Effect Of Proportion Of Helium-xenon Mixtures On The Flow And Heat Transfer Tharacteristics In The Coolant Channel Of Reactor

The gas-cooled reactor combined with the closed Brayton cycle has wide application prospects in exploration of deep space and sea.Helium-xenon mixtures is often used as coolants in gas-cooled reactors for good flow and heat transfer performance and compression performance.The change of the proportion of helium-xenon mixed gas has a great influence on its flow heat exchange performance,thus affecting the core thermal efficiency and safety margin.However,there are many studies on the compressibility of the helium-xenon mixed gas,and most of the research on the flow heat transfer performance is theoretically derived.The influence of the change of the helium-xenon mixing ratio on the flow heat transfer characteristics of the core is less.Therefore,in this paper,the helium-xenon mixtures with different proportions is used as coolants to study the effects of the proportions on the flow and heat transfer in the core and clarify the principle and rules and point out whether the rules are already applicable when the external parameters such as velocity and temperature change to provide mechanism support for optimal design of gas-cooled reactor.First of all,based on the energy conservation,momentum conservation and conservation of quality equations,different coolant channels was modeled with STAR-CCM+ and set up the appropriate physical models,then the models were verified and contrasted,finally the separation flow model combined to realizable K-Epsilon turbulent flow model were selected to simulation.Based on the Prometheus planned gas-cooled reactor annular coolant channel and the geometric model and parameters,the flow and heat transfer characteristics of the single coolant channel and the 1/6 core coolant channel under different mixing ratios of helium and xenon are studied.Secondly,the annular coolant channel was selected for specific exploration.Keep main parameters stationary and change the proportion of helium-xenon mixtures to study the flow heat transfer principle and rules,then draw the conclusion that the proportion of helium-xenon mixtures mainly affects its properties of matter next affects the heat transfer performance.Combined with actual analysis,the inlet velocity range was set up 10-30m/s and the temperature change range is 911-1288 K.The effect of parameter changes on the obtained law in this range is analyzed.The results show that changes in speed,temperature and other parameters will cause changes in the density and dynamic viscosity of the helium-xenon mixed gas,which will affect its flow heat transfer characteristics and optimal ratio;within the limits of the inlet speed and temperature,that is,the Reynolds number below 50,000,the convective heat transfer coefficient of the helium-xenon gas mixture increases with the increase of the Reynolds number,the optimal molar mass of the helium-xenon gas mixture decreases with the increase of the Reynolds number,and the optimal molar mass varies from15.0-20.2 g/mol.Then it is pointed out that under the two heating boundaries of volumetric heat release rate and heat flow,the flow and heat transfer characteristics of the helium-xenon mixed gas vary basically with the Reynolds number,but the optimal molar mass varies with the Reynolds number.When the heat flow is the boundary,The change range is 15.0-25.1g/mol,when the volumetric heat release rate is the boundary,the range is 15.0-20.2 g/mol.In addition,it has been clarified that the optimal molar mass of the helium-xenon mixed gas is consistent at 15.0 g/mol under the conditions of different internal channel structures such as rings,circles,and rod bundles.Finally,the 1/6 core of the annular channel is modeled,and the parameters in the range of the front and rear ends of the fuel rod are selected for analysis.The mechanism and law of the influence of the mixing ratio of helium and xenon on the core flow heat transfer are clarified.The similarities and differences of the rules in the single tube point out that due to the flow distribution of the core and cavity vortex mixing,the flow heat exchange process of the helium-xenon mixed gas is more complicated,and the change of the mixed gas ratio affects the core flow heat transfer characteristics.The influence is greater than that of a single tube,and the optimal molar mass is also different from that of a single tube.When the Reynolds number is below 50,000,the optimal molar mass of the core varies from 15.0 to31.5 g/mol,covering the range of a single tube.These conclusions provide references for the selection of coolant parameters in the space reactor with the closed Brayton cycle.