Aleksandra DembkowskaMonika LewandowskaRafal Ortwein
8页
查看更多>>摘要：Thermal-hydraulic analyses of forced-flow cooled superconducting conductors designed for fusion magnets are typically based on 1-D mathematical models, which demand reliable predictive correlations for the transverse mass-, momentum- and energy transport processes occurring between different conductor components. Friction factor correlations, derived from pressure drop tests or Computational Fluid Dynamics (CFD) simulations of conductor samples, describe momentum transfer. High Temperature Superconductors (HTS) are promising materials to be applied in future fusion magnets, since they offer operating magnets at higher magnetic fields or higher temperatures as compared to the current conductors made of Low Temperature Superconductors (LTS). Various concepts of HTS cables for fusion applications are being developed, characterized and analysed. Recently three concepts of triplet HTS subsize-conductors for a quench experiment have been proposed by KIT. Each of them consists of three twisted CrossConductor (CroCo) strands enclosed in a stainless steel jacket, but they feature different copper stabilizer geometry. In the Option 1 and 2 conductors CroCo strands are contained in copper sheaths of different thickness, whereas in the Option 3 they are embedded in copper profiles with larger contact area. Hydraulic characteristics of such conductors were unknown. Three dedicated short dummy conductors with the geometry identical to Option 1-3 conductors were prepared by KIT to be tested for pressure drop. Option 1 and 2 samples were prepared and characterized earlier. In the present study we report the results of the hydraulic test of the Option 3 conductor, performed using demineralized water at different temperatures, as well as the outcomes of the CFD simulations using the ANSYS FLUENT commercial code. It was observed that the experimental values of friction factor in the turbulent regime are small (close to the respective values predicted by the smooth tube correlation). The friction factors obtained by the CFD simulations agreed with the experimental data within the range of measurement uncertainty. Based on experimental and simulation results we developed a friction factor correlation valid in a very wide range of Reynolds number which could be used in thermal-hydraulic analyses of similar HTS cables.
查看更多>>摘要：Piston offset in the helium valved linear compressor (VLC) deteriorates the cooling performance and operating life of Joule-Thomson (JT) refrigerators, especially in aerospace applications. To clarify the influence of piston offset on the VLC performance, an experimental investigation was carried out. Based on a laboratory developed VLC, the effects of piston offset on the suction and discharge pressure, pressure ratio, mass flow rate, motor efficiency, volume efficiency and adiabatic efficiency are systematically studied under two piston motion states (fixed piston displacements and full strokes). The results show that when the piston stroke is constant, the offset will increase the discharge pressure and mass flow rate, and decrease suction pressure. When the piston moves at full stroke, the offset will reduce the discharge pressure and mass flow rate, and increase suction pressure. Regardless of the working conditions, the existence of offset will affect the efficiency of the compressor, hence increasing the power consumption.
查看更多>>摘要：In the framework of JT-60SA Tokamak commissioning (Japan, 2021), all coils have to be cooled with supercritical helium forced-flow at the temperature of 4.5 K in order to reach superconducting state before energization. An important issue is to predict the Joule energy dissipated in Cable-In-Conduit Conductors (CICC) and the maximal temperature reached in case of an incidental quench occurrence. Therefore, quench simulations were performed on the Toroidal Field Coil (TFC) with the STREAM (Superconductor Thermal hydraulic and Resistive Electrical Analytical Model) code and with the SuperMagnet code (CryoSoft), coupling THEA (thermal hydraulic and electrical 1-D CICC model) and Flower (thermal hydraulic network model). The quench event was simulated for one TFC at nominal conditions of tokamak operation. External energy deposition over each pancake's first turn of the coil at the peak magnetic field location was applied for initiating the resistive transition. This way, the computed Joule energy dissipated by one TFC is conservatively evaluated to be 5.65 MJ. The Joule energy dissipation depends strongly on quench initiation conditions and on the number of fully and rapidly quenched pancakes (maximal quench propagation velocity of 19.5 m/s). Some further analyses were performed on the acceptance quench test realized at the Cold Test Facility (CEA Saclay, 2018) on TFC02. The different calculation results (helium temperature, mass flow rate in upstream and downstream manifolds, normal length propagation) are presented in the following study and are consistent with the measurements. This analysis brings information on the limits and the ability of STREAM code to model quench behaviour in CICC coils cooled by forced flow of supercritical helium. This tool could be useful for tokamak magnets protection during quench event and safe operation, notably thanks to its fast computing time.
查看更多>>摘要：Superconducting high-field magnets working in He II are usually immersed in a pressurized static He II bath. This pressurized He II bath is then connected through a heat exchanger to a saturated He II bath acting as a cold source. Due to the peculiar He II properties (very high heat conductivity), the conventional heat exchanger designs are not suitable here. Additionally, a compact design is often mandatory, as space inside cryostats is always an issue. In a recent paper [1], we presented different configurations of optimized multi tube heat exchangers depending on the available horizontal or vertical space. Such an optimized compact heat exchanger prototype has been built to fulfill the cooling needs and the integration constraints of the HL-LHC superconducting D2 recombination dipole [2]. The chosen design with hundred oxygen-free high-purity copper horizontal tubes penetrating inside the extremity of the D2 cold mass vessel is an efficient solution offering significant operating margins. From the thermal analysis, it appears that the profile and value of the temperature difference across the heat exchanger really depends on the ratio of the transverse conductance to the longitudinal conductance, the first being determined by the conductivity of the copper and the Kapitza conductance. Therefore, optimization and prediction of the thermal performance of such a heat exchanger is only possible when these thermal properties (i. e., the heat conductivity and Kapitza conductance of the copper tubes) or the sum of these three thermal resistances in series are well known. For that purpose, we built a dedicated test bench to perform these transverse resistance measurements on a pipe sample. The experimental results obtained on a single pipe were then used to infer the behavior of the complete heat exchanger. The comparison of the predictive code and the cryogenic measurements shows excellent agreement over a wide range of cryogenic operating conditions (temperatures, pressures, heat loads). This paper presents a guideline for designing compact and efficient He II/He II heat exchanger as well as a method to predict the performance of such heat exchanger accurately.
查看更多>>摘要：Super-conducting cables are an enabling technology for energy applications such as large magnetic-confinement nuclear fusion machine, and a promising key player in the power transmission of the next future, both in AC and DC conditions. While the thermal-hydraulic analysis of forced-flow superconducting cables for fusion application can only rely on commercial or proprietary numerical tools, such kind of tools for power transmission cables are not even available. Within the framework of Open Science, set as a priority by the European Commission in Horizon Europe, the novel software OPEN Super Conducting Cables (OPENSC2) has been developed to grant the entire research community the possibility to simulate thermal-hydraulic transients in forced-flow superconducting cables for energy applications. A Test-Driven Development has been adopted for the OPENSC2 within an object-oriented approach. Following the TDD approach, three test cases are considered of paramount interest for the OPENSC2 development, deriving the set of characteristics that the target object-oriented tool should comply with, and namely: 1) a heat slug propagation along an ITER-like 2-region cable-in-conduit conductor, with a thousand of mm-size low-critical-temperature superconducting (LTS) strands, cooled by supercritical helium (SHe); 2) the heat diffusion across the cross section of a twisted-slotted-core cable-in-conduit conductor, with high-critical-temperature (HTS) superconducting tapes, for fusion application, cooled by SHe and 3) the nominal operation of a single-phase HTS High-voltage, Direct Current power cable, with a 2-cryostat configuration and 2 different fluids adopted as primary coolant and thermal shield. In the object-oriented OPENSC(2 )the class "conductor " is defined, where each Conductor Object (CO) is the combination of different lower-level objects (both fluid and solid components) instantiated by the class. The choice of each component drives the automatic selection of the appropriate physical equation(s) in the code, as well as the possible interactions between them. Thermo-physical properties of different materials and cryogens can be attributed to the components of a conductor objects, taken form open datasets. A user-friendly GUI allows setting and monitoring the simulations while running. The software is tested in the three case studies targeted in the TDD, to show eventually how it allows modeling the three test cases presented here. The Verification and Validation of the CO methods performed through benchmarks against the 4C code is also presented and discussed.
查看更多>>摘要：The European Dipole (EDIPO) test facility is undergoing a major upgrade of its magnet assembly, which will provide ground for testing both fusion and high-energy physics superconducting samples at variable temperature and with a background field of 15 T. In view of a cooling of the superconducting magnet based on a saturated helium bath, a helium vessel has been designed and procured. In this work, we present a preliminary design of the pressure relief system of the helium vessel. After having introduced the main requirements of the cryogenic circuit, we describe a staged pressure protection concept. A bursting disc, chosen as safety pressure relief device, is then sized following the appropriate European norms and according to credible accidental scenarios. Finally, we introduce the need of pressure relief and helium recovery following a quench of the superconducting magnet, after having determined the actual heat load transferred to the helium bath. Numerical simulations are also employed to study the dynamics of the pressure and temperature evolutions, and ideas for future studies are briefly discussed.
查看更多>>摘要：A small-scale liquid helium cryogenic system has been designed for cooling the superconductive single-flux quantum circuits. With a special double inner cylinders structure and a PID control system, automatic control of the liquid helium level could be achieved. The cooling capacity recovered structure was added to the cold shield of the system in order to reduce the heat leakage of the system. Besides, A special composite magnetic shielding structure was designed to ensure the circuits working in an extremely low magnetic environment. Experiments were conducted to test the thermal performance and the magnetic shielding efficiency of the liquid helium cryogenic system. The results show that the storage time of the liquid helium is about 2 days with about 110 coaxial cables and the magnetic flux density at the chip location is below 5 nT at the temperature of 4.2 K.
查看更多>>摘要：A cryogenic capsule is the key component of the inertial confinement fusion device and has gained increasing attention in the world. The solid hydrogen-isotope fuel inside the capsule is required to have a uniformity greater than 99% for a successful ignition. This study is concerned with the growing characteristics of the fuel layer. A numerical model has been established, and the predicted results are in good agreement with the experimental data. The investigation results indicate that during the growing process, the DT ice layer gets thicker with a decreasing growth speed, and this is accompanied by a dramatical increase in the amplitudes of low modes, especially for mode 1. The uniformity of the fuel layer can be improved by the means of reducing the maximum temperature difference along the capsule, increasing the mass of the fusion fuel inside the capsule, and using the higher-tritium fusion fuel. For the content of tritium of the fuel, the modes amplitudes of the fuel layer decrease with the contents of tritium, and no obvious change is observed when the volume fraction of tritium becomes greater than 50%.
查看更多>>摘要：Self-regulating high temperature superconducting (HTS) flux pump is a promising candidate for realizing the quasi-persistent current mode operation of closed-loop HTS magnets. To characterize its performance and optimize accordingly, in this work, we have established a model in Matlab/Simulink. The effectiveness of the model has been validated based on the data obtained from the previous experimental counterpart. The calculated results show that this model is able to reproduce the experimental results with a satisfactory agreement. Based on the exploration of the model, we found that the charging performance of self-regulating HTS flux pump is mainly dependent on a range of typical design considerations, including the length of HTS bridge, the applied frequency of power source, the coupling coefficient of magnetic couplers, as well as the scale of HTS coils. Additionally, we proved that the charging speed can be accelerated and the saturated load current will correspondingly increase with the appropriate system parameters. The results obtained by this work provide some useful references for further optimization design of self-regulating HTS flux pump devices.
del Pozo, Carlos ArnaizAlvaro, Angel JimenezCasano, Juan Jose RoncalCloete, Schalk...
17页
查看更多>>摘要：Cryogenic air separation units (ASU) are the predominant method for delivering high-purity pressurized O2 at large capacities to relevant industrial processes. This study presents an exergoeconomic assessment of the integration of two-phase expanders (TPE) in two ASU configurations with (1) intermediate liquid oxygen pumping followed by gaseous O2 compression and (2) total liquid oxygen pumping to the delivery pressure. A comprehensive exergy analysis showed that TPE integration in the latter resulted in exergy efficiency increase of 1.1%-points and specific power consumption (SPC) reduction 15.5 kWh/ton (-4.4%), while for the former, the exergy efficiency increase amounted to 1.8%-points with 17.9 kWh/ton (-5.2%) lower SPC. A complete thermodynamic mapping for the different cases was presented. From an economic perspective, total liquid pumping reached levelized cost of oxygen reductions of 1.68 euro/ton (-4.7%), while in the configuration with gas compressors it was limited to only 0.45 euro/ton (-1.2%), relative to analogous ASU configurations with JouleThomson valve expansion. The total liquid pumping scheme with TPE presented a cost reduction of 4.3 euro/ton (-11.2%) relative to the gaseous O2 compression counterpart. N2 by-product monetization can further improve the plant economic performance. Based on this assessment, integration of reliable TPE technology for incremental efficiency gains of pressurized O2 production in ASUs presents a promising opportunity to profitably contribute to energy efficiency and decarbonization goals.
NSTL
Elsevier