机翼型微通道高效紧凑换热器流动换热特性

超临界二氧化碳（S-CO₂）布雷顿循环系统是第4代反应堆采用的新型高效热能转化系统,系统采用微通道高效紧凑换热器作为高低温回热器,其流动换热特性对整体系统热能转化效率有着显著影响。本文采用数值模拟方法,以S-CO₂为流动工质,建立机翼型翼片结构的换热器模型,研究翼片的不同间距对流动换热性能的影响。研究结果表明,交错排列翼片的综合流动换热性能优于翼片并排布置,翼片交错间距为左右间距一半时,增加左右间距,换热器流动换热性能更好。将机翼型微通道换热器与折线型微通道换热器模拟结果进行对比分析表明,机翼型微通道换热器在压降仅为折线型微通道换热器54.174%的情况下,换热性能提升了25.67%。     

熔盐堆超临界二氧化碳布雷顿循环系统与热力学分析

熔盐堆（MSR）能实现在线填料和后处理,出口温度较高,应配备一种与之出口温度相匹配的创新型循环方式,且可达到较高的循环效率。本文基于中国科学院上海应用物理研究所设计的小型模块化熔盐堆（smTMSR-400）设计超临界二氧化碳（SCO₂）布雷顿循环系统,使用控制变量法分析了分流比、压缩机/透平效率、主压缩机出口温度、低温换热器换热温差/阻力对SCO₂布雷顿循环系统的影响。分析结果表明:①存在最佳分流比使低温换热器两侧温差相等;②相较于压缩机效率,等幅度的透平效率提升可使系统循环效率和?效率更高;③主压缩机出口压力增大为系统带来正面影响,但循环效率/?效率与其斜率都逐渐降低;④换热器换热温差和流动阻力都为系统循环带来了可量化的负担: 换热温差每增加10 K,循环效率降低1.85%,?效率降低2.70%;流动阻力每增加1 MPa,循环效率降低6.58%,?效率降低10.22%。最后根据分析结果和系统?流变化设计了5种物理参考方案。      

超临界二氧化碳在印刷电路板式换热器内的流动换热特性研究

印刷电路板式换热器（PCHE）是一种微通道换热器，具有换热效率高、耐高温、耐高压等优势，可广泛应用于海洋工程、核能、光热发电等领域。本文采用数值模拟的方法，计算了跨拟临界点超临界二氧化碳（SCO₂）在印刷电路板式换热器内的流动换热特性。结果表明：SCO₂流体温度达到拟临界温度时，流通截面内流体温度分布最均匀，因为此时流体的有效导热系数最大；SCO₂侧对流换热热阻在总热阻中占比最大，其次为导热热阻，水侧对流换热热阻最小；采用等效厚度法计算得到的导热热阻偏大；雷诺数越大，在拟临界温度附近换热强化的程度越大。     

超临界二氧化碳动力循环在钠冷快堆中的应用综述

超临界二氧化碳循环系统在气冷快堆、铅冷快堆、钠冷快堆中极具应用前景。综述了应用于钠冷快堆的超临界二氧化碳动力循环系统及其样机关键部件研究现状和有关进展,结合钠冷快堆的热源特征,分别就典型超临界二氧化碳动力循环结构、印刷电路板式换热器换热特征系数、不同功率等级S-CO_2压缩机与透平类型选择以及轴承与密封关键特征进行了总结与分析,分析结果为后续开展适用于钠冷快堆的S-CO_2布雷顿循环设计及样机开发提供可借鉴的参考与依据。     

高温氦氙气体微通道回热器的传热流动特性分析

以氦氙气体作为工质的闭式布雷顿循环系统是大功率空间热电转换目前最可行的技术方案。高温氦氙气体回热器是闭式布雷顿循环系统的关键部件,其性能明显影响系统发电效率、系统发射质量以及系统布置的紧凑性。本文采用计算流体力学和传统理论分析方法,针对高温氦氙气体微通道的结构及成型工艺选择、工作温度与回热器回热度的关系、流量与性能参数的关系等进行了研究。研究结果表明,采用精雕工艺作为微通道的成型工艺可在不降低回热器换热性能的前提下降低压降40%,减少质量17%。在设计参数条件下,微通道之间设置联通通道不会增加换热能力。回热器回热度随流量的增加而减小,且存在拐点,对于拟研制回热器的设计参数,设计流量应不高于0.24 g/s。回热器结构合理性用单位压降和温降条件下换热面积与功率的比值来判断,降低雷诺数能有效提高回热器的结构合理性。     

双D形流道内超临界二氧化碳传热特性数值研究

对简单双D形流道内超临界二氧化碳传热特性进行数值研究。重点研究了热流体质量流速对换热功率和换热效能的影响,以及热流道失流工况对传热特性的影响。研究表明:随着热流体质量流速增加,换热器换热功率增加,换热器换热效能降低;换热器的换热能力受冷热流体温差驱动,热流体失流时换热器换热能力下降,壁面温度降低,与定热流密度传热存在一定差异。     

带定位格架的类三角形子通道内超临界水流动传热数值研究

针对超临界反应堆类三角形子通道的传热和流动特性,数值研究了不同栅距比定位格架作用下子通道内超临界水的流动传热特性、二次流及流动阻力特性。研究结果表明:定位格架对子通道内超临界水的换热影响显著;不同栅距比下的壁面温度、换热系数的轴向分布都具有相同的趋势,定位格架附近壁面温度下降,换热系数上升;定位格架下游壁面温度分布不均匀,且不均匀程度随栅距比减小而更加明显;定位格架下游截面形成四个对称旋涡,栅距比较小时,二次流强度较大;不同栅距比堆芯子通道流动阻塞率不同,流动阻力随栅距比减小而增大。     

超临界二氧化碳再压缩布雷顿循环变工况特性分析

超临界二氧化碳再压缩布雷顿循环是高效紧凑的能量转换方式。目前许多研究在分析循环的特性时,常假设压缩机和透平的效率为恒定,该假设与实际情况差别很大。本文使用MODELICA作为工具,建立了超临界二氧化碳再压缩布雷顿循环模型。对于压缩机和透平,加入了真实压缩机和透平的特性曲线模型。通过模拟计算发现,循环输入功率和循环流量的改变将对循环火用效率和各组件的火用损产生影响。循环偏离设计工况时,适当控制输入功率和循环流量可调节循环输出功率和火用效率。     

EAST阻性换热器多物理场耦合模拟计算

阻性换热器是EAST高温超导(HTS)电流引线的重要组成部分,目前有三头螺旋翅片和叠片两种结构形式,为了比较这两种阻性换热器的优劣,对它们的热工水力性能进行了多物理场耦合模拟计算,计算结果表明:两种阻性换热器在换热性能方面基本相当,均可满足快速换热的要求,但叠片换热器的流动阻力远小于三头螺旋翅片换热器的。实际运行过程中,三头螺旋翅片换热器中氮冷却回路的压力控制较为困难,经常需人工调节控制阀阀门,而叠片换热器中氮冷却回路的压力控制则较为简单,不需经常调节。因此,叠片式结构较三头螺旋翅片式结构更适合应用在EAST阻性换热器中。     

自然循环与强迫循环条件下阻力及换热特性对比

为研究自然循环和强迫循环条件下流动及换热特性的区别,以单面加热窄矩形通道为研究对象,在压力0.2 MPa、实验段入口欠热度30~60℃的条件下,分别进行了强迫循环和自然循环条件下流动及换热实验。等热流密度条件下的阻力实验研究表明:在层流区,强迫循环和自然循环条件下的阻力特性几乎相同;在湍流区,修正后的Blasius关系式能同时适用于强迫循环和自然循环条件下的阻力预测;通过对比发现,强迫循环和自然循环条件下的转捩点雷诺数以及过渡态雷诺数区间几乎相同。换热实验研究表明:在湍流区,适用于强迫循环条件下的Gneilinski关系式能对自然循环换热能力较好预测;通过分析发现,在本实验研究范围内,自然循环与强迫循环条件下换热能力无明显区别。     

Flow and Heat Transfer Characteristics of Swordfish Fin Microchannel

The supercritical carbon dioxide Brayton cycle is a new generation of thermal cycle used in the fourth generation of nuclear energy. As a high or low temperature recuperator of supercritical carbon dioxide Brayton cycle, the thermal hydraulic characteristics of the compact microchannel heat exchanger directly affect the power cycle efficiency. Reducing flow resistance of the temperature recuperator while maintaining high heat transfer efficiency is an important research for microchannel heat exchanger optimization design. The swordfish fin microchannel design considering bionics theory can significantly reduce the flow resistance. In this work, the swordfish fin heat exchanger model was established with supercritical carbon dioxide fluid as the flow medium. The effect of swordfish fin design with different arrangements on heat transfer characteristics was analyzed by three-dimensional numerical simulation. At the same time, the thermal hydraulic characteristics of swordfish fin design were compared with those of traditional commercial Z-shaped microchannel heat exchanger. The results show that under the same Reynolds number, the Nusselt number of the swordfish fin microchannel is twice as much as that of the Z-shaped microchannel, but the pressure drop is only half of that. Therefore, the thermal hydraulic performance of swordfish fin microchannel heat exchanger is obviously better than that of Z-shaped heat exchanger. It is obtained from optimization analysis that the optimal pitches for swordfish fin design is that the L_a＝8 mm along the flow direction, and the L_b＝6 mm perpendicular to the flow direction.     

Heat Transfer Characteristic of Airfoil Microchannel Efficient and Compact Heat Exchanger

Supercritical carbon dioxide (S-CO₂) Brayton cycle system is a new type of high-efficiency energy conversion system used in the fourth generation reactor. The microchannel efficient and compact heat exchanger is used in the system as high or low temperature recuperators. Besides, heat transfer performance and flow characteristics of heat exchanger have significant impacts on the overall energy conversion efficiency of the system. In this paper, the heat exchanger model of airfoil structure was established and the CFD method was used to study the influence of different spacing of fins on the overall heat transfer characteristics with S-CO₂ as the working fluid. The results show that the convective heat transfer performance of interlaced fins is better than that of side-by-side arrangement. When the interlaced spacing is half of the parallel spacing, the comprehensive performance of heat exchanger is better with the increase of the parallel spacing. The results of airfoil microchannel heat exchanger were compared with those of the Z-shaped microchannel heat exchanger, which shows that the pressure drop of airfoil microchannel heat exchanger is only 54.174% of the Z-shaped microchannel heat exchanger when the heat transfer capacity increases by 25.67%.     

应用于钠冷快堆的超临界二氧化碳动力转换系统研究

超临界二氧化碳（SCO₂）布雷顿循环由于高效、紧凑和可避免钠水反应等特性而成为钠冷快堆的理想动力转换系统。本文以1 200 MWe大型池式钠冷快堆为系统热源,钠回路温度及热负荷为循环系统运行边界,对比研究了不同SCO₂布雷顿循环系统性能和关键设备性能的变化规律。研究发现,级间冷却再压缩循环与钠冷快堆热源特性匹配性最佳,且循环效率最高（40.7%）。进而研究了不同运行参数对级间冷却再压缩循环效率的影响规律,给出了循环系统效率对各关键影响因素的敏感度,发现循环系统效率对冷端参数的敏感度最强,其次为分流比和透平入口参数,对主压缩机级间压比的敏感度最弱。     

Supercritical Carbon Dioxide Power Conversion System Applied to Sodium-cold Fast Reactor

Because of the high efficiency, compactness and avoiding sodium water reaction, the supercritical carbon dioxide (SCO₂) Brayton cycle is an ideal power conversion system for sodium-cooled fast reactors. In this paper, the 1 200 MWe Sodium-cooled Fast Reactor was used as the heat source of the system, and the temperature and heat load of the sodium loop were used as the operating boundary of the circulation system. The system performance and key equipment performance of different supercritical carbon dioxide Brayton cycles were compared. The coupling between the inter-stage cooling and recompression cycle and the characteristics of the heat source of the sodium-cooled reactor is the best, and the cycle efficiency is the highest (40.7%). Furthermore, the influence of different operating parameters on the efficiency of the inter-stage cooling and recompression cycle was studied, and the sensitivity of the efficiency of the circulation system to each of the key influencing factors was given. It is found that the efficiency of the circulation system is the most sensitive to the cold-end parameters, followed by the split ratio and turbine inlet parameters, and the weakest to the main compressor inter-stage pressure ratio.     

Modeling and sizing of the heat exchangers of a new supercritical CO2 Brayton power cycle for energy conversion for fusion reactors

TECNO_FUS is a research program financed by the Spanish Government to develop technologies related to a dual-coolant (He/Pb–Li) breeding blanket design concept including the auxiliary systems for a future power reactor (DEMO). One of the main issues of this program is the optimization of heat recovery from the reactor and its conversion into electrical power. This paper is focused on the methodology employed for the design and sizing of all the heat exchangers of the supercritical CO₂ Brayton power cycle (S-CO2) proposed by the authors. Due to the large pressure difference between the fluids, and also to their compactness, Printed Circuit Heat Exchangers (PCHE) are suggested in literature for these type of cycles. Because of the complex behavior of CO₂, their design is performed by a numerical discretization into sub-heat exchangers, thus a higher precision is reached when the thermal properties of the fluids vary along the heat exchanger. Different empirical correlations for the pressure drop and the Nusselt number have been coupled and assessed. The design of the precooler (PC) and the low temperature recuperator (LTR) is also verified by simulations using CFD because of the near-critical behavior of CO₂. The size of all of the heat exchangers of the cycle have been assessed.     

小型氟盐冷却高温堆耦合布雷顿循环系统分析与研究

为满足小型氟盐冷却高温堆（FHR）能量转换需求,开发与之匹配的高效、紧凑、无水冷却动力转换系统,本文对比了超临界二氧化碳（SCO₂）、空气、氩气（Ar）、氮气（N₂）、氙气（Xe）5种气体工质在不同布雷顿循环构型中的热电转换效率、?效率、?损失分布。研究发现,SCO₂布雷顿循环相比其它工质循环具有最高的热电转换效率和?效率,且结构更为紧凑,易于小型化和模块化,与小型氟盐冷却高温堆耦合更具优势;进而对SCO₂布雷顿循环进行构型优化,得出匹配小型氟盐冷却高温堆的最佳循环构型方式,构成固有安全模块化小型氟盐冷却高温堆热电转换系统,为西部能源利用提供新研究思路。