Experimental investigation of the heat transfer characteristic and dynamic model development of supercritical boiler water-cooled wall under low-load

This study investigates the heat transfer characteristics of the water-cooled wall in a supercritical once-through boiler under low-load in deep peak-shaving. Conventional heat transfer correlations are developed from steady-state experimental data and often fail to accurately predict wall-temperature evolution under rapid variations, leading to significant deviations during transient processes. To address this issue, a 20° inclined straight tube was selected as the test section based on the structural of the water-cooled wall in supercritical boiler. The experimental ranges were P = 6-19 MPa, mass flux at G = 200-1600 kg m⁻²·s⁻¹, and heat flux at q = 0-350 kW m⁻². The effects of heat flux, pressure, and mass flux on steady-state heat transfer characteristics were first clarified, and the applicability of conventional heat transfer correlations under transient conditions was then evaluated. The results show that conventional steady-state correlations can reproduce the overall trend of wall-temperature variation, but fail to capture the local transient response during rapid mass-flux changes. Based on the experimental results, an empirical model was developed by introducing a history-dependent correction to the quasi-steady heat-transfer correlation. The correction represents the combined the effects of wall thermal storage, fluid-side relaxation, and transient heat-flux redistribution. The proposed model predicts wall temperature during transient processes with an error of less than 3%. After further optimization by incorporating a Reynolds-number-dependent response time, the predicted convective heat transfer coefficients are mainly distributed within the error band of −5% to +18%. The model predicts 2591 apparent- HTC data points with a MAPE of 3.81%, while all relative errors fall within −12% to +21%. The proposed model provides an effective method for transient wall-temperature prediction and offers useful support for the thermal safety assessment and flexible operation of supercritical once-through boilers under low-load conditions.