Modelling of the test of the JT-60SA HTS current leads

The CURLEAD code, which was developed at the Karlsruhe Institute of Technology (KIT), implements an integrated 1D transient model of a high temperature superconducting (HTS) current lead (CL) including the room termination (RT), the meander-flow type heat exchanger (HX), and the HTS module. CURLEAD was successfully used for the design of the 70 kA ITER demonstrator and of the W7-X and JT-60SA CLs. Recently the code was successfully applied to the prediction and analysis of steady state operation of the ITER correction coils (CC) HTS CL. Here the steady state and pulsed operation of the JT-60SA HTS CLs are analysed, which requires also the modelling of the HX shell and of the vacuum shell, which was not present in the ITER CC. The CURLEAD model extension is presented and the capability of the new version of CURLEAD to reproduce the transient experimental data of the JT-60SA HTS CL is shown. The results obtained provide a better understanding of key parameters of the CL, among which the temperature evolution at the HX-HTS interface, the GHe mass flow rate needed in the HX to achieve the target temperature at that location and the heat load at the cold end.     

Using the Vincenta code to analyse pressure increases in helium during the quench of a superconducting magnet

The Vincenta code is used to simulate the pressure increases in helium in case of a quench in the superconducting coils. We focus on two classes of coil in which helium is in direct contact with the conductor: coils consisting of cable-in-conduit conductors (as in ITER or JT-60SA), in which supercritical helium is forced through long channels; and bath-cooled coils, in which static helium is confined in short channels perpendicular to the conductor and opening into a bath (as in Tore Supra or Iseult). Various physical phenomena are responsible for the pressure increases in helium, which is subjected to strong heat flux in the conductor during a quench: at the local level, i.e. in the heated channels, the inertial forces that must be overcome to expel the fluid and the friction forces due to the induced velocity; at the global level, i.e. throughout the cryogenic system, the adiabatic compression of non-heated volumes hydraulically connected to the heated channels. Here we analyse the thermohydraulic behaviour of helium to highlight the dominant phenomena, according to the geometry of the helium flow paths. The results are applied to numerical simulation of the pressure rise in case of quench in a JT-60SA cable-in-conduit conductor (CICC) and in the bath-cooled Iseult coil.     

Conductor and joint test results of JT-60SA CS and EF coils using the NIFS test facility

In 2007, JAEA and NIFS launched the test project to evaluate the performance of cable-in-conduit (CIC) conductors and conductor joints for the JT-60SA CS and EF coils. In this project, conductor tests for four types of coil conductor and joint tests for seven types of conductor joint have been conducted for the past eight years using the NIFS test facility. As a result, the test project indicated that the CIC conductors and conductor joints fulfill the design requirement for the CS and EF coils. In addition, the NIFS test facility is expected to be utilized as the test facility for the development of a conductor and conductor joint for the purpose of the DEMO nuclear fusion power plant, provided that the required magnetic field strength is within 9 T.     

Test results and analyses of conductor short samples for HT-7U

The experiments of Cable-in conduit conductor (CICC) short samples with high proportion of segregated copper strands have been carried out in SULTAN facility last September. These experiments aimed to investigate transient stability and AC losses of CICC conductor coated with different resistive barriers (Pb–30Sn–2Sb or Ni plating on strands) and to check the design of PF and TF CICC for HT-7U magnets. The resistive barriers’ influences on the stability and AC losses of CICC are evaluated. These experimental results are used for the choice of HT-7U TF and PF CICC design.     

Dynamic simulations for preparing the acceptance test of JT-60SA cryogenic system

Power generation in the future could be provided by thermo-nuclear fusion reactors like tokamaks. There inside, the fusion reaction takes place thanks to the generation of plasmas at hundreds of millions of degrees that must be confined magnetically with superconductive coils, cooled down to around 4.5 K. Within this frame, an experimental tokamak device, JT-60SA is currently under construction in Naka (Japan).The plasma works cyclically and the coil system is subject to pulsed heat loads. In order to size the refrigerator close to the average power and hence optimizing investment and operational costs, measures have to be taken to smooth the heat load.Here we present a dynamic model of the JT-60SA’s Auxiliary Cold box (ACB) for preparing the acceptance tests of the refrigeration system planned in 2016 in Naka. The aim of this study is to simulate the pulsed load scenarios using different process controls. All the simulations have been performed with EcosimPro® and the associated cryogenic library: CRYOLIB.     

CtFD-based correlations for the thermal–hydraulics of an HTS current lead meander-flow heat exchanger in turbulent flow

The Karlsruhe Institute of Technology is responsible for the design, construction and testing of the high temperature superconductor (HTS) current leads for the Wendelstein 7-X stellarator and for the JT-60SA tokamak. These HTS current leads mount a heat exchanger of the meander-flow type, in which the helium flows between the fins and is forced to cross flow with respect to the central Cu bar, which actually carries the current. Since an important issue in the operation of the HTS current lead is the optimization of the cooling power consumption, the helium thermal–hydraulics in such complex geometry becomes rather important.In this paper we extend a computational thermal fluid dynamics (CtFD) technique, previously introduced by the same authors and validated on short samples of meander flow heat exchanger and on the W7-X HTS current lead prototype, to a systematic analysis of the helium thermal-fluid dynamics inside different meander flow geometries. The first aim is to clarify under what operative conditions the flow regime can be considered turbulent and how the pressure drop as well as the heat transfer are related to the geometrical parameters and to the flow conditions. From the results of this analysis, correlations for the pressure drop and the heat transfer in the meander flow geometry have also been derived, which are applicable with good accuracy for the design of HXs over a broad range of geometries.     

0-D thermo-hydraulic approach for predicting pressure and temperature along HELIOS SHe closed loop under pulsed loads

Cryogenic systems for future large superconducting tokamaks (e.g. JT-60SA or ITER) are expected to cope with large pulsed heat loads due to cycling plasma operation. Their superconducting magnets are cooled down with forced flow supercritical helium.The aim of this paper is to verify to what extent a 0-D thermo-hydraulic model can well reproduce in space and time, the variations of pressure and temperature along a supercritical helium closed loop, subjected to pulsed heat loads.A 0-D model has been developed and the paper will present the corresponding equations and assumptions will also be justified. A pulsed heat load tokamak relevant scenario has been tested and the resulting variations of pressure and temperature have been compared with experimental data. The results of the 0-D model demonstrate the relevance of such approach for predicting transient behaviors in response of pulsed heat loads in a closed loop.This simple approach is also a justification to use process modeling codes where dynamics of the cryogenic circuits can be simulated with cryogenics components.     

制动工况参数对制动盘摩擦温度场分布的影响

车用盘式制动器是车辆中的重要零件。在紧急制动过程中,制动压力、整车参数以及轮胎与路面间附着系数之间的关系对制动器摩擦温度场分布有重要的影响。通过有限元仿真,探讨不同制动工况参数对瞬时温度场分布的影响。结果表明：如果忽略制动过程中摩擦热流强度的变化,会给温度场模拟带来较大的偏差。制动初始动能和摩擦力增长过程是影响盘表面温度场的关键因素。     

Relationship between dynamic characteristics of air film of aerostatic spindle and mid-frequency of surface topography

The dynamic characteristics of the gas film of an aerostatic spindle primary affect workpiece waviness in ultra-precision machining. To improve the machining accuracy of the machine tool and provide a firm theoretical basis for the design of an aerostatic spindle, a simulation model combining transient computational fluid dynamics (CFD) analysis and transient dynamic analysis is established in this study to investigate the dynamic characteristics of the spindle under unstable operating conditions. Based on a large eddy simulation, a three-dimensional flow model of an air film in an aerostatic spindle is established. The simulation results show that the gas flow in the throttle chamber is turbulent, and that complex vortices are formed. Using dynamic grid modeling technology, a CFD numerical model for the unsteady calculation of the spindle is established, and the dynamic characteristics of the gas film are obtained. A transient dynamic simulation model of an aerostatic spindle is established, and the effect of the nonlinear dynamic characteristics of the gas film on the spindle displacement response is investigated. Subsequently, a surface morphology prediction model is established. Results show that film fluctuation significantly affects the dynamic characteristics of the spindle and subsequently affects the generation of surface ripples on the workpiece.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-022-00391-4     

航空活塞发动机高空模拟试验台温度系统研究

在航空活塞发动机高空模拟试验中,模拟温度低、温度范围跨度大,高空模拟试验台（简称高空台）上应用了空气制冷和电加热两种调温措施,控制难度较大。将模拟温度划分为高温、常温、低温三个温度段,分别应用三种不同的调节方式进行温度控制;在系统数学建模和温度变化动态特性分析基础上,对高空台温度系统的调节过程进行了仿真研究,结果表明该方法能够满足温度的调节速度和控制精度要求。为了满足带涡轮增压器的航空活塞发动机对进气温度的要求,建立了涡轮增压器与中冷器之间的数学换热关系,以稳态时的发动机进气温度为例进行了仿真计算,结果与实际情况相符。     

Modelization of the thermal coupling between the ITER TF coil conductor and the structure cooling circuit

The ITER Toroidal Field (TF) coils are required not to quench during the most demanding event: a plasma disruption followed by a fast discharge of the Central Solenoid (CS), the Poloidal Field (PF) coils and the Correction Coils (CC). This event creates large heat deposition in the ITER magnet stainless steel structures in addition to the conductor AC losses. In order to prevent quench occurring in the TF conductor, cooling channels, implemented in the TF coil structure (TFCS), have to remove a large fraction of the heat deposited. The first integrated TF and structure mock-up has been manufactured and then tested in the HELIOS cryogenic test facility (CEA Grenoble) to determine the thermal coupling between the TFCS and the TF conductor, both actively cooled by supercritical helium at 4.4 K and 5 bar. It consists in a stainless steel casing, a cooling pipe glued with resin in the casing groove, winding pack (WP) ground insulation, a radial plate and a copper dummy cable-in-conduit-conductor (CICC). Steady state as well as transient thermal characterizations have been completed in May 2015. Simulation results by thermal hydraulic codes (VENECIA/SuperMagnet) and some of the experimental data are presented and discussed. The thermal coupling between the helium in the cooling tube and the TF coil structure is then modelled as an equivalent heat transfer coefficient in order to simplify the thermal hydraulic (TH) models. Comparison between simplified coupling and detailed coupling is presented.     

Superconductor Stability Revisited: Impacts from Coupled Conductive and Thermal Radiative Transfer in the Solid

Standard stability calculations following the Stekly, adiabatic or dynamic stability models apply purely solid thermal conduction mechanism, derive predictions under (quasi-) stationary and adiabatic conditions and assume ideal (mostly centrosymmetric) location of disturbances. Instead, the present paper takes into account also thermal radiative heat transfer in the superconducting solid, pool boiling, and considers the impact of random location and intensity of disturbances on the stability problem. The analysis is based on interplay between Monte Carlo radiative transfer calculations and a rigorous Finite Element method to calculate the resulting transient temperature field and stability functions. The combined Monte Carlo/Finite Element method is applied to 1G filament and 2G thin-film-coated high temperature superconductors. Results are strongly different from solutions achieved with standard, solely solid conduction thermal transport. It is not realistic, even in thin films, to assume uniform conductor temperature under transient disturbances. This may have significant consequences for design and simulation of performance of superconducting fault current limiters. There are doubts whether superconducting fault current limiters under any operation conditions could work in either pure flux flow or Ohmic resistive states.     

Solution of facility layout problems with pickup/drop-off locations using random search techniques

Due to non-polynomial hardness, the facility layout problem (FLP) becomes more critical when pickup/drop-off (P/D) locations are considered in the design of an open field layout under a manufacturing environment. This paper proposes an indigenous model of the facility layout problem based on random search techniques and its solution methodology using a genetic algorithm (GA), simulated annealing (SA) and a hybrid algorithm (HA). The paper illustrates the performance of different random search operating parameters in solving the facility layout problem considering P/D locations along the periphery of rectangular machine blocks. The preliminary experiments were carried out on three facility layout test problems having six, eight and ten machines in order to fix the different operating parameters such as crossover operator, crossover rate, initial temperature, temperature reduction factor, number of generations, population size, etc. The results of extensive preliminary experimentation were utilized to solve facility layout problems having 12 and 18 machines and, finally, were compared with the existing procedures in the literature. The experimental tables and related analysis performed via the solution methods by applying GA, SA and HA revealed that random-search-based modeling of FLP considering P/D and its solution as suggested in this paper is worth pursuing.     

液滴干燥过程的模拟研究

为更直观地体现液滴蒸发历程,详细分析液滴内部溶剂浓度与液滴比热、液滴表面饱和蒸气压、溶剂扩散系数之间的耦合关系,建立同时考虑液滴内部温度梯度变化及浓度梯度变化的单液滴蒸发模型,并基于网格重构技术解决液滴蒸发过程中的动边界问题,分别以纯水滴和硫酸钠溶液液滴蒸发为例,模拟分析不同操作工况下,液滴滴径、液滴内部温度梯度及溶质浓度梯度的瞬态变化。结果表明:数值模拟的结果与实验结果基本吻合。     

Radiation Heat Transfer and Its Impact on Stability Against Quench of a Superconductor

Stability functions are an important analytical/numerical tool for appropriate design of conductor geometry and dimensions to prevent conductor losses under a transport current. While standard stability calculations following the Stekly, adiabatic, or dynamic stability models apply purely solid thermal conduction mechanism and derive results under (quasi) stationary conditions, the present paper investigates if, and to which extent, also radiation heat transfer, in addition to solid conduction, can exert impacts on conductor stability. Further, the full transient conductor temperature evolution after a disturbance is calculated. The analysis applies an interplay between Monte Carlo radiative transfer calculations, to describe absorption of heat pulses and their distribution in the conductor, and a rigorous finite element method to calculate the resulting temperature field and stability functions. The results show that radiative heat transfer cannot be neglected in particular if periodic disturbances have to be considered that can arise, e.g., in a flux flow fault current limiter.     

Thermal investigations of an experimental active magnetic regenerative refrigerator operating near room temperature

In this paper, numerical and experimental investigations on a magnetic refrigeration device based upon the active magnetic regeneration (AMR) cycle operating near room temperature are presented. A numerical 1D model based on the transient energy equations is proposed for modelling the heat exchange between the magnetocaloric material and the carrier fluid in the regenerator bed. The validity of 1D AMR-numerical model is investigated through the recently developed magnetic cooling demonstrator by Clean Cooling Systems SA (CCS) at the University of Applied Sciences of western Switzerland (HES−SO). The obtained results including the temperature span, the coefficient of performance and the cooling power are presented and discussed. In general, good agreements have been noted between the experimental and numerical results.     

北京大兴国际机场航站楼核心区钢网格结构日照非均匀温度场研究

温度荷载在大跨空间结构的设计与施工过程中十分重要,由于太阳辐射以及各构件之间遮挡关系的复杂性,结构中的温度场一般是不均匀的。该文基于消隐算法,实现了圆截面杆系构件日照阴影的计算方法,编制了能够考虑地理气象信息的太阳辐射量计算程序。以北京大兴国际机场钢网格结构为背景,在ANSYS软件的热分析模块中模拟了结构的瞬态温度场,并对瞬态温度场的重要求解条件进行了讨论。结果表明,考虑太阳辐射后,大跨空间结构中的温度场具有明显的非均匀性与时变特征,日照阴影在温度场模拟中不可忽略。对于较为复杂的大跨空间结构,该文建议的温度场模拟方法为施工过程的精确模拟提供了重要基础。     

Thermo-hydraulic analyses associated with a CEA design proposal for a DEMO TF conductor

The future DEMO Toroidal Field (TF) magnets are likely to feature cable-in-conduit conductors (CICC) cooled by forced flow of supercritical helium. Design activities were carried out at CEA to provide a winding pack compatible with DEMO plant requirements. The CEA proposal comprises, for each of the 16 D-shaped windings, 10 double-pancakes (2 × 392 m long) wound in 10 turns. The conductor is a square-shaped Nb₃Sn double channel conductor with a central spiral, carrying a nominal current of 95.5 kA. We present a thermo-hydraulic analyses focused on the central, most critical pancake, where the maximum field is reached, aiming at evaluating the integrity of the proposed conductor design. Both normal and off-normal simulations were performed using detailed electromagnetic and neutron heating load maps as input, and evaluating operational quantities such as the temperature margin in burn conditions, and the hot spot temperature in quench conditions. We assessed the sensitivity of these quantities to some driving parameters, notably mass flow rate and the choice of friction factor correlation for the temperature margin, and quench initiation features for the hot spot temperature. Furthermore, the influence of the casing cooling on the temperature margin is analyzed. The study is carried out using two thermohydraulic models.     

On the possibility of steady-state solutions application to describe a thermal state of parts fabricated by selective laser sintering

The temperature distribution during selective laser sintering of a thin vertical stainless-steel wall has been simulated. The object is grown by successive deposition and laser melting of powder layers. An adjoint problem, including calculation of temperature in the part and the surrounding operating region, has been solved for different manufacturingprocess parameters within the plane statement based on two different approaches. The first approach considers transient heat conduction problem for a layer-by-layer grown body. The height of the calculation domain increases at each calculation step due to the addition of a new powder layer and a short-term laser treatment is applied to the layer region. The duration of one calculation step is determined by the time between two laser passes. The temperature distribution found at each step is used as the initial conditions for calculations at the next step. The thermal state achieved by the object under consideration after 500 calculation steps (i.e., after deposition and melting of 500 layers) is compared with a corresponding solution to the quasi-steady-state problem, which is found for a final geometry of the part, provided that a constant time-averaged heat flux is set to be supplied to the synthesis region. By example of the simple geometry under consideration, a quasi-steady-state solution can provide a fairly good estimate of the macroscopic thermal state of the synthesized part.