Study on a 5.0 W/80 K single stage Stirling type pulse tube cryocooler

A single stage Stirling pulse tube cryocooler was designed based on REGEN 3.2 and fabricated for testing. The experimental results show that the cooler can provide a cooling capacity of 5.0 W at 79.1 K, and produce a no-load temperature of 57.0 K, operating with an average pressure of 2.50 MPa and a frequency of 60 Hz, performance results that are very close to the calculated values. The cryocooler can be cooled from room temperature to 80 K in 8.5 min. The fast cooldown time is a result of the small regenerator.

Computational fluid dynamic simulation of an inter-phasing pulse tube cooler

An inter-phasing pulse tube cooler (IPPTC) consists of two pulse tube units, which are connected to each other at hot ends of the pulse tubes through a needle valve. This paper presents the computational fluid dynamic (CFD) results of an IPPTC using a 2D axis-symmetrical model. General results such as the phase difference between pressure and velocity at cold end and hot end, the temperature profiles along the wall, the available lowest temperature as well as its oscillations and the coefficient of performance (COP) for IPPTC are presented. The formation of DC flow and its effects on the performance of the cooler are investigated and analyzed in detail. Turbulence, which is partially responsible for the poor overall performance of a single orifice pulse tube cooler (OPTC), is found to be much reduced in IPPTC and its performance is improved significantly compared with the single OPTC.

中国大规模空分研究进展（英文）

中国钢铁、化工等行业对工业气体需求的快速增长，极大地促进了大规模空分技术的发展。目前，中国生产的单套空分设备最大氧产量达到了120000Nm^3／h，单位能耗为0．38kWh／m^3。本文介绍了中国大规模空分技术发展水平，回顾了中国大规模空分工业的发展历史。以成熟的60000Nm^3／h空分系统为例，详细介绍了分子筛吸附器、空压机、板翅换热器、透平膨胀机和精馏塔等主要设备的技术参数。然后介绍了中国正在发展中的80000～120000Nm^3／h空分工艺和装备。最后讨论了中国大规模空分技术存在的主要问题及未来发展方向。

基于数值模拟的低温风洞羽流扩散过程的参数敏感性分析（英文）

目的:低温风洞运行时大流量低温氮气被排放到大气环境中,对周围环境造成潜在的低温、缺氧危险。本文旨在研究羽流扩散过程中各变量(环境风速、环境风温度、相对湿度和排气出口流速)对羽流沉降的影响。创新点:采用考虑相变的低温羽流扩散模型,通过数值模拟对影响羽流扩散的各参数进行敏感性分析。方法:1.基于Hertz-Knudsen关系修正,考虑空气中水的相变,构建低温羽流扩散的数值模型;2.对照美国National TransonicFacility的羽流扩散数据和NASA的二阶分析模型的计算结果,验证本文所采用的数值模型的准确性;3.利用数值模拟,比较不同排放条件下近地面的最低氧含量和最低温度,并对各变量进行敏感性分析。结论:1.考虑相变的羽流扩散数值模型,相比NASA的二阶分析模型拥有更好的准确性。2.对于0.3m低温风洞的羽流扩散,高环境风速有利于羽流消散;高环境温度和高相对湿度能提升近地面的最低温度,但对近地面的最低氧含量影响甚微。3.当排气速度小于2 kg/s时,排气流速增大不利于羽流消散;当羽流速度大于2 kg/s时,排气流速增大有利于羽流消散。

液氮温区单级大功率斯特林型脉管制冷机工作特性研究（英文）

目的:探索充气压和运行频率等工作特性对大功率脉管制冷机最低制冷温度、制冷量以及回热器温度不均匀性的影响,期望进一步提升制冷机工作性能。方法:1.通过理论计算模拟工作频率在40–70 Hz,充气压力在1.5–2.5 MPa下工作特性对制冷机性能的影响;2.实验研究充气压力为1.7–2.4 MPa,并在谐振频率附近工作时制冷机性能以及回热器温度不均匀性随充气压力、运行频率以及输入功率的变化。结论:1.制冷机运行在1.9–2.1 MPa充气压力下,因平衡了制冷温度和焓流损失,故能取得优异性能,且每一个充气压力对应一个最优的工作频率;2.通过优化充气压力和工作频率,脉管制冷机能够达到46.9 K的最低制冷温度,此时工作频率为56.5 Hz,充气压力为2.0 MPa。在8.9 k W输入功率下制冷机能够在72 K时提供304 W制冷量。

Cavitation evolution and damage by liquid nitrogen in a globe valve

Valves are key components of the safety of fluid transportation systems because of induced disturbance and cavitation damage in them.In this study,a 2D model of a cryogenic globe valve with liquid nitrogen(LN_(2))as working fluid was established by Fluent,and thermal effects were specially considered in the simulation.The validity of the LN_(2) cavitation model was verified by the experimental data of hydrofoil LN_(2) cavitation from earlier studies by NASA.Cavitation characteristics of LN2 in the cryogenic globe valve under three typical working conditions were investigated.The average pressure and pressure pulse at different positions of the wall were further studied to reveal cavitation risks from fatigue and vibration.Results show that with similar valve structure and openings,the pressure pulsation frequencies of LN_(2) are lower than those of water,and the shape and location of the cavitation clouds also show significant differences.For LN_(2) cavitation,an extended period of valve opening at 66% should be avoided since its pressure pulse peak is the largest compared to openings of 33% and 100%,and reaches 5×10^(7) Pa.The opening of 33% should also be monitored because of the large torque caused by the pressure difference between the two sides of the valve baffles.To prevent resonance,a critical state for the valve opening and the connecting pipe length is proposed.These predictions of cryogenic cavitation in the globe valve are helpful for the safe and reliable operation of cryogenic fluid transport systems.

采用Gd_2O_2S回热填料的带预冷4K斯特林型高频脉管制冷机性能研究（英文）

研究目的:研究新型磁性回热填料Gd2O2S对液氦温区高频脉管制冷机多级回热器损失特性的影响。创新要点:确定了不同回热填料以及运行参数(频率、平均压力)下液氦温区多级脉管制冷机的制冷温度和各级预冷量,进一步明确了4 K高频回热损失机理。研究方法:采用理论研究与实验验证相结合的方法,基于一台两级G-M型低频脉管制冷机预冷的单极斯特林型高频脉管制冷机,研究多级回热器在高频以及4 K温区下的损失特性。选取新型回热填料Gd2O2S替代部分回热填料HoCu2,比较回热器采用两种填料时在不同运行频率及平均压力下的冷端制冷温度(图10)、各级预冷量和预冷温度(图11–12)。重要结论:采用孔隙率较小的新型磁性回热填料Gd2O2S可显著改善第一级回热器内压力波与质量流的相位关系,从而减小该级回热损失。减小平均压力可以降低制冷机无负荷制冷温度并减小第二级预冷量,但制冷工质氦的体积比热容会急剧增大,从而使低温级回热器的换热对频率非常敏感。此外,频率对高温级回热器的回热特性影响不明显。该方法可以为三级斯特林型4 K多级脉管制冷机提供设计依据。

大功率脉管制冷机的温度非均匀性（英文）

目的:大功率脉管制冷机中存在的温度非均匀性问题导致回热器效率低下,严重阻碍制冷机性能的提高。本文回顾回热器非均匀性问题的理论与试验研究,对当前理论与实验的研究结果进行细致的分类与探讨,并展望将来非均匀性研究可能的发展方向。方法:1.当前回热器非均匀性理论与实验研究主要包括形成机理、发展机制和抑制方法三个方面。其中对其形成机理和发展机制的研究以理论为主,抑制方法的研究以实验为主。2.回热器温度非均匀性的形成机理,按照其诱发因素的来源可划分为内源性与外源性因素,其中内源性因素包括与回热器相关和变径流道等,外源性因素包括自然对流效应及外界温度扰动。3.发展机制主要认为是气体粘度与温度之间的正向关系导致的回热器内温度与流阻的正反馈效应。4.抑制方法主要是增加回热器内径向热导率,阻断其发展机制,或增加回热器长径比,抑制其影响范围。结论:1.温度非均匀性形成机制复杂,为多因素耦合作用;2.气体粘度与温度之间的正向关系导致的回热器内温度与流阻的正反馈效应是导致非均匀性发展的主要因素;3.增加回热器径向热导率和回热器长径比可有效抑制非均匀性。