高频微型脉冲管制冷机的数值研究

利用数值方法模拟了高频微型同轴脉冲管制冷机内部气流交变流动和换热过程。给出了小孔型，双向进气型和多路旁通型脉冲管制冷机内部气流动态参数的瞬态变化。分析了各动态参数变化对制冷机整机性能的影响。     

脉冲管制冷机蓄冷器中交变流动过程理论分析

建立了交变流动蓄冷器热力学模型,分析了蓄冷器中气体微团的热力学变化过程,经计算得出了一周期内总热量和压力波与质量流之间相位的关系,对蓄冷器在制冷系统中的作用提出了新的认识,并通过对脉冲管蓄冷器中交变流动热力学特性的分析,对比一典型的双向进气型脉冲管制冷机的实验测量结果,分析了双向进气环流产生的直流分量对蓄冷器的影响,对脉冲管双向进气产生的直流分量对脉冲管制冷性能的影响提出了新的解释。     

On the numerical design of a new type of 4 K GM/PT hybrid refrigerators

In this paper we developed and designed, based on theoretical considerations, a new type of 4 K GM/PT hybrid refrigerators. The upper warm stage of the hybrid refrigerator is a typical GM refrigeration cycle, and the cold stage is a pulse tube refrigerator (PTR), on which is thermodynamically coupled the upper warm stage. Four different types of phase shifting assembly: (1) a cold auxiliary piston that is connected to the displacer of the upper GM refrigerator stage, (2) an orifice with reservoir encircled the cold head of the upper stage, (3) an orifice with double-inlet, and (4) in combination with the cold auxiliary piston, orifice and double-inlet, has been proposed and analyzed for the adjustment of the phase shift between the gas mass flow and pressure in the pulse tube. Numerical simulation is performed to understand the unique thermo-physical features, to reveal the time-dependent dynamic parameters and to quantify the overall cooling performance of the hybrid refrigerator. We rely on a one-dimensional, unsteady compressible flow numerical model that is based on a mixed Eulerian-Lagrangian method developed by the present author. The model will be first applied to analyze the cooling performance of the hybrid refrigerator with different types of phase shifting assembly. In what following, it is used to simulate the dynamic parameters in the cold stage of the pulse tube cycle. Next, optimization of the structure parameters and geometrical configuration of the new refrigerator will be presented. Finally, the influences of different hybrid regenerative materials on the cooling capacity of the new hybrid GM/PTR will be also discussed.     

CFD simulation and experimental validation of a GM type double inlet pulse tube refrigerator

Pulse tube refrigerator has the advantages of long life and low vibration over the conventional cryocoolers, such as GM and stirling coolers because of the absence of moving parts in low temperature. This paper performs a three-dimensional computational fluid dynamic (CFD) simulation of a GM type double inlet pulse tube refrigerator (DIPTR) vertically aligned, operating under a variety of thermal boundary conditions. A commercial computational fluid dynamics (CFD) software package, Fluent 6.1 is used to model the oscillating flow inside a pulse tube refrigerator. The simulation represents fully coupled systems operating in steady-periodic mode. The externally imposed boundary conditions are sinusoidal pressure inlet by user defined function at one end of the tube and constant temperature or heat flux boundaries at the external walls of the cold-end heat exchangers. The experimental method to evaluate the optimum parameters of DIPTR is difficult. On the other hand, developing a computer code for CFD analysis is equally complex. The objectives of the present investigations are to ascertain the suitability of CFD based commercial package, Fluent for study of energy and fluid flow in DIPTR and to validate the CFD simulation results with available experimental data. The general results, such as the cool down behaviours of the system, phase relation between mass flow rate and pressure at cold end, the temperature profile along the wall of the cooler and refrigeration load are presented for different boundary conditions of the system. The results confirm that CFD based Fluent simulations are capable of elucidating complex periodic processes in DIPTR. The results also show that there is an excellent agreement between CFD simulation results and experimental results.     

脉管制冷机的线性气流速度分析法

在焓流理论的基础上提出脉管制冷机的线性气流速度分析法，该方法着重求解脉管内气流速度的幅值和相位，给出的公式简单，概念直观，计算量少。对基本型、小孔型和双向进气型脉管进行了分析，获得的结果与数值模拟结果相似，说明了这是一种行之有效的分析方法。     

Visualization of oscillating flow in a double-inlet pulse tube refrigerator with a diaphragm inserted in a bypass-tube

The double-inlet pulse tube refrigerator that has a diaphragm inserted in a bypass-tube, which enabled it to transmit a pressure oscillation whereas to obstruct a DC gas flow, was manufactured and tested. The oscillating flow behavior inside of the refrigerator was studied by using a smoke-wire flow visualization technique. It was found that if the diaphragm was optimized, the performance would be improved more than that of the refrigerator with a bypass valve due to the increase in the P–V work of the gas and the decrease in the convective heat loss caused by a secondary flow.     

A 115 K thermoacoustically driven pulse tube refrigerator with low onset temperature

After the modifications of jacket type water coolers and stacks, and the optimizations of the openings of orifice and double inlet valves, a refrigeration temperature as low as 115.4 K has been achieved by a thermoacoustically driven pulse tube refrigerator. By operating the double inlet valve of the pulse tube refrigerator, the onset temperature of the thermoacoustic system decreases from 550 to 340 °C. It provides the possibility of utilizing the low-grade heat energy.     

GM型脉冲管制冷机热力学损失分析

对GM型脉冲管制冷机及其旋转阀系统进行热力学分析，针对脉冲管内压力波为正弦波形的情况，推导出了制冷系数（COP）的理论公式，给出了COP的定量结果，并与斯特林型脉冲管制冷机进行了对比，结果发现，由于气体在旋转阀中的不可逆损失，使得压缩机功耗增大，降低了GM型脉冲管制冷机的COP，双向进气的效果取决了温降比，在较低的制冷温度（较大的TH/TL)时作用更加明显。     

一种新型制冷装置——低温阀切换式脉冲管制冷机

首次提出了一种称为低温阀切换式脉冲管制冷机的新型制冷装置。它可适用于气体液休分离等需要较大制冷功率的应用场合。在该装置中，用普通热交换器取代了回热器，切换阀置于脉冲管冷端。对带低温切换阀的小孔气库型脉冲管的等熵膨胀效率的初步实验结果表明，其等熵效率可达４０％以上，显示了一定的应用前景，。     

脉管制冷机工作过程数值模拟的Lax-Wendroff算法研究

提出将Lax—Wendroff数值方法应用于脉管制冷机气体流动和工作过程的数值模拟。分析了属于Lax—Wendroff数值方法类型、具有2阶精度格式、2阶段MacCormack算法及其相应的离散格式和算法组织。所进行的研究表明，将Lax-wen-droff算法类型应用于数值计算脉管制冷机工作过程所伴随的强烈热交换和流动损失现象的气体流动，可以获得很好的数值稳定性。     

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.     

Numerical analysis of different valve effects on the cooling performance of a two-stage GM type pulse tube cryocooler

The cooling performance of GM type pulse tube cryocoolers (PTCs) is strongly affected by the valve setting for phase shifting. In this research, the effects of different valve openings on the no-load temperatures in a two-stage GM PTC have been investigated by numerical simulation. Results show that the no-load temperature at the 1st stage mainly depends on the openings of 1st stage orifice valve, and both 1st and 2nd stage double-inlet valves. While the no-load temperature at the 2nd stage below 10 K sensitively depends on the openings of both 1st and 2nd stage orifice valves, and 2nd stage double-inlet valves. There exist several local minimum no-load temperatures at the 2nd stage under different valve openings below 7 K. The best valve setting corresponds to minimizing the cold end phase angle, making the cold end acoustic power compensate the real gas enthalpy flow with maximum degree.     

低于4K温度工作的二级脉管制冷机研制

介绍最近研制的一台双向进气带第二小孔阀型二极脉管制冷机实验情况。该机采用计算机时序控制，脉管热端均处于室温。文中给出了二级脉管制冷机的基本结构尺寸以及试验结果；一级脉管达到４５Ｋ；二级脉管无负荷最低制冷温度达到３．１Ｋ。能稳定，长期工作，讨论了制冷机性能的主要因素。     

L型脉管制冷机的试验研究

介绍了文中提出的L型脉管制冷机的特点：一是采用L型脉管结构而不是通常的直型（文中称为Ⅰ型）脉管结构,降低了冷端死容积,且降低了冷头加工难度;二是在脉管热端采用双小孔阀结构取代了通常的单小孔阀结构,用来分别控制脉管热端进排气的质量流率;以四阀型脉管制冷机作为实验样机,给出了此种新型结构在有阀氦压缩机驱动下的初步性能试验,初步试验结果表明本文中的L型脉管制冷机在频率为2．5Hz,采用200目青铜丝网作为蓄冷器填料下能够达到的最低温度为67．5K。     

The experimental investigation of a pulse tube refrigerator with a ‘L’ type pulse tube and two orifice valves

In order to simplify the structure of the cold end of the pulse tube refrigerator (PTR) and have a better utilization of the cold energy of the system, a single stage four-valve pulse tube refrigerator (FVPTR) with a ‘L’ type pulse tube structure and two orifice valves at the hot end of pulse tube has been constructed. Verification experiments show that a two-orifice valve structure gives different adjustments to the gas flow rate of the hot end of the pulse tube than that of the one-orifice valve structure, a lowest temperature of 72 K was obtained at a frequency of 2.5 Hz under a system average pressure of 1.6 MPa with 200 mesh bronze screens as regenerator material, 20 mesh copper screens as stuffing material of heat exchanger. Due to the difficulty in manufacturing the thin ‘L’ type pulse tube, the wall thickness of the pulse tube in the experiment is relatively bigger than that of the ordinary pulse tube, which resulted in relatively big system loss and affected the minimum temperature of the system to a certain degree.     

脉冲管制冷机交变流动动态特性数值研究：第一部分;基本方程和数值方法

针对脉冲管制冷机的特点建立了数值模拟模型，采用改进的数值模拟方法对脉冲管制冷机的内部交变流动，换热以及制冷过程进行了详尽的数值研究，得到了脉冲管制冷机内部各参数的动态变化，并分析了各动态参数变化对制冷机整机性能的影响。数值模拟分析与实验结果符合良好。该模拟方法从基本流动换热微分方程出发，尽可能多地考虑实际制冷机工作过程中的各种不可逆因素，包括实际气体的物性变化，各部件的流动阻力和传热损失。     

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.     

脉冲管制冷机交变流动动态特性数值研究：第二部分：数值模拟结果

第一部分给出了脉冲管制冷机数值模拟的基本方程和改进的数值计算方法。这一部分采用第一部分的方法对脉冲管制冷机的内部交变流动，换热以及制冷过程进行了详尽的数值模拟研究，得到了脉冲管制冷要内部各参数的动态变化，分析了各动态参数变化对制冷机整机性能的影响，并与实验结果进行了比较，数值模拟分析与实验结果符合良好，     

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.     

Numerical analysis of an OPTR: Optimization for space applications

A numerical study is reported here for the investigation of the flow and heat transfer processes in a co-axial type single stage orifice type pulse tube refrigerator (OPTR). The OPTR is driven by a cyclically moving piston at one end of the system with helium as the working fluid. The regenerator and the various heat exchangers are modeled as porous media and a thermal non-equilibrium model is applied in these regions. The simulations reveal interesting steady-periodic flow patterns that develop in the pulse tube due to the fluctuations caused by the piston and the presence of the inertance tube. When the secondary flow patterns are well-developed, they help isolate the cold and hot ends of the pulse tube and create a thermal buffer zone at the center of the pulse tube, enhancing the performance of the OPTR.