diameter, and feedwater temperature. The calculated heat transfer in the nucleate boiling flow was underpredicted as shown by a predicted superheat of only 11C (20F), whereas plant values range from 22-30C (40-60F). Existing heat transfer correlations used in thermal-hydraulic computer codes do not provide accurate predictions of the measurement-derived secondary convective heat transfer coefficients for steam generators because they were developed for flow inside tubes, not tube bundles. A new flow regime map for flow across bundles has been developed and implemented in the code. This new flow regime map predicts better transition criteria between bubbly-to-slug and slug-to-annular flow. Consequently, improved saturated conditions for the fluid flow at the entrance to the boiler were obtained. A new Chen-type correlation was developed to predict the boiling heat transfer for steam generator tube bundle geometries. This new correlation predicts better superheat.

Accurate predictions of steam generator bundles using new heat transfer correlations and flow regime maps Conference Paper