| The sodium-cooled fast reactor is one of the reactor types with the most development potential and the most likely to be commercialized fourth-generation nuclear energy system.In nuclear reactors,the cooling of the core has always been a concern.Meanwhile,a highefficiency heat exchanger is required in a sodium-cooled fast reactor to transport heat in the primary and secondary circuits.The printed circuit board heat exchanger has the advantages of compactness,high efficiency,high temperature and high pressure resistance,etc.,and meets the requirements of being an intermediate heat exchanger in a nuclear reactor.Liquid sodium metal has become one of the most popular coolants in high-temperature reactors because of its high thermal conductivity and high heat-carrying capacity.However,at the same time,because liquid metal sodium is very easy to react with water and oxygen that results in explosion,it is difficult to ensure the safety in experimental research.Therefore,this paper uses numerical simulation to study liquid metal sodium under different operating parameters and structural parameters.Based on the flow heat transfer characteristics in the rectangular channel,a high-precision flow heat transfer criterion formula was developed,which has reference significance for the design of the intermediate heat exchanger of the sodium-cooled fast reactor.In this paper,a three-dimensional steady-state numerical simulation method is established based on the FLUENT platform.By comparing with the experimental data,the reliability of the numerical method is verified,so that the turbulent Prandtl number model and SST turbulence model proposed by Jischa are used in the research.The calculation accuracy of the numerical method is the highest,and the relative error between the simulation results and the experiment is less than 5%,which meets the actual engineering requirements.Based on the above numerical methods,the effect of operating parameters on the flow and heat transfer of liquid metal sodium in straight rectangular microchannels was studied.The results show that the heat transfer capacity is stronger and the flow performance is weaker at high flow rate and low temperature.Compared with temperature,the effect of wall heat flux density is small and can be ignored.In comparing with straight rectangular microchannels,the sawtooth microchannels are staggered to the left or right at certain distances.The channel can enhance the heat transfer performance of the fluid by destroying the fluid boundary layer,but it also increases the flow loss.When studying the flow and heat transfer of liquid metal sodium in the sawtooth microchannel,the structure of the sawtooth microchannel was firstly optimized,and it was concluded that the channel with a pitch length of 80 mm had the bestflow heat transfer performance.Using this optimal structure,the effect of operating parameters on the flow and heat transfer characteristics of liquid sodium metal in the sawtooth microchannel was investigated,and the simulation results of the sawtooth microchannel and the straight rectangular microchannel were compared.The results show that the heat transfer coefficient of the straight rectangular microchannel is about 7% lower than that of the sawtooth microchannel,but the pressure drop is only about 50% of that of the sawtooth microchannel.As the flow rate increase,the difference in pressure drop is enlarge,while the change of the heat transfer coefficient is relatively stable.so in the heat exchanger with the sawtooth microchannel,the flow rate should be reduced as much as possible.Finally,based on the simulation results in this paper,the applicability of the criterion formula in the literature is analyzed.The analysis results show that none of the existing flow heat transfer criteria in the literature can accurately predict the flow and heat transfer characteristics of liquid metal sodium in straight rectangular microchannels and sawtooth microchannels.For the flow heat transfer criterion formulas in the straight rectangular microchannel and the sawtooth microchannel that proposed based on the simulation work or this paper,their error are controlled within ±3%,and the prediction accuracy is high. |
