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《Journal of Nuclear Science and Technology》2013,50(4):364-370
The prediction by a mathematical model of the separation of uranium isotopes using a gas centrifuge process is a hard task. The gas motion can be described by analytical or numerical solutions of the system of equations defined by the equation of continuity, the Navier-Stokes equation and the equation of energy. However, these calculations cannot be performed for actual centrifuges. Neural networks are an alternative for modelling complex problems that show too many difficulties to be solved by phenomenological models. The authors propose the use of neural networks for the simulation and prevision of the separative and operational parameters of a gas centrifuge separating uranium isotopes. The results from the uranium separation experiments (Zippe data) are compiled and presented to the neural network in the learning and testing processes. The prediction using the neural network model shows good agreement with the experimental data. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(6):242-262
Thermal convection and weak forced flows in a rotating cylinder were studied theoretically to find the mass velocity distributions in a gas centrifuge. Compressibility of the gas is taken into account in the form of a density stratification in the radial direction. First of all, a scaling analysis was made to verify the dominance of Coriolis force in the field of flow. The result of this analysis indicated that the body of the fluid in the centrifuge is composed of inviscid cores separated by a viscous layer concentric to the axis of rotation, and enveloped by other viscous layers lining the side and end faces of the cylinder. The transport of the gas from the feed ports to the discharge ports is made through these viscous layers. The thermal convection has its largest component near the side wall in the form of a recirculating flow, and its pattern is controlled by the temperature distribution of the wall. These theoretical results were verified in part by an experiment devised to permit visual observation of the air flow in a rotating cylinder. 相似文献
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为研究气体离心机中供料射流对环流的影响,采用直接模拟蒙特卡罗(DSMC)方法对径向射流的流动结构进行模拟。通过选择适当的边界条件和分子碰撞模型,得到了不同供料条件下的二维径向供料射流的流动分布图像,捕捉到了供料射流的波系结构,获得了流动参数分布。对计算结果分析可知:在靠近径向外边界处,流动参数存在明显的峰;供料气体速度越高,对离心机内部流场影响越大;除速度、密度、压强等流动参数外,供料射流对温度分布也有较大影响,出流边界处的温度可升至平均温度的两倍左右,对离心机分离性能有较大影响。 相似文献
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《Journal of Nuclear Science and Technology》2013,50(7):396-401
Centrifugally driven thermal convection near the cooled rotor conver of a centrifuge is treated. Boundary layer equations are reduced to ordinary differential equations by the Lees-Levy transformation, and solved numerically by applying the quasilinearization method. Sample solutions for radial and azimuthal velocity profiles are presented. The values of the axial velocity at the rotor center are calculated as a function of the temperature difference between the rotor cover and the contained gas. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(7):704-711
In this study, we carried out the numerical simulation of gas flow across a helically coiled tube bundle, which is fitted in the annular space between a central spine and an outer casing. We focused on the effect of clearances at the inner and outer radial boundaries on the gas flow distribution and thermal mixing in the tube bundle. The conservation equations of mass, momentum and energy were numerically solved by computational fluid dynamics. It was demonstrated from the numerical simulation results that (i) the gas flow distribution in the tube bundle is very sensitive to clearances at the inner and outer radial boundaries, and even a very small variation of clearances would lead to a considerable change in the average velocity profile, which correspondingly leads to a great deviation of the gas flow distribution away from the original one; (ii) the clearance effect on thermal mixing is not as strong as that on gas flow distribution;(iii) the Reynolds number has little effect on the gas flow distribution and thermal mixing, the latter of which is in agreement with the results of Achenbach experiments. 相似文献
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用源汇模拟同位素分离气体离心机流场的供取料驱动和机械驱动是离心机流场计算中的方法之一。通过重新推导流体动力学方程组中的源汇表达式,得到不同的表达式。推导出的表达式反映了源汇之间的互相关联以及流场与源汇之间的互相影响,即源汇耦合,这些在以往的计算过程中均被忽略。由于考虑了源汇耦合,使得计算过程中部分源汇成为未知量,需在流场求解过程中予以确定。通过比较有无考虑源汇耦合计算得到的离心机流场可知,不考虑源汇耦合得到的结果虽能反映出分离室中流动基本规律,但数值上存在差异,得到的分离功也有较大差别。因此,计算过程中应考虑源汇的耦合。 相似文献
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流体诱发振动广泛存在于管壳式换热设备中,而螺旋管式换热器由于体积小、换热效率高,近年来大量应用于各类工业换热设备。本文针对单根螺旋管进行流致振动分析,分别利用一维热工水力程序RELAP5、CFD软件FLUENT和有限元软件ANSYS计算螺旋管一、二次侧流体密度分布,一次侧流体的速度场和螺旋管模态振型,并在0、1、2、4、和8支承数下计算单根螺旋管的流弹失稳比和湍流抖振均方根位移比。计算结果表明,当螺旋管采用4个对称支承进行固定时可满足ASME流弹失稳和TEMA湍流抖振的设计标准。 相似文献
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文章分析用Onsager的薄层模型研究离心机中流场时,端盖边界条件的不同对流场求解的影响。端盖边界条件可有两种形式,一种由分析端盖上水平Ekman边界层得到(称为原始形式),另一种由对原始形式求导后得到(称为导数形式)。目前使用的是导数形式。然而,求导运算损失了原始形式边界条件中包含的部分信息,并复杂化了边界条件。在端盖上分别有热驱动、供取料情况下,分别对流场进行求解来分析两种形式边界条件的差别。结果表明,使用不同形式的边界条件所得流场总体上不同,为避免导数形式中的信息损失,建议使用原始形式。 相似文献
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《Journal of Nuclear Science and Technology》2013,50(5):328-340
An experimental study has been conducted to investigate the effect of gas introduction on the heat transfer characteristics for turbulent flow of a heat generating liquid in an adiabatic tube 20 mm in inside diameter. Heat generation within the fluid was brought about by passing an alternating current through the working fluid, which was an aqueous solution of sodium chloride mixed with air bubbles. The superficial liquid Reynolds number ranged 3,700–11,000. The quality was varied from 2.6×10?5 to 3.3×l0?3. Measurements were made of the temperature distributions in the fluid as well as on the tube wall. The experimental results were compared with theoretical analyses. In bubbly flow; the introduction of air into liquid brought forth a flat temperature distribution due to a considerable increase of turbulence and a saddle-shaped void distribution, which had a maximum near the tube wall. In slug flow, however, the void distribution changed to a dome-shaped profile with a maximum at the tube center and the rate of heat generation was higher near the wall than in the center region, resulting in a steep temperature distribution. 相似文献
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在压水堆换料过程中,乏燃料组件要通过水下通道完成从反应堆厂房到乏燃料水池的运输。为获得乏燃料组件在换热条件较恶劣的承载器顶角区域的传热特性,开展了试验研究,测量得到了2 400~20 000 W/m2不同热流密度下承载器顶角区域3根燃料棒顶部的沸腾换热系数,并拟合得到沸腾传热关联式。研究结果可为今后工程应用中评估燃料组件在转运过程中的热工安全状态和表面最高温度提供参考。 相似文献
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冷却剂流经核反应堆堆芯时,绝大部分通过燃料组件内部流过,带走裂变能量。另外一小部分作为旁流经过燃料组件外侧流道、控制棒导向管外侧及内侧流道流出。为确保反应堆在正常运行工况下的安全性,必须限制堆芯旁流流量。本文通过开展导向管外侧流道阻力特性实验研究,在不同流量工况下获得了分段压差,并进一步拟合了雷诺数与阻力系数的关系式。实验结果表明,导向管外侧流道压力损失主要集中在堆芯下栅格板处,当反应堆额定工况运行时,单组导向管外侧流量仅为0.196 m3/h。 相似文献
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《Journal of Nuclear Science and Technology》2013,50(11):843-848
An azimuthal flow of the gas motion in a rotating cylinder induced by the forced source-sink flow was measured using the laser Doppler anemometer in connection with the development of a gas centrifuge for 235U enrichment. The cylinder, held vertically, was driven in the air at an angular velocity of 10 π rad/sec. The air to which paraffin mist was added as the light scattering particles was fed into the cylinder through the inlet slit provided on the upper end plate at the relative radius of 0.43 and withdrawn through the outlet slit on the lower end plate at the relative radius of 1.0. The Ekman number E was approximately 5.6 × 10?5 in this experiment. The Ekman layer on the upper end plate was so thin that it was not observed, and that on the lower end plate was not either. The Stewartson E 1/4 layers on the side wall and at the feed radius were clearly observed and their profiles were quite similar to the result of the linear theory except the inviscid core region. The discrepancy in this region should be attributed to the fact that the Stewartson layers on the side wall and at the feed radius were thick enough to overlap each other. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(7):580-586
The drift-flux model is widely used for gas-liquid two phase flow analysis, because it is applicable to various flow patterns and a wide range of void fractions. The drift- flux parameters for upward gas flow in stagnant liquid, however, have not been well examined. In this study, the distribution parameter Co and the drift velocity Vgj for stagnant liquid were derived from the void fraction correlation and boundary conditions of drift-flux parameters, and then compared with Co and Vgj for high liquid velocities. Also using the two region model where a circular flow area was divided into an inner region of cocurrent up-flow and an outer annulus region of liquid down flow, Co and Vgj for stagnant liquid and for high liquid velocity were compared. The results showed that Co values for stagnant liquid were larger than values for high liquid velocity, while Vgj values were almost the same for both cases. 相似文献