Parametric study for the cooling of high temperature superconductor (HTS) current leads

The analysis of cooling of a binary HTS 20 kA current lead (CL) operating between 4.5 and 300 K has been carried out. Assuming that the HTS module is conduction-cooled, two cooling options for the copper heat exchanger (HEX) part of the CL have been considered, i.e. (1) cooling with a single flow of gaseous helium and (2) cooling with two flows of gaseous helium. The ideal refrigerator power required to cool the whole HTS CL has been calculated for both cooling scenarios and different values of input parameters and the thermodynamic optimization has been performed for both cooling options. The obtained results indicate that the cooling Option 2 cannot provide significant savings of the refrigerator power, as compared to the Option 1. However, it has been observed that at the same helium inlet temperature the temperature at the warm end of the HTS part, and the resulting number of HTS tapes, can be reduced in the Option 2 with respect to the Option 1.     

高温超导磁体的一种失超判别方法

高温超导同步电动机转子上的Bi2223／Ag带高温超导磁体,其结构特殊,且工作在旋转状态,必然给其失超信号的检测提出新的问题。试验表明,为快速、准确检测到失超信号,仅用经验失超判据Ec=1μV／cm是不够的。为此,通过对试验数据的分析提出dv／dt失超判别方法。此方法从磁体的电压一电流特性入手,根据每个励磁阶段的电压变化情况,设置相应的电压变化率的阈值。     

热虹吸油冷却系统：系统安装篇

从热虹吸油冷却系统的正确安装方式入手,结合实践经验,剖析十几种常见的错误安装方式,并分析热虹吸油冷却系统对制冷系统的负面影响,最后给出大型热虹吸油冷却系统的安装建议,进一步提高热虹吸油冷却系统的整体应用水平。     

Development of a cryogenic test bed for high amperage critical current measurement on high temperature superconductor wire

Many areas of research have benefited from the application of conduction-cooled superconducting magnet technology. The middle and small-scale magnets immersed in the liquid helium will be replaced by the easy-operating conduction-cooled superconducting magnet due to convenient operation, lower operating cost and easy for user. For the goal of superconducting magnet applications in the advanced testing for high temperature superconducting (HTS) wire and sample coils, a wide bore conduction-cooled superconducting magnet with available warm bore of ?186 mm and center field of 5-6 T for background magnetic field applications was designed, fabricated and tested. The system allows measurements to be performed in a repeatable and reliable fashion. In order to support the high stress in magnet, the detailed finite element (FE) analysis with electro-plastic model is proposed. The sample cryostat is designed with cryofree. It includes two GM cryocoolers. The detailed design, fabrication and thermal analysis are presented in the paper.     

Cryogenic system with the sub-cooled liquid nitrogen for cooling HTS power cable

A 10 m long, three-phase AC high-temperature superconducting (HTS) power cable had been fabricated and tested in China August 2003. The sub-cooled liquid nitrogen (LN₂) was used to cool the HTS cable. The sub-cooled LN₂ circulation was built by means of a centrifugal pump through a heat exchanger in the sub-cooler, the three-phase HTS cable cryostats and a LN₂ gas-liquid separator. The LN₂ was cooled down to 65 K by means of decompressing, and the maximum cooling capacity was about 3.3 kW and the amount of consumed LN₂ was about 72 L/h at 1500 A. Cryogenic system design, test and some experimental results would be presented in this paper.     

Improved thermal resistance network model of motorized spindle system considering temperature variation of cooling system

In the motorized spindle system of a computer numerical control (CNC) machine tool, internal heat sources are formed during high-speed rotation; these cause thermal errors and affect the machining accuracy. To address this problem, in this study, a thermal resistance network model of the motorized spindle system is established based on the heat transfer theory. The heat balance equations of the critical thermal nodes are established according to this model with Kirchhoff's law. Then, they are solved using the Newmark-β method to obtain the temperature of each main component, and steady thermal analysis and transient thermal analysis of the motorized spindle system are performed. In order to obtain accurate thermal characteristics of the spindle system, the thermalconduction resistance of each component and the thermalconvection resistance between the cooling system and the components of the spindle system are accurately obtained considering the effect of the heat exchanger on the temperature of the coolant in the cooling system. Simultaneously, high-precision magnetic temperature sensors are used to detect the temperature variation of the spindle in the CNC machining center at different rotational speeds. The experimental results demonstrate that the thermal resistance network model can predict the temperature field distribution in the spindle system with reasonable accuracy. In addition, the influences of the rotational speed and cooling conditions on the temperature increase of the main components of the spindle system are analyzed. Finally, a few recommendations are provided to improve the thermal performance of the spindle system under different operational conditions.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0239-4     

Experimental investigation on the detachable thermosiphon for conduction-cooled superconducting magnets

A detachable thermosiphon, as a transient thermal switch for conduction-cooled superconducting magnet, is designed, fabricated and tested. A thermosiphon between the first and second stages of a cryocooler can reduce the cool-down time of a conduction-cooled superconducting magnet by using the large cooling capacity of the first stage. The thermosiphon is a very efficient heat transfer device until all the working fluid in it freezes (off-state). After the working fluid freezes and the second stage temperature becomes lower than that of the first stage, however, the thermosiphon then becomes a conduction heat leak path between two stages of the cryocooler. Considering a very small cooling capacity of the second stage of the cryocooler around 4.2 K, the conduction heat loss is not negligible. Therefore, a detachable thermosiphon, made of a metal bellows, is considered to be able to eliminate such a conduction heat leak. The mock-up magnet is cooled down with the thermosiphon and the thermodynamic states of the thermosiphon and the mock-up magnet are precisely examined during the whole cool-down process. At off-state, the thermosiphon is detached mechanically from the magnet. In this way, the conduction heat leak path through the thermosiphon wall is completely eliminated. This paper describes the detailed transient operation of the detachable thermosiphon using nitrogen as the working fluid.     

A study on the surface flashover characteristics for a HTS cable termination

Terminal technology is important component to a HTS cable as well as a conventional cable. HTS cable terminations are required when the insulated shield HTS cables connect with other conductors such as a bus or a overhead lines. HTS cable terminations must span a temperature range from 77 K to 300 K. The termination is insulated with insulating oil or air, cryogenic gaseous nitrogen and liquid nitrogen. Particularly, difficult conditions for high voltage insulation had to be overcome with HTS cable. And, several environments can substantially raise the flashover possibility at the HTS cable termination. Therefore, in order to insulating design of HTS cable termination, this paper will report on experimental investigations of the surface flashover characteristics under various surface length and GFRP thickness in the atmospheric air, transformer oil, LN₂ at atmospheric pressure and complex condition.     

Influence of the Air Gap between Adjacent Permanent Magnets on the Performance of NdFeB Guideway for HTS Maglev System

For the permanent magnet guideway (PMG) of the high temperature superconducting (HTS) magnetic levitation (Maglev) vehicle system, there should be many air gaps between two adjacent permanent magnets by connecting, which may fluctuate magnetic field in the propulsion direction of the vehicle. A three-dimensional (3D) model of a PMG is built up using FLUX 3D software. The magnetic field density of an NdFeB PMG is measured and simulated by 3D and 2D models. Comparison among their results indicate that the simulation results of the 3D model agree better with the measuring results than that of the 2D model, and thus the 3D model is more suitable to describe the PMG. By the model, the influence of the air gap on the uneven of the magnetic field density in the propulsion direction is studied. It is found that the magnetic field 15 mm above the PMG is roughly even in the propulsion direction, although the magnetic field at 2 mm is not even. Since the working height 15 mm is a sensitivity parameter for the onboard high temperature superconductor (HTSC), the levitation force at working height 15 mm above PMG is measured, which indicates that the influence of the air gap on the levitation force is very small so as to be ignored in the quasi-static state.     

Fundamental performance of novel power supply for HTS magnet using solar energy system

A technical fusion is an important option to establish renewal development in the mutual fields. We have proposed a novel superconducting power supply that is combined with superconducting power supply and solar energy system. An eternal electric energy can be converted by solar energy system, which contains solar panel, photovoltaic (PV) controller and energy-storing battery, can be utilized in the utility power of superconducting power applications. The novel power supply could operate without external utility power to charge the HTS load magnet due to the solar energy. We can improve the operating efficiency and install it in remote locations where utility power is not available. In this paper, as a first step of this work, we showed the possibility of technical fusion between a superconducting power supply and a solar energy system.     

Dielectric resonator as a possible standard for characterization of high temperature superconducting films for microwave applications

The performance of several designs of dielectric resonators used for microwave characterization of FITS films has been analyzed from the point of view of accuracy, sensitivity, and range. Designs discussed include Hakki-Coieman shielded types as well as open-ended resonators with sapphire, rutile and (ZrSn)TiO₃ dielectrics. The best dielectric resonators have proved to have an uncertainty in surface resistance measurements only twice the uncertainty in theQ-factor. high sensitivity, and ability to measure a wide range of surface resistances. Hence the dielectric resonator technique can be considered as a standard for measurements of surface resistance of HTS films for wireless and PCS communication systems applications provided that adequate measurement procedures of theQ ₀-factor are followed.     

臭氧处理冷水机组循环冷却水的节能试验研究

从目前循环冷却水系统中普遍存在的结垢问题入手,引出臭氧水处理法,它是一种环保、安全、高效的水处理方法。臭氧在处理循环冷却水时能起到杀菌、缓蚀、阻垢及脱垢的作用。简要阐述臭氧处理循环冷却水的阻垢及脱垢原理,分析污垢对冷水机组性能的影响。臭氧处理冷水机组循环冷却水的试验表明,臭氧水处理方法能够显著提高冷水机组的COP。     

Knowledge-based system (KBS) for creep crack growth of high temperature components in HIDA Project

The paper reports current work on the development of a knowledge-based system (KBS) in the BRITE/EURAM project HIDA (project reference: BE 1702). It describes the main concept, architecture, interface and some modules of the system, as well as the data, information and knowledge “sources” used for KBS within the project. The crack assessment part of the system is described in more detail; combination of different modules are within single steps, application of different models within single modules etc. An outlook regarding future use and application of the system among HIDA partners and elsewhere is presented too.     

Impact of the non-homogenous temperature distribution and the coatings process modeling on the thermal barrier coatings system

The present study deals with a numerical investigation of the residual stresses arising during the plasma-sprayed coatings process and their effects on the final stress state of the thermal barrier coatings system (TBCs) during service. A new thermo-mechanical finite element model (FEM) has been designed to function using a non-homogenous temperature distribution. Several phenomena are taken into account in the model such as: residual stresses generated during the spraying of coatings, morphology of the top-coat/bond-coat interface, oxidation at the top-coat/bond-coat interface, thermal mismatch of the material components, plastic deformation of the bond-coat and creep of all layers during thermal cycling. These phenomena induce local stresses in the TBCs that are responsible of micro-crack propagation during cooling and thermal cycling, specifically near the ceramic/metal interface.     

联合除湿式低温低湿恒定装置的试验研究

目前在除湿工程中冷冻方式较为普遍，但是在低温低湿所要求的温湿度条件下，纯冷冻的除湿方式使蒸发器在结霜工况下工作，制冷系统的COP较低，能耗较高。笔者设计了一套双蒸发器切换的联合除湿制冷系统，分别进行了吸附-冷却式和吸附-冷却-吸附式的试验研究，对试验结果进行了对比分析。结果表明吸附-冷却-吸附式方案具有良好的低温低湿性能。吸附冷却方式可以简化冷冻除湿制冷系统，有很强的抗干扰能力，而且蒸发温度高，系统的COP值增加。     

Experimental results of a solar powered cooling system at low temperature

A solar thermochemical prototype producing low-temperature cold has been built and tested during the summer and autumn 2005 in Perpignan, France. It cools a 560 L cold box down to about −25 °C using only low-grade heat produced by two simple flat plate solar collectors. The process involves two cascaded thermochemical systems using BaCl₂ salt reacting with ammonia. Its working mode is discontinuous, as it alternates between one decomposition mode at high pressure (daytime) and one cold production mode at low pressure (nighttime). Experimental results prove the feasibility of this new concept of solar cold production, with temperatures as low as −30 °C, demonstrate its potential use in housing, by the acceptable size and weight of the system and show the system performances during the sunniest months of the year, with a rough solar coefficient of performance (COP) of about 0.031 over the test period. The major meteorological parameters influencing the process efficiency are the solar irradiation and the outside temperature.     

Experimental study on heat transfer and rheological characteristics of hybrid nanofluids for cooling applications

The enhancement of heat transfer and rheological behaviour of hybrid nanofluids (HyNF) flowing through the tubular heat exchanger system were experimentally analysed. In this study, the effects of Nusselt number, Peclet number, Reynolds number, heat transfer coefficient and pressure drop were investigated for various volume concentrations of copper-titania hybrid nanocomposite (HyNC). The experiments were performed for various HyNC volume concentrations in the base fluid (cold water) ranging from 0.1% to 1.0%. The experimental results showed that the convective heat transfer coefficient of the HyNF increased by 59.3% for the particular volume concentration of 0.7% of HyNC. The friction factor and pressure drop of HyNF for 1.0% volume concentration were expected to be 0.8% and 5.4%, respectively. This implies for experiencing penalty in the pumping capacity. The experimental measurements, on the other hand, were validated using a newly developed correlation. For all the volume concentrations of HyNF, the deviation obtained for the experimental data and the prediction was observed to be +8% and ?8%, respectively. The present correlation has been found to be in good agreement with the experimental data, which can be helpful in predicting the heat transfer characteristics of the HyNF.     

基于脉冲强磁场的高温超导薄膜YBa2 Cu3 O6.45霍尔效应研究

对高温超导材料常态特性的研究与理解,将会对超导电性机理本身的研究提供关键参考信息.在常态特性研究中,以常态电荷传输特性尤其是霍尔效应的测量最为引人注目.然而,T＜Tc时试样常态特征被材料本身的超导电性掩盖了,为获得材料在Tc温度以下的常态特性,我们在高达50T的脉冲强磁场中进行霍尔效应测量,可有效抑制超导电性.本文主要介绍了50T左右脉冲强磁场的实验技术,特别是脉冲磁体、实验探钟及测量线路的设计.随后,对高温超导薄膜YBa2Cu3O6.45在强磁场中的霍尔效应测量进行了详细阐述.     

空间用高温超导滤波器与制冷机集成结构设计

介绍了准备投入空间试验用高温超导接收机前端中的高温超导滤波器与斯特林制冷机耦合集成结构设计.首先介绍了结构设计所考虑的因素及总体结构方案设计,然后对集成系统中重要零、部件从材料的选取、结构的详细设计,以及热力学和机械强度校核计算等方面将设计过程进行了介绍,通过理论分析结合以往设计经验,认为该设计能够满足试验要求.     

A study on the mechanical properties of self-compacting concrete at high temperature and after cooling

Self-compacting/consolidating concrete (SCC) is certainly one the most innovative material used today by the construction industry, because of its astonishing workability and low permeability, both properties being ensured by the large amounts of fine aggregates, the special additives and the fillers, that characterize SCC??s mix compared to traditionally-vibrated concrete (VC). Since many of the structures where SCC is used (like tunnel linings, off-shore structures, containment shells, bridge decks, slabs on grade) are often required to face severe environmental conditions, such as fire, information on SCC??s behavior at high temperature is badly required, because SCC??s more dense or compact microstructure, with smaller and less connected pores, may in principle make this material more heat-sensitive than VC, as occurs in high-performance/high-strength concrete. While the thermal effects on VC have been extensively investigated in the last 20?years and several studies have been devoted to SCCs spalling in fire, only in the last few years due attention has been paid to the mechanical properties of SCCs at high temperature (??hot?? properties) and/or after cooling (??residual?? properties). The few of papers on this subject, however, give limited information on the stress?Cstrain curves in compression and on the tensile behavior, that are the first objective of this project, with reference to three self-compacting ??limestone?? concretes (target strength f _c?=?50, 80 and 95?MPa). The second objective is to synthesize the test results available in the literature and to make systematic comparisons, something that is not as simple as one may expect, because of the different heating rates, specimen types, and procedures in data treatment and presentation. The agreement, however, is more than satisfactory and confirms what has been more or less overtly indicated in previous studies, that the thermal and mechanical behavior of SCC at high temperature is hardly different from that of VC, at least in quasi-static thermal conditions and uniaxial loading.