共查询到17条相似文献,搜索用时 203 毫秒
1.
2.
HTR-10堆芯球流运动的唯象学DEM模拟 总被引:1,自引:1,他引:0
清华大学研发的10 MW高温气冷堆(HTR-10)是国际上重要的先进实验反应堆,球流运动的研究具有基础性地位。通过唯象的方法对HTR-10堆芯的球流运动进行了离散元数值模拟,通过已由实验验证的计算程序,采用与HTR-10堆芯1∶1的计算模型,计算了27 000个元件单元的运动,包括不同摩擦系数f和不同底部锥角A下的球流运动。结果表明:在HTR-10堆芯设计条件下,球流运动较均匀,堆芯底部不存在滞留区;f越大或A越大,堆芯球流越均匀,表现出更好的整体性向下运动;当f达到0.8上限时,HTR-10堆芯球流依然保持了整体性运动,底部无任何被滞留的球。本工作对进一步优化球床式高温气冷堆堆芯设计具有重要意义。 相似文献
3.
4.
5.
6.
对冷却流体在球床模块堆内燃料颗粒填充区域中的流动和传热过程进行了研究.数值模拟突然停堆后燃料颗粒区在温差作用下的自然对流过程,分析了瑞利数Ra对燃料填充区域内流场、温度场和局部努塞尔数Nu以及壁面摩擦阻力系数的影响.计算结果表明:当球床模块堆突然停堆时燃料填充区域可形成加热壁面流体上升流动、冷却壁面下降流动的自然循环流动;随着Ra数增大,回流中心向上移动;沿轴向壁面局部Nusselt数和摩擦阻力系数存在极值,并且极值点随Ra数增大而向上移动;与氮气相比,氦气作为冷却介质停堆后具有更均匀的堆芯轴向温度分布. 相似文献
7.
8.
9.
10.
摇摆运动作为一种典型海洋条件,对管内的气液两相流动过程产生较大影响。本工作通过摇摆条件下空气 水泡状流在矩形通道内流动阻力特性的实验,研究摇摆运动对两相流动过程的影响。实验在常温、常压下进行,通道尺寸为40 mm×10 mm,摇摆角度为10°、15°和30°,摇摆周期为8、12和16 s。结果表明,摇摆条件下瞬态摩擦压降的变化具有明显周期性,随着两相雷诺数变大,瞬态摩阻系数的波动幅度和平均水平均变小;摇摆周期越小,摇摆振幅越大,即摇摆运动越剧烈,摩擦压降的波动幅度也越大。 相似文献
11.
氦冷固态增殖包层是中国聚变工程实验堆(CFETR)的3种候选包层概念之一,氚增殖球床是包层的核心部件,采用硅酸锂颗粒作为氚增殖材料。球床结构对氚在球床内的输运行为及流动和传热均有重要影响。本文基于离散单元法(DEM)生成了满足氚增殖球床填充率要求的随机堆积结构,通过CFD计算获取了球床结构下氚在吹扫气体内的等效扩散系数及吹扫气体的流动特性,包括速度分布、压力分布及进出口压降;开展了外加热流及有内热源两种工况下球床等效导热系数的模拟。计算结果表明,球床结构下氚在吹扫气体内的等效扩散系数为二元气体扩散系数的40%;受球床结构影响,球床内存在流动迟滞区,壁面出现流动加速;拟合得到Ergun方程的黏性阻力系数C1=87;有内热源工况下的球床等效导热系数低于外加热流工况下的球床等效导热系数。 相似文献
12.
Xiaowei Luo 《Nuclear Engineering and Design》2010,240(10):2674-2681
Recently, the role of friction and wear in the safety of pebble bed reactors was reconsidered. The friction properties of graphite were analyzed in this paper. In the first part of this paper, we investigated the past research of graphite and analyzed the influence of environment gas, temperature and radiation on friction coefficient. The variation laws of friction coefficient with the effect factors were given, especially in helium environment (including pure helium and HTGR helium). In the second part, the mechanical behavior of pebble bed is discussed while considering the influence of the friction properties of graphite. The results indicated that the fuel elements cannot be crushed failure even though the fuel elements have a large friction coefficient. 相似文献
13.
Xinlong Jia Nan Gui Xingtuan Yang Jiyuan Tu 《Journal of Nuclear Science and Technology》2017,54(1):111-126
Improved particle tracking velocimetry (improved PTV) is proposed for experimental study of very slow dense pebble flow in a silo bed by combining the relaxation method and Voronoï diagram. The improved PTV method is validated by comparison with DEM (discrete element method) simulation and experimental result. Velocity and fluctuation characteristics on different streamlines are investigated to show the macroscopic kinematics of pebble flow. Bulk arches on different locations of the pebble bed are identified. Two local arching characteristics including size distribution and horizontal span are analyzed, and their effects on whole flow regime are discussed. It is found that the arch size distribution follows second-order polynomial distribution in semi-logarithmic scale. The horizontal span of arches provides evidence for transition between the ordered and disordered regimes. The probability distribution of successive angles between the neighbors of arching particles is a good indicator of arch stability. The relation between arch breakdown and contact network change is demonstrated by correlation analysis. High correlation between arching structure and mean velocity in targeted regions is indicated. The characteristic lifetime of arches and autocorrelation time of fluctuation velocity present positive correlation. The bulk arching dynamics is the main reason for fluctuations of particle velocities. 相似文献
14.
15.
16.
The micromechanical behavior of an assembly of binary and polydisperse spherical pebbles is studied using discrete element method (DEM) accounting for microscopic interactions between individual pebbles. A in-house DEM code has been used to simulate the assemblies consisting of different pebble diameters and the results of the simulations are compared with that of mono-size pebble assemblies. The effect of relative radii and volume fraction of the pebbles on the macroscopic stress–strain response is discussed. Furthermore, the effect of packing factor and coefficient of friction on the overall stress–strain behavior of the system is studied in detail. The shear (tangential) stiffness between the particles is also another influencing parameter. For a very small shear stiffness the system shows a strong dependence on the packing factor while a pebble material dependent shear stiffness shows a rather moderate dependence on the packing factor. For a similar packing factor, the mono-size assembly shows a stiff behavior during loading compared to binary assembly. However, the simulations do not show a significant difference between the two behaviors in contrast to the observations made in the experiments. The discrepancy can be attributed to (i) probable difference in packing factors for mono-size and binary assemblies in the experiments, (ii) arbitrary friction coefficient in the current model and (iii) the tangential interaction (constant shear stiffness) implemented in the present model which needs further modification as a function of the load history on the pebbles. Evolution of other micromechanical characteristics such as coordination number, contact force distribution and stored elastic energy of individual pebbles as a function of external load and system parameters is presented which can be used to estimate important macroscopic properties such as overall thermal conductivity and crushing resistance of the pebble beds. 相似文献
17.
有效导热系数用来表征高温气冷球床堆堆芯综合传热能力,提高球床有效导热系数的预测精度对于高温气冷球床堆的热工设计和安全分析十分重要。为了优化球床壁面区域有效导热系数模型,本文针对无序石墨球床有效导热系数开展数值研究,分析了无序堆积球床主体区域、近壁面区域以及壁面区域有效导热系数的分布特性。结果表明:壁面区域有效导热系数相对于主体区域和近壁面区域显著降低,其平均降幅约为22%。因此引入了修正系数Cw对ZBS模型在壁面区域进行优化,对于球床主体区域及近壁面区域修正系数Cw=1,对于壁面区域,修正系数Cw=0.78。通过与前期无序球床实验数据和南非HTTU实验数据的对比,验证了优化后的ZBS模型能较好地预测球床壁面区域有效导热系数。 相似文献