Accurate predictions of steam generator bundles using new heat transfer correlations and flow regime maps
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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 11°C (20°F), whereas plant values range from 22-30°C (40-60°F). 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.
author list (cited authors)
Blanchat, T., & Hassan, Y.