The pebble-bed reactor is one of the most promising designs for the nuclear energy industry. In this paper,a discrete element method-computational fluid dynamics(DEM-CFD) approach that includes thermal conduction, rad...The pebble-bed reactor is one of the most promising designs for the nuclear energy industry. In this paper,a discrete element method-computational fluid dynamics(DEM-CFD) approach that includes thermal conduction, radiation, and natural convection mechanisms was proposed to simulate the thermal-fluid phenomena after the failure of forced circulation cooling system in a pebble-bed core. The whole large-scale packed bed was created using the DEM technique, and the calculated radial porosity of the bed was validated with empirical correlations reported by researchers. To reduce computational costs, a segment of the bed was extracted, which served as a good representative of the large-scale packed bed for CFD calculation. The temperature distributions simulated with two different fluids in this DEM-CFD approach were in good agreement with SANA experimental data. The influence of the natural convection mechanism on heat transfer must be taken into account for coolants with strong convective capacity. The proposed DEM-CFD methodology offers a computationally efficient and widely applied method for understanding the heat transfer process in a pebble-bed core. The method can also be easily extended to assess the passive safety features of newly designed fluoride-salt-cooled pebble-bed reactors.展开更多
基于计算流体力学-离散单元法(computation fluid dynamics-discrete element method,CFD-DEM)对含有印染污泥和煤粉颗粒的埋管流化床内气固两相流动力学特性进行了模拟研究。对流化过程中颗粒的混合指数、速度分布、数量比、固含率分...基于计算流体力学-离散单元法(computation fluid dynamics-discrete element method,CFD-DEM)对含有印染污泥和煤粉颗粒的埋管流化床内气固两相流动力学特性进行了模拟研究。对流化过程中颗粒的混合指数、速度分布、数量比、固含率分布、平均动能分布进行了统计和讨论。实验结果表明,初始上污泥下煤粉填充时,随着气流速度的增大,加剧了煤粉污泥颗粒的分离,过大的气流速度会出现局部完全分离现象。当气流速度达到3.0 m·s^(-1)时,床内煤粉污泥混合填充相较于分层填充时不易发生分离现象。改变流化床内2种颗粒数量的比例时,发现增加煤粉数量可以使污泥分布更加均匀,埋管上方颗粒的平均动能与下方相差较大。展开更多
结合有限元离散元方法(finite-discrete element method,FDEM),对计算流体力学(computational fluid dynamics,CFD)软件FLOW-3D进行二次开发,建立了基于CFD-DEM的流固耦合模型,模拟了多块石入水、沉降以及触底的动力过程,分析了不同块...结合有限元离散元方法(finite-discrete element method,FDEM),对计算流体力学(computational fluid dynamics,CFD)软件FLOW-3D进行二次开发,建立了基于CFD-DEM的流固耦合模型,模拟了多块石入水、沉降以及触底的动力过程,分析了不同块石等效直径、形状和入水速度对触底速度和反力的影响。研究发现,块石入水后速度迅速减小,并逐渐趋于定值,随后做动态平衡沉降运动,直至与底面发生碰撞。块石抛填的触底速度随等效直径的增大而增大,不同等效直径下球形块石触底速度绝对值最大,其次是纺锤形块石,最小为圆盘形块石。最大触底反力也随等效直径的增大而增大,成非线性关系,通过拟合得到了触底反力的经验公式。显著性分析结果表明,块石等效直径对触底反力影响最大,其次是块石形状,最小为入水速度。展开更多
经过三十余年的发展,离散单元法(discrete element method,DEM)已经发展成为一种广泛应用于过程工程领域中颗粒体系研究的数值方法,特别是将DEM与计算流体力学(computational fluid dynamics,CFD)相结合形成的CFD-DEM耦合方法,已经在流...经过三十余年的发展,离散单元法(discrete element method,DEM)已经发展成为一种广泛应用于过程工程领域中颗粒体系研究的数值方法,特别是将DEM与计算流体力学(computational fluid dynamics,CFD)相结合形成的CFD-DEM耦合方法,已经在流态化研究领域得到广泛应用。首先对DEM模型进行了综述,包括DEM模型的基本原理、颗粒形状模型、接触力模型、非接触力模型、流体作用力模型等;然后对CFD-DEM耦合方法及其在流态化领域的一些主要应用进行了介绍,包括在流化床、气力输送以及过程工程领域里的一些其他应用。最后对DEM模型以及CFD-DEM耦合方法的发展趋势进行了预测,希望能促进DEM方法的发展,并推动其在过程工程领域中的应用。展开更多
基金supported by the Chinese TMSR Strategic Pioneer Science and Technology Project(No.XDA02010000)the Frontier Science Key Program of the Chinese Academy of Sciences(No.QYZDY-SSW-JSC016)
文摘The pebble-bed reactor is one of the most promising designs for the nuclear energy industry. In this paper,a discrete element method-computational fluid dynamics(DEM-CFD) approach that includes thermal conduction, radiation, and natural convection mechanisms was proposed to simulate the thermal-fluid phenomena after the failure of forced circulation cooling system in a pebble-bed core. The whole large-scale packed bed was created using the DEM technique, and the calculated radial porosity of the bed was validated with empirical correlations reported by researchers. To reduce computational costs, a segment of the bed was extracted, which served as a good representative of the large-scale packed bed for CFD calculation. The temperature distributions simulated with two different fluids in this DEM-CFD approach were in good agreement with SANA experimental data. The influence of the natural convection mechanism on heat transfer must be taken into account for coolants with strong convective capacity. The proposed DEM-CFD methodology offers a computationally efficient and widely applied method for understanding the heat transfer process in a pebble-bed core. The method can also be easily extended to assess the passive safety features of newly designed fluoride-salt-cooled pebble-bed reactors.
文摘化学链燃烧技术是一种基于固体载氧体颗粒的新型无焰燃烧技术,对于助力碳减排具有重要意义。载氧体颗粒的寿命制约着该技术的进一步应用。文中针对载氧体颗粒的碰撞磨损问题,采用计算流体力学-离散元法(computational fluid dynamics-discrete element method,CFD-DEM)双向耦合数值计算法,建立非规则载氧体颗粒模型,从颗粒速度场、碰撞频率场及碰撞功率场三方面,探究冷态流化床内载氧体颗粒的运动状态、分布特征及碰撞情况。结果表明,冷态流化床内载氧体颗粒呈现上下无序周期性运动,单周期内流化床空间上出现颗粒密相区与稀相区。其中,稀相区颗粒速度大而碰撞频率小,颗粒具有高动能与高重力势能;密相区内颗粒速度小而碰撞频率高,最大碰撞频率对应的颗粒多为大粒径、较小长径比,且颗粒能量低;颗粒最易磨损区即碰撞最大功率区(最大7.8×10^(−8)W)位于颗粒密相区与稀相区的交界面,颗粒碰撞磨损能量由颗粒动能与重力势能累积提供。研究结果揭示了冷态流化床内载氧体颗粒的碰撞磨损机制。
文摘结合有限元离散元方法(finite-discrete element method,FDEM),对计算流体力学(computational fluid dynamics,CFD)软件FLOW-3D进行二次开发,建立了基于CFD-DEM的流固耦合模型,模拟了多块石入水、沉降以及触底的动力过程,分析了不同块石等效直径、形状和入水速度对触底速度和反力的影响。研究发现,块石入水后速度迅速减小,并逐渐趋于定值,随后做动态平衡沉降运动,直至与底面发生碰撞。块石抛填的触底速度随等效直径的增大而增大,不同等效直径下球形块石触底速度绝对值最大,其次是纺锤形块石,最小为圆盘形块石。最大触底反力也随等效直径的增大而增大,成非线性关系,通过拟合得到了触底反力的经验公式。显著性分析结果表明,块石等效直径对触底反力影响最大,其次是块石形状,最小为入水速度。
文摘经过三十余年的发展,离散单元法(discrete element method,DEM)已经发展成为一种广泛应用于过程工程领域中颗粒体系研究的数值方法,特别是将DEM与计算流体力学(computational fluid dynamics,CFD)相结合形成的CFD-DEM耦合方法,已经在流态化研究领域得到广泛应用。首先对DEM模型进行了综述,包括DEM模型的基本原理、颗粒形状模型、接触力模型、非接触力模型、流体作用力模型等;然后对CFD-DEM耦合方法及其在流态化领域的一些主要应用进行了介绍,包括在流化床、气力输送以及过程工程领域里的一些其他应用。最后对DEM模型以及CFD-DEM耦合方法的发展趋势进行了预测,希望能促进DEM方法的发展,并推动其在过程工程领域中的应用。
