Research Of Vapor-liquid Two-phase Flow With Dirt Blockage Effect Inside Channel With Grids

The reactor core is the key equipment of the first loop in PWR nuclear power plant, which provides energy for the whole reactor system. Fuel assembly is the main component of the core, flowing field characteristics of fuel assembly is very important for its structure design. Due to the complexity of test technology measuring the flow field of fuel assembly, the CFD method has now been widely used to study its flow field characteristics.ANSYS software was applied to study of vapour-liquid two phase flow and heat transfer characteristics in a quarter of channel with dirt blockage. Through the establishment of the 3D numerical model for a quarter of the fuel bundle, the effect of different thickness and thermal conductivity of dirt layers in the channel have been analyzed. Data have obtained about the distributions of the temperature along the channel, buld temperature outside of the tube, the void fraction of the vapour and liquid, heat transfer coefficient of the tube. The structured grid method proposed in this paper, can not only be used in the fuel assembly with local structure and whole structure, but also can be applied to tube channel and rod channel to greatly improve CFD solution’s speed and precision of flow in the complicated fuel bundle. The research results obtained from the three types of fuel assembly including 3-D flow domain and turbulence characteristics can be used as guidance for safe and steady operation of the reactor, and be useful for the structure design of the grid spacer, design of the the thermal-hydraulic. Main contents and conclusions are as follows:1. The scientific and validation of the research method have been analyzed. Especially comparison of experiments done in the industry have been made to verify the applicability and scientificity of the numerical simulation method used in this dissertation, including the choice of the heat transfer model, the energy equation and momentum equation.2. Hexahedral structured grid was generated to verify the grid independent solution, and the reliability of numerical simulation. By comparing the influence of different gridnumber on results under the same working conditions, the same channel, the same parameters, it is concluded the grid independent solution, namely the optimal grid number is around 1.3million.3. Different dirt thermal conductivity with same thickness effect on the vapour void fraction, the bulk temperature, the coefficient of heat transfer of wall were studied.4. Results obtained about different thickness of the dirt layer with same dirt thermal conductivity influence on the gas void fraction, the bulk wall temperature, the wall thermal conductivity.The results show that the heat flux of this study does not reach the critical heat flux, and the phenomenon of evaporation to dryness did not appear. With the increase of the dirt thickness, the heat transfer coefficient of the wall is rapidly decreased, and at the same time, the surface temperature of the shell increased dramatically.