13 K thermally coupled two-stage Stirling-type pulse tube refrigerator

A pulse tube refrigerator (PTR), without moving com-ponents in low temperature region, occupies a number of advantages, such as simplicity, reliability, long-life, low vibration and so on. This novel refrigerator is a potential substitute for the common cryocoolers (e.g. G-M coolers and Stirling coolers), capable of cooling infrared detectors and superconductive devices and liquefying cryogenic fluids. Multi-stage PTRs have been developed to attain a cooling temperature below 20 K and to s…     

A novel coupling configuration for thermoacoustically-driven pulse tube coolers： Acoustic amplifier

A thermoacoustically-driven pulse tube cooler has re-cently reached temperatures below 77 K[1] by modifying the resonance tube of the thermoacoustic engine and the hot end phase adjuster of the pulse tube cooler. Normally, the pulse tube cooler is directly connected with the ther-moacoustic engine so that pressure ratio available to the pulse tube cooler is limited by what the thermoacoustic engine can provide[1,2]. To obtain temperatures below 70 K, the high frequency pulse tube cooler genera…     

A heat-driven thermoacoustic cryocooler capable of reaching below liquid hydrogen temperature

A "double-gas acoustic amplifier" is introduced to couple a thermoacoustic heat engine and a two-stage pulse tube cooler in this paper. Compared with previous acoustic amplifiers, this new acoustic amplifier maintains the function of amplification for pressure amplitude. In particular, the novel acoustic amplifier with a reservoir makes it possible to install an acoustic transparent but gas blocking elastic membrane between the engine and the cooler. Thus, the engine can use nitrogen as the working gas to work at low frequency; and meanwhile, the cooler can still use helium as the working gas to maintain its high performance. With this new amplifier, the cooling temperature of a two-stage pulse tube cooler driven by an energy-focused thermoacoustic engine reached 18.7 K.     

A separate two-stage pulse tube cooler working at liquid helium temperature

A novel 4 K separate two-stage pulse tube cooler (PTC) was designed and tested. The cooler consists of two separate pulse tube coolers, in which the cold end of the first stage regenerator is thermally connected with the middle part of the second regenerator. Compared to the traditional coupled multi-stage pulse tube cooler, the mutual interference between stages can be significantly eliminated. The lowest refrigeration temperature obtained at the first stage pulse tube was 13.8 K. This is a new record for singlestage PTC. With two compressors and two rotary valves driving mode, the separate two-stage PTC obtained a refrigeration temperature of 2.5K at the second stage. Cooling capacities of 508mW at 4.2K and 15W at 37.5K were achieved simultaneously. A one-compressor and one-rotary valve driving mode has been proposed to further simplify the structure of separate type PTC.     

High efficiency linear compressor driven pulse tube cryocooler operating in liquid nitrogen temperature

The inertance tube is one of the key components of a pulse tube cryocooler. It has great influence not only on the efficiency of the pulse tube cryocooler, but also on the efficiency of the linear compressor. Meanwhile, it is very difficult to predict the impedance of an inertance tube because of the turbulent flow. In this paper, using a quasi-turbulent model, the inertance tube is optimized to match a linear compressor driven pulse tube cryocooler. Experimental results show that this model can predict the impedance quite well. With 127 W input electric power, the pulse tube cryocooler obtains 9.4 W cooling power at a temperature of 77 K. The relative Carnot efficiency of the whole system reaches 19.8%.     

Investigation on regenerator temperature inhomogeneity in Stirling-type pulse tube cooler

Regenerator is one of the most crucial components to pulse tube cooler (PTC) and thermoacoustic engine. As such regenerator is scaled up to high-power, the thermal and hydrodynamic communication transverse to the acoustic axis gets weaker and weaker. Under this condition, any unsymmetric factor could cause serious instability to the cooler or engine, which degrades their performance. Investigation has been carried out on a high-power two-stage thermal-coupled U-shape Stirling-type PTC. By detailed circumferential temperature measurements along the middle heat exchanger and second stage regen-erator, a kind of temperature inhomogeneity caused by unsymmetric pre-cooling effect of inter-stage thermal bridge was found in the lower part of the regenerator of the PTC. The temperature inhomoge-neity originating from the middle heat exchanger of the second stage regenerator amplified itself in the lower part of the regenerator and then internal streaming formed. The maximal radial temperature dif-ference could reach 30―40 K. Experimental results show that the temperature inhomogeneity intensi-fies with increased pre-cooling power and its direction can be reversed by changing the pre-cooling effect of the first stage PTC to heating effect by using external thermal load. This research shows that it is important to maintain the heating or cooling effects of heat exchangers uniform in high-power re-generative coolers and engines.     

直管套管内超临界二氧化碳热力性能研究

为了解决气冷器内不可逆损失对换热性能的影响问题,提高直管套管式气冷器的热力性能,对超临界二氧化碳套管式气冷器内二氧化碳与冷却水之间的热量传递过程进行了研究。采用Fluent数值模拟软件与熵产分析方法,通过改变操作压力、二氧化碳质量流量及冷却水的质量流量和进口温度进行数值计算,得出气冷器中二氧化碳和冷却水沿管长的温度分布情况,并依据热力学第二定律熵产分析方法,对直管套管内热力过程进行计算,得出沿管长的熵产分布情况。结果表明,随着压力的增加,沿管长方向的熵产逐渐增大;随着二氧化碳质量流量的增加,熵产逐渐减小;随着冷却水质量流量的增加,熵产增加幅度不明显;随着冷却水进口温度的增加,熵产随之减小。研究结果可为二氧化碳热泵气冷器运行参数与结构的设计以及二氧化碳热泵的工程应用提供一定的参考。     

斯特林制冷机性能改进的实验研究

对斯特林制冷机用于制冷温区进行了探讨，提出一种复合型的低温制冷机型式－脉管型斯特林制冷机，并从理论上分析了其制冷机理和性能，同时展开了实验研究，与单一的斯特林制冷机进行了性能对比，得出了有益的结果，脉管型斯特林制冷机用于２４５Ｋ以上温区较单一的斯特林制冷机具有优势。     

滑油冷却器小型化研究

通过对新型混合管束式双流程滑油冷却器的大量实验研究,发现其具有很强的换热能力．新型混合管束式双流程滑油冷却器与光管弓形折流板式滑油冷却器,在流动条件总体相似的情况下进行的试验说明,新型混合管束双流程滑油冷却器的单位体积换热量很高,而压降相对较小,综合性能优越．     

He-H_2 mixture and Er_3NiH_χ packing for the refrigeration enhancement of pulse tube refrigerator

The computation with the theory of modified Brayton Cycle indicates that higher cooling power and coefficient of performance for a pulse tube refrigerator can be achieved with He-H_2 mixture as working gas than those with pure He in the temperature region of 30 K. In addition, it is found that Er_3Ni, a regenerative material, is able to absorb H_2 and produces Er_3NiH_x. The computation presents that the regenerative performance of Er_3NiH_x is better than that of Er_3Ni due to its higher volume specific heat. Experimental results show that the pulse tube refrigeration performance in 30 K temperature region is enhanced greatly with He-H_2 mixture and Er_3NiH_x packing.     

超临界CO2热泵蛇形管气冷器传热特性研究

为了减少能源消耗、提高CO₂热泵的效率,基于Fluent软件,采用数值模拟方法对超临界CO₂在蛇形管气冷器中的传热特性进行研究。主要探究蛇形管内超临界CO₂的流动特性,通过改变操作压力、CO₂和冷却水的质量流量,分析蛇形管的传热性能。结果表明,蛇形管中离心力周期反向,会使温度和速度梯度呈周期性的内侧和外侧交互扩散的趋势;超临界CO₂压力越靠近临界点,平均传热系数越高,压力为8 MPa下的平均传热系数相较于9 MPa和10 MPa分别提高了24.37%和42.53%;超临界CO₂的平均传热系数随着CO₂质量流量的增加而增大,随着冷却水质量流量的增加而降低,冷却水质量流量的增加不会对峰值点的传热系数产生影响,但会使峰值点出现的位置提前。研究结果为超临界CO₂热泵蛇形管气冷器的设计、运行及热效率的提升提供了理论依据。     

过热度和高压压力对跨临界CO2汽车空调系统的影响

为对跨临界CO2空调系统进行优化设计,考虑压缩机绝热效率随压比的变化,分析了过热度、气体冷却器出口温度以及高压压力等对系统性能系数(COP)的影响,并与不考虑压缩机绝热效率随压比变化的情况进行了对比。结果表明:系统存在最佳高压和最佳过热度;最佳过热度随着气体冷却器出口温度的提高而增大;气体冷却器和压缩机效率是影响系统性能的主要因素;在较大高压压力下,与气体冷却器和压缩机效率相比,过热度的影响可以忽略不计。     

200K/40W自由活塞斯特林制冷机的实验研究

针对温度为200 K低温冰箱,研制了一台大冷量自由活塞斯特林制冷机.实验测试了充气压力和制冷温度对压缩机共振频率的影响;研究了膨胀机固有频率和运行频率对位移相位差的影响关系;采用多点热负荷静态复温法测试了制冷机的静态冷损,证明了氦气和丝网导热对静态冷损影响极小.该样机在200 K时最大制冷量可达40 W(250 W输入).     

200 K/40 W自由活塞斯特林制冷机的实验研究

针对温度为200 K低温冰箱,研制了一台大冷量自由活塞斯特林制冷机.实验测试了充气压力和制冷温度对压缩机共振频率的影响;研究了膨胀机固有频率和运行频率对位移相位差的影响关系;采用多点热负荷静态复温法测试了制冷机的静态冷损,证明了氦气和丝网导热对静态冷损影响极小.该样机在200 K时最大制冷量可达40 W(250 W输入).     

新西兰ROTORUA市KUIRAU热泉Na-K地球化学温标研究

Na-K地球化学温标在计算热储温度时，使用Na^ 、K^ 浓度的比值，因而地热水的混合稀释及蒸气损失对温度的计算影响不大。Na-K地球化学温标的依据是：在一定温度条件下，Na-feldspar(钠长石) K^ =K-feldspar(钾长石) Na^ 反应达完全平衡状态。但当热流体运动速度慢或被浅层地下水稀释而导致温度降低时，反应平衡会被打破，并形成新的平衡。新平衡形成之前为部分平衡状态。以新西兰著名的ROTORUA市KUIRAU公园热泉为例，讨论了在部分平衡条件下，Na-K地热温标的应用。     

高温陶瓷过滤器循环过程的热态实验研究

在一套由3根滤管组成的高温陶瓷过滤实验装置上。在常温至573K范围内进行了过滤与脉冲反吹循环性能实验，分析了操作温度、过滤气速、反吹压力等操作参数对循环性能的影响。实验结果表明，过滤循环初始阶段滤管残余压降上升较快，随后上升趋势逐渐变缓；随着温度的升高，滤管的初始压降升高，形成的粉尘层也越疏松。过滤气速越低，滤管初始压降越低，反吹间隔越长。提高反吹压力有利于提高清灰效果，但压力过高反吹间隔反而变短。最后通过在573K下的连续循环实验得出了滤管残余压降，为高温陶瓷过滤器的工程设计提供了依据。     

跨临界CO2制冷循环性能的研究

文中对理想的跨临界ＣＯ２制冷循环,进行了理论分析和性能计算,揭示了该循环的一些特点：对于一定的冷却器出口温度,对应一个使系统性能系数最佳的冷却压力,而且系统性能系数最佳时的冷却器出口温度与冷却压力的对应关系,可以用一个简单的代数式表示;提高蒸发温度可显著提高循环的性能系数;当冷却压力较低时,提高循环的吸气过热度,可显著地提高系统的性能系数;冷却器出口温度越高,效果越明显,当蒸发温度和冷却器出口温度较高时,减小回热器传热温差,可有效地提高系统的单位容积制冷量和性能系数．这些结论,对于跨临界ＣＯ２制冷系统的运行操作具有重要的指导作用．     

He-H2 mixture and Er3NiHx packing for the refrigeration enhancement of pulse tube refrigerator

The computation with the theory of modified Brayton Cycle indicates that higher cooling power and coefficient of performance for a pulse tube refrigerator can be achieved with He-H2 mixture as working gas than those with pure He in the temperature region of 30 K. In addition, it is found that Er3Ni, a regenerative material, is able to absorb H2 and produces Er3NiHx. The computation presents that the regenerative performance of Er3NiHx is better than that of Er3Ni due to its higher volume specific heat. Experimental results show that the pulse tube refrigeration performance in 30 K temperature region is enhanced greatly with He-H2 mixture and Er3NiHx packing.     

六棱柱滚筒冷渣机传热效率影响研究

冷渣机是CFB（circulating fluidized bed）锅炉的重要辅机,其传热效率对CFB锅炉的连续稳定运行发挥着重要作用,为了进一步分析颗粒传热效率的关系。以一种多管式六棱柱滚筒冷渣机为研究载体,冷渣管内高温灰渣颗粒为研究对象,基于离散元方法及其数值模型,运用商用软件EDEM（extended discrete element method）来模拟分析高温灰渣颗粒在冷渣管内的传热过程。将颗粒温度T规范化处理为量纲温度T?,以平均温度、温度概率密度函数T-PDF和颗粒运动规律为指标定量分析滚筒转速和颗粒直径对灰渣颗粒传热过程的影响。其中,六棱柱冷渣管边长L=200 mm,长500 mm,壁厚10 mm,管初始温度360 K,颗粒初始温度1200 K。结果表明：颗粒的传热效率随着转速的增加而增加,n=10 r/min相对于n=4 r/min的散热效率增加了61.1%;颗粒的传热效率随着粒径的增大而减小,d=5 mm相对于d=3 mm散热效率的下降了30.7%。转速是通过翻转次数来影响传热效率,粒径是影响接触点碰撞次数来影响传热效率。     

一种MEMS热电制冷器的设计

研究一种基于MEMS工艺的微型热电制冷器.采用薄膜热电材料减小器件的尺寸,采用微机械加工工艺形成的硅杯结构降低衬底的热泄漏.器件在材料和工艺上都与微电子工艺兼容,易于与电子器件集成.分别讨论了热电臂长度、厚度及绝缘膜厚度等结构参数对器件最大制冷温差、制冷系数、制冷功率等性能的影响,得出最优的设计参数.分析中考虑了绝缘层热泄漏,制冷区的热对流和热辐射,以及接触电阻等非理想因素.分析结果表明,器件工作时达到的最大温差为40 K;冷端温度为290 K时,制冷功率为3 mW.