1.8K常压超流氦低温系统的设计与分析

中国科学院等离子体物理研究所ITER CC导体测试装置背景超导磁体,由4.2 K液氦浸泡冷却,能够提供7 T背景场,为了满足超导导体测试需要更大背景场(10 T)的要求,将采用1.8 K超流氦浸泡冷却。针对该测试装置的低温系统设计了一种1.8 K常压超流氦低温系统,给出了该系统的关键组成部分并对获取1.8 K常压超流氦的流程进行了分析。针对预冷与节流相结合获取1.75 K超流氦方案进行了分析和计算,同时针对此方案给出了其物理过程的T-s图,计算了1.75 K超流氦液体得率。     

氦-3的汽化热和熔解热

基于Clausius-Clapeyron方程、维里方程和最新开发的氦-3相平衡曲线方程计算了氦-3在平衡曲线上的两个重要性质:汽化热(0 K～3.315 7 K)和熔解热(0.001 K～35 K).计算结果覆盖的温度范围广,精度也满足工程应用的需求.     

1K～100K温区He-3低温热物性数据计算

由于量子效应的影响，低温下He-3的性质与He-4有很大差异，对于4K－20K气相He-3的性质可利用改进的Strobridge方程来计算，而在20K－100K温区，通过引入对比德布罗意波长作为第三参数来描述量子效应而建立的改进量子对比态模型可用于计算该温区He-3的性质，基于上述计算方法，采用计算机程序设计，建立了He-3低温热物性数据库，该数据库可以计算压力在10MPa以下，温度介于1K－100K之间He-3的pVT性质，焓、内能、熵，热导率和粘度，其计算精度基本可以满足工程需要。     

吸附势理论在10K低温吸附器设计中的应用

以氢气在活性炭中22 K、27 K、32 K、37 K、77.3 K、89 K温度下的吸附数据为基础,根据Polanyi吸附势理论得到了跟温度无关的吸附特征曲线,并利用特征曲线反推对应温度下的吸附等温线;发现吸附势理论对氢气在活性炭中临界温度以下温区较低压力下(小于0.01 MPa)吸附量的预测跟实验数据吻合较好;并根据吸附势理论得到了10 K下氢气在活性炭上较低压力下(小于0.01MPa)的吸附等温线,并设计了250 W@4.5 K氦制冷机工作于10 K温度下的吸附器。     

1.8 K常压超流氦低温系统漏热分析及真空泵抽速计算

给出了1.8K常压超流氦低温系统的工作原理.对HeⅡ腔的漏热进行了分析和计算,包括环氧隔热板、安全阀、支撑杆以及测量线与电流引线底座同He Ⅰ腔的导热,真空夹层之间的残余气体导热以及HeⅡ腔内杜瓦与其外周冷屏的辐射换热.根据漏热值,对所需真空泵的抽速进行了计算,同时给出了预冷与节流相结合获取1.75 K超流氦方案物理过程的温-熵图.     

AlFeCoNiMo0.2高熵合金热变形行为及热加工图

目的 确定AlFeCoNiMo0.2高熵合金的热加工工艺参数,为该合金热挤压工艺的制定及优化提供有效依据.方法 采用Gleeble-3800热模拟试验机,在变形温度为900～1150℃,应变速率为0.001～1 s-1,真应变量为0.6的条件下对AlFeCoNiMo0.2高熵合金进行热压缩实验.基于Arrhennius模型对热压缩实验数据进行拟合,建立AlFeCoNiMo0.2高熵合金的Arrhennius本构方程,并绘制AlFeCoNiMo0.2高熵合金在不同真应变下的热加工图.结果 AlFeCoNiMo0.2高熵合金的流变应力值与应变速率呈正相关,与变形温度呈负相关;Arrhennius热变形本构方程的平均相对误差为3.97％;该合金热加工图中的流变失稳区分别为900～1120℃/0.1～1 s-1和1120～1150℃/0.2～1 s-1;热加工安全区为1075～1150℃/0.001～0.01 s-1;最佳热加工工艺参数为:1090～1125℃/0.001～0.002 s-1.结论 AlFeCoNiMo0.2高熵合金的热变形过程为加工硬化和动态再结晶为主的动态软化,建立的Arrhennius本构方程可较好地描述该合金的热变形行为,绘制的热加工图可为该合金热挤压工艺的制定及优化提供有效指导.     

GWN751K镁合金热压缩实验研究

在Gleeble-1500D热模拟机上进行了单向热压缩试验,研究了GWN751K镁合金在变形温度为623-773K,应变速率为0.002-2s-1条件下热变形行为,变形量为60%.结果表明,在相同变形温度条件下,流变应力随变形速率的增加而上升,在相同的应变速率条件下,流变应力随着变形温度的升高而下降,计算出其平均激活能Q为228.61kJ/mol,应力指数n为4.2.根据材料动态模型,计算并分析了GWN751K合金的热加工图,并确定了合适的挤压加工条件为723K,0.01/s.通过对合金的挤压试验研究,验证了加工条件,挤压后的合金断裂强度为320MPa,延伸率为18%,较铸态合金有显著提高.     

混合工质R134a/R23焓-浓度图的绘制

使用PR(Peng-Robinson)方程对混合工质R134a/R23进行了气液相平衡的预测和焓、熵的计算.针对PR方程液相精度比较差的问题,对PR方程引入了修正系数,重新推导了逸度系数、余函数等表达式,并将计算结果与实验数据进行了比较.根据计算得到的R134a/R23热物性数据,绘制了工程上广泛使用的二元混合工质的焓-浓度图,为基于该混合工质的循环计算,提供了重要的基础数据.     

4～10 K温区活性炭对氦气的吸附特性及其在4 K温区回热式制冷机中的潜在应用（英文）

活性炭对氦气的吸附量数据是低温领域中吸附式制冷机、气隙式热开关和制冷机回热器研究中的重要参数。活性炭作为制冷机蓄冷材料时,其对氦气的高吸附量导致的高比热有望解决4 K制冷机目前磁性蓄冷材料蓄冷能力严重不足的瓶颈问题,另外还存在着无磁性优点。然而,目前液氦温区活性炭对氦气的吸附量还没有充足的实验数据。本文通过搭建实验台,测试了活性炭在4～10 K,0.5～3.5 MPa范围内的吸附量数据,并计算了吸附热。另外,为了充分验证使用吸附的氦气作为蓄冷材料的可行性,分别计算和测试了比热与流动阻力。结果表明,吸附氦气后的活性炭比热明显高于常规的回热器材料,其流动阻力也与目前Er_3Ni等颗粒材料相当,能够适用于4 K制冷机回热器的蓄冷材料。     

CO_2水合物蓄冷系统的循环特性实验研究

本文采用直接接触式蓄冷实验台,研究了初始充注压力为3.5～4.0 MPa时CO_2水合物蓄冷系统的循环特性和蓄冷特性。通过实验数据绘制了不同初始充注压力下系统的循环p-h图和蓄冷速率图。分析发现:在初始充注压力为3.5、3.6 MPa时,系统循环在亚临界区;在初始充注压力为3.7、3.8、3.9、4.0 MPa时,系统循环进入跨临界区,在跨临界区的时间分别为8、10、9、8 min,系统循环在跨临界区的时间比例依次为38%、58%、60%、73%;初始充注压力越高,系统的蓄冷时间越短,系统蓄冷速率下降速度越快,蓄冷速率曲线越陡峭,蓄冷特性越好。     

Thermodynamic Diagrams of 3He from 0.2 K to 300 K Based Upon its Debye Fluid Equation of State

On the basis of the equation of state and the phase equilibrium equations of helium-3 (³He), a computer program for calculating the thermodynamic properties of ³He has been created. With this program, many iso-property tables were prepared for generating p–h and T–s diagrams of ³He over the range of temperature from 0.2 K to 300 K and pressures up to 300 MPa. Compared with the previous diagrams plotted with interpolated experimental data sets, the new ones are more thermodynamically consistent and cover a broader temperature and pressure range. The estimated overall random errors of the diagrams are within 2 %.     

A practical density equation for saturated vapor of helium-3 from 0.01 K to the critical point

Based on the ideal gas state equation and the saturated vapor pressure equation of helium-3, a saturated vapor density equation is proposed, which can be applied for calculating the saturated vapor density of helium-3 from 0.01 K to the critical temperature. Above 1.4 K, the average deviation between the results by this equation and experimental data is about 0.66% and the maximum is 2%. Below 1.4 K, the results of this work show a comfortable agreement with those by virial state equation (the deviations are generally within 0.1%). Based on this new vapor density equation, the compressibility factor of saturated vapor is determined and the vaporization heat is calculated.     

Thermodynamic Properties of Air from 60 to 2000 K at Pressures up to 2000 MPa

A thermodynamic property formulation for standard dry air based upon experimental P––T, heat capacity, and speed of sound data and predicted values, which extends the range of prior formulations to higher pressures and temperatures, is presented. This formulation is valid for temperatures from the solidification temperature at the bubble point curve (59.75 K) to 2000 K at pressures up to 2000 MPa. In the absence of experimental air data above 873 K and 70 MPa, air properties were predicted from nitrogen data. These values were included in the fit to extend the range of the fundamental equation. Experimental shock tube measurements ensure reasonable extrapolated properties up to temperatures and pressures of 5000 K and 28 GPa. In the range from the solidification point to 873 K at pressures to 70 MPa, the estimated uncertainty of density values calculated with the fundamental equation for the vapor is ±0.1%. The uncertainty in calculated liquid densities is ±0.2%. The estimated uncertainty of calculated heat capacities is ±1% and that for calculated speed of sound values is ±0.2%. At temperatures above 873 K and 70 MPa, the estimated uncertainty of calculated density values is ±0.5%, increasing to ±1% at 2000 K and 2000 MPa.     

Densities of liquid R 114 at temperatures from 310 to 400 K and pressures up to 10 MPa

Density measurements for liquid R 114 (dichlorotetrafluoroethane) have been obtained with a variable-volume method. The results cover the high-density region from 1007 to 1462 kg·m^–3 along ten isotherms between 310 and 400 K at 16 pressures from 0.5 to 10.0 MPa. The experimental uncertainty in the density measurements was estimated to be no greater than 0.2%. Based on the present results the derivatives with respect to temperature and pressure were calculated, and numerical values of the volume expansion coefficient and of the isothermal compressibility are tabulated as a function of temperature and pressure.     

Theory of quantum nucleation of bubbles in liquid helium

We calculate the rate at which bubbles form by quantum tunneling in liquid helium-3 and helium-4 at negative pressure. We find that quantum tunneling should be observable at temperatures below about 0.1 K in helium-3 and 0.2 K in helium-4, and at pressures close to the critical negative pressure at which the liquid becomes unstable against long wavelength density fluctuations.     

A three-stage Stirling pulse tube cryocooler operating below the critical point of helium-4

Precooled phase shifters can significantly enhance the phase shift effect and further improve the performance of pulse tube cryocoolers. A separate three-stage Stirling pulse tube cryocooler (SPTC) with a cold inertance tube was designed and fabricated. Helium-4 instead of the rare helium-3 was used as the working fluid. The cryocooler reached a bottom temperature of 4.97 K with a net cooling power of 25 mW at 6.0 K. The operating frequency was 29.9 Hz and the charging pressure was 0.91 MPa. It is the first time a refrigeration temperature below the critical point of helium-4 was obtained in a three-stage Stirling pulse tube cryocooler.     

New reference data on the thermodynamic properties of sodium vapor

Based on our previously published semiempirical equation of state derived using the results of new precision spectroscopic measurements, tables of reference data are compiled on the thermodynamic properties of sodium vapor and their root-mean-square deviations (errors) in the temperature range from 700 to 2500 K at pressures from the saturation line to 3 MPa     

Thermal properties of superheated rubidium vapor at temperatures up to 2150 K and pressures up to 5 MPa

Based on generalized experimental data, an equation of state is developed for superheated rubidium vapor, from which thermodynamic properties are calculated and tables that cover the parametric regions of 0.1–5.0 MPa pressure and 975–2150 K temperature are constructed.Deceased.Sergo Ordzhonikidze Moscow Aeronautical Institute. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 1, pp. 55–65, January–February, 1995.