多元混合工质节流制冷机逆流换热器综合传热系数的实验研究

逆流换热器是多元混合工质低温节流制冷机中最为关键的部件之一，本文针对多元低温混合工质节流制冷机经常采用的管套管式逆流换热器进行实验研究，得出了采用不同工质下的换热器温度、压力沿程分布情况，并进一步得到了混合工质逆流换热器的整机换热系数，实验中各条件都是真实制冷机的典型运行工况，实验结果加深了我们对采用多元混合工质在具有相变传热情况下的工作特性的了解，对今后制冷机换热器的设计具有很大的帮助。     

低温冷冻治疗的新冷源--多元混合工质节流制冷

报道了一种应用于低温医疗的多元混合工质节流制冷机。文中建立了多元混合工质节流制冷热力循环,优化分析模型,包括多元混合工质选配与循环运行参数设计原则。同时,设计制作了一台样机,并采且两种混合工质进行了相关实验研究,分别取得了在－７０℃有２０Ｗ和－１２０℃有１１Ｗ的制冷量的实验结果。结果表明,多元混合工质节流制冷机是一种非常有前任的低温冷冻治疗仪.     

多元混合物节流制冷工质量佳配比计算

混合物作为节流工质能大大提高制冷机的热力性能,然而即使采用相同组元件组成的混合物在配比不同的情况下,节流制冷机的性能也会不同。报道了针对应用于Ｊ－Ｔ节流制冷机的混合物工质配比的优化计算。     

小型混合工质J-T制冷机

报道了节流制冷机工作的一般原理和发展状况,对节流装置和节流换热器的研究动态作了较详细的介绍,综述了混合物作为节流工质大大提高了制冷机的热力性能,得出了一些有益的结论并提出了需进一步研究的问题。     

微型压缩机驱动的微型混合工质J-T制冷器实验研究

为研究微型混合工质节流制冷器的降温性能,搭建了微型压缩机驱动微型混合工质节流制冷器的制冷系统,并得到了初步实验研究结果。采用Aspen微型压缩机驱动微型J-T节流制冷器,应用混合制冷剂实现深度制冷。微型J-T节流制冷器采用微小通径的不锈钢毛细管制作,其通道特征尺寸为0.3mm。初步实验表明,微型J-T节流制冷器达到了180K温区。由于采用微型压缩机驱动,系统结构紧凑,可在便携生物储存设备、低温医疗以及电子器件冷却等领域应用。     

采用混合物作工质的J—T节流制冷机

报告了国内外采用混合物作工质的Ｊ一Ｔ节流制冷机的实验研究情况。理论计算的两个重要参数（等温节流效应和正常沸点）与这些实验的结果作了对比。另外，给出了工作在不同压力下的一种混合工质及纯氮的焓温图。从理论计算和实验的结果可以看出混合工质Ｊ一Ｔ节流制冷机比单纯工质的Ｊ一Ｔ节流制冷机有更大的制冷量和更高的热效率。     

多元混合物节流制冷工质最佳配比计算

混合物作为节流工质能大大提高制冷机的热力性能。然而即使采用相同组元组成的混合物在配比不同的情况下,节流制冷机的性能也会不同。报道了针对应用于Ｊ－Ｔ节流制冷机的混合物工质配比的优化计算。以热力学完善度为目标函数,采用复合形优化算法,设计了一套混合物最佳配比优化计算程序。计算结果对实际混合物制冷循环设计有一定指导意义。     

空调压缩机驱动的80K温区的微型JT节流制冷机的试验研究

首次报道了在国内采用空调压缩机驱动的８０～７０Ｋ温区的闭式混合物工质ＪＴ节流制冷机的试验研究情况。由于采用了商用长寿命的空调压缩机作为动力源，将有可能使该种制冷机真正成为一种高可靠性、低价格的低温制冷机商品。     

多元混合工质节流制冷机内工质组分浓度变化特征的实验研究

建立了专门实验系统来研究多元混合工质闭式循环节流制冷机内工质组元浓度动态变化特征，针对三个典型制冷温区的三种混合物工质进行了实验研究，研究结果表明，混合物工质浓度在不同运行时期发生变化，最大变化会达到6％，另外系统内浓度不均匀更会高达12％，甚至更高，实验研究对修正理论模拟模型以及制冷机设计具有帮助。     

詹姆斯·韦伯太空望远镜中红外仪低温制冷系统的流程分析及优化

针对詹姆斯·韦伯太空望远镜的中红外仪冷却系统中J-T节流循环的热力学计算分析结果表明,适当地降低末级预冷温度、提高压比和提高末级间壁式换热器效率是J-T节流循环制冷性能提升的关键。考虑该复合型低温制冷机的整机效率,结合当前脉管制冷机和驱动J-T节流循环的线性压缩机的性能水平,探讨了预冷温度和J-T节流循环压力的优化方法。计算结果表明优化后的预冷温度和J-T节流循环压力使复合型低温制冷机的性能高于原预冷温度和J-T节流循环压力下性能的计算值,实际具体的脉管制冷机和J-T节流循环压缩机性能是实现准确优化的必要条件。     

Characterization of a thermoelectric/Joule–Thomson hybrid microcooler

Micromachined Joule–Thomson (JT) coolers are attractive for cooling small electronic devices. However, microcoolers operated with pure gases, such as nitrogen gas require high pressures of about 9 MPa to achieve reasonable cooling powers. Such high pressures severely add complexity to the development of compressors. To overcome this disadvantage, we combined a JT microcooler with a thermoelectric (TE) pre-cooler to deliver an equivalent cooling power with a lower pressure or, alternatively, a higher cooling power when operating with the same pressure. This hybrid microcooler was operated with nitrogen gas as the working fluid at a low pressure of 0.6 MPa. The cooling power of the microcooler at 101 K operating with a fixed high pressure of 8.8 MPa increased from 21 to 60 mW when the precooling temperature was reduced by the thermoelectric cooler from 295 to 250 K. These tests were simulated using a dynamic numerical model and the accuracy of the model was verified through the comparison between experimental and simulation results. Based on the model, we found the high pressure of the microcooler can be reduced from 8.8 to 5.5 MPa by lowering the precooling temperature from 295 to 250 K. Moreover, the effect of TE cooler position on the performance of the hybrid microcooler was evaluated through simulation analysis.     

Numerical analysis of clogging dynamics in micromachined Joule–Thomson coolers

Micromachined Joule–Thomson (JT) coolers are of interest for cooling small electronic devices. The long-term performance of JT microcoolers is limited by the clogging phenomenon caused by the deposition of water molecules present as impurity in the working fluid. This work investigates the clogging dynamics in a JT microcooler operating with nitrogen gas. A numerical model is developed to calculate the temperature profile and the deposition rate of water molecules along the counter flow heat exchanger and the restriction of a microcooler. The deposition process is modeled by considering the diffusion of water molecules in nitrogen gas and the kinetic process of water molecules on wall surface, which are both temperature dependent. Numerical results show that the clogging rate during cool down is influenced by gas impurity and gas pressure. The effects of gas purity, gas pressure and cold-end temperature on the continuous operating time of the microcooler are also investigated.     

A micromachined Joule–Thomson cryogenic cooler with parallel two-stage expansion

There is an increasing need for localized cooling in integrated circuit/microfluidic chips, where cooling is currently achieved by relatively large and bulky cooling systems. Joule–Thomson (JT) cryocoolers are suitable to address these size limitations because they have no cold moving parts and, therefore, can be easily miniaturized. We present a JT microcooler with parallel two-stage expansion that cools down to a no-load temperature of 83 K with an ambient temperature of 295 K, whereas a single-stage microcooler typically cools to about 100 K. In addition, this microcooler has the attractive feature of providing cooling powers at two temperature levels without additional manufacturing or processing steps. In changing the temperature at the first expansion position, the cooling power can be exchanged between the two expansion stages. A dynamic model was developed to predict the actual performance of the microcooler. The accuracy of this model was verified through the comparison between experimental and simulation results.     

Design and experimental investigation of a cryogenic system for environmental test applications

This paper is concerned with the design, development and performance testing of a cryogenic system for use in high cooling power instruments for ground-based environmental testing. The system provides a powerful tool for a combined environmental test that consists of high pressure and cryogenic temperatures. Typical cryogenic conditions are liquid hydrogen (LH2) and liquid oxygen (LO2), which are used in many fields. The cooling energy of liquid nitrogen (LN2) and liquid helium (LHe) is transferred to the specimen by a closed loop of helium cycle. In order to minimize the consumption of the LHe, the optimal design of heat recovery exchangers has been used in the system. The behavior of the system is discussed based on experimental data of temperature and pressure. The results show that the temperature range from room temperature to LN2 temperature can be achieved by using LN2, the pressurization process is stable and the high test pressure is maintained. Lower temperatures, below 77 K, can also be obtained with LHe cooling, the typical cooling time is 40 min from 90 K to 22 K. Stable temperatures of 22 K at the inlet of the specimen have been observed, and the system in this work can deliver to the load a cooling power of several hundred watts at a pressure of 0.58 MPa.     

Cryogenic helium gas circulation system for advanced characterization of superconducting cables and other devices

A versatile cryogenic test bed, based on circulating cryogenic helium gas, has been designed, fabricated, and installed at the Florida State University Center for Advanced Power Systems (FSU-CAPS). The test bed is being used to understand the benefits of integrating the cryogenic systems of multiple superconducting power devices. The helium circulation system operates with four sets of cryocooler and heat exchanger combinations. The maximum operating pressure of the system is 2.1 MPa. The efficacy of helium circulation systems in cooling superconducting power devices is evaluated using a 30-m-long simulated superconducting cable in a flexible cryostat. Experiments were conducted at various mass flow rates and a variety of heat load profiles. A 1-D thermal model was developed to understand the effect of the gas flow parameters on the thermal gradients along the cable. Experimental results are in close agreement with the results from the thermal model.     

低温风洞电动推杆热防护结构设计及传热分析

为解决低温风洞中电动推杆的热防护问题,设计了使其能够在低温风洞高温工况(323 K)和低温工况(110 K)下正常工作的热防护结构。采用数值模拟方法校核了热防护结构强度及刚度,分析了电机发热功率,冷却气体流量和加热片加热功率等因素对推杆元件温度的影响。结果表明:低温风洞内压力达到极值0.35 MPa时,由厚度5 mm,材料S30408不锈钢制成的圆筒形热防护结构最大变形量为0.397 mm,最大应力为160.62 MPa;冷却气体流量大于等于0.005 kg/s时,高温和低温工况下电机最高温度均不大于418 K的允许工作温度;当加热功率达到500 W时,缸杆端部各考察截面温度均高于263 K;在高温工况和加热功率为500 W的低温工况下,冷却气体流量为0.005 5kg/s时,缸体、缸杆均能维持在263—313 K的工作温度,且高温工况最大温升与温差分别为3.62、2.81 K,低温工况最大温降与温差分别为4.94、6.82 K,满足温度稳定性与均匀性要求。     

Heat transfer performance of cryogenic oscillating heat pipes for effective cooling of superconducting magnets

The cryogenic oscillating heat pipe (OHP) for conduction cooling of superconducting magnets was developed and the function was demonstrated successfully. OHP is a highly-efficient heat transfer device using oscillating flow of two-phase mixture. The working fluids that are employed in the present research are Nitrogen, Neon and Hydrogen, and the operating temperatures are 67–91 K, 26–34 K and 17–27 K, respectively. The estimated effective thermal conductivities from the measurement data of the OHP were higher than one of the solids such as copper at low temperature. These results revealed that the cryogenic OHP can enhance the performance of cooling system for magnets.     

热真空低温环境实验台研制

为满足低温实验的环境要求,建设了液氮温度级别(80 K)的热真空冷阱低温环境实验台,可进行低温实验中压力与压差、温度与温差、流量与热负荷的测量.该实验台采用附加液氮冷阱的真空多层绝热结构,冷阱温度最低可达80 K,无负载时冷箱真空度可达0.000 03 Pa;在采用外循环工质时,测试压力范围为0-1 MPa、压差范围为...     

Development of a miniature cryogenic fluid circuit and a cryogenic micropump

This article presents the development of a miniaturized cryogenic fluid circuit for distributed cooling of low-temperature tracking detectors in high-energy physics (HEP). The heart of the circuit is a prototype cryogenic micropump. This volumetric pump is compatible with cooling powers of about 10-100 W, and capable of producing pressure heads of up to around 0.3 MPa. Besides detector and electronics cooling in HEP, potential applications are found in the field of superconductor technology.     

New packages for disc type power diodes

The paper presents a press-pack package integrated with a microchannel cooling system, which is a new thermal solution for power devices, e.g. diodes. In comparison with conventional solutions enforcing the use of either an air cooling system or a liquid one, the novel package is characterised by considerably smaller dimensions, lower weight and significantly higher thermal performance. The conducted measurements of the manufactured model showed that a thermal resistance of 0.0182 K/W can be obtained for an allowable pressure drop for electronic applications.