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1.
The thermodynamic cycle performance of Gadolinium (Gd) and Gd0.87Dy0.13 used as the working substance in regeneration magnetic Brayton and Ericsson refrigeration cycles are investigated under different external magnetic field conditions. Based on the experimental iso-field heat capacities of Gd with different magnetic fields, the effects of magnetic field change on thermodynamic performances including the magnetic entropy change, cooling quantity, non-perfect regeneration, net cooling quantity, and coefficient of performance (COP) are analyzed and discussed. The present work shows the possibility of reducing the regenerative losses and thereby improving the net cooling quantity for a given field change by selecting optimal initial and final magnetic field values. The similar analysis and calculation of the related thermodynamic performances are further applied to the magnetic material Gd0.87Dy0.13 which exhibits better net cooling quantities when compared to Gd at low temperature. 相似文献
2.
《Materials Letters》2007,61(11-12):2359-2361
The magnetic phase transition and magnetocaloric effect of the alloys of Gd0.74Tb0.26 and (Gd0.74Tb0.26)5(SixGe1−x)4 (x = 0.43, 0.50, 0.505) have been investigated by magnetization measurement. Experimental results show that partial substitution of the Gd by Tb in Gd5(SixGe1−x)4 system keeps the first order magnetic transition. Although the values of transition temperature decrease, the as-cast (Gd0.74Tb0.26)5(Si0.43Ge0.57)4 and annealed (Gd0.74Tb0.26)5(Si0.50Ge0.50)4 alloys display large magnetic entropy change up to 18.89 J kg− 1 K− 1 and 13.79 J kg− 1 K− 1 near their transition temperatures in the low magnetic field change of 0–2.0 T, respectively. 相似文献
3.
《低温学》2015
The adiabatic demagnetization refrigerator (ADR) system in this paper is composed of a conduction-cooled current cycling high-temperature superconducting (HTS) magnet system, a magnetic bed assembly, its heat exchange parts and an auxiliary precooling stage (a commercial GM cryocooler and a liquid nitrogen vessel). The whole magnetic refrigeration system including the conduction-cooled HTS magnet is cooled by the precooling stage to absorb the rejection heat of the ADR cycle. The packed bed type magnetic bed consists of tiny irregular powders of Dy0.9Gd0.1Ni2 enclosed in a thin walled stainless steel container (22.2 mm in O.D., 0.3 mm in thickness and 40.0 mm in height). The precooled heat transfer fluid (helium) travels through the magnetic material when heat rejection is required; otherwise the helium stagnates within its pores (pseudo-adiabatic process). Flow of the heat transfer fluid substitutes for the function of a traditional heat switch, creating, essentially, a forced-convection type heat switch. The magnetic bed assembly is periodically magnetized and demagnetized at the center of the conduction-cooled HTS magnet which can stably generate both strong and alternating magnetic field from 0 T to 3.0 T (0–130 A) with an average ramp rate of 0.24 T s−1. The cooling capacities of the ADR system at 20 K which is the normal boiling point (NBP) of hydrogen, are 11.1 J cycle−1, 6.3 J cycle−1 and 1.9 J cycle−1 when the temperature spans are 1 K, 2 K and 3 K, respectively. We describe the detailed construction of the ADR system and discuss the test results with the operational parameters (the entrained helium pressure, the mass flow rate of helium and the operating temperature span) in the 20 K region. 相似文献
4.
《低温学》2014
This paper reviews the status of magnetic refrigeration system for hydrogen liquefaction. There is no doubt that hydrogen is one of most important energy sources in the near future. In particular, liquid hydrogen can be utilized for infrastructure construction consisting of storage and transportation. When we compare the consuming energy of hydrogen liquefaction with high pressurized hydrogen gas, FOM must be larger than 0.57 for hydrogen liquefaction. Thus, we need to develop a highly efficient liquefaction method. Magnetic refrigeration using the magneto-caloric effect has potential to realize not only the higher liquefaction efficiency >50%, but also to be environmentally friendly and cost effective. Our hydrogen magnetic refrigeration system consists of Carnot cycle for liquefaction stage and AMR (active magnetic regenerator) cycle for precooling stages. For the Carnot cycle, we develop the high efficient system with >80% liquefaction efficiency by using the heat pipe. For the AMR cycle, we studied two kinds of displacer systems, which transferred the working fluid. We confirmed the AMR effect with the cooling temperature span of 12 K for 1.8 T of the magnetic field and 6 s of the cycle. By using the simulation, we estimate the efficiency of the hydrogen liquefaction plant for 10 kg/day. A FOM of 0.47 is obtained for operation temperature between 20 K and 77 K including LN2 work input. 相似文献
5.
The influence of Dy on the magnetocaloric effect in Gd0.97 ? xDyxV0.03 (x = 0.1, 0.2, 0.3) alloys has been studied. These alloys were prepared by arc melting on a water-cooled copper hearth under an argon atmosphere. The magnetization behavior has been analyzed by X-ray diffraction and a vibrating sample magnetometer. Results indicate that the Curie points of Gd0.97 ? xDyxV0.03 alloys decrease linearly with increasing content of Dy. The values of maximum magnetic entropy change (ΔSM) and relative cooling power (RCP) for x = 0 ~ 0.2 is larger than that of Gd alone over a wider temperature range. The Gd0.97 ? xDyxV0.03 alloys have promising potential as working substance candidates for magnetic refrigeration due to their tunable Curie temperature and the favorable properties of the magnetocaloric effect. 相似文献
6.
《材料与设计》2015
The effect of the short milling times on R5(Si,Ge)4 R = Gd, Tb magnetocaloric material properties was investigated. In particular, the effect of milling on atomic structure, particles size and morphology, magnetic, and magnetocaloric effect was studied. With short milling times (< 2.5 h), a reduction of the Gd5Si1.3Ge2.7 and Tb5Si2Ge2 particles size was achieved down to approximately 3.5 μm. For both compositions the main differences are a consequence of the milling effect on the coupling of the structural and magnetic transitions. In the Gd5Si1.3Ge2.7 case, a second-order phase transition emerges at high temperatures as a result of ball milling. Consequently, there is a decrease in the magnetocaloric effect of 35% after 150 min of milling. Interestingly, an opposite effect is observed in Tb5Si2Ge2 where a 23% increase of the magnetocaloric effect was achieved, driven by the enhancement of the coupling between magnetic and structural transitions arising from internal strain promoted by the milling process. 相似文献
7.
T.X. Li R.Z. Wang J.K. Kiplagat L.W. Wang R.G. Oliveira 《International Journal of Refrigeration》2009,32(7):1570-1578
A combined double-way thermochemical sorption refrigeration thermodynamic cycle was proposed and tested. Both adsorption refrigeration and resorption refrigeration processes were combined in order to improve the system performance. Two different consolidated composite materials were used as the reactive sorbents and ammonia was used as the refrigerant. Experimental results showed that a system operating with such proposed cycle can have two useful cold productions during one cycle at the expense of only one heat input at high temperature. The average specific cooling power (SCP) during the adsorption refrigeration phase was 301 W kg?1. Analysis of the experimental data showed that the driving equilibrium drop during the resorption process was much lower than that during the adsorption process, when the cold production temperature was similar. The proposed combined double-way sorption cycle has a larger cooling capacity per unit of heat input and the maximum theoretical coefficient of performance (COP) is 1.24 when MnCl2 and BaCl2 are used as the reactive sorbents. 相似文献
8.
M.S. Anwar Shalendra Kumar Faheem Ahmed Nishat Arshi Bon Heun Koo 《Materials Research Bulletin》2012,47(10):2977-2979
A new complex magnetic material La0.65Sr0.35V0.1Mn0.9O3, suitable for the magnetic refrigeration, has been investigated. X-ray diffraction result showed that this compound had rhombohedral structure. The substitution of manganese with V leads to a decrease in the Curie temperature, TC from 378 K to 353 K. Using Arrott plots; it was found that the phase transition for this compound is of the second-order. The magnetocaloric study exposed a quite large value of the magnetic entropy change ~ 1.56 J/kg K and the relative cooling power value of 67 J/kg at magnetic field variation of 1 T. 相似文献
9.
《Optical Materials》2014,36(12):2128-2131
Green-emitting (Gd1−x−yLaxTby)2O(WO4)2 (0 ⩽ x ⩽ 0.05, 0.05 ⩽ y ⩽ 0.15) phosphors were synthesized in a single phase form by the conventional solid-state reaction method, and their photoluminescent properties were characterized. The (Gd1−x−yLaxTby)2O(WO4)2 phosphors showed strong and broad excitation bands from 230 to 350 nm, corresponding to the energy transition from the 4f8 to 4f75d configuration of Tb3+ and the charge-transfer (CT) transition of O2−−W6+. The oxytungstate phosphors exhibited typical emission peaks assigned to the transition from 5D4 to 7FJ (J = 6, 5, 4, and 3) of Tb3+, and the luminescence emission intensity was effectively enhanced by the La3+ doping into the host Gd2O(WO4)2 lattice. The highest green emission intensity was obtained for (Gd0.87La0.03Tb0.10)2O(WO4)2, where the relative emission intensity was 63% that of a commercial green-emitting (La0.52Ce0.31Tb0.17)PO4 phosphor. 相似文献
10.
《低温学》2015
The Vuilleumier (VM) refrigerator, known as heat driven refrigerator, is one kind of closed-cycle Stirling type regenerative refrigerator. The VM refrigerator with power being supplied by liquid nitrogen was proposed by Hogen and developed by Zhou, which shows great potential for development below 10 K. This paper describes the experimental development of a VM cryocooler operating below 8 K, which was achieved by using liquid nitrogen as a heat sink of middle cavity. The regenerator was optimized by using a part of metallic magnetic regenerator material Er3Ni to replace the lead sphere and a no-load temperature of 7.8 K was obtained. Then all the lead spheres were replaced by Er0.6Pr0.4 material and a no-load temperature of 7.35 K was obtained, which is the lowest temperature for this kind of refrigerator reported so far. The cooling power at 10 K is about 500 mW with a pressure ratio near 1.6 and a charge pressure of 1.8 MPa. Especially, the magnetic material Er0.6Pr0.4 was found to be a potential substitution for the conventional lead. 相似文献
11.
《低温学》2017
We describe the development and experimental results of a proof of concept Superfluid Magnetic Pump in this work. This novel low temperature, no moving part pump can replace the existing bellows-piston driven 4He or 3He-4He mixture compressor/circulators used in various sub Kelvin refrigeration systems such as dilution, Superfluid pulse tube, Stirling, or active magnetic regenerative refrigerators. Due to the superior thermal transport properties of sub-Lambda 4He this pump can also be used as a simple circulator to distribute cooling over large surface areas. Our pump was experimentally shown to produce a maximum flow rate of 440 mg/s (averaged over cycle), 665 mg/s (peak) and produced a maximum pressure difference of 2323 Pa using only the more common isotope of helium, 4He. This pump worked in an “ideal” thermodynamic state: The experimental results matched with the theoretical values predicted by a computer model. Pump curves were developed to map the performance of this pump. This successful demonstration will enable this novel pump to be implemented in suitable sub Kelvin refrigeration systems. 相似文献
12.
Na3Gd(PO4)2, Na3Gd0.94(PO4)2:0.06Tb3+ and Na3Gd0.94(PO4)2:0.06Eu3+ are prepared by solid-state reaction and their photoluminescence (PL) properties are investigated in the ultraviolet (UV) and vacuum ultraviolet (VUV) region. The obtained results show that Na3Gd0.94(PO4)2:0.06Tb3+ has an efficient emission under 147 nm excitation, but the emission efficiency of Na3Gd0.94(PO4)2:0.06Eu3+ is low under 147 nm excitation. We discuss the energy absorption and transfer process in the VUV region to solve the special phenomenon. 相似文献
13.
CoGdxFe2 ? xO4 (x = 0.0, 0.1, 0.3, 0.5) nano magnetic ferrite particles were synthesized by chemical co-precipitation method. The variation of dielectric parameters like dielectric constant, dielectric loss, capacitance and resistance for different Gd3+ compositions has been measured at room temperature for frequency dependence in the range of 100 Hz to 10 MHz using impedance analyzer. Results of measurements reveal strong dependence of dielectric parameters on frequency and Gd3+ ion content. Dielectric constant, dielectric loss, capacitance and resistance decrease with increasing frequency for all the CoGdxFe2 ? xO4 compositions. Increase in Gd3+ ion composition in material, increases the values of dielectric constant, dielectric loss and capacitance while decreases the electrical resistance of nano-particles. A qualitative explanation is given for the composition and frequency dependence of dielectric parameters. 相似文献
14.
《Optical Materials》2014,36(12):2183-2187
This paper reports the microstructure, luminescence and thermal stability properties of the NaSr1−xPO4:xTb3+ powders (x = 0.008, 0.01, 0.02, 0.04 and 0.06) via the conventional solid-state sintering at 1200 °C for 5 h. The X-ray diffraction result verifies all diffraction peaks are pure phase of NaSrPO4. The luminescence results show that the NaSrPO4:xTb3+ powders mainly excited at 370 nm have a series of the emission-states, related to the typical 4f → 4f intra-configuration forbidden transitions of Tb3+, and a major emission peak of around 546 nm. The concentration quenching of the NaSr1−xPO4:xTb3+ phosphors is appeared at x = 0.02. The decay time values of the NaSr1−xPO4:xTb3+ phosphors for the 5D4 state of the Tb3+ are around 3.30 ms to 3.60 ms. It is also found the chromaticity coordinate of NaSrPO4:Tb3+ phosphor varies with the increase of the concentration of Tb3+ ions from blue to green. Moreover, the thermal stability of the NaSrPO4:xTb3+ phosphors is slightly better than that of conventional YAG phosphors. 相似文献
15.
Tb3+-doped ZnMoO4 green phosphor was synthesized by a co-precipitation method. The morphology and structure of the phosphor were characterized by Scanning electron microscopy (SEM) and X-ray diffraction (XRD). Photoluminescence (PL) spectra were also used to characterize the ZnMoO4:Tb3+ samples. The results show that ZnMoO4:Tb3+ phosphor has triclinic structure with diameters ranging from 1.0 to 2.0 μm. The obtained ZnMoO4:Tb3+ phosphor emits green light emission centered at 541 nm corresponding to the 5D4 → 7F5 transition of Tb3+ when excited by 378 nm or 488 nm. The optimized concentration of Tb3+ is 15 mol.% for the highest emission intensity at 541 nm, and the concentration quenching occurs when the Tb3+ concentration is beyond 15 mol.%. The concentration quenching mechanism can be interpreted by the quadrupole–quadrupole interaction of Tb3+ ions. The present work suggests a convenient, cost-effective method for green phosphor, which may lead to potential applications in white light-emitting diodes (WLED). 相似文献
16.
A novel filling method of regenerator materials, which we name a co-axial layout, is experimentally investigated. The 2nd stage regenerator of a Gifford–McMahon cryocooler was packed with 50% by volume of the co-axial layout (low temperature side) that consisted of 20% Gd2O2S and 30% HoCu2 spheres. The warm temperature side was packed with 50% lead spheres as a single layer. The experimental results show that the cooling power of co-axial layout is almost the same as that of a three-layer layout, 20% Gd2O2S, 30% HoCu2 and 50% lead, at temperatures between the ultimate low temperature (3.0 K) and 6 K. Moreover, at the temperatures above 10 K, the co-axial layout has 1.7–2.0 times the cooling power of the three-layer layout. Thus the co-axial layout produces a major improvement in cooling power. In this paper, the performance of five types of material assortments is discussed. 相似文献
17.
The vacuum ultraviolet spectroscopic properties of GdOCl:Re3+ (Re3+ = Ce3+, Tb3+, Eu3+, and Dy3+) are investigated in detail for the first time. The host absorption band is determined to be around 179 nm, and the f–d transition bands as well as the charge transfer bands are assigned. Upon 179 nm excitation, Re3+ (Re3+ = Ce3+, Tb3+, Eu3+, Dy3+) ions shown their characteristic emissions. Energy transfers from Gd3+ to Re3+ ion were observed. A broad band ranging from 350 to 400 nm corresponding to the d–f transition of Ce3+ is observed. Eu3+ has typical red emission with the strongest peak at 620 nm; Tb3+ shows characteristic transition of 5D3,4 → 7Fj, and its spin-forbidden and spin-allowed f–d transitions in VUV region are calculated with Dorenbos’ equations, these calculated values agree well with the experimental results. Dy3+ presents yellow emission (4F9/2 → 6H13/2) with the strongest peak at 573 nm. 相似文献
18.
19.
《低温学》2016
As superconducting materials find their way into applications, there is increasing need to verify their performance at operating conditions. Testing of critical current with respect to temperature and magnetic field is of particular importance. However, testing facilities covering a range of temperatures and magnetic fields can be costly, especially when considering the cooling power required in the cryogenic system in the temperature range below 65 K (inaccessible for LN2). Critical currents in excess of 500 A are common for commercial samples, making the testing of such samples difficult in setups cooled via a cryocooler, moreover it often does not represent the actual cooling conditions that the sample will experience in service. This work reports the design and operation of a low-cost critical current testing facility, capable of testing samples in a temperature range of 10–65 K, with magnetic field up to 1.6 T and measuring critical currents up to 900 A with variable cooling power. 相似文献
20.
The dependence of magnetization M on the applied magnetic field H and temperature T was measured carefully, near the Curie temperature TC for the perovskite manganite sample Pr0.6Sr0.4MnO3. The experimental results indicate that this specimen exhibit ferromagnetic (FM) to paramagnetic (PM) transition at TC ~ 320 K. In the 200 K–45 K temperature range the spontaneous magnetization was decreasing, probably due to spin canted state between manganese and praseodymium spin systems. At 46 K the magnetization presents a second little transition, which can be ascribed to very weak traces of secondary Mn3O4 phase, and remains constant between 10 K and 46 K. The maximum value of the magnetic entropy change obtained from the M(H) plot data is |ΔSMmax| = 2.3 Jkg? 1 K? 1 for applied magnetic field of 2.5 T. At this value of magnetic field the relative cooling power (RCP) is 34.5 Jkg? 1. The temperature corresponding to ΔSM maximum value is almost equal to TC. The large entropy change can be attributed to the fact that the ferromagnetic transition enhances the effect of the applied magnetic field greatly. It is suggested by the results that this compound can be used as the working material in an active magnetic regenerative refrigerator above room temperature. 相似文献