查看更多>>摘要：SPIRAL2 is a superconducting LINAC subject to cryogenic thermoacoustic oscillations occurring in its valves boxes. 4 years of monitoring and experimental investigations with thousands of datasets turned these unwanted effects into an opportunity to study and understand thermoacoustics in a complex environment such as a real life accelerator. Without digging deep into Rott's thermoacoustics theory, thoroughly shown in other works, this paper describes the instrumentation and the methods that prepare more advanced modeling of these phenomena either to damp or to harness the energy of cryogenic thermoacoustics.
查看更多>>摘要：A series of lanthanide-rich oxyborates LiLn(6)O(5)(BO3)(3) (LLnOB, Ln = Gd, Tb, Dy, and Ho) have been synthesized using high temperature solid state method. Their magnetic and magnetocaloric properties were investigated upon magnetic susceptibility (chi), magnetization (M), and isothermal magnetic entropy change (delta S-m) measurements. The maximum delta S-m, max of LiGd6O5(BO3)(3 )is 44.7 J kg(-1) K-1 at 4 K and delta mu H-0 = 9 T, which is higher than the one of commercial Gd3Ga5O12 (GGG, delta S-m,( max )= 41.8 J kg(-1) K-1 at 2 K for delta mu H-0 = 9 T). For LiHo6O5(BO3)(3), delta S-m, (max) is 14.12 J kg(-1) K(-1 )at 3 K and delta mu H-0 & nbsp; = 2 T, which is also larger than that of Ho3Ga5O12 (HoGG, -delta S-m, max = 4.38 J kg(-1) K-1 at 2 K for delta mu H-0 & nbsp;= 2 T) and Dy3Ga5O12 (DGG, delta S-m, max = 11.0 J kg(-1) K-1 at 2 K for delta mu H-0 & nbsp;= 2 T). These results indicate that LiGd6O5(BO3)(3) and LiHo6O5(BO3)(3) may be competitive candidates for applications as magnetic refrigerants. Moreover, thermal stability, infrared spectrum (IR), and ultraviolet-visible-near-infrared diffuse reflectance spectrum (UV-Vis-NIR) were carried out to characterize the title compounds.
查看更多>>摘要：The isobaric subcooling cryogenic propellants are of higher density, lower vapor pressure and higher sensible cooling capacity over their saturated state, which could bring beneficial impacts on the vehicle weight, engine performance and storage time. Among several subcooling methods, pumping decompression method and heat exchange method are emphatically compared, and three system schemes including subcooling before, during and after loading are illustrated and analyzed. For the target of rapidly obtaining subcooled LO2 below 70 K, the simultaneous subcooling scheme with an atmospheric and a subatmospheric LN2 bath heat exchangers is rec-ommended, where the water-ring vacuum pump is adopted to realize the depressurization. A semi-industry scale experiment facility was designed and built up. Results show that, with conditions of LO2 flow rate ranged from 0.2 L/s to 2.7 L/s, the temperature of LO2 at the outlet of the secondary heat exchanger was always below 70 K, successfully verifying the feasibility and effectiveness of this subcooling system. The minimum subcooling temperature of LO2 was about 66.6 K at around 2.2 L/s (the rated flow rate was designed as 2.0 L/s), indicating the reasonability of the system design. The present study can provide reference for the future applications of the subcooling cryogenic propellants.
查看更多>>摘要：A numerical model is established to calculate the temperature and pressure distributions of the 3 km long high temperature superconducting (HTS) power cable. The model assumes that the configuration of HTS power cable is three phase co-axial shape with counter-flow cooling method. In the numerical model, the circulating nitrogen enters the inner channel of the HTS power cable for cooling at the one end, flows to the other terminal, returns through the outer channel, and exits from the HTS power cable. The numerical model considers the mass, the momentum, and the energy balances of nitrogen, and the heat diffusion inside the HTS layer to obtain the realistic temperature and pressure distributions of the cable. When the long HTS cable is cooled by subcooled liquid nitrogen, the result shows that the maximum temperature of the compact HTS layer cannot be kept under 80 K even though the subcooled liquid nitrogen is supplied at the melting temperature. In order to supply nitrogen with lower enthalpy for ensuring sufficient cooling through the whole cable region, we suggest using slush nitrogen, and analyze it in the detailed numerical model. Thermo-hydraulic equations for slush nitrogen are incorporated in the numerical model. The results show that the maximum temperature of the HTS layer decreases by 6.4 K when slush nitrogen with solid volume fraction of 30% is supplied to the HTS cable. The effect of the inlet enthalpy of nitrogen and the heat transfer characteristics to the temperature distribution is discussed and further elucidated in this paper.
查看更多>>摘要：The deep-sea natural gas resources are safely and efficiently sent to the energy market through the offshore liquefied natural gas (LNG) industry chain, which provides a feasible idea for the utilization, development, storage and transportation of deep-sea natural gas fields. The offshore LNG industry chain includes production equipment (LNG-FPSO, LNG Floating Production Storage and Offloading Unit, also known as FLNG) and receiving equipment (LNG-FSRU, LNG Floating Storage and Regasification Unit). Due to the influence of sea conditions, the key cryogenic heat exchangers in LNG-FPSO and LNG-FSRU have the problem of insufficient heat transfer caused by uneven distribution of multiphase flow, which affects the performance index of liquefaction and gasification process. In this work, the visualization experimental device and numerical simulation model of falling film flow in LNG-FPSO and multiphase flow of intermediate medium in LNG-FSRU have been established, based on the sloshing platform system, camera and processing system, VOF two-phase flow model and dynamic grid technology. The measures are put forward to improve the offshore adaptability of multiphase flow in offshore LNG industry chain. When the anti-sloshing angle of the cover plate is 15 degrees, the liquid fluctuation index (FI) is small and the anti-sloshing resistance is good. The optimal number of transverse anti-sloshing separators is 3, and the anti-sloshing partition number required for unit axial length is 7.5.
You, ShuangrongMiyagi, DaisukeBadcock, Rodney A.Long, Nicholas J....
8页
查看更多>>摘要：AC loss is one of the key issues need to be considered in designing high temperature superconducting (HTS) devices. An effective method for AC loss reduction is applying magnetic flux diverters (MFDs) in close proximity of the HTS coil windings. In this work, two types of low-loss powder-core MFDs -high flux (HF) and molypermalloy-powder (MPP) MFDs -were applied to a REBCO coil assembly for reducing the AC loss. The measured and simulated results show that both types of MFDs can significantly reduce the total loss (the summation of the losses in the HTS windings and the MFDs) in the coil assembly. At 77 K and 40 A coil current, compared with the coil assembly without MFDs, the total loss with HF and MPP MFDs was reduced by 77 % and 81 %, respectively. Although MPP MFDs show slightly better performance in reducing total loss in the coil assembly than HF MFDs at low coil current, HF MFDs are more obvious option for AC loss reduction in high magnetic field applications owing to their relatively high saturation magnetic field.
查看更多>>摘要：The cryogenic sliding induced surface deformation and tribological behavior of TA2 pure titanium were investigated in the present work. Friction and wear tests under dry sliding condition at room and cryogenic temperatures were conducted separately. An external cryogenic device was designed to produce a steady cryogenic environment through liquid nitrogen during the sliding process. Microstructure of subsurface under beneath the worn surface were detected by Optical Microscope (OM), Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). The results showed that sliding at room temperature induced a severe plastic deformation (up to 50 mu m in depth), while the deformation layer was converted to a work-hardening layer (10 mu m) and a gradient microstructure was formed under cryogenic sliding condition. Sliding at cryogenic temperature induced the formation of dislocation walls and alpha phase sub-grains, which hindered the dislocation motion during sliding process and was responsible for the decrease of plastic deformation. Furthermore, the refinement of alpha phase grains in this hardening layer could be attributed to the strain accumulation and severe local deformation at cryogenic temperature. With the effects of subsurface deformation, wear rate of TA2 samples was decreased by up to 66% under cryogenic sliding condition. The wear mechanism followed the general characteristics of oxidation and adhesive wear under dry sliding wear condition at room temperature. Under cryogenic sliding, a successive tribological behavior consisting of strain concentration, cracks generation and propagation, and fatigue fracture can be induced by the formation of work-hardening layer in the subsurface of the sample.
查看更多>>摘要：The main component of liquefied natural gas (LNG) is methane. The regasification process of LNG is usually under a supercritical condition. In this paper, a three-dimensional model is established to study the heat transfer and flow mechanism of supercritical methane in a heating process. The special physical properties of supercritical methane are compiled and imported through user-defined database. The standard k-epsilon model with the standard wall function is selected for simulation. The results show that deterioration of heat transfer occurs on the upper surface of the channel, which is most evident when the bulk temperature approaches the pseudocritical temperature. And the heat transfer coefficient increases first and then decreases along the channel with the bulk temperature rising. The peak value appears near the pseudocritical temperature. The pressure also has a great influence on heat transfer and flow. Besides, the buoyancy effect is strong near the pseudocritical point, leading to nonuniform distribution of temperature and density on the cross section, and causing significant radial circulation. The heat transfer deterioration can be effectively reduced by using special structures such as fins to hinder the buoyancy.
查看更多>>摘要：The single-screw extruder is used for the continuous formation of solid rod of hydrogen ice and its isotopes. The extruded rod, further, requires to be cut into pellets and injected into the magnetically confined, hot plasma for the fuelling of long-pulse fusion reactors. An extruder is capable to produce and continuously supply the pellets at a frequency of 1-40 Hz. The design and development of a solid hydrogen screw-extruder system require a study of the visco-plastic behaviour of solid hydrogen and its effects on the pressure and speed of the extruder. A CFD tool (Polyflow) from ANSYSTM is employed to estimate the characteristics of the pressure developed by the extruder at different rotational speed of the screw. In the simulations, different Shear Stress Models developed by various researchers are implemented and the results of the same are investigated systematically for Single-Screw Hydrogen Extruder. The results obtained from these simulations are validated with the experimental results on single screw extruder from literature.
查看更多>>摘要：Recently, combination models, in which two or more advanced methods are employed, have been studied to explore various approaches to simulating large-scale ReBCO coils efficiently. However, modeling the combina-tions could be more complex if the methods are not integrated well. In this paper, an ingenious combination of thin-strip, homogeneous and multi-scale methods is presented. In particular, we build the thin strips as both the analyzed HTS tapes and the boundaries of the homogeneous bulks where the non-analyzed tapes are merged. Thus, the coil geometry is re-constructed with several bulks, but the bulks' boundaries and domains are tackled with different electromagnetic properties, and solved by T and A formulations, respectively. Firstly, we introduce the modeling process and highlight the differences and advantages over the previous models. Then, the accuracy of the proposed model is validated by comparing the results with those from the reference model based on a 2000-turn coil. The distributions of normalized current density, magnetic flux density and hysteresis losses from the two models are highly consistent, and the error of the total loss is less than 1%. Besides, the combination model is the most time-saving among all the advanced models. Furthermore, the proposed method can be applied in 3D simulations, and the high accuracy and efficiency are validated by simulating a 50-turn racetrack coil. The study shows that the combination method is a feasible approach to simulating large-scale HTS coils, and can be a powerful tool to design and optimize HTS systems.
NSTL
Elsevier