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 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：In the magnetic levitation system consisted of permanent magnets (PMs) and high-temperature superconductors (HTSs), the magnetization direction of the PM is often inconsistent with the c -axis of the HTS. Therefore, the interaction between the PM with an angle and the HTS should be studied to obtain the effects of the angle on the levitation properties due to the anisotropy property of the critical current density. In this paper, as the PM dipole oriented with the angle with respect to the c -axis of the HTS moves laterally above the semi-infinite HTS, the exact expressions for the lateral and vertical forces, the torque, and the total potential energy are obtained by using the advanced frozen-image model. The dependence of these physical quantities upon the angle and the initial cooling height have been systematically studied. Under the same conditions, the predicted force and torque calculations provided by the advanced frozen-image model qualitatively agree with the previous exper-imental and theoretical results. The study can provide some theoretical references for designing the HTS levi-tation system with the angle.
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.
NSTL
Elsevier