Based on the Chinese National Standards involving heat pump water heater and space heating system, performances of the R744/R290 subcritical heat pump system have been discussed and compared with those of the R22 syst...Based on the Chinese National Standards involving heat pump water heater and space heating system, performances of the R744/R290 subcritical heat pump system have been discussed and compared with those of the R22 system, which is widely used in heat pump systems in China nowadays. It can be indicated that R744/R290 mixture can work efficiently as a refrigerant for heat pumps with a large heat-sink temperature rise. When mass fraction of R290 is increased, discharge pressure is reduced. Under the nominal working condition, there is an optimum mixture mass fraction of 20/80 for R744/R290 under conventional condensation pressure. Both the heating COPhs （coefficient of performance） and volumetric heating capacity are increased by about 12.62% and 34.24% respectively compared with those of R22 based system. But for the heat sink with a small temperature rise, R744/R290 system has poorer performances than R22 system. When heat transfer pinch point in evaporator and condensation processes is considered, the degree of superheat has a negative influence upon system performances under the given conditions.展开更多
The utilization of reactive alkali metals in solid-state synthesis poses significant challenges for large-scale production of iron-based superconductors(IBS).Particularly for Ba_(1-x)K_(x)Fe_(2)As_(2)(BaK122),an IBS w...The utilization of reactive alkali metals in solid-state synthesis poses significant challenges for large-scale production of iron-based superconductors(IBS).Particularly for Ba_(1-x)K_(x)Fe_(2)As_(2)(BaK122),an IBS with proven high-field applicability,the extreme air sensitivity and explosive hydrolysis of potassium(K)metal hinder its practical manufacturing.In this work,an innovative approach substitutes elemental K with air-stable potassium fluoride(KF)to achieve the first successful synthesis of BaK122 superconductors,eliminating hazardous handling while maintaining stoichiometric control.The transition temperature of the BaK122 synthesized with KF(KF-based)reaches 38.5 K,consistent with those prepared using elemental K.IBS tapes were manufactured using the KF-based precursors via the powder-in-tube(PIT)method.The effects of thermal treatments at varied temperatures were thoroughly examined,with optimized tapes exhibiting high critical current density(J_(c)).Comprehensive microstructural analysis uncovers grain structure and compositional homogeneity,offering essential guidance for additional J_(c)enhancement.KF is confirmed as a reliable potassium source that avoids the intrinsic instability of metallic K,facilitating industrial-scale fabrication of BaK122 superconductors.This materials innovation also establishes a novel strategy for the safe fabrication of potassium-containing inorganic nonmetallic materials.展开更多
Iron-based superconductors(IBSs)are compelling candidates for high-field magnet applications due to their excellent intrinsic properties.The hot isostatic pressing(HIP)effectively enhances their critical current densi...Iron-based superconductors(IBSs)are compelling candidates for high-field magnet applications due to their excellent intrinsic properties.The hot isostatic pressing(HIP)effectively enhances their critical current density by increasing core density.However,IBS tapes are highly stress-sensitive after heat treatment.This necessitates fabricating magnets prior to the HIP process.Consequently,the requirement for large-volume HIP furnaces for full-scale magnets presents significant technological and cost barriers.To circumvent this manufacturing bottleneck,this paper introduces a novel“pre-HIP”two-step annealing process.The principle involves an initial,low-temperature HIP(pre-HIP)heat treatment on IBS tapes to achieve densification.Subsequently,the tapes are wound into the desired magnet or conductor geometry,followed by a final heat treatment at atmospheric pressure(AP).This strategy allows large-scale magnets to be treated in conventional,cost-effective furnaces.We systematically evaluated the effect of the pre-HIP temperature(370-450℃at 50 MPa)on the transport properties and bend performance of 7-filamentary Ba_(1-x)K_(x)Fe_(2)As_(2)(Ba-122)tapes.Results show that pre-HIP significantly enhances the critical current.However,a critical trade-off was identified:higher pre-HIP temperatures yield superior critical performance but induce local grain growth,causing severe degradation during bending.Samples pre-HIP at 370℃retained 78%of their initial performance after bending to 10 mm diameter,whereas the 450℃samples degraded significantly.This study confirms that pre-HIP is a cost-effective method to improve IBS magnet performance when the optimal temperature is selected.展开更多
Profit from their low anisotropy and high upper critical field,iron-based superconductors(IBSs)have great potential for high magnetic fields applications.Significant progress has been made for the current density impr...Profit from their low anisotropy and high upper critical field,iron-based superconductors(IBSs)have great potential for high magnetic fields applications.Significant progress has been made for the current density improvement of(Sr,Ba)0.6K0.4Fe2As2(122-type)IBS wires over the past fourteen years.In this article,an overview of the preparation procedures and key issues affecting the critical current performance of 122-type IBS wires is given,to provide a fundamental understanding of what controls the transport critical current density of 122-type IBS wires.Additionally,the recent developments for 122-type IBS wires are presented and future prospect and challenges in the development of 122-type IBS wires for practical applications are discussed.展开更多
文摘Based on the Chinese National Standards involving heat pump water heater and space heating system, performances of the R744/R290 subcritical heat pump system have been discussed and compared with those of the R22 system, which is widely used in heat pump systems in China nowadays. It can be indicated that R744/R290 mixture can work efficiently as a refrigerant for heat pumps with a large heat-sink temperature rise. When mass fraction of R290 is increased, discharge pressure is reduced. Under the nominal working condition, there is an optimum mixture mass fraction of 20/80 for R744/R290 under conventional condensation pressure. Both the heating COPhs （coefficient of performance） and volumetric heating capacity are increased by about 12.62% and 34.24% respectively compared with those of R22 based system. But for the heat sink with a small temperature rise, R744/R290 system has poorer performances than R22 system. When heat transfer pinch point in evaporator and condensation processes is considered, the degree of superheat has a negative influence upon system performances under the given conditions.
基金supported by the National Natural Science Foundation of China(Grant Nos.52107031,52177026,52172275,52377032 and 52377033)the Strategic Priority Research Program of Chinese Academy of Sciences,China(Grant No.XDB25000000)the International Partnership Program of Chinese Academy of Sciences,China(Grant No.116GJHZ2023005MI).
文摘The utilization of reactive alkali metals in solid-state synthesis poses significant challenges for large-scale production of iron-based superconductors(IBS).Particularly for Ba_(1-x)K_(x)Fe_(2)As_(2)(BaK122),an IBS with proven high-field applicability,the extreme air sensitivity and explosive hydrolysis of potassium(K)metal hinder its practical manufacturing.In this work,an innovative approach substitutes elemental K with air-stable potassium fluoride(KF)to achieve the first successful synthesis of BaK122 superconductors,eliminating hazardous handling while maintaining stoichiometric control.The transition temperature of the BaK122 synthesized with KF(KF-based)reaches 38.5 K,consistent with those prepared using elemental K.IBS tapes were manufactured using the KF-based precursors via the powder-in-tube(PIT)method.The effects of thermal treatments at varied temperatures were thoroughly examined,with optimized tapes exhibiting high critical current density(J_(c)).Comprehensive microstructural analysis uncovers grain structure and compositional homogeneity,offering essential guidance for additional J_(c)enhancement.KF is confirmed as a reliable potassium source that avoids the intrinsic instability of metallic K,facilitating industrial-scale fabrication of BaK122 superconductors.This materials innovation also establishes a novel strategy for the safe fabrication of potassium-containing inorganic nonmetallic materials.
基金supported by the National Natural Science Foundation of China(Grant No.52307035 and 12275063the Beijing Municipal Natural Science Foundation(Grant No.3222061).
文摘Iron-based superconductors(IBSs)are compelling candidates for high-field magnet applications due to their excellent intrinsic properties.The hot isostatic pressing(HIP)effectively enhances their critical current density by increasing core density.However,IBS tapes are highly stress-sensitive after heat treatment.This necessitates fabricating magnets prior to the HIP process.Consequently,the requirement for large-volume HIP furnaces for full-scale magnets presents significant technological and cost barriers.To circumvent this manufacturing bottleneck,this paper introduces a novel“pre-HIP”two-step annealing process.The principle involves an initial,low-temperature HIP(pre-HIP)heat treatment on IBS tapes to achieve densification.Subsequently,the tapes are wound into the desired magnet or conductor geometry,followed by a final heat treatment at atmospheric pressure(AP).This strategy allows large-scale magnets to be treated in conventional,cost-effective furnaces.We systematically evaluated the effect of the pre-HIP temperature(370-450℃at 50 MPa)on the transport properties and bend performance of 7-filamentary Ba_(1-x)K_(x)Fe_(2)As_(2)(Ba-122)tapes.Results show that pre-HIP significantly enhances the critical current.However,a critical trade-off was identified:higher pre-HIP temperatures yield superior critical performance but induce local grain growth,causing severe degradation during bending.Samples pre-HIP at 370℃retained 78%of their initial performance after bending to 10 mm diameter,whereas the 450℃samples degraded significantly.This study confirms that pre-HIP is a cost-effective method to improve IBS magnet performance when the optimal temperature is selected.
基金supported by the National Key R&D Program of China(2018YFA0704200 and 2017YFE0129500)the National Natural Science Foundation of China(51861135311,U1832213 and 51721005)+2 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(XDB25000000)the Key Research Program of Frontier Sciences of Chinese Academy of Sciences(QYZDJ-SSW-JSC026)the International Partnership Program of Chinese Academy of Sciences(182111KYSB20160014)。
文摘Profit from their low anisotropy and high upper critical field,iron-based superconductors(IBSs)have great potential for high magnetic fields applications.Significant progress has been made for the current density improvement of(Sr,Ba)0.6K0.4Fe2As2(122-type)IBS wires over the past fourteen years.In this article,an overview of the preparation procedures and key issues affecting the critical current performance of 122-type IBS wires is given,to provide a fundamental understanding of what controls the transport critical current density of 122-type IBS wires.Additionally,the recent developments for 122-type IBS wires are presented and future prospect and challenges in the development of 122-type IBS wires for practical applications are discussed.
