Research On Heat Transfer Characteristics Of New Spallation Target Working Medium

The goal of "emission peak and carbon neutrality" has provided great opportunities for the development of nuclear energy in China.However,while nuclear energy has brought many conveniences to the development of human society,it has also brought about a worldwide problem of rational and effective disposal of nuclear waste.Accelerator Driven subcritical System(ADS)is one of the effective solutions to the problem of nuclear waste disposal.As one of the coupling components in ADS,spallation target plays an important role in the safe operation and power level of the whole system.At present,particle flow target and liquid metal target are both candidates for China initiative Accelerator Driven System(Ci ADS)project.The two target materials can both generate spallation neutrons and act as cooling medium for conduction deposition heat.Based on the two new spallation target working medium—tungsten alloy particles and liquid lead-bismuth eutectic,the flow characteristics and heat transfer mechanism of the two new spallation target working medium in the heat exchanger were studied by combining numerical simulation and experimental verification.Firstly,the heat transfer mechanism of the working medium—tungsten alloy particles in the granular flow target was studied.After summarizing several contact heat transfer processes of dense phase particles,several independent heat transfer processes were combined to obtain the total thermal resistance of effective heat transfer process by comparing experimental and simulation results,and a contact heat transfer model of dense phase particles was proposed.The effective heat transfer coefficient of granular heat exchanger under different working conditions is obtained experimentally and compared with the calculated results of dense particle contact heat transfer model.The calculated results are in good agreement with the experimental results.Since the heat transfer performance of particles is closely related to its flow state,the flow field distribution of particles in the heat exchanger is experimentally studied,and it is found that the particles in the heat exchanger have two flow patterns:funnel flow and mass flow.A three-dimensional model of heat exchanger was established to explore the conditions of mass flow in the heat exchanger.It is found that a stable mass flow can be formed in the heat exchanger when the geometric parameters and material properties are within a certain limit range.The residence time model of particles in heat exchanger was proposed by considering the flow field and heat transfer mechanism.Considering the mass flow formation condition,effective heat transfer coefficient and residence time,the optimized design of 250 kW beam deposited heat granular flow heat exchanger was carried out.Secondly,the flow heat transfer of lead-bismuth eutectic in annular pipe was numerically simulated by combining three turbulence models and four different Prandtl number models.Compared with the experimental results,it is found that the combination of realizable k-ε and SST kω turbulence models and Cheng Prandt I number turbulence model has higher computational accuracy.SST kω turbulence model and Cheng Prandtl turbulence model were used to optimize the heat conduction oil channel and lead-bismuth eutectic flow channel in liquid lead bismuth/heat conduction oil heat exchanger.The change of inlet flow rate and inlet temperature of heat conduction oil and lead-bismuth eutectic will affect the heat transfer performance of heat exchanger.Based on the above calculation results,the liquid lead-bismuth heat exchanger with 250 kW beam deposition heat was also optimized.Finally,two kinds of spallation target working medium are compared and analyzed.The heat transfer of liquid lead-bismuth eutectic in the heat exchanger is mainly lead-bismuth eutectic convective heat transfer.The contact heat transfer between the particle and the wall is the most important contribution to the heat transfer of granular flow in the heat exchanger,and the granular heat transfer is also affected by the residence time.Comparing the heat transfer coefficient of two spallation target heat exchangers under the same heat transfer power condition,it is found that the heat transfer coefficient of the lead-bismuth eutectic heat exchanger are much larger than that of granular flow heat exchanger.That is,under the same heat transfer power condition,the size of lead-bismuth eutectic heat exchanger is smaller than that of granular heat exchanger,which has more advantages in the application compact target.