液氦温区回热器高频损失特性研究

回热器是回热式低温制冷机的核心部件,如何有效地减小回热器中的损失是提高脉管制冷机性能的关键。在不同的温区以及不同工况下,回热器中的主导损失是不一样的。随着温度的不断下降(尤其是20 K温区以下),实际气体损失所占的比例越来越大。本文基于回热器数值模拟程序REGEN3.3着重研究了液氨温区回热器在高频下的各种损失特性,并指出了减小各种损失的方向。基于一台带预冷的4 K斯特林型脉管制冷机,开展了液氨温区高频脉管制冷机回热特性的实验研究。     

基于新物性库的低温回热器REGEN模拟

REGEN程序是用于回热式低温制冷机中回热器部分的仿真模拟软件。在仅内嵌有氦元素工质的基础上,工作新增了包含N2、H2、Ne、Ar和甲烷等13种低温工质的物性库,介绍了其适用温度、压力区间及计算精度等情况。在保留原有氦-4(4He)的基础上补充了当前最新的4He状态方程的研究成果,以此验证了新物性库与原物性库的衔接性和复现性。使用基于新物性库的REGEN3.3a程序对He、H2和Ne为工质的斯特林型脉管制冷机,进行了模拟优化计算并比较了采用不同工质时制冷机的制冷系数。     

带预冷的4K斯特林型脉管制冷机设计

本文提出了采用两级G-M型脉管制冷机预冷一台单级斯特林型脉管制冷机来研究液氦温区斯特林型脉管制冷机性能的实验方案.基于回热器数值模拟软件REGEN3.3,重点研究了液氦温区回热器长度、回热器填料、气体工质对回热器效率的影响.采用低温惯性管作为斯特林型脉管制冷机调相装置,在小声功系统中实现了理想相位关系的调节,有效提高小型斯特林型脉管制冷机的效率.     

60K斯特林制冷机回热器结构优化和试验研究

回热器作为回热式低温制冷机的核心部件,其效率的提升对低温制冷机具有重要意义。对研制的60K斯特林制冷机回热器进行优化设计和试验研究,获得了最佳回热器填料。通过对回热器冷端换热器结构的优化,讨论了其空隙率及局部损失对整机性能的影响,得到了冷端换热器的最佳空隙率,有效提高了制冷机的制冷量及其温度稳定性。在制冷机质量小于2.0kg以下,获得了1.8W/60K@23℃制冷性能。     

VM型脉冲管制冷机数值模拟与实验研究

本文介绍了由VM型热压缩机驱动的脉冲管制冷机基本结构、数值模拟与实验研究。热压缩机借鉴VM制冷机产生压力波动的方式,即依靠室温与冷源之间的温度差产生压力波动,驱动低温级脉冲管制冷机。利用液氮温区制冷机为热压缩机提供所需要的冷量,避免使用低温液体带来的不便。低温级脉冲管制冷机的回热器与脉管采用U型布置,调相机构采用小孔气库加双向进气方式。这种结构不使用有阀压缩机,可以产生低频压力波动,保证回热器在低温区高效工作。在原有结构的基础上,改造热压缩机回热器尺寸与填料,使用Sage软件进行了整机模拟,对调相机构进行优化,考察其在不同的运行频率、平均压力、排出器位移下的制冷性能。对改造后的脉冲管制冷机进行了初步的实验研究,获得14.4K无负荷制冷温度。     

液氮温区小型斯特林制冷机回热器特性的理论研究

定量获取小型斯特林制冷机回热器的不可逆性对整机优化设计与性能改进具有重要意义 ,一直是当前小型制冷机研究的难点。文中建立了小型斯特林制冷机回热器的理论模型 ,通过对控制方程进行无量纲化处理及合理简化 ,推导出非常容易求解的零阶一维控制方程 ,推导出了表征小型斯特林制冷机回热器的不可逆性的熵流方程     

大功率4K脉管制冷机模拟和实验研究

提高液氦温区脉管制冷机的制冷量对于冷却超导磁体和氦液化具有重要意义。本文将已成功应用于单级脉管制冷机和4 K G-M制冷机模拟的回热器模拟软件REGEN用于液氦温区脉管制冷机二级回热器的模拟。计算结果显示,脉管制冷机在4.2 K的制冷量一定程度上随着二级质量流量的增加而增大。在此基础上,我们在实验中采用不同质量流量的压...     

液氮温区混合回热器斯特林制冷机数值模拟研究

自由活塞斯特林制冷机具有温区广、制冷效率高、结构紧凑、振动小以及寿命长的特点。回热器作为制冷机的核心部件,决定着制冷机的性能。为了提高液氮温区斯特林制冷机的效率,本文提出采用卷绕聚酯酰胺(简称PI)薄膜和不锈钢丝网混合填充的回热器,并对该混合回热器进行了数值模拟研究。首先分析了液氮温区混合回热器的填充参数,接着设计制冷机的尺寸参数并建立制冷机整机的数值模型,最终揭示回热器长度、两种填料填充比以及相位特性对混合回热器制冷性能的影响,并将混合回热器与单一填料回热器进行对比。结果表明,混合回热器在液氮温区具有明显优势,在混合回热器长度为8 cm、卷绕PI薄膜和不锈钢丝网混合填充比例为7:1、排出活塞领先动力活塞60°时获得最佳制冷性能。室温300 K、输入声功为451 W,在77 K获到58.1 W的制冷量,声功计的相对卡诺效率为37.26%,比单一填充卷绕PI薄膜和层叠不锈钢丝网的回热器分别高了6.26%和17.33%。     

交变流动下丝网回热器中压降特性的数值分析

本文建立了低温制冷机回热器的多孔介质模型,推导出丝网型多孔介质中渗透率和惯性项系数的表达式,该式考虑了回热器的结构尺寸、交变流动及频率、大温差等的影响.在此基础上,通过数值方法研究了交变流动中不同工作频率下的回热器的压降特性,结果表明,回热器两端压降幅值与系统工作频率基本成线性关系;回热器中大温差引起的气体物性变化在交变流动阻力计算中不容忽视,考虑温差影响时计算的压降幅值与实验符合较好,而忽略温差影响时最大偏差达20%以上.     

热声制冷机回热器的数值研究

以驻波型热声制冷机的回热器作为研究对象,通过对二维可压缩形式的连续性方程、N-S方程、能量方程和理想气体状态方程的数值求解,得到了热声核区域内工作介质的能流密度矢量和能量迹线云图.结果表明:在轴向方向上影响能量传递的主要因素为气体的热传导项.     

Modeling of rotational supercavitating evaporator and the geometrical characteristics of supercavity within

In this paper, a rotational supercavitating evaporator (RSCE) was at first modeled by means of theoretical analysis approach. The geometrical characteristics of supercavity in the modeled RSCE were then studied through numerical simulations. The current research objectives consist in determination of shape of the supercavitator (which in the plane of rotation generates supercavity occupying the most volume between blades), and location of the area suitable for steam extraction by revealing the inner structure of supercavity. Analytical analysis was performed by solving empirical equations for the shape of RSCE, through which an evaluation of two-dimensional relative position of supercavity trailing edge for different shapes of the supercavitator has been realized. Numerical simulation was then carried out, by numerically solving the unsteady Navier-Stokes equations in their conservation form coupled with the Rayleigh-Plesset cavitation and Shear-Stress Transport turbulence models, for verification of the results obtained from empirical equations. Despite unreliable assumption of applicability of empirical equations we have confirmed similarity of the supercavity shapes obtained by both methods for the same RSCE. Therefore, the shape of supercavitator calculated by using empirical equations is acceptable, which provides a simple but reliable approach for design of RSCE. The inner structure of supercavity obtained by numerical simulation has indicated position and parameters for steam extraction openings for further numerical and experimental studies on the performance of RSCE. Practical application of steam or gas extraction is suggested for solving of some problems associated with cavitating pumping of cryogenic liquid.     

Theoretical and experimental research on cryogenic Yb:YAG regenerative amplifier

Based on the theory of quasi-three-level rate equations modified by amplified spontaneous emission,the stored energy density and the small signal gain of the cryogenic Yb:YAG regenerative amplifier for a given geometry for pulsed pumping in three dimensions are theoretically studied using the Monte Carlo simulation.The present model provides a straightforward procedure to design the Yb:YAG parameters and the optical coupling system for optimization when running at cryogenic temperature.A fiber-coupled laser diode end-pumped cryogenic Yb:YAG regenerative amplifier running at 1 030 nm is demonstrated with a maximum output energy 10.2 mJ at a repetition rate of 10 Hz.A very good agreement between the experiments and the theoretical model is achieved.     

低温直立管道中两相自然循环流动过程的数值计算

由于低温系统中直立管中喷泉现象对系统的危害有两点 :一是水锤冲击 ,二是系统卸压影响。文中建立了低温直立管两相自然循环流动模型 ,并且对喷泉过程进行数值仿真计算 ,给出汽弹的大小和汽弹涌出管段破灭的时间间隔。数值计算结果为分析低温输液系统安全性提供基础     

G-M制冷机辐射屏温度随动控制

该文提出低温与超导系统温度控制新方法 -基于泛逻辑代数的温度随动控制。这是一种以低温实验为基础 ,依据概念和专家知识的泛逻辑控制 ,控制特性用一组泛逻辑代数方程描述 ,从而可以有效解决 G- M制冷机辐射屏温度的随动控制问题。该系统可应用于低温界面热阻实验和超导材料热物性测试等。温度随动控温范围为 4 0 K- 15 0 K,精度优于3K。这对低温与超导技术等有重要意义     

Formation of dust-acoustic shock waves in a strongly coupled cryogenic dusty plasma

The nonlinear propagation of ultra-low-frequency dust-acoustic (DA) waves in a strongly coupled cryogenic dusty plasma has been investigated, by using the Boltzmann distributed electrons and ions, as well as modified hydrodynamic equations for strongly coupled charged dust grains. The reductive perturbation technique is used to derive the Burger equation. It is shown that strong correlations among negatively charged dust particles acts like a dissipation, which is responsible for the formation of the DA shock waves. The latter are associated with the negative potential, i.e. with the compression of negatively charged cryogenic dust particle density. It is also found that the effective dust-temperature, which arises from electrostatic interactions among negatively charged dust particles, significantly affects the height of the DA shock structures. New laboratory experiments at cryogenic temperature should be conducted to verify our theoretical prediction.     

Calculation of Direct Drive Targets for Megajoule Laser Facilities with Radiation in the Second and Third Harmonics of Nd Laser

Physics of Atomic Nuclei - The numerical results for cryogenic direct drive targets of megajoule facilities with radiation in the second and third harmonics of a Nd laser are presented. The...     

HeII的粘度理论分析与计算

在一般的分析与计算中,超流氦的粘度往往成为一个被忽视甚至被省略的一个物理量。但是在某些低温系统中,需要完成超流氦长距离输送,粘度成为确定其流动阻力损失的一个重要物理量。目前各具特色的理论和计算关系式很多,但是迄今为止,还没有任何一种理论体系或计算关系式可以适用于所有的物质或所有的温度和压力范围,因此如何应用和借鉴现有的粘度理论或关系式以及实验结果,实现对HeII这种特殊流体粘度的分析和计算是一项十分重要的工作。     

Approach for simulating gas–liquid-like flows under supercritical pressures using a high-order central differencing scheme

This study proposes an approach for simulations of cryogenic fluid mixing under supercritical pressures using high-order schemes. In this approach, we introduce a pressure evolution equation and consistently construct numerical diffusion terms to maintain the velocity and pressure equilibriums at fluid interfaces. The interfaces with high density and temperature ratio are successfully captured without the generation of spurious oscillations, while a high-order central differencing scheme resolves the flow fields. The present method preserves the mass and momentum conservation properties, while the poor energy conservation property is recognized. The one-dimensional single and multi-species interface advection and two-dimensional cryogenic jet mixing problems demonstrate the superiority and robustness of the present method over a conventional fully conservative method.     

火箭低温液体推进剂增压系统数学模型

针对火箭低温液体推进剂增压系统建立了数学模型,目的是为获得满足工程精度要求的飞行期间贮箱内气相空间的压力、温度以及贮箱壁壁温的变化规律.数学模型被证明有较好的计算精度,且模型能适应不同种类的增压气体,甚至混合型增压气体,能适应加注后停放期间和飞行期间的计算.     

X射线相衬成像法在线表征冷冻靶技术

阐述了冷冻靶类球面物体X射线相衬成像机理;Tracepro软件模拟研究证明了X射线相衬成像法能用于冷冻靶燃料层参数的表征;研制了在线表征冷冻靶的X射线相衬成像实验装置,利用该装置开展了二乙烯基苯泡沫球壳及实际氘氘冷冻靶的X射线相衬成像实验研究,获得了玻璃微球内氘氘冷冻层X射线相衬图像,成像分辨力达1.5 m;利用X射线相衬成像法可同时表征烧蚀球壳及冷冻燃料层,为惯性约束聚变实验提供冷冻靶参数。