Abstract
Rare earth barium copper oxide (REBCO) coated conductor has emerged as one of the high
T
c
superconductors suitable for future ultrahigh field superconducting magnet applications. In the ...design and fabrication of such ultrahigh field REBCO magnets, it is essential to understand the behavior of REBCO coated conductor. The effect of heating on the properties of commercial REBCO coated conductors is very important for many practical reasons. Nevertheless, a comprehensive study on this effect have not yet been presented in the published literature. This work studies a commercial REBCO coated conductor heat-treated at temperatures between 175 °C and 300 °C for various durations. Critical current and lap joint resistivity were measured at 77 K and 4.2 K for the heat-treated samples. We found that critical current degrades with heat treatment time and temperature. This degradation can be described by a one-dimensional oxygen out-diffusion model with a diffusion coefficient of
D
= 2.5 × 10
−6
exp (−1.17eV kT
−1
) m
2
s
−1
. The heat treatment also causes appreciable increase in joint resistivity. Comprehensive structural and chemical analyses were performed on Cu/Ag/RECBO interfaces by transmission electron microscopy. Our electron energy loss spectroscopy study provided direct evidence of oxygen deficiency in the heat treated REBCO samples. In addition, it is found that the oxygen diffused out of the REBCO layer forms mostly Cu
2
O at both Ag/REBCO and Cu/Ag interfaces. Cu
2
O is also observed at grain boundaries of the Ag layer. The oxygen out-diffusion model proposed in this work is used to predict REBCO thermal degradation in several engineering scenarios.
There are growing concerns about the stresses created by shielding currents in high field superconducting magnets fabricated from tape conductors leading to reduced performance and lifetime. This ...paper presents results of stress/strain calculations caused by shielding currents assuming the conductor deformations follow a linear constitutive relation. An anisotropic bulk approximation approach was used to calculate the electromagnetic field distributions in a REBCO high field coil with a stack of pancakes and a large number of turns first, and then the Lorentz force distribution and mechanical response characteristics were studied in the two-dimensional axisymmetric configuration. A new discrete contact mechanical model implemented by the finite element method, which is able to simulate the contact and separation behaviors between adjacent turns during the deformation, was proposed to analyze the distributions of hoop stress, hoop strain, radial stress and radial displacement in the coil. The influences of shielding current on those mechanical responses were obtained by comparing the simulation cases with and without taking shielding current into account. Besides, a continuum bulk mechanical model, which is parallel to the discrete contact mechanical model and treats the pancakes as continuum bulks, was modeled as well in order to understand the influences of different models on the simulation results. Furthermore, we studied the influences of a couple of practical factors (including the n -value, ramp rate, and operating mode of the REBCO coil winding) on the shielding current and hoop stress. A couple of novel and important conclusions were found. (1) Neglecting the shielding current behavior would significantly underestimate the maximum local hoop stress in a REBCO high field coil. (2) The continuum bulk mechanical model is not adequate for the stress analysis of dry-wound high field coils, by which unreasonably large tensile radial stresses could be obtained. (3) The highest local hoop stresses at the fully-charged moment and the fully-discharged moment are located in a certain pancake near the end of the coil winding and the end pancake, respectively. (4) Decreasing the n -value and the ramp rate of the REBCO coil could be two auxiliary ways to suppress the shielding current and maximum local hoop stress in the coil. (5) For the ramp-and-hold operating mode, the REBCO coil experiences the highest stress level at the moment when it right achieves the goal field. (6) The cycling operation of a REBCO high field coil can cause the tape experiencing alternative positive and negative hoop stresses and this may decrease the fatigue life of the tape and then the life of a magnet.
•A membrane-based liquid desiccant dehumidification system is examined.•Simulation is carried out for the complete system with hot and cold water units.•The system effectiveness increase with NTUde ...before reaching its critical value.•System latent cooling output is much higher than sensible cooling output.•Total cooling capacity and COP increase with solution inlet concentration.
A complete membrane-based liquid desiccant dehumidification system is investigated under the steady operating condition, which mainly consists of a dehumidifier, a regenerator, three heat exchangers, a cold and a hot water supply units. A finite difference mathematical model is developed for the complete system to investigate the system dehumidification performance and energy requirement, and validated by experimental data. The dehumidification performance is evaluated by the system sensible and latent effectiveness and moisture flux rate, while its energy performance is assessed by the total cooling capacity and coefficient of performance. It is found that the number of heat transfer units in the dehumidifier side and solution to air mass flow rate ratio have the most considerable impact on the system performance, while the number of heat transfer units in the regenerator side and solution inlet concentration in the dehumidifier have comparatively weak influences. The system sensible and latent effectiveness can be improved by increasing the dehumidifier side number of heat transfer units before reaching its critical value of 6. However, the amount of moisture being absorbed, total cooling capacity and coefficient of performance decrease with the dehumidifier side number of heat transfer units at the low air flow rate. The critical value of solution to air mass flow rate ratio varies with number of heat transfer units, and it is preferable to keep the flow rate ratio at or below its critical value as further increasing solution flow rate would reduce the system coefficient of performance.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•This paper presents a literature review on the recent research progress in liquid desiccant dehumidification and air conditioning systems.•The physical features of various liquid desiccant materials ...and their dehumidification performances have been summarized.•Various types of dehumidifiers and their integration with liquid desiccant dehumidification system have been reviewed.•The combination of liquid desiccant dehumidification system with solar collector, vapour compression system, heat pump system, CHP system have been grouped and compared.
This paper presents a literature review on the recent research progress in liquid desiccant dehumidification and air conditioning systems. The physical features of various liquid desiccant materials and their dehumidification performances have been summarized. With the aim to improve the dehumidification characteristics, mixed solvents desiccants have become research hot topics recently. Various types of dehumidifiers and their integration with liquid desiccant dehumidification system have been reviewed. The combination of liquid desiccant dehumidification system with solar collector, vapour compression system, heat pump system, CHP system, etc. have been grouped and compared. It is shown that the majority of the recent research work for liquid desiccant dehumidification systems has concentrated on numerical simulations, a considerable amount of works are still required for the practical investigations of innovative material (mixed solvents) and hybrid systems.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The National High Magnetic Field Laboratory (NHMFL) has completed testing and commissioning of a unique ultrahigh field magnet that provides 36 T in a 32 mm bore with field inhomogeneity and ...stability better than 1 ppm over a cylinder of 1 cm diameter and length and a duration up to a few hours. While the magnet meets all its primary performance goals, there were some unexpected observations during the testing and commissioning activities. Primarily, while the magnet reaches full current and field, we are unable to charge the magnet as quickly as was anticipated. Also, the magnet occasionally quenches for no apparent reason. Charging the magnet at slower rates reduces the probability of quenches.
The nitrogen-doped graphene (C
3
N) had special physical and chemical properties, thus it was widely used in various fields, especially as a lithium-ion batteries (LIBs) anode material. However, the ...electric field was one of the important factors affecting the performance of C
3
N as an anode electrode material for LIBs. Consequently, in this work, first-principal calculations were adopted to investigate the adsorption and migration properties of lithium ions on C
3
N surface by electric field. Calculation results show that the C
3
N monolayer exhibited a narrower band gap (0.0191 eV) and lower diffusion barrier (0.107 eV) under the application of the electric field, and the negative value of the adsorption energy increased by degrees with the increase of the electric field. Bader charge analysis and charge density difference calculations also provided forceful evidence for the ability of C
3
N to adsorb lithium ions. As a result, our theoretical results demonstrated that C
3
N should be a new type of anode material for LIBs.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Currently, numerous studies have carried out to research the effect of biochars remediation soil heavy metals (HMs) contaminated, but there have been fewer explorations of the effect of biochars ...tubule on soil HMs remediation. This work aimed to study the effect of passivation and remediation of lead (Pb) and chromium (Cr) contaminated soil after insert sewage sludge biochar (SSB) tubule. The results showed that the high risky fractions of Pb and Cr could be transformed into more stable fractions; also, Pb and Cr total contents are significantly decreased by SSB tubule. The mechanisms include adsorption, ion exchange, complexation, and precipitation which are concluded from the characteristic analysis. Detailly, the passivation of Pb and Cr is better when the moisture is 25% and 35%, respectively Pb: exchangeable (F1), carbonate bound (F2) decreased by 25.1%, 16.8%, Fe-Mn oxides bound (F3) increased by 18.5%; Cr: F1 decreased by 73.0%, F2, F3, organic matter bound (F4) increased by 13.2%, 23.9%, 30.8%), respectively. The remediation of Pb and Cr is better when the moisture is 25% and 35%, respectively, (Pb: decreased by 23.3%; Cr: decreased by 38.4%, respectively). The findings showed that the SSB tubule is effective when used for soil HMs contaminated.
Full text
Available for:
CEKLJ, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The 45-T Hybrid at the National High Magnetic Field Laboratory (NHMFL) has been the only facility in the world capable of providing a dc field of above 40 T. The 45-T hybrid magnet, consisting of a ...superconducting outsert and resistive insert, was commissioned in 2000 reaching a field of 45 tesla. The cryogenic system for the NHMFL has been in service since 1994 and has provided cryogenic service for the 45-T hybrid superconducting outsert since testing in 1998. It was recently upgraded, replacing a majority of the original system. The 45-T Hybrid was cooled down successfully with the new cryogenic system in February 2014. The new cryogenic system has been proved more efficient and reliable in the past years, providing increased availability to the users. After the upgrade of the cryogenic system, a standard index heating test was performed on the outsert of the hybrid. This test is mainly for evaluating the performance of the outsert, particularly the degradation of the innermost Nb3Sn coil of the outsert that suffered an unprotected quench in 2000 and degradation since then. The results of index heating tests in the past are compared and presented.
The neutron Larmor diffraction technique has been implemented using superconducting magnetic Wollaston prisms in both single-arm and double-arm configurations. Successful measurements of the ...coefficient of thermal expansion of a single-crystal copper sample demonstrates that the method works as expected. The experiment involves a new method of tuning by varying the magnetic field configurations in the device and the tuning results agree well with previous measurements. The difference between single-arm and double-arm configurations has been investigated experimentally. We conclude that this measurement benchmarks the applications of magnetic Wollaston prisms in Larmor diffraction and shows in principle that the setup can be used for inelastic phonon line-width measurements. The achievable resolution for Larmor diffraction is comparable to that using Neutron Resonance Spin Echo (NRSE) coils. The use of superconducting materials in the prisms allows high neutron polarization and transmission efficiency to be achieved.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
In cold climates, the application of heat recovery is restricted by the issue of frost, which causes potential damage to heat exchangers and degrades their effectiveness. Membrane energy exchangers ...(MEEs), which enable simultaneous heat and moisture transfer, can reduce and delay frost formation and accumulation in cold climates. MEEs are recognized as the essential component for the new generation of Heating, Ventilation, and Air Conditioning (HVAC) systems. Despite of extensive studies on heat and mass transfer characterising and increased use of MEEs, the evaluation of suitable frost control strategies for the emerging MEEs in cold climates are still missing. This study presents numerical models of a quasi-counter-flow membrane energy exchanger (QCFMEE) and a quasi-counter-flow heat exchanger (QCFHE). Three different frost prevention strategies are examined: preheating outdoor air, heating room air and bypassing outdoor air. These strategies’ threshold values to prevent frost are calculated numerically and validated against experimental measurements. The results show that QCFMEE has lower threshold values and thus better frost tolerance ability compared with QCFHE because of mass transfer through the membranes. Moreover, the frost prevention strategies are evaluated based on annual energy consumption, energy saving ratio (ESR), and complexity of control for real-life applications. The simulated results show that among the discussed frost prevention strategies, preheating outdoor air has the advantage of the lowest energy consumption and highest ESR. Meanwhile, heating room air consumes the most energy and faces the problem of overheating outdoor air. Finally, concerning the bypassing outdoor air strategy, the significant fluctuation of its threshold values increases the complexity of control for real-life applications.
•Numerical models of frost thresholds for heat and energy recoveries are developed.•Comparison of three frost control approaches in different cold climates.•Establishment of performance indicators for real-life applications.•Evaluation of frost control strategies for the emerging membrane energy exchangers.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
