The MMR (Micro Miniature Refrigerator) is a novel Joule-Thomson cryocooler manufactured by micro-machining technology, its axial length is significantly shorter than the traditional Joule-Thomson cryocoolers that are used in infrared detectors. So MMRs can greatly reduce the size of infrared detectors once they are successfully integrated. To study the working mechanism of MMRs a micro-channel flow calculation model is established considering the gas compressibility, the Joule-Thomson effect at the throttling section and the distributed Joule-Thomson effect along the micro channels and the calculation model is verified with experiments. The characteristics of heat transfer, micro-channel distribution and heat losses are further investigated, leading the model to describe the working condition of the MMR more correctly. The temperature and pressure distribution in the micro channels and the theoretical cooling performance of the MMR is thus obtained, and a set of MMR geometry parameters with superior theoretical cooling performance are acquired. Furthermore, a MMR prototype is fabricated, and a testing platform is built and the cooling performance of the prototype is experimentally studied. The experimental results agree well with the prediction of the calculation model. The MMR prototype achieves 110K and 119K cooling temperature under 10MPa N2 and Ar working condition, the cooling power reaches 231mW and 479mW, and the cool down time is 250s and 70s respectively. As a result, the cooling performance of the MMR prototype can meet the cool down requirement of infrared detectors, providing a new approach to infrared detectors’ miniaturization.

芯片级节流制冷器(MMR)在冷却微小元件领域应用广泛,采用材料生长、减薄、键合及光刻刻蚀等微加工技术制成.最小的节流结构尺寸为1μm.本文对芯片级节流制冷器的最新结构进行了多目标、多结构参数的数值计算优化研究,对制冷器高压侧和低压侧换热器的换热和流动性能进行了优化,数值计算结果与文献中经验关联式吻合良好.计算结果表明:高压侧换热器的努塞尔数Nu较优化前提高了5.8％,摩擦因子f降低了25.7％;低压侧换热器的Nu较优化前提高了14.5％,f降低了2.3％.获得了Nu和f随各结构参数的变化规律,为芯片级节流制冷器换热器结构参数和性能优化提供了参考.

斯特林制冷机具有结构紧凑、效率高等优点,广泛应用于红外芯片冷却.红外探测器系统通常采用恒压电源对斯特林制冷机供电.针对红外探测器多温区制冷需求,研究了多个独立工作的斯特林制冷机对系统恒压电源输出特性的影响.通过搭建斯特林制冷机驱动控制试验系统,发现制冷机驱动控制电路会使恒压电源输出电流产生较大波动,影响电源的可靠性.提出采用两台制冷机反相驱动的控制策略,明显降低了电流波动,可为红外探测器多制冷机多温区制冷设计提供依据.

采用不锈钢为材料以金属蚀刻芯片和真空扩散焊接工艺制成了芯片型节流制冷器,搭建了微型节流制冷器系统,以高压氮气和氩气为工质,研究了不同入口压力下无负荷节流的制冷温度和流量特性.实验结果表明:采用氮气为工质时,在入口压力为10.5 MPa工况下,最低制冷温度为102.9 K;采用氩气为工质时,在压力为8.6 MPa工况下可获得112.0 K的最低制冷温度,降温速度也有效提升.在大流量下,低压通道阻力增大将导致节流后背压和蒸发温度提高,采用氮气和氩气作为工质在压力分别高于10.5 MPa和8.6 MPa时,制冷温度开始回升.验证了基于金属微通道蚀刻工艺技术的芯片型节流制冷器可行性,表明采用金属微流道芯片可以大幅提高耐压能力、机械强度和降温速率.

微机电系统MEMS(micro-electro-mechanical system)是一种集合了微电子与机械工程技术的新型高科技装置,其制造工艺可以进行最小至纳米尺度的加工以及高度集成化的微型制造.其产品微小体积、高度集成化以及高性能高产热的特性也决定了其需要匹配相应的制冷解决方案,本文重点阐述了基于MEMS制造工艺并同时应用于MEMS产品的微型制冷器的工作原理、性能及发展趋势.分别分析了微型半导体制冷器以及微型节流制冷器各自的优势和不足,对微型制冷器的未来发展提出了建议.

芯片级节流制冷器（MMR）是一种采用独特的微加工工艺制成的微型节流制冷器,其结构微小,最小体积可达15 mm×2 mm×0.5 mm。MMR在制冷量需求较小的微型元件冷却领域有着广泛的应用。介绍了MMR制造工艺的发展历程,分析了MMR的不同材料的选择、刻蚀方法、制冷器片密封方法以及制冷器气路、电路连接方法的特点,对比了各个工艺方法的优势和不足,并初步进行了MMR的制造加工和性能实验,得到了能够在7 MPa下稳定工作的MMR样品,并实现了32.6 K的制冷温降。对MMR工艺技术的改进和未来发展提出了一些建议。

The Joule-Thomson (J-T) cryocooler is widely used in a variety of infrared devices.Maximizing the cooling capacity in finite structures is one of the foremost problems in J-T cryocooler miniaturization.In this study, a one-dimensional model based on the thermodynamic properties of real gas and heat leakage of components is established.The effects of three structural parameters (fin height, fin thickness, and fin pitch) used in a helical finned tube heat exchanger on the performance of a cryocooler are calculated and optimized using a genetic algorithm.The results show that the calculated data are in good agreement with the experimental data.In the specific working conditions and structural parameters employed, an increase in fin height and fin thickness would increase the entropy production and cooling capacity of the cold end of the heat exchanger, whereas an increase in fin pitch would have the opposite effect.Optimal parameters exist for maximizing the cooling capacity of the heat exchanger in this study.The analytical method established in this study could provide a simple and effective means of optimizing and designing a J-T in engineering applications.

The miniature Joule Thomson (J-T) cryocooler has been widely used in many applications. Herein, a transient model that considers the real gas properties, the distributed throttling effects and the compressible flow is developed. The density correction term is incorporated in the pressure correction equation to improve the convergence. The mass flow equation of the orifice is coupled with the momentum equations of the high-pressure fluid as the boundary condition. The proposed numerical model is verified against the experimental results, and the effects of distributed throttling, inlet pressure, inlet temperature, load temperature, and pressure vessel discharge are investigated. The developed model and the results can be used for the accurate prediction of the system performance and optimization of the J-T cryocooler.

建立了微通道节流制冷器系统热力学模型,通过对微通道换热器性能优化和所适配的节流结构设计,依据最小熵产法,提出了制冷器性能优化方法.对制冷器内部的流动换热进行了数值仿真,并对换热器的结构尺寸(长、宽、高)进行优化,得到了125 K制冷温度且质量流量在1-5 mg范围内换热器结构的最优设计参数.基于优化后的换热器结构,分别对节流结构进行设计,以满足系统运行工况参数要求.最后,将换热器的优化结构和设计的节流结构组成的微通道节流制冷器行系统仿真,对优化设计参数进行校核,校核偏差小于1％.

The starting-up process of a J-T cooler is unsteady process. There is still a large error in the simulation of a J-T cooler's start-up process until now. Establishing the experimental model of different pitch finned tube heat exchanger to verify the effect on a J-T cooler start-up time. The experimental results show that the change of a heat exchanger fin pitch has impact on a J-T cooler start-up time,and the impact is not a linear relationship,there is an inflection point. In the model of this paper,the optimum pitch of fin tubes is 0.2 mm. The study is useful for the design of the J-T cooler.

Compared to the Stirling cooler,miniature Joule-Thomson cooler(J-T cooler)has the advantages of small size,light weight,short cool-down time,high reliability,low cost and the cold end without moving part,which is wildly applied in infrared seeker.In order to optimize cool-down time and gas consumption,designing a bellows self-regulated fast-cool-down J-T cooler with precooler.Compared to other kinds of J-T coolers by experiment,the J-T cooler with pre-cooler cool down faster than the single self-regulated J-T cooler,and its' gas consumption is less than the non-self regulat-ed J-T cooler with precooler.The cool down time of the J-T cooler with precooler is 12 s@90 K,15 s@80 K,and its' gas consumption is optimized.

The numerical model based on the two-phase closed thermosyphon (TPCT, which is also called gravity heat pipe)is established to describe its phase change and heat transfer essence of the evaporation and condensation.The volume of fluid (VOF)model is used to describe the interface between vapor and liquid phases,and the working process of the heat pipe using water and R134a as working fluids is analyzed by simulation.The study results show that the multiphase model can successfully simulate the evaporation and condensation in the heat pipe better,which directly reflects the heat and mass transfer process.

In this study, experiments were performed to study the saturated flow boiling heat transfer characteristics of saturated nitrogen in a horizontal stainless steel heated tube with an internal diameter of 2.92 mm and length of 1000 mm. The heat transfer coefficients (1134 data points) were obtained under a wide range of operation conditions (109 cases), e.g. heat flux of 1.4-43.7 kW/m(2), mass flux of 17-0310 kg/(m(2) s), inlet pressure of 192-350 kPa, and vapor quality of 0.0015-0.71. Results showed that nucleate boiling dominated the heat transfer mechanism in the small-diameter horizontal tube under the conditions in the tests. The heat transfer coefficients had little dependence on mass flux or vapor quality but had strong correlation with heat flux and working pressure. Instability of heat transfer was also observed in the experiments when the vapor quality is greater than 0.2. In the experiments, the temperature oscillations show a relatively strong relationship with vapor quality rather than heat flux, suggesting the flow pattern change from steady bubble or plug flow to unsteady annular flow or intermittent local dry out when vapor quality is about 0.2. The correlation of Tran et al. can give predictions in good agreement with the experimental data, and therefore it is recommended in predicting heat transfer coefficient of saturated nitrogen flow boiling in small-diameter horizontal tubes. (C) 2017 Elsevier Inc. All rights reserved.

The self-regulated J-T cryocooler is widely applied in the field of infrared guidance because of simple structure,fast response and stable long working hours.As the main part of self-regulating mechanism of J-T cryocooler,the stiffness of nickel-based closed bellow is very important to achieve stable and reliable self-adjusting process.A model based on finite element was modified to calculate the stiffness.And the values were compared with other methods.Some parameters affected the stiffness,such as temperature,wall thickness,wave height,fillet and wave pitch.The change regulation of stiffness was analyzed.The results show that finite element method is more accurate than other methods.The wall thickness is positive but the temperature and wave height is negative.The effect of fillet radius change can be ignored.And the influence of the wave pitch is not stable,the stiffness trend decreases and then increases.

The two-phase flow boiling characteristics of liquid nitrogen (LN2) in horizontal circular mini-tubes were experimentally studied. Experiments were performed in a wide range of flow conditions, e.g. inlet pressure from 0.17 to 0.35 MPa, mass flux from 140 to 330 kg/m(2) s, heat flux from 0.5 to 69.4 kW/m(2) and tube diameters of 2.92 mm and 3.96 mm. The influences of mass flux, heat flux, and inlet pressure on the pressure drop were discussed. The results indicated that the pressure drop increases with the increasing mass flux and heat flux but decreases with the increasing inlet pressure. But the influence of heat flux on the frictional pressure drop of LN2 was weaker than mass flux and inlet pressure. The frictional pressure drop of two-phase flow of LN2 was compared with homogeneous model and several semi-empirical correlations. An improved correlation based on the Lockhart-Martinelli model, which used coefficient C as a function of Reynolds number and Weber number was proposed. (C) 2017 Elsevier Ltd. All rights reserved.

微小型节流制冷器具有体积小、重量轻、可靠性高、启动速度快、冷端无运动部件等突出优势,在红外探测器、红外导引头以及其他电子器件冷却领域实现了大量应用.自调式节微型流制冷器特有的自调机构通过感应节流后温度变化来进行流量(制冷量)的调节,不仅能够有效利用有限的循环工质获得最大的制冷量,而且能够实现高的温度稳定性.为了实现对自调式微型节流制冷器自调机构形变的量化分析,指导自调机构波纹管选型,文中针对内充式自调机构充压波纹管建立了三维数值模型,采用变物性参数,分析了不同充注工质及不同波纹管材料下的低温条件形变特性.研究结果表明,所建立的数值分析模型预测结果与实际测量误差在5％以内,证实了模型的准确性.波纹管是自调机构发生形变的主要部件,除充注压力外,自调机构温度分布的不均匀,对于其形变特性也有一定影响.

With the advantages of small size,light weight,high reliability,quick start and the cold end without mov-ing part,miniature JT cryocooler is wildly applied in infrared seeker. Gas consumption is different for different types of J-T cooler. The volume,weight,working time of an infrared seeker bottle is determined by a JT cryocooler' s gas consump-tion. We have done some experimental research on Gas consumption about four kinds of Joule-Thomson Cooler in differ-ent condition. Some advices are supplied for different engineering applications by the research.

本文充分考虑了流道的几何形状、流体物性的变化、纵向导热损失以及辐射漏热损失,建立了Hampson型J-T节流制冷器的稳态数理模型,对其稳态热力特性进行了性能仿真及可用能分析,并采用响应面优化法和可用能损失最小化对换热器结构进行了参数优化.结果表明:与实验值相比较,误差在1％左右,证明了该稳态热力模型的准确性;在可选结构参数范围内,存在最优结构配置使换热器的可用能损失最低,即换热器的性能最佳,并进一步验证了响应面分析法的合理性,为J-T节流制冷器的优化提供了新的思路和方法.

In this paper, a numerical study is performed to investigate the effects of geometrical parameters on the thermodynamic performance of the helically coiled recuperative heat exchanger in a Joule-Thomson (J-T) cryocooler. A novel optimization model is developed based on the available work loss minimization for the recuperative heat exchanger. The experiments kare conducted based on four factors: L, D-t, S, D-s, one level: N-d, and the results are analyzed according to the principle of Response Surface Methodology (RSM). The final predicted optimum combination of geometrical parameters for the heat exchanger is: L = 430.5 mm, D-t = 0.45 mm, S = 5.41, D-s = 4.3 mm. The optimization results are in good agreement with our model, and the deviations of predicted values are less than 1.32%. The model and results presented here for the optimization of the heat exchanger can provide helpful guidance and a new way for the optimization of J-T cryocooler. (C) 2015 Elsevier Ltd and International Institute of Refrigeration. All rights reserved.