Innovative phase shifter for pulse tube operating below 10 K

Stirling type pulse tubes are classically based on the use of an inertance phase shifter to optimize their cooling power. The limitations of the phase shifting capabilities of these inertances have been pointed out in various studies. These limitations are particularly critical for low temperature operation, typically below about 50 K. An innovative phase shifter using an inertance tube filled with liquid, or fluid with high density or low viscosity, and separated by a sealed metallic diaphragm has been conceived and tested. This device has been characterized and validated on a dedicated test bench. Operation on a 50–80 K pulse tube cooler and on a low temperature (below 8 K) pulse tube cooler have been demonstrated and have validated the device in operation. These developments open the door for efficient and compact low temperature Stirling type pulse tube coolers. The possibility of long life operation has been experimentally verified and a design for space applications is proposed.     

Performance analysis and optimization of high capacity pulse tube refrigerator

High capacity pulse tube refrigerator (HCPTR) is a new generation of cryocoolers tailored to provide more than 250 W of cooling power at cryogenic temperatures. The most important characteristics of HCPTR when compared to other types of pulse tube refrigerators are a powerful pressure wave generator, and an accurate design. In this paper the influence of geometrical and operating parameters on the performance of a double inlet pulse tube refrigerator (DIPTR) is studied. The model is validated with the existing experimental data. As a result of this optimization, a new configuration of HCPTR is proposed. This configuration provides 335 W at 80 K cold end temperature with a frequency of 50 Hz and COP of 0.05.     

Enthalpy flow rate of a pulse tube in pulse tube refrigerator

An integration formula of enthalpy flow rate along a pulse tube in pulse tube refrigerators is described on the assumption of sinusoidal mass flow rate and sinusoidal pressure fluctuation. For ideal double inlet and ideal orifice pulse tube with helium as working medium, it is simplified to a polynomial formula. Polynomial formulas for roughly evaluating the volume of the pulse tube in ideal double inlet and ideal orifice pulse tube refrigerators are also given.     

Numerical method of inertance tube pulse tube refrigerator

A nodal analysis method for simulating inertance tube pulse tube refrigerators is introduced. The energy equation, continuity equation, momentum equation of gas, energy equation of solid are included in this model. Boundary condition can be easily changed to enable the numerical program calculate thermal acoustic engines, inertance tube pulse tube refrigerators, double inlet pulse tube refrigerators, and others. Implicit control volume method is used to solve these equations. In order to increase the calculation speed, the continuity equation is changed to pressure equation with ideal gas assumption, and merged with momentum equation. Then the algebraic equation group from continuity and momentum equation becomes one group. With this numerical method, an example calculation of a large scale inertance tube pulse tube refrigerator is shown.     

CFD analysis of thermodynamic cycles in a pulse tube refrigerator

The objectives of this paper are to study the thermodynamic cycles in an inertance tube pulse tube refrigerator (ITPTR) by means of CFD method. The simulation results show that gas parcels working in different parts of ITPTR undergo different thermodynamic cycles. The net effects of those thermodynamic cycles are pumping heat from the low temperature part to the high temperature part of the system. The simulation results also show that under different frequencies of piston movement, the gas parcels working in the same part of the system will undergo the same type of thermodynamic cycles. The simulated thermal cycles are compared with those thermodynamic analysis results from a reference. Comparisons show that both CFD simulations and theoretical analysis predict the same type of thermal cycles at the same location. However, only CFD simulation can give the quantitative results, while the thermodynamic analysis is still remaining in quality.     

Experimental research of Stirling type pulse tube refrigerator with an active phase control

A Stirling type pulse tube refrigerator with an active phase control has been experimentally investigated. A phase shifter, which controls the phase angle between the mass flow and the pressure inside a pulse tube, plays a key roll in the performance of pulse tube refrigerators. In this study, an electrically driven and mechanically damped linear compressor, which is directly connected at the warm end of the pulse tube using a connecting tube, is used as the active phase controller (APC). Therefore, this active phase control pulse tube refrigerator (APCPTR) has no reservoir. Amplified electric signals of a function generator are supplied to both the main linear compressor, which is used as the pressure wave generator (PWG), and the APC. The type of these two linear compressors is a dual-opposed piston. The advantage of this phase sifter is easy to control the electric input power and the phase angle between the PWG and the APC. In order to clarify the characteristics of the APCPTR, the cold end temperature and the gas pressure have been measured.     

Vibration generation in a pulse tube refrigerator

The cold head of a pulse tube refrigerator does not contain moving parts, therefore, is traditionally thought of as producing low vibration and having extended lifespan. Thus, such cryogenic engines are especially attractive for use in vibration-sensitive instrumentation, such as scanning electron microscopes, superconductive quantum interference devices, etc. However, even relatively low-level vibration of a pulse tube, resulting from oscillation of a gas pressure, may be excessive for the above vibration-sensitive OEM instrumentation. By making use of the finite element analysis and the full-scale experimentation, the authors identify the sources of a pulse tube vibration.     

主动调相型脉管制冷机数值模拟与实验研究

设计了一台主动调相型斯特林脉管制冷机,采用线性压缩机作为脉管制冷机主动调相控制器(APC),连接于冷指热端出口。通过控制调相压缩机与驱动压缩机(PWG)间的位移相位角实现主动调相,从而调节质量流和压力波之间的相位关系,优化制冷性能。利用模拟软件进行数值模拟并进行实验研究。研究结果表明,定输入功下APC与PWG位移相位角为-110°及扫气容积比(PWG扫气容积/APC扫气容积)2.98时,无负载制冷温度最低,同时比卡诺效率最高,能够达到原惯性管型脉管制冷机同样的效率。     

Multi-objective optimization of a stirling-type pulse tube refrigerator

A genetic algorithm (GA) optimization method which is coupled to a one-dimensional finite volume method is proposed and implemented as a computer program for the modeling and optimization of a stirling-type pulse tube refrigerator (PTR). The multi-objective optimization procedure is applied to provide the optimization design parameters which are charge pressure, operating frequency, and temperature of after-cooler as well as swept volume of compressor. The procedure is selected to obtain the maximum coefficient of performance (COP) and the minimum cooling temperature (T_cold) as two objective functions. In order to validate the simulation code, the results were compared with the results of other models and experiments. The results showed a reasonably well agreement between simulation output and experimental data. The results of optimal designs are a set of multiple optimum solutions, called Pareto optimal solutions. Moreover, the closed form relations between two objectives are derived for Pareto optimal solutions of pulse tube refrigerator. Finally, a sensitivity analysis of the variation of each design parameter on both objective functions was carried out as well and the results are presented. As a result, the COP is more sensitive than T_cold in the optimum design points. The frequency of refrigerator is the most sensitive factor which affects the COP even with little changes.     

Experimental investigation of pulse tube refrigerator with displacer

This article has done the first experimental research on the pulse tube refrigerator with rod type displacer. The displacer with a rod is both used for a phase shifter to adjust the phase angle between the pressure wave and the mass flow, and used to recover the expansion work from the hot end of the pulse tube. How the charge pressure, the operational frequency and the input power affect the performance of the refrigerator is discussed in this article by experimental research. No-load temperature of 38.9K is reached in the preliminary experiment.     

Expansion efficiency of pulse tube in pulse tube refrigerator including shuttle heat transfer effect

This paper describes simple analysis of the pulse tube expansion efficiency. Four dimensionless operating parameters of pulse tube refrigerator are needed to express the enthalpy flow at the cold end of the pulse tube. In this analysis, the expansion efficiency is calculated from the ratio of the diathermic enthalpy flow (non-zero gas-to-wall heat transfer) to the adiabatic enthalpy flow (zero gas-to-wall heat transfer). The analytic procedure is carried out under several simplified assumptions, and the resultant expression is remarkably simple and useful. The optimal design of pulse tube refrigerator can be greatly assisted by the enthalpy flow calculation with four dimensionless parameters introduced in this paper.     

Experimental results on V-M type pulse tube refrigerator

This article mainly introduces experimental results on a new type pulse tube refrigerator named as V-M type pulse tube refrigerator. The main difference from Stirling type or G-M type pulse tube refrigerator is that thermal compressor similar to that of a V-M cryocooler is used instead of mechanical compressor. By using temperature difference between room temperature and liquid nitrogen, pressure wave with high to low pressure ratio around 1.2 is obtained. This pressure wave is used to generate cooling effect at the cold end. With a 20 K pre-cooler, this machine reaches lowest temperature 5.25 K by using helium⁴ at 0.77 Hz, 19 bar charge pressure. DC flow plays an important role in our system. It not only influences the final obtainable lowest temperature, but also is used to increase cold end cool-down speed. Total volume of the V-M type pulse tube refrigerator is around 3.3 l. However, dead volume inside rotor housing occupies about 2.8 l and can be much reduced.     

多路旁通型高频脉冲管制冷机及固定调相装置比较实验

研制了一台低于40 K温区的单级同轴型高频脉冲管制冷机,采用多路旁通结构,在输入功率为222 W时,其最低温度达到34.22 K,并比较了惯性管、惯性管加双向进气、惯性管加多路旁通以及惯性管加双向进气加多路旁通4种固定调相装置的差异(其中双向进气采用喷嘴结构).实验结果表明:惯性管、喷嘴、多路旁通组合方式是一种非常有效的降低制冷温度的方式,是应用深低温区单级脉冲管制冷机调相方式的最佳选择;而惯性管则是应用于较高温区大冷量的最佳的调相方式.实验还表明,多路旁通加喷嘴结构能够降低脉冲管内部的直流,有效地提高脉冲管制冷机的性能.     

单级G-M型同轴脉冲管制冷机实验

介绍了单级G-M型同轴脉冲管制冷机,双向进气方式采用两个方向相反的阀门并行布置.在压缩机输入功率为6 kW的条件下,该制冷机获得了18.1 K的无负荷最低制冷温度,这是目前单级G-M型同轴脉冲管制冷机所能达到的最低无负荷制冷温度,30 K 时的制冷量为12 W.     

Condensation stage of a pulse tube pre-cooled dilution refrigerator

In our article, experiments with a pulse tube (PTR) pre-cooled dilution refrigerator (DR) are presented, where an upgraded ³He condensation stage has been tested. The DR had a ³He flow rate of up to 1.1 mmol/s. The ³He gas entering the refrigerator was first pre-cooled to a temperature of ～50 K at the first stage of the PTR. In the next cooling step, the ³He was run through a recently installed heat exchanger, which was attached to the regenerator of the second stage of the pulse tube cryocooler; at the outlet of this heat exchanger the temperature of the ³He was as low as ～4 K. Due to the non-ideality of the helium gas, the second regenerator of a two stage PTR has excess cooling power which can be made use of without affecting the base temperature of this stage, and it is this effect which was put to work, here. Finally, the ³He was further cooled in a heat exchanger, mounted at the second stage of the PTR, before it entered the dilution unit of the cryostat.The installation of a heat exchanger at the regenerator of the second stage of the PTR is especially important for the construction of DRs with high refrigeration capacities; in addition, it allows for a plain design of the subsequent Joule–Thomson (JT) stage, and herewith facilitates considerably the construction of “dry” DRs. The condensation rate of the ^3,4He mash prior to an experiment was increased. The pressure during condensation could be kept near 1 bar, and thus a compressor was no longer necessary with the modified apparatus.     

A new tapered regenerator used for pulse tube refrigerator and its optimization

The results of numerical simulation and theoretical analysis of the local heat transfer coefficient and the average remaining gas mass with the length of a uniform cross-sectional regenerator are presented in this paper. It was found that there are some serious thermodynamic limitations in the uniform cross-sectional regenerator and thus the efficiency of the regenerator can not fully exert. In order to further reduce the loss of the regenerator and improve the heat transfer of the cold end, the authors bring forward a design principle: the variation trend of the cross-section of the regenerator will be consistent with the direction of the temperature gradient, and introduce two kinds of tapered regenerators including convergent and divergent in order to improve the performance of the pulse tube refrigerator. Two models were introduced with governing equations to simulate two kinds of pulse tube refrigerators with tapered regenerator. The simulation results showed that there exist an optimum cone angle for tapered regenerator. When the cone angle is close to a certain value, the pulse tube refrigerator with convergent type regenerator can improve the performance which means increasing the cooling power, decreasing the working power, and eliminating the DC-flow rate. But the divergent type regenerator deteriorates the performance. In order to further validate the feasibility of this structural design, based on the enthalpy flow theory, the mechanism of the improvement of the performance of a PTR with tapered regenerator is systemically analyzed.     

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.     

Effect of pulse tube volume on dynamics of linear compressor and cooling performance in Stirling-type pulse tube refrigerator

In a Stirling-type pulse tube refrigerator (PTR), the pulse tube volume affects the dynamic behavior of a linear compressor as well as the cooling performance of PTR. In this study, PTRs which have different pulse tube volume are tested and simulated. The simulation code is verified with the experimental measurement of piston displacement, pressure wave, input power and cooling capacity. And then, the power transfer from the electric power input to the cooling capacity is explained with the simulation results. The smaller pulse tube increases the resonant frequency of a linear compressor and suppresses the piston motion because it imposes larger gas spring effect and also larger gas damping effect to the piston. The smaller one allows larger power transfer from electric power to expansion PV work despite the smaller piston displacement, but shows less cooling capacity due to larger thermal losses.     

丙纶填充式回热器单级脉管制冷机性能研究

采用丙纶纤维作为回热器新型填充介质,对单级脉管制冷机进行了试验研究。对丙纶微尺度空间结构及物理性能进行了分析,基于充气压力分别为3.5、3.0、2.8、2.5、2.0、1.5 MPa的工况下,进行了降温性能、频率性能、制冷性能试验,获取了最低制冷温度,最佳工作频率及最大比卡诺效率。研究结果表明,充气压力对丙纶填充回热器的制冷机整体性能影响较大,工作频率的影响不是很明显。最终获得了最大比卡诺效率9.46%@170 K/10.06 W/77 W,最大制冷量为5.47 W@120 K/2.5 MPa,12.02 W@150 K/3.0 MPa,16.49 W@170 K/3.0 MPa,并获得了96.4 K的最低制冷温度。     

Influence of resonance tube length on performance of thermoacoustically driven pulse tube refrigerator

A resonance tube is an important component of a thermoacoustic engine, which has great influence on the performance of the thermoacoustically driven pulse tube refrigerator. A standing wave thermoacoustic engine is simulated with linear thermoacoustics. Computed results show that an appropriate accretion of the resonance tube length may lead to a decrease of the working frequency and an increase of the pressure amplitude, which will improve the match between the thermoacoustic engine and the pulse tube refrigerator. The theoretical prediction is verified by experiments. A refrigeration temperature as low as 88.6 K has been achieved with an optimized length of the resonance tube, helium as working gas, and 2200 W of heating power.