Numerical Simulation Of Flow And Heat Transfer Characteristics In Helical Cruciform Fuel Rod Bundles

In recent years,the use of nuclear energy has received increasing attention,and the proportion of total nuclear power generation in total power generation has increased year by year.In order to meet the needs of the rapid development of society,nuclear reactors are also facing the problem of optimal design and replacement.The development of new high-performance nuclear fuel is an important research direction to improve the thermal and hydraulic performance of the reactor.Among them,the design of spiral fuel rods to improve the geometry of nuclear fuel rod bundles has great potential.At present,the computational fluid dynamics method is helpful for the research on the thermal hydraulic characteristics of spiral fuel rods,and there are few studies on the influence of structural parameters and operating parameters on the flow and heat transfer characteristics of coolant in the rod bundle channel.The flow heat transfer empirical relationship(Fanning factor and Nusselt number)is basically blank.Therefore,based on the different fuel assemblies composed of spiral fuel rods,this paper explores the influence of structural parameters and operating parameters on the flow and heat transfer characteristics,and develops a flow heat transfer empirical relationship suitable for spiral fuel rods.First of all,in this paper,on the premise of keeping the fuel rod charging volume equal,the complex cross-sectional shape of the spiral fuel rod is split into several parts composed of simple geometric elements such as arcs and straight lines,according to the geometry Through mathematical derivation,the value range of each part is obtained,from which a complete set of spiral fuel rod structure size design criteria is obtained,and its correctness and reliability are verified.Secondly,using the SST k-? turbulence model,the influence of the four structural parameters of transition radius RE,pitch h,arrangement of rod bundle and petal petal number on the flow heat transfer characteristics of the fuel assembly was studied.Quantitative comparison of coefficients and qualitative analysis of velocity field and temperature field determine the structural parameters with the best comprehensive performance of flow and heat transfer within the scope of this paper: RE=3mm,100 cm pitch,quadrangular spiral type with the first arrangement Fuel rod.Then,the effects of the three operating parameters of coolant inlet speed,operating pressure and coolant inlet temperature on the flow and heat transfer characteristics of the fuel assembly were studied.High flow rate will cause an increase in pressure drop,but at the same time it will greatly improve the heat transfer performance.Therefore,it has good comprehensive performance;under the condition that the inlet mass flow rate is equal,low operating pressure and high inlet temperature can improve the overallperformance.Finally,this paper compares the numerical simulation calculation results with the predicted values of the existing flow heat transfer empirical relationship in the literature,and points out that due to the large differences in the coolant thermal properties and fuel rod structural parameters,the existing empirical relationship has been It cannot be used to predict the flow and heat exchange in spiral fuel bundles.Further,based on the database of numerical simulation in this paper,an empirical relationship formula with high accuracy suitable for spiral fuel rods is developed.The maximum error between the predicted value of the Fanning factor,the Nusselt number relationship formula and the numerical calculation result are all Control within 5%,with high prediction accuracy.