Numerical Investigation On Thermal-hydraulic Of Steam Generator Based On Two-fluid Model

Steam generator is a critical heat exchanger between the primary and secondary loop inthe pressurized water reactor nuclear power plant. It’s essential for refining the planttechnology to improve steam generator thermal-hydraulic characteristic. Porous model isgenerally used by most researchers to investigate thermodynamic and hydrodynamicperformance of steam generator. Internal heat sources and thermal boundary conditions aretreated as U-tubes in the model, ignoring turbulent transfer and heat conduction among tubebundles, which can not actually reveal the coupled flow and heat transfer process of primaryand secondary sides in the steam generator. Therefore, thermal-hydraulic characteristic withina full-scale steam generator is numerically investigated by using CFD methodology.According to operating parameters and structure of steam generator at Daya BayNuclear Power Plant, a three-dimensional unit cell model is established under the guidance ofthe similarity principle. Coupled heat transfer and flow between primary and secondary sidesis calculated through two-fluid model, thermal phase change model is employed to describevapor-liquid two-phase flow boiling behavior, and MUSIG model is utilized to predict bubblyflows. CFD investigation of steady-state thermal-hydraulic characteristic for steam generatoris consequently carried out. The simulation reveals key parameter distributions underoperating conditions and structural parameters, such as steam quality, heat transfer coefficient,inner and outer wall temperature, primary and secondary pressure, etc. With the aid of thesethermal-hydraulic characteristics, fluid energy across the U-bend tubes is obtained, which isstrongly associated with fluid-induced vibration. Meanwhile, the influence of tube supportplates on thermal-hydraulic characteristic is revealed by calculating unite cell model coupledwith quatrefoil-shaped tube support plates.The calculated results show that nonuniform boiling phenomena within the cold leg andhot leg of steam generator is captured reasonably and slip ratio of vapor and liquid increasesquickly in preheating region and then decreases slowly in boiling region. The averaged heattransfer coefficient agrees well with results calculated using Rohsenow’s correlation. Basedon the flow energy distributions, fluid-induced vibration damage is predicted to be mostsevere at angles of θ=60°on the cold-leg side and θ=115°on the hot-leg side of U-bend tubes region. The tube support plates guide flow structure, which results in recirculationdistribution and the generation of local vortex in these regions. These elements can enhancethe concentration of aggressive solutes or impurities around the tube support plates. Thecircumferential dependence of outer wall temperature shows a periodic characteristic at thetube support plates. The corresponding temperature difference between the support locationand flow hole gradually decays in the primary flow direction. According to comparison offluid energy calculated by the models with and without tube support plates, fluid-inducedvibration isn’t influenced significantly by adding supports. MUSIG model, with regard to thecoalescence and break-up of bubbles, reveals the periodic distribution from small to largebubble diameter between adjacent tube support plates. The CFD methodology can providetechnical support for structural design and thermal-hydraulic analysis of steam generator.