Research On Flow And Heat Transfer Of Supercritical Water In Natural Circulation Loop

Supercritical water reactor (SCWR) is the only pressurized water reactor chosen by the IAEA. It has many comprehensive advantages such as, economical efficiency, duration, sustainability and so on. It was proposed based on the design, construction and operation experiences of pressurized water reactor, boiling water reactor and supercritical fossil power plant. Supercritical water reactor (SCWR) uses supercritical water as the primary coolant. Its working pressure is 25MPa, and its core outlet coolant temperature is about 500℃. The study of natural circulation flow and heat transfer of supercritical water will have deep meaning for the remission of core accident and the design of core residual heat removal system of supercritical water reactor.First of all, the method of factorial analysis was introduced to study the influences of different factors and their coupled interactions on the supercritical natural circulation stability, mass flow and oscillation period. The results showed that, inlet resistance coefficient had the biggest influence percentage contribution rate, of about 70.89%, to the steady state mass flow. Then was the influence of interaction of heating zone length and inlet temperature, which contributed to about 13.26%. The next one was the heating zone length, and its percentage contribution rate was about 12.32%. As for the oscillation period, the heating zone length had the biggest influence percentage contribution rate, of about 68.47%. Then was the influence of inlet resistance coefficient, which contributed to approximately 24.04%. Based on the results of factorial analysis, throttle valve for the inlet and oulet of experimental facility of supercritical water could be installed to ensure the control of the inlet and outlet resistance coefficient during the design period. Furthermore, the heater could be blocked into three independent sections, making the length of the heating section adjustable. With the help of the results of factorial analysis and the inhome designed program EFDSCW1.0, the supercritical water natural circulation experimental facililty was designed and built. At the same time, the twin channel test section for forced circulation was designed as well, which laid the foundation for experimental section modification in future.Then,3-D simulation of supercritical water flow instability of the designed natural circulation loop and parallel channels were performed. The stability boundaries in the natural circulation system> together with the variation trend of oscillation amplitude and period with different thermal parameters were obtained. The mass flow of natural circulation would first grow with the heating power and then drop. The steady state mass flow changed little with the system pressure increasing. In case of asymmetrical heating in twin channel system, the oscillation amplitude increased, while the oscillation period decreased along with the increase of the extent of asymmetrical heating. The influence of the inlet temperature on flow oscillation was not monotonic. There exsited a threshold of inlet temperature, below which the system stability declined with the inlet temperature, and above which the stability increased with the inlet temperature. Moreover, the system stability would be enhaced when increasing the inlet mass flow.Then again, in ordor to study the flow instability deeply in supercritical water, the supercritical water experimental data from the existing references were introduced. The similarities and differences between supercritical water and two phase flow were studied. In channels with small size, the flow instabilities in both supercritical water and two phase flow were more likely to occure than in big channels. With the same inlet mass flow, system pressure and inlet temperature, if the heating power of the system was lifted gradually, there would be a threshold of heating power. If higher than the threshold, the system would become unstable. There were density and wave flow instability and flow excursion in both supercritical water and two phase flow. But the flow excursion seldom happened in parallel channels. The phenomenon that the existing of local instability would destroy the adjacement wall-film like layer periodically, which would enhance the heat transfer was discovered. Based on the open experimental data, a new friction coefficient model was proposed, which was superior to the existing models.At last, By means of the experimental analysis and the introduction of genetic neural network method, the heat transfer deterioration in supercritical water was analysed. The heat transfer deterioration phenomenon could be simulated very well by the genetic neural network in spite of lacking experimental data. Different from two phase flow, the heat transfer coefficient varied with time. The heat transfer coefficient of supercritical water would increase with the heating power, when reaching a peak vaule, it would drop suddenly, or would oscillate then drop. Heat transfer deterioration mechanism of supercritical water was found, that is, the existing of buoyancy would thicken the boundary layer, and the existing of the thermal acceleration would make the fow laminarization, and both of them would make heat transfer deterioration happen in advance. Besides, a novel model for supercritical water heat transfer was proposed as well. The new model agreed well with Chen’s experimental data and the errors falls in the margin of±20%.