Application of water loop variable refrigerant flow air-conditioning system in large-scale buildings in northern China

A water loop variable refrigerant flow（WLVRF）air-conditioning system is designed to be applied in large-scale buildings in northern China.The system is energy saving and it is an integrated system consisting of a variable refrigerant flow（VRF）air-conditioning unit,a water loop and an air source heat pump.The water loop transports energy among different regions in the buildings instead of refrigerant pipes,decreasing the scale of the VRF air-conditioning unit and improving the performance.Previous models for refrigerants and building loads are cited in this investigation.Mathematical models of major equipment and other elements of the system are established using the lumped parameter method based on the DATAFIT software and the MATLAB software.The performance of the WLVRF system is simulated.The initial investments and the running costs are calculated based on the results of market research.Finally,a contrast is carried out between the WLVRF system and the traditional VRF system.The results show that the WLVRF system has a better working condition and lower running costs than the traditional VRF system.

Thermodynamic design of a cascade refrigeration system of liquefied natural gas by applying mixed integer non-linear programming

Liquefied natural gas(LNG) is the most economical way of transporting natural gas(NG) over long distances. Liquefaction of NG using vapor compression refrigeration system requires high operating and capital cost. Due to lack of systematic design methods for multistage refrigeration cycles, conventional approaches to determine optimal cycle are largely trial-and-error. In this paper a novel mixed integer non-linear programming(MINLP)model is introduced to select optimal synthesis of refrigeration systems to reduce both operating and capital costs of an LNG plant. Better conceptual understanding of design improvement is illustrated on composite curve(CC) and exergetic grand composite curve(EGCC) of pinch analysis diagrams. In this method a superstructure representation of complex refrigeration system is developed to select and optimize key decision variables in refrigeration cycles(i.e. partition temperature, compression configuration, refrigeration features, refrigerant flow rate and economic trade-off). Based on this method a program(LNG-Pro) is developed which integrates VBA,Refprop and Excel MINLP Solver to automate the methodology. Design procedure is applied on a sample LNG plant to illustrate advantages of using this method which shows a 3.3% reduction in total shaft work consumption.

Optimization Analysis and Simulation of the EAST Cryogenic System

This paper presents the optimization cycle of the EAST cryogenic system. A simulation analysis and simulation of the main Claude program of this cycle was developed on the basis of the characteristics of the components and verified with the experimental results. The built-in volume ratio of the No. 7 compressor was tested with the purpose of finding the optimum internal pressure ratio to comply with the external pressure ratio so as to increase the isothermal efficiency and cycle efficiency. In addition, the UA （U, heat transfer coefficient; A, heat transfer area） values of the heat exchangers, efficiencies of turbines, mass flow fraction of the turbine stream were analyzed in order to improve the capacity or efficiency of the cycle. Finally, in view of the estimated heat loads of EAST in future, an upgraded operational cycle of 1500 W/4.5 K ＋1000 W/3.5 K ＋5 g/s is proposed according to the simulation.

Present status and one upgrading method with a cold compressor of the EAST sub-cooling helium cryogenic system

Since 2006, the superconducting toroidal field（TF） coils of the Experimental Advanced Superconducting Tokomak（EAST） have been successfully cooled by supercritical helium at a temperature of 4.5 K and a pressure of 4 bara in eleven experiments. To obtain higher operating currents and magnetic fields it is necessary to lower the operating temperature of the TF coils.The EAST sub-cooling helium cryogenic system, with a warm oil ring pump（ORP）, was tested twice in cool-down experiments, which made the TF coils operate at 3.8 K. However, the long term operational stability of the sub-cooling system cannot be guaranteed because of the ORP＇s poor mechanical and control performance. In this paper, the present status of the EAST subcooling helium cryogenic system is described, and then several cooling methods below 4.2 K and their merits are presented and analyzed. Finally, an upgrading method with a cold compressor for an EAST sub-cooling helium cryogenic system is proposed. The new process flow and thermodynamic calculation of the sub-cooling helium system, and the main parameters of the cold compressor, are also presented in detail. This work will provide a reference for the future upgrading of the sub-cooling helium system for higher operation parameters of the EAST device.

The Application and Improvement of Helium Turbines in the EAST Cryogenic System

The helium cryogenic system supplies supercritical helium cooling capacity at 4.5 K for the superconducting magnets in the EAST superconducting tokamak.Four low-temperature helium turbines are used in the 2 kW helium refrigeration system,and their performance and reliability are critical for the continuous operation of the tokamak.The turbines were made by the Helium Mechanics Company in Russia.The start-up process is very unstable,easily broken,and thus testing and improvements are needed.In this paper,we analyze the structure of the helium turbine,make improvements,and describe the testing process and results of the improved helium turbines.Some of the operational experiences during the start-up process and tests are also presented.

Recent progress in the development of RE_(2)TMTM’O_(6)double perovskite oxides for cryogenic magnetic refrigeration

The magnetic functional materials play a particularly important role in our modern society and daily life.The magnetocaloric effect(MCE)is at the basis of a solid state magnetic refrigeration(MR)technology which may enhance the efficiency of cooling systems,both for room temperature and cryogenic appli-cations.Despite numerous experimental and theoretical MCE studies,commercial MR systems are still at developing stage.Designing magnetic solids with outstanding magnetocaloric performances remains therefore a most urgent task.Herein,recent progresses on characterizing the crystal structure,magnetic properties and cryogenic MCE of rare earths(RE)-based RE_(2)TMTM’O_(6)double perovskite(DP)oxides,where TM and TM’are different 3d transition metals,are summarized.Some Gd-based DP oxides are found to exhibit promising cryogenic magnetocaloric performances which make them attractive for active MR ap-plications.

Refrigeration technologies of cryogenic chips

Cryogenic electronics refers to the devices and circuits operated at cryogenic temperatures(below 123.15 K),which are made from a variety of materials such as insulators,conductors,semiconductors,superconductors and topological materials.The cryogenic electronics are endowed with some unique advantages that cannot be realized in room temperature,including high computing speed,high power performance and so on.Choosing the appropriate refrigeration tech-nology is critical for achieving the best performance of the cryogenic electronics.In this review,the cryogenic technology was divided into non-optical refrigeration and optical refrigeration,where non-optical refrigeration technologies are relatively conventional refrigeration technologies,while optical refrigeration is an emerging research field for the cooling of the chips.In the current work,the fundamental principles,applications and development prospects of the non-optical refrigeration was introduced,also the research history,fundamental principles,existing problems and application prospects of the optical refrigeration was thoroughly reviewed.

氦低温透平膨胀机热力性能数值模拟与实验测试

为了深入研究氦透平膨胀机在降温过程及低温条件下的热力学特性,依托ADS 500 W/4.5 K低温制冷机建设了80 K温区的实验系统,进行了氦透平膨胀机的低温变工况测试。测试的氦透平膨胀机主轴轴径为12.00 mm,采用动压氦气体轴承支承,最高转速可以达到252130 r·min^(-1)。在膨胀比为1.88时,膨胀机最大出口温降达到8.1 K;在膨胀比为2.07时,等熵效率达到最高值71.2%。以实验用氦透平膨胀机尺寸及测试工况为基础,建立了透平的数值模型。采用商业软件ANSYS CFX对透平的热力性能及降温特性进行了数值模拟,得到了相应的理论温降曲线。研究结果表明:所建数值模型能够较好地预测该氦透平膨胀机的温降过程,膨胀机出口温度的实验值和计算值结果最大相对偏差为0.45%;所测试的低温氦透平具有优良的热力性能和降温特性,测试的动压氦气体轴承表现出良好的支承稳定性,数值计算和实验结果可为后续相关研究和大科学装置的应用提供参考。

R600a/R32用于自复叠低温冰箱的实验研究

设计搭建了一套小型低温冰箱自复叠制冷系统,实验对比分析了R600a/R32和R600a/R290两种制冷剂组合的系统循环性能,结果表明R600a/R32组合更符合-50℃低温冰箱的工况要求。通过实验进一步对比了R600a/R32在不同充注比例下的系统循环特性,得到R600a/R32最佳充注比例为0.61/0.39。此配比下,环境温度为25℃时,该系统冷冻室温度可以达到-51.8℃。由于小型制冷装置的空间限制,部分运行参数无法测得,对此提出一种制冷运行数据的分析模型,利用回热器换热平衡和气液分离器质量守恒计算出关键数据,并得到混合工质总运行浓度比例,以便进行系统性能的分析。

基于GM制冷机的4K顶部换样低温设计及试验验证

在接收微波信号用的低噪声放大器的红外探测元件,常用密闭循环的小型制冷机冷却中,进行电学、光学和磁热性能等基础实验。本文在以GM制冷机为基础,设计了一款4K顶部换样的结构,并进行了详细的理论分析和试验验证,确认了该结构的尺寸,取得一定的进展和成果。

关于医用低温冰箱校准布点位置的探讨

医用低温冰箱校准时,温度是最重要的校准参数。由于现行的技术依据中,箱体内部测温位置点的放置、实际应用中样品的位置及与箱体内壁距离不一致,影响了测量结果的科学性和准确性。因此,本文针对部分箱体测量点位置的分布及实际样品摆放位置进行探讨,为其校准提供参考。

Process Modeling and Dynamic Simulation for EAST Helium Refrigerator

In this paper,the process modeling and dynamic simulation for the EAST helium refrigerator has been completed.The cryogenic process model is described and the main components are customized in detail.The process model is controlled by the PLC simulator,and the realtime communication between the process model and the controllers is achieved by a customized interface.Validation of the process model has been confirmed based on EAST experimental data during the cool down process of 300-80 K.Simulation results indicate that this process simulator is able to reproduce dynamic behaviors of the EAST helium refrigerator very well for the operation of long pulsed plasma discharge.The cryogenic process simulator based on control architecture is available for operation optimization and control design of EAST cryogenic systems to cope with the long pulsed heat loads in the future.

ENTROPY CHARACTERISTICS OF MAGNETIC REFRIGERANTS

Mathematical models for predicting magnetic entropy,lattice entropy and electron entropy of magnetic refrigerants are carried out from the molecular field appoximation,the Debye model and the electron energy level theory respectively of quantum mechanics.Using theabove models the temperature and magnetic field dependences of the calculated magnetic entropy,lattice entropy,electron entropy and the total entropy of gadolinium,which is a typical magnetic refrigerant near room temperature,are obtained.The Influences of kinds of entropy on the performance of magnetic refrigeration are discussed,and some general rules for selecting magnetic refrlyerants are drawn to hely the develoyment of highly economic magnetic refrigerators.

Design and analysis of dual mixed refrigerant processes for high-ethane content natural gas liquefaction

Recovery and purification of ethane has a significant impact on economic benefit improvement of the high-ethane content natural gas.However,current LNG-NGL integrated processes mainly focus on conventional natural gas,which are not applicable to natural gas with high ethane content.To fill this gap,three dual mixed refrigerant processes are proposed for simulation study of high-ethane content natural gas liquefaction.The proposed processes are optimized by a combination method of sequence optimization and genetic algorithm.Comparatively analysis is conducted to evaluate the three processes from the energetic and exergetic points of view.The results show that the power consumption of Process 3 which compressing natural gas after distillation is the lowest.For safety or other considerations,some common compositions of the mixed refrigerant may need to be removed under certain circumstances.Considering this,case studies of mixed refrigerant involving six composition combinations are carried out to investigate the effects of refrigerant selection on the process performance.

氢液化与低温高压储氢技术发展现状

H_(2)来源广泛、清洁无碳,是未来重要的清洁二次能源载体,在世界能源格局中占重要地位。H_(2)低温致密化技术可大幅提高储氢密度,有效解决H_(2)低密度、低沸点带来的大规模储运难题。综述了氢液化与低温高压储氢2种低温储氢技术的发展现状,对比了各类低温储氢流程的性能和特点,总结了未来发展方向,为H_(2)储运技术的发展提供参考。其中低温液态储氢(氢液化)的储氢密度高且储氢压力低,是目前主流的大规模氢储运方法之一;低温高压储氢则可达到与液氢接近的储氢密度,且本征能耗低、无需正仲氢转化,极具发展潜力;而采用以混合工质节流制冷循环为代表的闭式低温制冷循环替代液氮对H_(2)进行预冷或冷却,可显著降低H_(2)低温致密化能耗,是2种低温储氢技术的重要发展趋势。

Large reversible cryogenic magnetocaloric effect in rare earth iron carbides of composition RE_(2)FeC_(4)(RE=Ho,Er,and Tm)

At cryogenic temperatures,the investigations of magnetic phase transition and magnetocaloric effect in RE_(2)FeC_(4)(RE=Ho,Er,and Tm) compounds were performed.Ho_(2)FeC_(4)and Er_(2)FeC_(4)compounds undergo two magnetic phase transitions with the temperature decreasing:from paramagnetic(PM) to ferromagnetic(FM) transition at their respective Curie temperature(Tc) and from FM to antiferromagnetic(AFM) or ferrimagnetic(FIM) transition below 2 K.Tm_(2)FeC_(4)compound exhibits only a second-order PM to FM phase transition at TC=K.Large reversible MCE without hysteresis loss is observed in RE_(2)FeC_(4)(RE=Ho,Er,and Tm) compounds.Particularly,the maximum value of magnetic entropy change(-ASM)is 21.62 J/(kg K) under the magnetic field change(Δ_(μ0)H) of 0-5 T for Er_(2)FeC_(4).The Er_(2)FeC_(4)compound presenting excellent magnetocaloric performance makes it a competitive cryogenic magnetic refrigeration material.

斯特林型-80℃低温冷库研究

-80℃低温冷库在血站、医院以及医疗研究机构的应用越来越多,目前该温区低温冷库多为传统的复叠式制冷方式,本文设计了一座采用斯特林制冷方式的小型-80℃超低温冷库。基于斯特林制冷机低温效率高的优点,结合低温冷库和斯特林制冷机的特点,设计了一座容积为8 m^(3)的-80℃低温冷库,分析了低温冷库的结构特点,研究了真空绝热板和聚氨酯发泡层组成的复合绝热层结构,给出低温冷库漏热损失计算方法。基于冷库热负荷选配课题组研制的斯特林制冷机,开展实验研究并验证了设计方案的可行性,单台斯特林制冷机在200 W输入功空载条件下10 min以内制冷温度可达-80℃,50 min后最低制冷温度稳定在约-160℃,在500 W输入功下制冷量为180 W,对应COP为0.36。

Structure, magnetism and magnetocaloric effects in Er_(5)Si_(3)B_(x)(x=0.3,0.6) compounds

We investigate the structure, magnetic properties, magnetic phase transitions and magnetocaloric effects(MCEs) of Er5Si3Bx(x=0.3,0.6) compounds. The Er5Si3Bx(x = 0.3, 0.6) compounds crystalize in a Mn5Si3type hexagonal structure(space group: P63/cm) and exhibit a successive complicated magnetic phase transition. The extensive magnetic phase transitions contribute to the broad temperature range of MCEs exhibiting in Er_(5)Si_(3)B_(x)(x=0.3,0.6) compounds, with maximum magnetic entropy change(-ΔSM_(max)) and refrigeration capacity of 10.2 J·kg^(-1)·K^(-1), 356.3 J/kg and 11.5 J·kg^(-1)·K^(-1),393.3 J/kg under varying magnetic fields 0–5 T, respectively. Remarkably, the δTFWHMvalues(the temperature range corresponding to 1/2×|-ΔSM_(max)|) of Er5Si3Bx(x=0.3,0.6) compounds were up to 41.8 K and 39.6 K, respectively. Thus, the present work provides a potential magnetic refrigeration material with a broad temperature range MCEs for applications in cryogenic magnetic refrigerators.

Experimental investigation of control updating period monitoring in industrial PLC-based fast MPC： Application to the constrained control of a cryogenic refrigerator

In this paper, a complete industrial validation of a recently published scheme for on-line adaptation of the control updating period in model predictive control is proposed. The industrial process that serves in the validation is a cryogenic refrigerator that is used to cool the supra-conductors involved in particle accelerators or experimental nuclear reactors. Two recently predicted features are validated： the first states that it is sometimes better to use less efficient （per iteration） optimizer if the lack of efficiency is overmcompensated by an increase in the updating control frequency. The second is that for a given solver, it is worth monitoring the control updating period based on the on-line measured behavior of the cost function.

便携式斯特林深冷冰箱研制

研制了一种以斯特林低温制冷机为冷源,有效容积6L,工作温度范围-60℃^-160℃的深冷冰箱。小型斯特林制冷机采用直线电机驱动,电机与压缩机一体化设计,采用氦气制冷工质。斯特林制冷机的冷指置于冰箱内底端直接冷却。圆柱形箱体采用了内环为真空层、外环为硬质聚氨酯发泡层的复合绝热技术,设计了具有3层辐射屏的内盖和真空箱盖。该冰箱具有环境友好、热效率高、制冷温区宽、制冷量易控和体积小等特点,可以满足低温保存和实验等需求。输入功率170W时冰箱内温度低于-150℃,对应-100℃低温时的制冷量为7W。