Fouling deposition and its impact on heat transfer performance in the helical coil once-through steam generator

The flow and heat transfer within a helical coil once-through steam generator (HCOTSG) are highly complex, and the long-term deposition of corrosion products can significantly impair its heat transfer performance. Therefore, the coupled analysis of fouling deposition and thermal-hydraulic characteristics is critical for the design, operation, maintenance, and cleaning optimization of HCOTSG. In this study, a fouling deposition model and a fouling thermal resistance model were developed to describe the transport, adhesion, and removal of impurities in single-phase and two-phase flows, and a multi-scale coupled analysis approach was proposed. The accuracy of the model was validated against the magnetite deposition experiments of Basset and Turner. Coupled analyses were performed for a typical HCOTSG, revealing that fouling in the saturated boiling region was substantially higher than in single-phase regions. After three years of operation, the deposited mass in the 0.9-3.0 m height region accounted for 85.6%, with the first-year deposition contributing 73.6% of the total. The fouling-induced thermal resistance was found to reduce heat transfer and result in a downstream shift of the dryout point. After three years of operation, the total heat transfer decreased by 3.26%, the outlet steam quality dropped from 1.10 to 1.05, and the inlet-to-outlet pressure drop decreased by 5.9%.