单直线压缩机驱动双脉管冷指的实验研究

为了在不同位置获得不同的制冷性能,设计了一台线性对置压缩机驱动两台同轴型脉管冷指的实验方案并搭建了试验台.通过实验研究两台脉管制冷机耦合的制冷性能.实验结果显示:两台设计相同的脉管冷指性能不同,经过耦合后制冷性能差异更大,可同时达到1.79 W@60 K和1.384 W@60 K制冷量.     

回热器丝网填充率对85 K型同轴脉管制冷机性能的影响分析

通过建立一维数值模型,分析85 K型同轴脉管制冷机热力学参数随回热器丝网填充率变化的关系,揭示了丝网填充率对制冷机性能影响的机理。通过改变丝网填充率,分别进行了24.8%、25.5%、26.37%填充率的制冷机性能试验研究,研究发现12 W@85 K制冷量时的输入功随着丝网填充率的增加而增大,与数值模拟结果相符。通过对实验和模拟数值结果进行对比分析,验证了模型的准确性。     

分离型二级脉管制冷机的实验研究--Ⅱ:液氦温区二级脉管制冷机

研制1台新型液氦温区分离型二级脉管制冷机,该制冷机由2台独立的脉管制冷机组成,一级回热器冷端和二级回热器中部通过热桥相连,从根本上弥补了传统直接耦合型多级脉管制冷机级间干扰的不足.采用双压缩机双旋转阀驱动该二级脉管制冷机,第二级最低温度达到了2.5 K,在4.2 K下有508 mW制冷量,同时一级在37.5 K有15 W制冷量.第二级充气压力由1.7 MPa增大到1.85 MPa,制冷机在4.2 K下的制冷量可以达到590 mW.为了能简化结构、扩大应用,提出采用单压缩机单旋转阀驱动该分离型脉管制冷机,达到了相同的制冷性能.     

液氦温区脉管制冷机的频率特性

着重研究了操作频率对液氦温区脉管制冷机性能的影响,在实验和分析的基础上,明确了制冷温度、制冷量、制冷效率与工作效率之间的关系,并与4K G－M制冷机的情况进行比较,得出了一些有益的结论。通过频率优化,脉管制冷性能得以较大提高。在初步试验中,分别在1．2Hz和1．1Hz获得了30W@70K,500mW@4.2K以及20W@65K,590mW@4.2K的制冷量。同时还给出了脉管制冷湿度稳定性的测试结果。试验结果表明,研制的脉管制冷机温度波动均小于同类商品型4K GM制冷机及脉管制冷机。     

大功率单级脉管制冷机回热器性能模拟与实验

为了提高单级脉管制冷机在20 K-40 K温区的制冷量,对自行设计制作的1台单级G-M型脉管制冷机采用REGEN3.3进行了计算模拟,获得了铅丸直径选择、不同温区回热器材料最佳组合等结果。在此基础上,对该台单级脉管制冷机进行了试验,实验结果表明该脉管制冷机在20.6K和29.9 K可分别获得20 W和40 W的制冷量,输入功率为7.5 kW。     

基于传输管的三级级联脉管制冷机实验研究

为提高脉管制冷机制冷效率,通过引入一根特殊设计的传输管,将本应在前一级脉管制冷机脉管热端耗散声功回收,理论上多级级联脉管制冷机制冷效率可达卡诺效率。基于该理论,在已有两级级联脉管制冷机基础上串入第三级制冷机。实验结果显示,该三级级联脉管制冷机最高可获得253.6 W@233 K制冷量,较单级制冷机制冷效率增加39.9%,制冷效率进一步趋于卡诺效率。     

大功率脉管制冷机回热器填料优化研究北大核心CSCD

对一台液氮温区百瓦级制冷量的大功率斯特林型脉管制冷机的回热器填料进行了理论优化和实验研究。实验结果发现,在回热器冷端适当组合不同目数的丝网后,会把回热器分成两个部分,这在一定程度上能抑制大功率脉管制冷机回热器中的二次流动,降低回热器中部的温度非均匀性。通过实验得出该脉管制冷机中回热器填料的最优组合为300目不锈钢丝网搭配250目不锈钢丝网,组合比例为10∶1,最终在80 K获得了381.3 W的制冷量。回热器中部最大温差为30.3 K,相较于在回热器中填充单一300目不锈钢丝网的情况,降低了25.6 K。     

双温区高效脉管制冷机性能研究

采用单压缩机驱动的双温区脉管制冷机可以同时在不同制冷温度提供制冷需求。基于阻抗匹配特性,采用一台活塞直径为26 mm的动磁式线性压缩机,分别驱动高温区脉管冷指(HCF,110～170 K)和低温区脉管冷指(LCF,60～80 K)工作在不同制冷温区。一台冷指的制冷负载发生变化会对两台冷指的入口压力波动、压缩机位移以及另一台的制冷性能产生影响,典型的制冷性能为5.7 W@80 K10.9 W@110 K和3.3 W@60 K20 W@170 K,满足空间、能源以及医疗等应用。     

压缩机驱动方式对主动调相型两级脉管阻抗特性影响研究

对双压缩机驱动和单压缩机驱动两种驱动方式下,两级脉管的声阻抗特性和制冷效率随运行压力和运行频率的变化进行对比,研究了单压缩机驱动时冷指的声功分配和制冷效率。一台工作温区为20 K和80 K的主动调相型两级脉管制冷机,冷指入口声阻抗幅值随着运行频率的增加和运行压力的减少而减少。随着运行压力和运行频率的增加,一级制冷效率提升,二级制冷效率降低。单压缩机驱动时通过降低运行频率,选择最优的运行压力来改善第二级制冷性能,在40 Hz,2.8 MPa的运行参数下,400 W输入功时获得了0.37 W@20 K,6.7 W@80 K的制冷性能。     

10W@77K自由活塞斯特林制冷机的设计和实验研究

为满足高温超导、红外探测和气体液化等领域对高效率、高可靠性、长寿命低温制冷机的需求,对10 W@77 K自由活塞斯特林制冷机进行了研究。制冷机设计为整体式结构,由动磁式直线电机驱动。基于Sage建立制冷机整机模型开展了数值求解,并根据数值计算结果对运行频率、工作压力以及回热器填料等对制冷机性能的影响规律进行了分析。计算结果表明,在制冷机结构参数优化的条件下,工作压力为2.1 MPa、运行频率为60 Hz时,制冷量可达11.87 W@77 K,COP为0.068。根据参数优化设计结果研制样机并开展实验研究,实测制冷量达到10.62 W@77 K,COP为0.062。将制冷机连续运行200 h,制冷量波动范围小于0.5 W(即总制冷量的±4.7%),显示出良好的性能稳定性。     

Intermediate cooling from pulse tube and regenerator in a 4 K pulse tube cryocooler

This paper introduces intermediate cooling by thermally attaching heat exchangers on the second stage pulse tube and regenerator in a commercial 4 K pulse tube cryocooler. Due to the large enthalpy flow in the 2nd stage pulse tube and regenerator, both intermediate heat exchangers on the pulse tube and regenerator can provide cooling capacities in the temperature range of 5–15 K without or with minor effect on the performance of the 4 K stage. Extracting cooling capacity from the pulse tube or regenerator reduces the 1st stage cooling performance in the present study. The joint intermediate heat exchanger on the pulse tube and regenerator has demonstrated promising results for applications.     

A two-stage Stirling-type pulse tube cryocooler with a cold inertance tube

A thermally coupled two-stage Stirling-type pulse tube cryocooler (PTC) with inertance tubes as phase shifters has been designed, manufactured and tested. In order to obtain a larger phase shift at the low acoustic power of about 2.0 W, a cold inertance tube as well as a cold reservoir for the second stage, precooled by the cold end of the first stage, was introduced into the system. The transmission line model was used to calculate the phase shift produced by the cold inertance tube. Effect of regenerator material, geometry and charging pressure on the performance of the second stage of the two-stage PTC was investigated based on the well known regenerator model REGEN. Experimental results of the two-stage PTC were carried out with an emphasis on the performance of the second stage. A lowest cooling temperature of 23.7 K and 0.50 W at 33.9 K were obtained with an input electric power of 150.0 W and an operating frequency of 40 Hz.     

斯特林型两级脉管制冷机的改进

在最近研制的1台直线压缩机驱动的两极脉管制冷机的初步试验的基础上,对直线压缩机的线圈重新进行了设计和制作,解决了由于绕制圈数过多而无法输入足够电功率的问题。对冷头的热端法兰及回热器热端热交换器进行了改进,采用了微槽式水冷却器,解决了压缩热无法得到充分冷却引起的制冷机热端温度过高的问题。改进后制冷机的性能得到了显著的提高,在2.0 MPa充气压力和40 Hz频率的条件下,该制冷机获得了14.2 K的最低制冷温度。并且,第一级和第二级在97.8 K和34.9 K时,分别具有2.5 W和1 W的制冷量。     

Two-stage pulse tube refrigerator in an entire coaxial configuration

In this paper, we introduce a new kind of two-stage pulse tube refrigerators. The chosen entire coaxial configuration combines the advantages of the coaxial design with the two-stage pulse tube concept. Lead coated screens build the inhomogeneous regenerator matrix of the second stage. Without any rare earth compounds the refrigerator reaches a no load temperature of 6.6 K at the second stage cold tip. The active type of phase shifting is generated by a rotary valve combined with two needle valves at the hot end of each pulse tube (compressor Leybold RW 6000, 6 kW input power). This paper focuses on the design parameters and first performance measurements.     

Influence of the connecting tube at the cold end in a U-shaped pulse tube cryocooler

In some special applications, the pulse tube cryocooler must be designed as U-shape; however, the connecting tube at the cold end will influence the cooling performance. Although lots of U-shape pulse tubes have been developed, the mechanism of the influence of the connecting tube on the performance has not been well demonstrated. Based on thermoacoustic theory, this paper discusses the influence of the length and diameter of the connecting tube, transition structure, flow straightener, impedance of the inertance tube, etc. on the cooling performance. Primary experiments were carried out in two in-line shape pulse tube cryocoolers to verify the analysis. The two cryocoolers shared the same regenerator, heat exchangers, inertance tube and straightener, and the pulse tube, so the influence of these components could be eliminated. With the same electric power, the pulse tube cryocooler without connecting parts obtained 31 W cooling power at 77 K; meanwhile, the other pulse tube cryocooler with the connecting parts only obtained 27 W, so the connecting tube induced more than a 12.9% decrease on the cooling performance, which agrees with the calculation quite well.     

High frequency two-stage pulse tube cryocooler with base temperature below 20 K

High frequency (30-50 Hz) multi-stage pulse tube coolers that are capable of reaching temperatures close to 20 K or even lower are a subject of recent research and development activities. This paper reports on the design and test of a two-stage pulse tube cooler which is driven by a linear compressor with nominal input power of 200 W at an operating frequency of 30-45 Hz. A parallel configuration of the two pulse tubes is used with the warm ends of the pulse tubes located at ambient temperature. For both stages, the regenerator matrix consists of a stack of stainless steel screen. At an operating frequency of 35 Hz and with the first stage at 73 K a lowest stationary temperature of 19.6 K has been achieved at the second stage. The effects of input power, frequency, average pressure, and cold head orientation on the cooling performance are also reported. An even lower no-load temperature can be expected from the use of lead or other regenerator materials of high heat capacity in the second stage.     

Investigation on the internal thermal link of pulse tube refrigerators

Within a pulse tube refrigerator (PTR) in coaxial configuration the pulse tube is located inside the regenerator matrix in axial direction. An internal thermal contact between these two main components of the coldfinger occurs. The experimental investigation of the direction and the quantity of transferred heat is in focus of this paper. Intermediate cooling of the regenerator by the corresponding part of its own pulse tube can improve the cooling performance of a PTR. Therefore, a well-adapted geometrical arrangement between the pulse tube and the regenerator is essential, considering the temperature distribution inside the coldfinger. We deduce design parameters to optimise the configuration of coaxial PTRs.     

An approach for estimating acoustic power in a pulse tube cryocooler

Acoustic power at the cold end of regenerator is the measure of gross cooling capacity for a pulse tube cryocooler (PTC), which cannot be measured directly. Conventionally, the acoustic power can only be derived from the measurement of velocity, pressure and their phase angle, which is still a challenge for an oscillating flow at cryogenic temperatures. A new method is proposed for estimating the acoustic power, which takes use of the easily measurable parameters, such as the pressure and temperature, instead of the velocity and phase angle between the pressure and velocity at cryogenic temperatures. The ratio of acoustic powers at the both ends of isothermal components, like regenerator, heat exchangers, can be conveniently evaluated by using the ratio of pressure amplitudes and the local temperatures. The ratio of acoustic powers at the both ends of adiabatic components, like transfer line and pulse tube, is obtained by using the ratio of pressure amplitudes. Accuracy of the approach for evaluating the acoustic power for the regenerator is analyzed by comparing the results with those from REGEN 3.3 and references. For the cold end temperature range of 40–80 K, the deviation is less than 5% if the phase angle at the cold end of regenerator is around −30°. The simple method benefits estimating the acoustic power and optimizing the PTC performance without interfering the cryogenic flow field.     

20K温区单级脉管制冷机漏热分析

漏热冷损是影响低温制冷机性能的一个重要因素.对1台工作在20 K温区的单级脉管制冷机进行了漏热计算,并对其进行了部分实验验证.结果表明:在系统总漏热中,脉管和回热器的壁面轴向导热所占的比例最大.