Study On Water Bubble Characteristics In Leadbismuth Reactor Based On MPS Method

The PBWFR(Pb-Bi-cooled direct contact boiling water fast reactor)reactor feeds subcooled water into a lead-bismuth alloy coolant through a feedwater pump to remove heat from the core,accompanied by intense flow heat transfer.In engineering,volume heat transfer coefficient and interface heat transfer coefficient are usually used to reflect the heat transfer level,but the volume heat transfer coefficient is not universal.The interfacial heat transfer coefficient can accurately reflect the heat transfer capacity,but the measurement of the contact surface area of water or steam bubbles and lead-bismuth alloys has always been a factor restricting its development.The Moving Particles Semi-implicit Method(MPS)method can effectively track the deformation problem of the flow interface and has wide application in the nuclear energy field.This paper will use this advanced numerical simulation method to study the flow and heat transfer characteristics of water bubble interface in PBWFR reactor.This paper first gives a systematic overview of the research status of direct contact flow heat transfer between lead-bismuth alloys and water,the application and development status of MPS methods.This article uses Fortran language to develop MPS programs,adds new modified models(ADM,ECS)on the basis of traditional MPS methods,uses higher-order models(HL,FDZ),polyphase Poisson equations and Contour Continuum Surface Tension model(CCSF).This makes it possible to handle multiphase interface flow problems with large density ratios and large viscosity ratios.Secondly,the two-phase Poisson flow and square droplet deformation verify the correctness of the viscosity model and surface tension model of the improved MPS program;on this basis,the rise of bubbles in water is simulated,and a small single bubble rise experiment is carried out,the simulation results are compared with the experimental results to verify that the program can better simulate the bubble rise motion;it is further verified that the program can effectively simulate the interface deformation problem based on the dimensionless criterion in the literature.This program is used to numerically simulate the free rising process of water bubbles in the PBWFR reactor.The water bubble displacement,flow velocity,shape change,velocity field,contact perimeter,heat exchange power and interface heat transfer coefficient are studied and analyzed.The interface recognition model performs accurate calculations.The results show that water bubbles in the lead-bismuth alloy change from spherical to horseshoe-shaped during the ascent process,and then split.The contact perimeter varies greatly,and the peak time of the contact perimeter lags behind the speed peak time during the entire process.Numerical simulations of water bubbles and steam bubbles in lead-bismuth alloys under different pressures are performed.The results show that the steam bubble is oblate in the rising process,and no sub-bubble splitting occurs,mainly due to the influence of surface tension.The interface heat transfer coefficients of water bubbles and lead-bismuth alloys are similar at atmospheric pressure and 7 MPa,but the interface heat-transfer coefficients of steam bubbles and leadbismuth alloys at different pressures are quite different.Finally,this paper compares the effects of different wall effects,bubble diameters,and initial bubble velocities on the flow and heat transfer of water bubbles in lead-bismuth alloys,and summaries and analyzes the changes of flow velocity,shape,contact perimeter,heat transfer power,and interface heat transfer coefficient under different influencing factors.And use this program to simulate the double bubble fusion,repulsion phenomenon and the dynamic characteristics of the bubble group.