基于SINDA/FLUINT的低温回路热管整机仿真分析

基于热流分析软件SINDA/FLUINT,对低温回路热管进行了仿真模型分析,得到了它的工作温度、漏热、压降等随热负载的变化关系。将计算结果与实验进行对比,在一定的热负载范围内,仿真结果与实验结果吻合,验证了仿真模型的正确性。通过分析模型的计算结果,可为以后低温回路热管的设计和实验提供参考。     

乙烷温区低温环路热管设计与实验

为了研究低温环路热管在乙烷温区的启动及运行特征,通过自行设计的样机进行了实验.实验表明,在0.7W的驱动功率下,低温环路热管可顺利实现降温启动;运行时,可传递12W的冷量,并且在9W时,传热热阻最小,为1.14 K/W.     

自然循环在新型低温传热元件中的性能

针对自然循环与低温热管耦合的新型传热元件稳态特性进行了数值计算.基于一些合理假设,利用一维均相流模型对液氮在自然循环管路中的流动与传热过程进行计算,得到了两相流动中干度沿管程方向的分布,循环流量、干度等参数随外加热负荷变化的规律,以及不同管径对循环流量、干度分布、冷头稳定温度的影响,并与实验结果进行了比较与分析,为优化实验装置提供了理论依据.     

Thermal behavior of a cryogenic loop heat pipe for space application

This paper discusses a prototype of cryogenic loop heat pipe (CLHP) working around 80 K with nitrogen as the coolant, developed at CEA-SBT in collaboration with the CAS/TIPC and tested in laboratory conditions. In addition to the main loop it features a pressure reduction reservoir and a secondary circuit which allow cooling down the loop from the room temperature conditions to the nitrogen liquid temperature and transferring the evaporator heat leaks and radiation heat loads towards the condenser. The general design, the instrumentation and the experimental results of the thermal response of the CLHP are presented, analyzed and discussed both in the transient phase of cooling from room temperature (i) and in stationary conditions (ii). During phase (i), even in a severe radiation environment, the secondary circuit helped to condense the fluid and was very efficient to chill the primary evaporator. During phase (ii), we studied the effects of transferred power, filling pressure and radiation heat load for two basic configurations of cold reservoir of the secondary circuit. A maximum cold power of 19 W with a corresponding limited temperature difference of 5 K was achieved across a 0.5 m distance. We evidenced the importance of the filling pressure to optimize the thermal response. A small heating power (0.1 W) applied on the shunted cold reservoir allows to maintain a constant subcooling (1 K). The CLHP behaves as a capillary pumped loop (CPL) in such a configuration, with the cold reservoir being the compensation chamber of the thermal link. The radiation heat loads may affect significantly the thermal response of the system due to boiling process of liquid and large mass transfer towards the pressure reduction reservoir.     

微膨胀型低温热开关研究

低温热开关是空间制冷中多机并联的关键技术之一,主要用于耦合备用制冷机以减少非运转机上的寄生热载.在比较了各种空间用低温热开关的性能的基础上,详细介绍了中国科学院理化技术研究所研制的被动型热开关的设计及实验情况.其工作原理是根据不同材料的热胀冷缩性能不同进行的,结构总长度在20～40 mm之间,仅由3部分组成.设计了长寿命实验的自动测试实验台,并进行1 500次的开关循环实验,证明此装置的可靠性.实验结果表明,该热开关闭合热阻小于1.1 K/W,断开热阻大于1 400 K/W.     

Validation of an EcosimPro® model for the assessment of two heat load smoothing strategies in the HELIOS experiment

HELIOS experiment, installed at CEA Grenoble, is a scaled down helium loop for investigating high pulsed loads on superconducting magnet cooling circuits of Tokamak. Heat loads have to be smoothed down in order to ensure refrigerator stability. A real time simulation is of interest for reproducing the thermohydraulic phenomenon observed experimentally. The modelling work has been carried out with EcosimPro simulation software combined with a specific cryogenic library. Existing components were modified with additional features, particularly for taking into account 1D fluid transport. The model comprises a closed loop with forced flow supercritical helium at 4.4 K and 5 bar connected through heat exchangers to a saturated helium bath at 1.1 bar. The new heat load mitigation strategies presented in this paper are based on two kinds of regulations in order to smooth the helium mass flow retuning to the refrigerator. First strategy uses the bath as a thermal buffer by acting on bath outlet control valve. Second one uses the variation of the circulator speed to induce a delay in the arrival of the heat loads into the helium bath. The model with the two controls is validated against comparisons with experimental data.     

Performance measurements of a 7 mm-diameter hydrogen heat pipe

A gravity assisted heat pipe with 7-mm diameter has been developed and tested to cool a liquid hydrogen target for extracted beam experiments at COSY. The liquid flowing down from the condenser surface is separated from the vapor flowing up by a thin wall 3 mm diameter plastic tube located concentrically inside the heat pipe. The heat pipe was tested at different inclination angles with respect to the horizontal plane. The heat pipe showed good operating characteristics because of the low radiation heat load from the surroundings, low heat capacity due to the small mass, higher sensitivity to heat loads (to overcome the heat load before the complete vaporization of the liquid in the target cell) due to the higher vapor speed inside the heat pipe which transfers the heat load to the condenser.     

A coupled numerical analysis of shield temperatures, heat losses and residual gas pressures in an evacuated super-insulation using thermal and fluid networks: Part II: Unsteady-state conditions (cool-down period)

This paper analyses the cool-down period of a 300 L super-insulated cryogenic storage tank for liquid nitrogen. Storage tank and evacuated shields are the same as described in part I of this paper where stationary states were investigated. The aim of the present paper is to introduce thermal resistance networks as a tool to quantitatively understand and control also unsteady-states like cool-down of super-insulations. Numerical simulations using thermal resistance networks have been performed to determine time dependence of local shield temperatures and heat loss components. Coupling between radiation and solid conduction is investigated under these conditions. Using the numerical results, we have checked an experimental method suggested in the literature to separate heat losses through the insulation from losses through thermal bridges by measurement of unsteady-state evaporation rates. The results of the simulations confirm that it takes the outer shields much longer to reach stationary temperature; cool-down does not proceed uniformly in the super-insulation. Coupling between different heat transfer modes again is obvious. Thermal emissivity is important also during the early phase of cool-down. Using the obtained numerical results, the experimental method to separate heat loss components could only roughly been confirmed for thick metallic foils.     

Al6063管件外增量成形工艺研究

目的 研究6063铝合金管件外增量成形过程,分析管件的成形效果,改进管件成形质量。方法 设置3组目标成形管件,使用Abaqus软件进行成形过程的数值模拟,通过考察成形管件的几何精度、壁厚分布、表面质量、成形力,分析成形质量和可能出现的问题。通过使用长120 mm、直径50 mm、壁厚1.5 mm的Al6063铝管进行管件外增量成形实验,验证数值模拟结果的可靠性。结果 成形管件会发生管端变形现象,具体表现为管端不圆与轴向伸长,成形件管端椭圆度为10.11%,管端变形程度与成形道次成正比,且在距离管端越近的成形区域,管端变形越明显。管壁成形区厚度增大并呈现不均匀分布。成形件管壁直线度偏差为0.34,且表面质量与径向进给量和轴向进给速度成反比,管件的圆角尺寸难以严格控制。径向力是成形过程中主要的成形力,其大小与工具头直径成正比。结论 管件外增量成形原理可靠,基于此能够实现多种目标管件的成形。由于成形原理的限制,成形件的成形质量还有很大的提升空间,合理制定工艺参数对提高成形质量十分重要。     

EAST超导托卡马克热负荷波动对低温系统液氦槽的影响

EAST超导托卡马克的纵场和极向场磁体均采用NbTi超导材料,由3.8 K超临界氦冷却.在托卡马克实验运行时,极向场的放电脉冲和等离子体破裂产生的交流损耗带来的热负荷增加,经过超临界氦流带到低温系统控制阀箱内的液氦槽和过冷槽,造成槽内的液氦蒸发量增加.蒸发的氦回到制冷机中,从而影响制冷机的稳定运行.通过对实际超临界管道和液氦槽、过冷槽中换热过程建立换热模型,进行热工分析,分析液氦槽和过冷槽中的压力等参数的变化,指导低温系统的设计.     

Cryogenic system of the MAX-Wiggler

A novel insertion device for electron storage rings called the MAX-Wiggler has been constructed and commissioned at MAX-lab. The MAX-Wiggler is a cold bore superconducting wiggler magnet with 47 3.5 T poles and a period length of 61 mm aimed for the production of X-rays at the 1.5 GeV electron storage ring MAX-II at MAX-lab. This note describes the cryogenic system of the MAX-Wiggler, theoretical predictions of the heat loads to the cryostat, and measured heat loads at operation. The cryostat is a helium cooled bath type cryostat. The design criterion for the cryostat was to have a liquid He boil-off less than 3 l/h, which corresponds to a heat load of 2.1 W. The theoretical calculations predicted a heat load of 0.87 W to the liquid He bath. Of the 0.87 W predicted heat load, 0.17 W was predicted to be induced by the stored beam in MAX-II, 0.12 W from synchrotron radiation and 0.05 W from image currents. The measured heat load to the liquid He bath is larger than predicted from the theoretical calculations and at nominal working conditions it is 1.7 W. The measured contribution to the total heat load from the stored beam of 200 mA in MAX-II is 0.86 W, 0.59 W from image currents and 0.26 W from synchrotron radiation. The measured contribution from the image current is 0.59 W, about 10 times larger than expected from the theoretical calculations, which is assumed to depend on that the Cu plating of the inner surfaces of the cold bore has a lower electrical conductivity than foreseen. The higher than expected heat load from synchrotron radiation is assumed to come from a positioning error of the upstream absorber for synchrotron radiation. There is no observable increase of the heat load with the wiggler at full field. Even though the heat loads are higher than expected, the design criterion of obtaining a cryostat with a liquid He boil-off inferior to 3 l/h with 200 mA of stored current in MAX-II has been met.     

环形正负电子对撞机大型探测器超导磁体虹吸实验初步研究

对环形正负电子对撞机大型探测器超导磁体拟采用的低温虹吸实验进行了研究,通过液氮虹吸实验发现了倾斜角度对虹吸换热效果的影响。热虹吸管在15°时换热效果最佳(最大换热温差在4 K内),倾角增大,热虹吸管冷热端温差逐渐增大。对液氦虹吸实验装置进行设计和搭建,并进行了初步探索,研究发现蒸发侧热负荷为0.5 W时,管路换热温差为1.2 K,且装置本体漏热为0.5 W。     

Development and investigation of compact cooler using a pulsating heat pipe

Results are given of development and investigations of a compact cooler for application in electronics, based on an open-loop oscillating heat pipe. The cooler operation is investigated, where water, methanol, and R141b Freon are used as working fluids under conditions of uniform and concentrated heat input. The effective operation of the device is demonstrated in the heat load range from 5 to 250 W. The “heat source-ambient air” minimal thermal resistance of 0.35°C/W was reached with water under uniform heat load of 250 W. The maximal value of heat load density is 75 W/cm² with the heat flux concentration on the surface of 1 cm², where methanol is used as working fluid.     

CPC热管真空管式热水器实验研究

研制了一种CPC(复合抛物面聚焦)热管真空管式太阳能热水器。该热水器在普通玻璃真空管热水器的基础上耦合热管技术,并增加了CPC聚光板。对该热水器与全玻璃真空管太阳能热水器进行了热性能对比实验研究。结果表明,在300 W/m2~800 W/m2日照条件下,该新型热水器单位面积集热功率最高可达610 W/m2;平均集热效率约为80%,比全玻璃真空管太阳能热水器的瞬时效率高10%~20%;导热介质的最高温度达到103℃。证明增加CPC聚光板及运用导热油可有效提高集热品位,利用热管技术可解决严寒地区的抗冻问题,所以,CPC热管真空管式太阳能热水器将具有较广阔的市场前景。     

EAST窗口插件式低温泵热辐射特性的数值模拟研究

EAST窗口插件式低温泵是用于偏滤器粒子排出的重要部件,辐射热负荷对其抽气性能具有显著影响。本文首先设计了基于不同挡板形式的低温泵主要结构,并用仿真软件COMSOL分析低温板所受的辐射热。结果表明采用百叶窗挡板时低温板的辐射热负荷是人字型挡板的三倍左右,对照分析得到较为合理的挡板结构;对低温泵的表面处理方法进行探究,发现冷屏内壁抛光和发黑对低温板所受辐射热负荷的影响基本相当,但相比发黑,抛光可降低冷屏所受的辐射热量。在对低温板辐射热负荷的影响不大的前提下,对辐射挡板部分表面抛光可使其所受辐射热量比全部表面发黑处理减小40%左右。最后分析了挡板阵列和低温板阵列辐射热负荷的分布情况,为其冷却结构设计提供指导。研究为EAST窗口插件式低温泵的研发提供数据参考和设计依据。     

Relative increase in heat transfer in viscous-inertial regimes of flow of helium at supercritical pressure in a heated pipe

Results are presented from an experimental study of an increase in heat transfer to a turbulent flow of supercritical helium in a pipe.     

Transient burn-out in liquid helium with rapid rise of heat flux

This Paper presents the results of experimental and theoretical investigations of transient burn-out in liquid helium moving freely. Heat input in the open vertical channel with liquid helium was increased linearly. The rate of increase of heat flux was varied from 100 to 23 000 W m⁻² s⁻¹, ensuring both quasi-steady and transient conditions. When heat input rose rapidly, burn-out simultaneously appeared over the entire channel length. This can be explained by the peculiarities of unsteady hydrodynamics. A physical model of transient boiling burn-out in a pool and in channels is presented. Relationships for some forms of heat flux variation in time have been derived on the basis of this model. Present experimental data and results of other authors are verified by means of the developed model.     

Numerical and experimental study on heat transfer characteristic and thermal load of the freezer gasket in frost-free refrigerators

The present study has been carried out to analyze the heat transfer characteristics and thermal load near the freezer gasket region of a 649 L domestic frost-free refrigerator/freezer. Both 3D numerical simulations and experimental test were performed. The numerical models for different freezer gasket sections were developed, while considering the non-uniform distribution of temperature inside the freezer cabinet. The calculated temperatures showed acceptable agreement with the measured temperatures. The total thermal load of gasket region is 10.57/6.68 W, in the status of compressor on/off. Thermal load of cold-bridge accounts for 23.8%/25.8% of the total thermal load, and thermal load of gasket bulk holds 76.2%/74.2%, respectively. When the compressor on–off time ratio is 7:3, total thermal load near the freezer gasket region is 9.40 W during an on–off cycling operation of compressor, accounting for 17.1% of the total thermal load in the freezer cabinet.     

乙烷脉动热管的CFD数值模拟研究及实验对比

为了更好地了解脉动热管内部的内在运行机制,本文在实验的基础上采用VOF模型对乙烷脉动热管的传热特性进行了数值模拟研究.结果表明:充注工质后,脉动热管内部形成了随机的气液分布;在启动过程和稳定运行过程中,温度波动的频率随着加热功率的增大而增大;在稳定运行过程中,脉动热管内的流型也在不停地变化.将模拟结果与前期的实验结果进...     

Effect of number of turns and configurations on the heat transfer performance of helium cryogenic pulsating heat pipe

The pulsating heat pipe (PHP) is a potential alternative to highly conductive metals such as copper for long distance heat transfer. Effective thermal conductivity and heat transfer capacity of a PHP are two of the most critical factors for practical applications. In this paper, a helium based PHP, which consists of 48 parallel tubing sections, was developed. The lengths of the evaporator, adiabatic and condenser sections are 50 mm, 100 mm and 50 mm respectively. The condenser section was thermally anchored to a Gifford-McMahon cryocooler (GM cryocooler) with a cooling capacity of 1.5 W at 4.2 K. A maximum effective thermal conductivity of 12330 W/m∙K was obtained when 1.1 W heat was applied to the evaporator section at a fill ratio of 70.5%. With the same geometric parameters and operational parameters, the effect of the number of turns on the heat transfer performance was figured out by comparing the 48-turn PHP with an 8-turn PHP. The results show that the temperature difference between the evaporator and condenser sections of the 48-turn PHP is much smaller than that of the 8-turn PHP. The dry-out temperature response, effective thermal conductivity and heat transfer capacity of them are obtained and analyzed. Furthermore, two configurations of the 48-turn PHP, a parallel configuration and a series configuration, are defined. An optimum configuration is proposed and makes a reference to the design of a cryogenic PHP for applications.