密度锁界面下方稳态温度场的实验研究及分析

本文通过实验模拟了密度锁内分层界面下方流体稳态温度场分布,发现这部分流体的稳态温度分布曲线存在一个升温结束点,它是导热层与恒温层的分界,只有将升温结束点控制在密度锁内才能有效地抑制传热.本文建立了一个能够描述该部分流体稳态温度分布的数学模型,通过该模型可以给出升温结束点的位置.它为优化密度锁高度提供了理论依据.     

密度锁内流体稳态传热模型的建立

根据温度场的特点,将密度锁分为混合区、导热区和恒温区,并分别进行建模。用该模型对密度锁进行稳态传热计算,并与实验结果进行对比。结果表明:本工作建立的稳态传热模型能较好地计算出密度锁内的温度场。研究建立了密度锁的热损失量计算式,并对热损失量最小值的情况进行了讨论。     

密度锁内分层传热特性的初步探讨

通过可视化观察方法,对3种不同实验管内的流体分层传热特性进行实验研究,同时,建立传热计算模型,对密度锁内的传热机理进行分析.结果表明:密度锁内的分层工质自上而下分为:混合层、界面层、导热层.混合层内的传热以对流为主,其余两部分的传热以导热为主.对不同管径的研究表明,密度锁内的蜂窝通道能有效地抑制扰动作用,减小混合层的厚度,降低通过密度锁的热量传递.     

密度锁内分区模型研究

通过实验研究流速对密度锁内温度场和分层的影响,并建立了分区模型。研究结果表明:密度锁可分为混合区、分层区和恒温区,其中分层区又可分为强分层与弱分层,分层界面则位于混合区与分层区之间。此外,本文还将密度锁内温度场分为5类,其中第2类温度场最好,是密度锁正常工作时的最佳选择。     

真空石墨加热器温度场数值模拟与分析

石墨加热器是测量球床堆芯等效导热系数实验的关键部件,加热器温度场对系统安全及数据准确性有重要影响。本文基于Fluent计算平台,分别采用DTRM模型、P1模型、ROSSELAND模型、DO模型对真空保护环境下的石墨加热器温度场进行数值模拟,确定适合真空保护石墨加热器温度场的计算方法并讨论石墨导热系数、表面发射率对温度场分布的影响。比较分析表明：DO模型计算得到的温度分布较为接近真实情况,导热系数小于35W/(m•K)时,最高温度对其敏感;导热系数大于35W/(m•K)时,其对加热体最高温度影响较小,最高温度较为稳定。     

密度锁内稳态分层特性的实验研究

通过可视化观察方法,对3种不同实验管内的冷热流体分层特性进行实验研究,同时,根据界面力的平衡条件,对密度锁内分层的稳定性进行了分析。稳态工况下,密度锁内冷热流体间存在一界面层,且界面层内具有较大的温度梯度;界面层的稳定性受温度交界面处的扰动速度及界面层内温度梯度的影响,稳定的界面层对阻止冷热流体搅混具有积极作用。另外,对实验管内有无隔板情况进行分层特性对比实验,表明密度锁内的蜂窝通道不但有利于界面层的稳定,且有利于界面形成位置的控制。     

密度锁启动过程中传热特性的实验研究

分别在无扰动以及扰动大小不同的实验情况下,对密度锁启动过程中的传热特性进行了实验研究.研究结果表明,密度锁能抑制热量下传.根据传热情况,密度锁内过渡区可分为强分层、弱分层和无分层3种情况.强分层和弱分层情况下,密度锁都能有效地阻止热量下传,且强分层向下传热量更小.而在无分层情况下热量连续不断地从密度锁传出,导致密度锁失效.     

从结构热传导角度分析CEFR内钠温度变化速率限值的合理性

CEFR提升功率时要求钠温度变化速率不超过30 ℃/h,为从理论上论证限值30 ℃/h的合理性,通过理论分析和ANSYS软件数值模拟两种方式,研究了介质温度变化条件下平板的非稳态热传导响应过程及平板温度进入稳定状态所需的时间。结果表明,换热条件直接影响结构温度达到稳定状态所需的时间,换热条件好时结构和介质温变基本同步,换热条件差时30 ℃/h的堆内介质温度变化速率能保证介质温度稳定时结构温度达到温变总幅度的60%以上。30 ℃/h钠介质温度变化速率基本使换热条件差的条件下结构温度场进入稳定状态的速率与堆内钠介质温度变化相对同步,降低了温度变化带来的热应力分布和变化的复杂性,基本保证了结构实际温度与稳态设计温度的一致性。     

密度锁内分层界面的作用分析

进行了冷态和热态实验,结合理论分析研究了密度锁的抗扰动机理。冷态时,流体流动产生的压力差引起了密度锁中各通道流体的大环流运动;热态时,密度锁内分层界面的形成对大环流运动起到了阻碍作用。结果表明:由于压力差作用,密度锁内分层界面向一侧倾斜产生重位差;当压力差与重位差相平衡时,大环流运动被阻止,流体达到分层平衡。     

密度锁内分层界面位置的实验研究及分析

建立了计算密度锁内流体分层界面位置的理论模型,比较了计算值与实验观察值,并分析了两者的区别,最后讨论了扰动速度和温差对界面位置的影响.结果表明:扰动速度增加,界面位置降低;温差变大,界面位置升高.在一定的温度和管径等条件下,分别拟合出界面位置与扰动速度及理查森数(Ri)的经验关系式.     

Transient Heat Transfer Analysis of a Layer by Considering the Effect of Radiation

The transient heat transfer analysis of a layer has been studied much less than the steady state. However, transient temperature distribution resulted from including radiation and conduction simultaneously, is significantly different from those obtained by considering conduction alone. In order to include the effect of radiation heat transfer, we must insert the gradient of radiative flux in the energy equation. For this purpose, a variety of multi-flux methods have been suggested. A simplified procedure is the two-flux method, which is the one used in the present paper. This paper is focused on one-dimensional transient heat transfer of a layer using Finite Difference Method. To this end, a computer implementation has been written, which is based on implicit finite difference formulation and is capable of considering effect of radiation. By subjecting the layer to various boundary conditions, the effect of variation of refractive index and scattering on transient temperature distribution is discussed.     

膨润土-砂混合物缓冲层轴向热传导性研究

膨润土-砂混合物作为高放废物处置库缓冲材料,在高放废物衰变释热作用下,其物理力学性能对处置库的稳定和安全性具有重要影响。本研究采用自行设计的装置,对按比例缩小后的不同干密度、含水率、掺砂率试样进行热传导模拟试验,并对缓冲层热-力耦合过程进行数值模拟分析,得到了缓冲层温度、应力和应变的变化及分布情况,重点分析了温度的影响。结果表明,增大试样干密度、含水率和掺砂率均可提高其导热性,应变也随之增大,应力受温度影响较早达到平衡;缓冲层靠近热源的位置温度、应力和应变最大,沿轴向方向递减,初始时刻变化明显。     

Calculation of the Heat Flux on the First Wall During Disruption on Tokamak

Disruptions are the most dangerous instabilities in tokamak plasma. During plasma disruption, the large amounts of energy will be deposited on Plasma Facing Components (PFCs) which is a damaging threat for the divertor target and the first wall materials. Therefore, studying the characteristic of heat deposition on the first wall is very significant. The Infrared (IR) camera is an effective tool to measure the surface temperature profile on the first wall on the Experimental Advanced Superconducting Tokamak (EAST). With a finite difference method, the heat flux arrived to the divertor can be calculated from the surface temperature. However, the surface layer on the divertor has a great influence on the calculation of the heat flux on the divertor. The numerical method for solving heat conduction for semi-infinite model is given in this paper. And the thermal resistance of surface layers is considered in this numerical method. In addition, the distribution of heat flux on the divertor during disruption is also shown.     

Effects of Boundary Conditions on Thermal Response of a Cellulose Acetate Layer Using Hottel’s Zonal Method

Energy can transfer internally by radiation in addition to conduction in translucent polymers. Since radiant propagation is very rapid, it can provide energy within the layer more quickly than diffusion by heat conduction. Thus, the transient thermal response of a layer for combined radiative and conduction may be extremely different from that of conduction alone. In this paper, the behavior of a heat conducting, absorbing, and emitting layer of Cellulose Acetate layer is investigated during the transient interval when both conductive and radiative heat transfer are considered. Specifically, the effects of boundary conditions on the response of the layer are considered here. These boundary conditions include both conductive boundary conditions, such as convection coefficient and convective fluid temperature, and radiation boundary conditions, like radiation surrounding temperature and specular reflectivity. To this end, the governing differential equations including the equation of radiative heat transfer within the material coupled to the transient energy equation with radiative terms are presented. The solution procedure is based on nodal analysis and Hottel’s zonal method extended by the ray tracing method. The transient energy equation including the radiative internal energy source is solved using a time marching finite difference procedure with variable space and time increments.     

Transient natural convection cooling of a vertical circular cylinder

A numerical solution is presented for transient natural convection cooling of a finite vertical circular cylinder standing on a semi-infinite horizontal base. The method used is the quasi-finite element approach introduced by Mansour et al. in the determination of the steady state temperature field in metal cutting. The method is able to solve heat transfer problems in a more economical way (memory and computing time requirements) than the classical finite element method and the finite difference techniques.     

Neutron distribution influence on the thermal design of a nuclear fuel rod

The object of the present paper is to look into the thermal and thermoelastic state in a nuclear fuel rod with gap and cladding, including a neutron flux distribution deduced by diffusion theory. The steady state temperature and the thermal stresses in the rod are analytically determined solving a set of differential and integral equations, deriving from heat conduction and Hooke's law. The mathematical technique here utilized is based on the modified first kind Bessel functions theory; the solution presents a very compact and simple form.

The results so obtained are related and a comparison is made with the analogous results deduced implying a constant heat source distribution in the fuel, i.e., neglecting the actual neutron flux distribution. Some numerical results are finally reported with reference to a common boiling water reactor and shortly discussed.     

Numerical simulation of nanosecond laser ablation and plasma characteristics considering a real gas equation of state

Based on the governing equations which include the heat conduction equation in the target and the fluid equations of the vapor plasma,a two-dimensional axisymmetric model for ns-laser ablation considering the Knudsen layer and plasma shielding effect is developed.The equations of state of the plasma are described by a real gas approximation,which divides the internal energy into the thermal energy of atoms,ions and electrons,ionization energy and the excitation energy of atoms and ions.The dynamic evolution of the silicon target and plasma during laser ablation is studied by using this model,and the distributions of the temperature,plasma density,Mach number related to the evaporation/condensation of the target surface,laser transmissivity as well as internal energy of the plasma are given.It is found that the evolution of the target surface during laser ablation can be divided into three stages:(1)the target surface temperature increases continuously;(2)the sonic and subsonic evaporation;and(3)the subsonic condensation.The result of the internal energy distribution indicates that the ionization and excitation energy plays an important role in the internal energy of the plasma during laser ablation.This model is suitable for the case that the temperature of the target surface is lower than the critical temperature.     

固态热管反应堆模拟装置热工水力特性分析

热管反应堆具有小型化、结构简单、固有安全性高等优势,有着广泛的应用前景和研究意义。本文采用CFD方法对热管反应堆模拟装置进行了稳态工况下的热工水力特性分析,并与实验结果进行对比。结果表明,热管各测点温度相对误差不超过5.5%,温差发电器热端各测点温度相对误差不超过3.1%,证明了该模型方法的可行性和正确性。本研究为热管反应堆的数值模拟提供理论指导与方法支撑。