含气率对PTS时压力容器内流动与传热的影响

本文对反应堆压力容器紧急安注时的流动与传热特性在1/10的模型上进行了流动可视化、局部传热系数以及混合函数的试验研究。针对三个热冲击敏感区域的部分测点,比较了环腔流速为0.5m/s、安注流速为1～30 m/s时不同含气率对下降环腔内流动与传热特性的影响,得出并分析了不同测点传热系数、混合函数的变化规律。研究结果表明:随着含气率增大,安注流体与环腔流体的混合增强;下降环腔内的含气率对小安注流速时的流动与传热影响显著,而对大安注流速时影响较小。     

基于FLUKA计算压力容器快中子注量的可行性研究

基于知识产权的考虑,通过与蒙特卡罗程序MCNP计算结果比对,研究使用FLUKA程序替代MCNP程序进行反应堆压力容器快中子注量计算的可行性。通过修改和调用子程序对次级粒子堆栈进行操作,解决了关闭裂变中子这一关键问题,FLUKA程序的计算结果与MCNP程序的计算结果相对偏差在5%以内,符合得较好,证明使用FLUKA程序替代MCNP程序用于计算反应堆压力容器快中子注量在技术上是可行的。     

非均匀余弦加热垂直圆管在模拟压水堆失水事故喷放工况下的传热研究

一、引言 为了确保核电站反应堆的安全传热,许多学者研究了模拟压水堆均匀发热堆芯燃料元件在失水事故下的传热情况,但实际上由于反应堆中子通量非均匀分布、从而热流密度沿轴向分布也是非均匀的,而且这种分布随着堆的寿期和控制棒插入的位置而发生变化。为了模拟这种工况,我们进行了试验工作段上游均匀加热、下游余弦分布加热(模拟堆寿期后期)和上游余弦分布加热、下游均匀加热(模拟堆寿期前期)时失水事故喷放工况下的     

连续型与打孔型波纹传热表面热力性能试验研究

波纹型传热表面是工程中常用的高效紧凑型传热表面之一,其热力性能与结构形式及几何参数有直接的关系。本文用试验的方法对连续型波纹翅片及打孔型波纹翅片的传热及阻力性能进行了研究,得出了相应的传热准则方程式及阻力性能曲线。试验研究结果表明,在传热性能相同时,打孔型传热表面的流动阻力大于连续型传热表面,亦即在泵功率消耗相同的条件下,连续型表面的传热性能优于打孔型。     

并联平板重力热管传热性能实验研究

为了研究安装角度、工质及管径对并联平板重力热管传热性能和启动特性的影响,本文搭建了性能测试实验台并进行了对比实验研究.实验结果表明:在90°～60°倾角范围内,倾角对热管传热性能的影响不明显,随倾角的继续减小,热管运行热阻增大,传热极限减小;在低加热功率下充注丙酮的热管具有更好的传热性能,而在高加热功率时充注乙醇的热管...     

基于FLUENT的核热耦合程序反应性反馈参数敏感性

将计算流体力学模型与中子动力学模型耦合来进行反应堆瞬态安全分析的方法,由于可以开展复杂几何结构的三维流动传热分析,因此受到很大的关注。基于FLUENT用户自定义功能（UDF）开发了一套可用于池式铅堆瞬态安全分析的核热耦合程序,程序耦合了临界/次临界点堆中子动力学模型和燃料棒模型。由于反应堆处于不同寿期时,随着燃料燃耗、可燃毒物积累等因素导致反应性反馈系数有较大变化,因此使用开发的核热耦合程序对中国科学技术大学提出的小型自然循环铅冷快堆进行不同关键反馈系数下无保护的瞬态超功率事故安全分析。调整点堆模块考虑到的四个反应性反馈系数,可以发现燃料多普勒系数对堆安全的影响最大,同时定量的分析结果表明超功率事故引入时间长短对事故演化有重要影响。     

基于遗传算法的SOBER-SJ10池沸腾传热研究

基于遗传算法构建了沸腾过程中加热固壁一维瞬态导热反问题计算方法,采用具有精确解的半无限瞬态导热问题构造了一个校核算例,验证了该算法具有较高的准确度和抗干扰能力,能够准确反演计算沸腾传热瞬态热流密度。基于该算法分析了 SOBER-SJ10地面和空间实验中沸腾传热特性,结果表明微重力环境中单相传热被严重抑制,热流密度远小于地面数值;不同重力条件下核态沸腾传热曲线落在同一位置,显示出低热流密度时核态沸腾传热具有某种重力无关特征;但微重力条件下核态沸腾曲线起始于远低于地面的热流密度,同时在远比地面小的热流密度值时达到临界热流状态,并转变为过渡沸腾模式。     

梯度折射率介质瞬态辐射-导热耦合传热

多维辐射-导热耦合传热问题有广泛的应用背景。本文采用有限元法对辐射传递方程的离散坐标形式进行离散,并采用有限元法求解瞬态辐射-导热耦合能量方程,研究二维方腔半透明参与性梯度折射率介质内瞬态耦合传热,考虑第一类热边界条件,分析了折射率分布、衰减系数、散射反照率及散射相函数对对瞬态耦合传热的影响。结果表明,梯度折射率对瞬态耦合传热影响显著。     

射流冲击下高温壁面在淬冷过程中的传热特性的实验研究

本文对射流冲击下的瞬态快速冷却过程的传热特性进行了实验研究,并分别对膜态沸腾、过渡沸腾、临界热流密度和核态沸腾等传热阶段进行了分析,讨论了表面冷却速率对沸腾过程产生影响的原因,将实验数据归纳整理成若干个半经验关系式。     

泡沫金属电磁感应传热机理研究

研究了电磁感应加热下泡沫金属填充液体的磁–热能量转换及瞬态升/降温传热过程,搭建了泡沫金属填充液体在感应加热与液体冷却下的联合控温实验系统,采用“频域–瞬态”和“松耦合”方法求解电磁–传热耦合数值模型,揭示了泡沫金属填充液体的电磁场与热源分布规律、温度响应特性、温度均匀性以及泡沫金属结构和材质等参数的影响规律。结果表明,泡沫金属填充液体的电磁感应传热特性与泡沫金属的结构和材质密切相关。     

蒸发性对燃油瞬态喷雾撞击壁面的动态传热影响

直喷发动机燃油喷雾撞击壁面形成油膜,导致燃烧效率降低,颗粒物排放增加.伴随撞壁的动态传热过程对油膜蒸发具有重要影响.本文针对正戊烷、甲醇、甲醇-汽油混合燃料瞬态喷雾撞击壁面,研究了不同条件下蒸发性对燃油瞬态喷雾撞击壁面动态传热影响.结果表明,提高喷油温度可促进燃油雾化,增大喷油压力或降低喷油距离可提高液滴撞壁强度,缩短...     

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采用两相流的流动换热理论,建立二维几何模型,运用FLUENT对稳定入口流速下注入气体的铅铋流动段作了模拟。模拟研究注入气体的体积份额或速度改变对压力和铅铋与注入气体之间换热与影响,得到了不同条件下的温度与压力分布。分析结果发现,体积份额减小,铅铋流体的径向温度分布更加均匀,中心温度更低;随着体积份额的减小,铅铋的总压呈现出一种下降的趋势。注入气体速度不同对铅铋整体的换热影响不大;中心处的动压有较大增加,总压改变甚微。     

Computational Model of Thermal‐Fluid Flow in a Radio‐Frequency Plasma Torch

The paper aims to clarify the modelling results concerning the heat transfer and fluid flow in a radio‐frequency plasma torch with argon at atmospheric pressure. Fluid numerical simulation requires the coupling of magnetohydrodynamics (MHD) and thermal phenomena. This model combines Navier–Stokes equations with the Maxwell's equations for compressible fluid and electromagnetic phenomena successively. A numerical formulation based on the finite element method is used. In this study, fluid flow and temperature equations are simultaneously solved (direct method, instead of using the indirect method) using a finite elements method (FEM) for optically thin argon plasmas under the assumptions of local thermodynamic equilibrium (LTE) and laminar flow. Appropriate boundary conditions are given, and nonlinear parameters such as the thermal and electrical conductivity of the gas and input power used in the simulation are detailed. We have found that the source of power is located on the torch wall in this type of inductive discharge. The center can be heated by conduction and convection via electromagnetic phenomena (power loss and Lorentz force). (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Peristaltic Flow of Shear Thinning Fluid via Temperature-Dependent Viscosity and Thermal Conductivity

In this paper Williamson fluid is taken into account to study its peristaltic flow with heat effects. The study is carried out in a wave frame of reference for symmetric channel. Analysis of heat transfer is accomplished by accounting the effects of non-constant thermal conductivity and viscosity and viscous dissipation. Modeling of fundamental equations is followed by the construction of closed form solutions for pressure gradient, stream function and temperature while assuming Reynold's number to be very low and wavelength to be very long. Double perturbation technique is employed, considering Weissenberg number and variable fluid property parameter to be very small. The effects of emerging parameters on pumping, trapping, axial pressure gradient, heat transfer coefficient, pressure rise, velocity profile and temperature are analyzed through the graphical representation. A direct relation is observed between temperature and thermal conductivity whereas the indirect proportionality with viscosity. The heat transfer coefficient is lower for a fluid with variable thermal conductivity and variable viscosity as compared to the fluid with constant thermal conductivity and constant viscosity.     

焦炭填充床内非稳态传热和流动的研究

采用实验方法研究了干熄炉内焦炭的冷却过程,得到了实验条件下不同位置焦炭的冷却曲线和气体温度、压力损失的变化趋势。根据多孔介质理论建立了非稳态传热和流体流动数学模型,对模型计算值和实验测量值进行了比较分析,结果表明模型具有较好的适用性,给出了二者存在偏差的原因。     

平板热管蒸发段多孔介质内流动和传热分析

通过假定平板热管多孔芯内流体的压力分布,对流动和传热进行了分析,得出结论:边界对于速度分布和流量计算的影响比惯性影响大,对于液层的分布二者影响都很小;多孔介质底部温度分布均匀,热流密度方向基本垂直于边界.     

高温吸热管内超临界CO2传热特性的数值模拟

研究超临界CO2在高温吸热管内的传热特性是将其应用于聚光太阳能热发电技术中的基础.本文对此进行了数值模拟研究,分析了流体温度、流动方向、系统压力、质量流率和热流密度对对流传热系数和Nu数的影响.结果表明:高温区(800—1050 K)的对流传热系数和Nu数受流动方向和系统压力的影响均很小,但都随着质量流率的增大以及热流密度的减小而明显增大;而随着流体温度的升高,对流传热系数近似线性增大,Nu数则近似线性减小.另外,本文研究发现在高温区可忽略浮升力对传热的影响,而由高热流密度引起的流动加速效应会明显恶化传热.最后,选取了八种管内超临界流体传热关联式与模拟结果进行对比,发现使用基于热物性修正的关联式对高温区传热数据预测的结果优于使用基于无量纲数修正的关联式得到的结果,且其中预测效果最优的关联式得到的计算结果与模拟结果之间的平均绝对相对偏差为8.1%.     

Experimental Study of the Influence of Structured Capillary-Porous Coatings on the Dynamics of Development of Transient Processes and the Crisis Phenomena at Stepwise Heat Release

The effect of structured plasma-sprayed capillary-porous coatings on transient processes and the development of crisis phenomena at boiling under pulsed heat release was studied. The working fluid was liquid nitrogen on the saturation line at atmospheric pressure. It is shown that under unsteady heat release, there is a degeneration of the development of the boiling crisis on heaters with structured capillary-porous coatings at q < q_CHF (critical heat flux at steady heat release). Under unsteady pulsed heat release, no rapid transition to the film boiling regime (without passing through the nucleate boiling stage) is observed on heaters with such coatings until the thermal load is more than two times higher than the critical heat flux for steady heat release. This significantly increases the times of transition to post-critical heat transfer. Analysis of synchronized measurements of surface temperature of heaters and high-speed video recording of transient processes shows that the degeneration of the heat transfer crisis at q < q_CHF on samples with coatings occurs due to significantly lower liquid boiling temperature differences and specific features of the dynamics of propagation of self-sustaining evaporation fronts in comparison with a smooth heater.     

Modeling of humps formation during deep-penetration laser welding

A 3-D transient modeling based on the numerical resolution of the fluid flow ant the heat transfer equations is developed for deep-penetration laser welding at high-welding speed regime, which results in the humping phenomenon. The physical mechanisms included in our model concern matter melting, vaporization inducing a recoil pressure, and resolidification. The implementation of developed procedures called User Defined Functions (UDFs) working interactively with the CFD Fluent code and a dynamic mesh method allowed us to treat the problem with specific and complex boundary conditions. The recoil pressure, fusion, resolidification, and the temperature dependence of the physical properties were thus taken into account. As a result, regular humps could be observed after resolidification on the weld seam.