Dryout quality prediction in helical coils based on non-uniform liquid film thickness distribution: A model study

Abstract

Dryout occurrence has an adverse effect on the thermal efficiency of helically coiled steam generators used in thermal energy storage systems. In this study, a mechanistic model based on the non-uniform annular liquid film thickness distribution was developed to evaluate the quality of dryout occurrence in helical coils. The inner-side and outer-side liquid films were investigated, including the local effects of entrainment, deposition, and dryout, while the film interface profile in the tube cross-section was simplified as a half-ellipse. The deposition correlations reported in the literature were modified by considering the centrifugal effect. The entrainment correlations were compared and optimized to improve the dryout prediction. The proposed model achieved satisfactory agreement on a boiling crisis dataset of 994 test points with a mean absolute error of 35.2%, which is better than existing models. The current work can be used in thermohydraulic design and performance prediction for thermal energy storage systems.