Modeling and Simulation on Wall Evaporating Heating Surface in Supercritical Once-through Boiler

Within the range of pressures from 9 to 28MPa, mass velocities from 600 to 1200kg/(m2.$), and heat fluxes from 200 to 500kW/m2. Based on the paper [4], it was found that the heat transfer to water in the inclined upward internally ribbed tube with the inclined angle of 19.5 degree, the maximum outer diameter of 38.1 mm, and the thickness of 7.5mm: heat transfer enhancement of the internally ribbed tube could postpone departure from nucleate boiling at the sub-critical pressure. At supercritical pressure, the temperature difference between the wall and fluid increased near the pseudo-critical temperature. When pressure was close to the critical pressure, the temperature difference between the wall and fluid greatly increased near the pseudo-critical temperature. Heat transfer to supercritical water in the inclined upward internally ribbed tube was enhanced or deteriorated near the pseudo-critical temperature with the variety of ratio between the mass velocity and the heat flux. Based on the basic equation of the energetic processes, this paper establishes lumped parameter dynamic model which is appropriate for simulation of Wall Evaporating Heating Surface in DG-1900/25.4 supercritical once-through boiler. A simplified model of linear lumped parameter is built, which is fit for small disturbance simulation in rated condition. The transfer function for rated condition is developed. The influence of major boiler control variables (fuel input,feed-water valve) on dynamic characteristics is studied. The proposed model well reflects dynamic characteristics of wall evaporating heating surface in supercritical once-through boiler in rated condition, and the outcomes have certain value for the research on supercritical unit controllers.