On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State vip House. Leaders from the China Household Electric Appliance Research Institute, the Chi... On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State vip House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……展开更多
Disassembly and recycling of E-waste creates a series of environmental problems. The selection of a technologically reliable, environmentally friendly, economically affordable and socially acceptable recycling technol...Disassembly and recycling of E-waste creates a series of environmental problems. The selection of a technologically reliable, environmentally friendly, economically affordable and socially acceptable recycling technology for E-waste is a significant question. This study establishes a Monte-Carlo mathematical model of cost minimization, given the constraints of environmentally sound handling of the e-waste, in the context of Crystal Ball risk assessment and evaluation software. By following the streams of the different treatment processes, which consist of various technologies including disassembly, recycling and disposal, the econom-ics of various possibilities were identified and the optimal recycling technology proposed. The key factors of the proposed scenarios were determined by using sensitivity analysis. The results of this study show that, for discarded refrigerators, the operating life span plays the key role. The model supports maintenance and resale of the short lived refrigerators. For the longer lived refrigerators material recycling is recommended by the model. Sensitivity analysis shows that purchase cost, plastic sale price, condenser sale price and disassembly costs are the main effects. This study provides a significant technical support for policy making in E-waste management.展开更多
We have successfully developed cryogen-free dilution refrigerators with medium cooling power that can be applied to quantum experiments. Breakthroughs have been made in some key technologies and components of heat swi...We have successfully developed cryogen-free dilution refrigerators with medium cooling power that can be applied to quantum experiments. Breakthroughs have been made in some key technologies and components of heat switches and dilution units. Our prototype has been running continuously and stably for more than 100 hours below 10 m K, with a minimum temperature of 7.6 m K and a cooling power of 450 μW at 100 m K. At the same time, we have also made progress in the application of dilution refrigerators, such as quantum computing, low-temperature detector, and magnet integration. These indicators and test results indicate good prospects for application in physics, astronomy, and quantum information.展开更多
We investigate the finite-time performance of a quantum endoreversible Carnot engine cycle and its inverse operation-Carnot refrigeration cycle,employing a spin-1/2 system as the working substance.The thermal machine ...We investigate the finite-time performance of a quantum endoreversible Carnot engine cycle and its inverse operation-Carnot refrigeration cycle,employing a spin-1/2 system as the working substance.The thermal machine is alternatively driven by a hot boson bath of inverse temperatureβ_(h)and a cold boson bath at inverse temperatureβ_(c)(>βh).While for the engine model the hot bath is constructed to be squeezed,in the refrigeration cycle the cold bath is established to be squeezed,with squeezing parameter r.We obtain the analytical expressions for both efficiency and power in heat engines and for coefficient of performance and cooling rate in refrigerators.We find that,in the high-temperature limit,the efficiency at maximum power is bounded by the analytical valueη_(+)=√sech(2r)(1-η_(C)),and the coefficient of performance at the maximum figure of merit is limited byε_(+)=√sech(2r)(1+ε_(C))/sech(2r)(1+ε_(C))-εC)-1,whereη_(C)=1-β_(h)/β_(c)andε_(C)=β_(h)/(β_(c)-β_(h))are the respective Carnot values of the engines and refrigerators.These analytical results are identical to those obtained from the Carnot engines based on harmonic systems,indicating that the efficiency at maximum power and coefficient at maximum figure of merit are independent of the working substance.展开更多
The dynamic stability analysis of an irreversible refrigerator working at the minimum power input P for given cooling load R was investigated.An irreversible refrigerator model was established based on coupled differe...The dynamic stability analysis of an irreversible refrigerator working at the minimum power input P for given cooling load R was investigated.An irreversible refrigerator model was established based on coupled differential equations.The global asymptotic stability characteristics were proved by constructing Lyapunov function based on Lyapunov stability theory and analyzed by sketching global phase portraits.The influence of parameters such as initial and operating parameters were studied for different values.It was found that an equilibrium point of nonlinear system was the global stability point,and the temperature of the working fluids converged to the stability value as time t approximated to positive infinite.Besides,numerical integrations were carried out to corroborate the global asymptotic stability properties of the system.Finally,the dynamic stability and the thermodynamic properties of the system were analyzed.It was found that the energetic characteristics and the dynamic stability properties were deteriorated as the dimensionless cooling load R~* and the thermal conductance ratio b increased.展开更多
In this paper,an irreversible thermionic refrigerator model based on van der Waals heterostructure with various irreversibilities is established by utilizing combination of non-equilibrium thermodynamics and finite ti...In this paper,an irreversible thermionic refrigerator model based on van der Waals heterostructure with various irreversibilities is established by utilizing combination of non-equilibrium thermodynamics and finite time thermodynamics.The basic performance characteristics of the refrigerator are obtained.The effects of key factors,such as bias voltages,Schottky barrier heights and heat leakages,on the performance are studied.Results show that cooling rates and coefficients of performances(COPs)can attain the double maximum with proper modulation of barrier heights and bias voltages.Increasing cross-plane thermal resistance as well as decreasing electrode-reservoir thermal resistance and reservoir-reservoir thermal resistance can enhance the performance of the device.The optimal performance region is the interval between the maximum cooling rate point and the maximum COP point.By modulating the bias voltage,the working state of the device can fall into the optimal performance region.The optimal performance of the refrigerator when using single layer graphene and a few layers graphene as electrode material is also compared.展开更多
The regenerative refrigeration is an important reverse work-heat conversion cycle with a theoretical coefficient of performance(COP)identical to the Carnot efficiency.Practical regenerative refrigerators are capable o...The regenerative refrigeration is an important reverse work-heat conversion cycle with a theoretical coefficient of performance(COP)identical to the Carnot efficiency.Practical regenerative refrigerators are capable of working down to 4 K and largely fulfill the refrigeration requirement of modern technologies in many fields,especially for space applications.However,the enthalpy flow associated with the pressure dependence,abbreviated as pressure-induced enthalpy flow,brought about by real gas effects degrades the theoretical COP of the refrigerator to below about 30% of the Carnot efficiency at the temperatures of below the critical point.This paper reviews the long history of exploring the real gas effects which dates back to the 1970 s and continues to now.Important explorations of uncovering the loss mechanism and reducing such losses are summarized.The theories that are in accordance with experimental results and simulation results are expounded.We further carry out analyses on the expansion components,including the pulse tube and the clearance gap.Several inferences are made in order to explore the long-lasting puzzles about real gas effects.It is emphasized that the underlying cause of the loss in the regenerator is an indirect effect of the real gas properties.Further study about carrying out a direct verification of the theory is proposed.展开更多
As a novel generation of a rotational gas wave machine,the wave rotor refrigerator(WRR)is an unsteadyflow device used for refrigeration,in whose passages pressured streams directly contact and exchange energy due to th...As a novel generation of a rotational gas wave machine,the wave rotor refrigerator(WRR)is an unsteadyflow device used for refrigeration,in whose passages pressured streams directly contact and exchange energy due to the movement of pressure waves.In this paper,the working mechanism and refrigeration principle are inves-tigated based on the one-dimensional unsteadyflow theory.A basic limitation on main structural parameters and operating parameters is deduced and the wave diagram of WRR to guide designing is sketched.The main influential factors are studied through an experiment.In the DUT Gas Wave Refrigeration Studying and Development Center(GWRSDC)lab,the isentropic efficiency can now reach about 65%.The results show that the WRR is a feasible and promising technology in pressured gas refrigeration cases.展开更多
The pulse tube refrigerator （PTR） is a promising small-scale cryocooler. This paper first briefly introduces the history of the pulse tube refrigerator. It has pointed out that technology improvements and theoretica...The pulse tube refrigerator （PTR） is a promising small-scale cryocooler. This paper first briefly introduces the history of the pulse tube refrigerator. It has pointed out that technology improvements and theoretical developments of the pulse tube refrig- erator closely relate with the internal streaming effects. Then the discovering history and classification of the streaming or DC （direct current） flow effect are summarized. It proposes for the first time that the physical significance of the streaming con- tains the driving mechanisms and the transport mechanisms. It demonstrates that the driving mechanisms are the asymmetry of fluid flow and temperature while the transport mechanisms are a loop or vorticity, which transmits nonlinear dissipations. The important advancements have been made over the past two decades all over the world in research of streaming of the pulse tube refrigerator including Gedeon DC flow, Rayleigb streaming, the third type of DC flow and the regenerator circulation. With regard to Gedeon DC flow, theoretical and experimental analyses have been made and different suppression methods are summarized. In the aspect of Rayleigh streaming, it mainly focuses on the analytical solution of the second-order mass flow and the research of tapered pulse tubes. In particular, limited research on the third type of DC flow and regenerator circulation is presented. The experimental measurement techniques of streaming also are summarized. Finally, this paper briefly discusses the key scientific and technical issues of the current research, and foretells the future development trends of streaming research in PTR.展开更多
In recent years, microchannel heat exchangers have begun to be used in refrigeration and air conditioning systems. This paper introduces a microchannel condenser for domestic refrigerators with a theoretical model to ...In recent years, microchannel heat exchangers have begun to be used in refrigeration and air conditioning systems. This paper introduces a microchannel condenser for domestic refrigerators with a theoretical model to evaluate its performance. The model was used to obtain the optimal design parameters for different numbers of tubes and tube lengths. The results show that the needed tube height of the down- ward section decreases with the number of tubes and the tube diameter. Compared with the original con- denser, the present optimal design parameters can reduce the total metal mass by 48.6% for the two wall two side design and by 26% for the two wall one side design. Thus, the present condenser is much better than the condensers usually used in actual domestic refrigerators.展开更多
Two international standards,ISO 18501:2025,Performance rating of positive displacement refrigerant compressor,and ISO 18483:2025,Performance rating of centrifugal refrigerant compressor,were released at an event held ...Two international standards,ISO 18501:2025,Performance rating of positive displacement refrigerant compressor,and ISO 18483:2025,Performance rating of centrifugal refrigerant compressor,were released at an event held by GREE and Hefei General Machinery Research Institute Co.,Ltd.in Zhuhai,South China’s Guangdong province on June 12.展开更多
Waste heat generation,upgrading,and refrigeration are the fundamental ways to recover and utilize waste heat.Rationalizing the use of refrigerants also contributes to creating energy savings and minimizing carbon emis...Waste heat generation,upgrading,and refrigeration are the fundamental ways to recover and utilize waste heat.Rationalizing the use of refrigerants also contributes to creating energy savings and minimizing carbon emissions.This study evaluates the thermodynamics,economics,and environment of different refrigerants in three waste heat recovery schemes:generate electricity,heat pump,and refrigeration.Based on this,the entropy weight and technique for order preference by similarity to an ideal solution are combined to assess the overall performance of the refrigerants.A thorough analysis reveals that R1234ze(E)could replace R245fa and R123 in the organic Rankine cycle.The best refrigerant for vapor compression refrigeration and high-temperature heat pump systems is R1243zf.In addition,the multi-objective decision analysis shows that the performance difference among the nine selected refrigerants is the total cost,followed by the environmental impact.The approach successfully recognizes the variations between different refrigerants in the same waste heat recovery scheme and gives a thorough evaluation.It sets instructions for the future use of eco-friendly refrigerants and their application of waste heat recovery schemes.展开更多
[Objectives]This study was conducted to investigate the influence mechanisms of microbial succession in raw milk under cold storage at different temperatures.[Methods]A raw milk sample was collected from a local large...[Objectives]This study was conducted to investigate the influence mechanisms of microbial succession in raw milk under cold storage at different temperatures.[Methods]A raw milk sample was collected from a local large-scale farm in Tangshan and divided into four treatment gradients:a control group(M)rapidly frozen at-80℃,and three experimental groups stored at 4℃(T),6℃(F),and 8℃(Y),respectively.A time series experiment was carried out according to time intervals of 24,48 and 72 h in each experimental group.Traditional microbial culture methods and 16S rRNA high-throughput sequencing were combined to analyze the dynamic changes in microbial abundance and structural variation.[Results]Plate counting revealed significantly lower total bacterial count and psychrotrophic bacteria in the 4℃storage group within 24 h compared with other treatment groups(P<0.01),confirming that maintaining low-temperature cold chain integrity and controlling treatment time(<24 h)can effectively inhibit microbial metabolic activity.16S rRNA sequencing analysis revealed high initial microbial diversity in raw milk,with dominant genera being Lactococcus,Acinetobacter,and Pseudomonas.Low-temperature treatment effectively reduced theαdiversity index of the microbial community.During the later stage of cold storage at 4℃,the relative abundance of Pseudomonas increased to over 90%,making it the dominant bacterial genus.[Conclusions]This study has significant application value for maintaining the quality of milk and dairy products and prolonging their shelf life.展开更多
To accomplish on-site separation, preconcentration and cold storage of highly volatile organic compounds(VOCs) from water samples as well as their rapid transportation to laboratory, a high-throughput miniaturized pur...To accomplish on-site separation, preconcentration and cold storage of highly volatile organic compounds(VOCs) from water samples as well as their rapid transportation to laboratory, a high-throughput miniaturized purge-and-trap(μP&T) device integrating semiconductor refrigeration storage was developed in this work. Water samples were poured into the purge vessels and purged with purified air generated by an air pump. The VOCs in water samples were then separated and preconcentrated with sorbent tubes. After their complete separation and preconcentration, the tubes were subsequently preserved in the semiconductor refrigeration unit of the μP&T device. Notably, the high integration, small size, light weight, and low power consumption of the device makes it easy to be hand-carried to the field and transport by drone from remote locations, significantly enhancing the flexibility of field sampling. The performances of the device were evaluated by comparing analytical figures of merit for the detection of four cyclic volatile methylsiloxanes(cVMSs) in water. Compared to conventional collection and preservation methods, our proposed device preserved the VOCs more consistently in the sorbent tubes, with less than 5% loss of all analytes, and maintained stability for at least 20 days at 4℃. As a proof-of-concept,10 municipal wastewater samples were pretreated using this device with recoveries ranging from 82.5% to 99.9% for the target VOCs.展开更多
Superelastic martensitic transformation(MT)confers a considerable elastocaloric response to shape memory alloys,but the significant hysteretic loss cripples the energy conversion efficiency.In the present work,large e...Superelastic martensitic transformation(MT)confers a considerable elastocaloric response to shape memory alloys,but the significant hysteretic loss cripples the energy conversion efficiency.In the present work,large elastocaloric effect with high refrigeration efficiency is realized in a polycrystalline Co_(50)V_(35)Ga_(15)Heusler alloy.Experimental results show that the studied alloy undergoes a paramagnetic type MT from L2_(1)cubic austenite to D0_(22)tetragonal martensite with a small thermal hysteresis(ΔT_(hys))of~3 K.By carefully examining the strain rate dependence of superelastic response,it is also found that the stress hysteresis(Δσ_(hys))consists of two components including intrinsic stress hysteresis(Δσ_(hys)^(int.))caused by inherent attribute of MT and extrinsic stress hysteresis(Δσ_(hys)^(ext.))aroused by applied strain rate.Accordingly,we put forward a strain relaxation equation to separate the relative contributions betweenΔσ_(hys)^(int.)andΔσ_(hys)^(ext.)quantitatively,which demonstrates that a smallΔT_(hys)is conducive to substantial decrease inΔσ_(hys)^(int.).Moreover,associated with stress-induced superelastic MT,large reversible adiabatic temperature changes(ΔT_(ad))higher than 11 K are achieved under an applied strain of 6.5%over a temperature range of at least 60 K.With the combination of a large elastocaloric cooling capacity and a low energy dissipation,significant improvements in refrigeration efficiency can be obtained in a wide strain range,being superior to those reported in most of typical elastocaloric materials near room temperature.展开更多
Frustrated lanthanide oxides with dense magnetic lattice and suppressed ordering temperature have potential applications in cryogenic magnetic refrigeration.Herein,the crystal structure,magnetic properties,magnetic ph...Frustrated lanthanide oxides with dense magnetic lattice and suppressed ordering temperature have potential applications in cryogenic magnetic refrigeration.Herein,the crystal structure,magnetic properties,magnetic phase transition(MPT)together with magnetocaloric effect(MCE)of LnOF(Ln=Gd,Dy,Ho,and Er)compounds were investigated.Crystallographic study shows that these compounds crystallize in the centrosymmetric space group R3m with an ideal triangular lattice.No long-range magnetic ordering is observed above 2 K for LnOF(Ln=Gd,Ho,and Er).However,DyOF compound undergoes an MPT from paramagnetic(PM)to antiferromagnetic(AFM)at the Neel temperature(TN≈4 K).Considerable reversible MCE is observed in these triangular-lattice compounds.Under the magnetic field change(μ0ΔH)of 0-2 T,the maximum values of magnetic entropy change(-ΔSMmax)of them are 6.1,9.4,12.7,and 14.1 J/(kg·K),respectively.Interestingly,the value of ErOF with Ising-like spin is 2.3 times that of GdOF,which provides an approach for exploring magnetic refrigerants with excellent low-field cryogenic magnetocaloric effect.展开更多
In the organic Rankine cycle,the refrigerant inevitably interacts with the lubricating oil.This study investigates the interaction mechanism between the fourth-generation refrigerant R1336mzz(Z)and the polyol ester(PO...In the organic Rankine cycle,the refrigerant inevitably interacts with the lubricating oil.This study investigates the interaction mechanism between the fourth-generation refrigerant R1336mzz(Z)and the polyol ester(POE)which is a representative component of the lubricating oil,using molecular dynamics simulations.The research focuses on pentaerythritol ester(PEC)with medium to long chain lengths,specifically PEC9.Relevant parameters such as solubility parameters,diffusion coefficients,binding energies,and radial distribution functions were calculated to elucidate the interaction dynamics.The variation in solubility parameters suggests that the miscibility of PEC9 and R1336mzz(Z)diminishes as the number of PEC9 chains increases.Additionally,the compatibility between these two components deteriorates with rising temperature,which is accompanied by a reduction in their binding energy.The simulation results presented in this study offer theoretical insights into the behavior of refrigerant R1336mzz(Z)upon contact with lubricating oil during actual operation,as well as implications for the operational efficiency of the equipment.展开更多
As one of the core components of a magnetic refrigerator,magnetic refrigeration materials are expected to have not only a considerable magnetocaloric effect but also excellent thermal conductivity.The poor thermal con...As one of the core components of a magnetic refrigerator,magnetic refrigeration materials are expected to have not only a considerable magnetocaloric effect but also excellent thermal conductivity.The poor thermal conductivity of many competitive oxide-based magnetic refrigerants,exemplified by EuTiO3-based compounds,acts as a major limitation to their practical application.Therefore,improving the thermal conductivity of magnetic refrigeration materials has become a research emphasis of magnetic refrigeration in recent years.In this work,a series of EuTiO_(3)(ETO)/Cu composites with different copper additives was prepared using a solid-phase reaction method by introducing appropriate amounts of copper powder.The influence of the introduction of copper on the phase composition,microstructure,thermal conductivity,and magnetocaloric effect of the composites was systematically investigated.Unexpectedly,the thermal conductivity of the composites is enhanced by up to 260%due to copper addition,accompanied by only a 5%decrease in magnetic entropy change and refrigerating capacity.Copper additive forms localized thermal conductive networks and promotes the densification process,resulting in significantly enhanced thermal conductivity of the composites.This work demonstrates the feasibility of improving the thermal conductivity of oxide-base d magnetic refrigeration materials by introducing highly thermally conductive substances.展开更多
The barocaloric effect is considered as one of the most promising refrigeration with the potential to replace traditional gas compression refrigeration.One of the main obstacles to the application of barocaloric mater...The barocaloric effect is considered as one of the most promising refrigeration with the potential to replace traditional gas compression refrigeration.One of the main obstacles to the application of barocaloric materials lies in the requirement for high driving pressures.In this paper,we report on the barocaloric effect of Pb_(3)(VO_(4))_(2),which exhibits a ferroelastic transition from a high-temperature trigonal structure to a low-temperature monoclinic structure at 357 K,accompanied by a substantial volume change.The entropy change induced by hydrostatic pressure can reach up 14 J·kg^(-1)·K^(-1)under a relatively low pressure of 80 MPa.This work is expected to expand the selection range of barocaloric materials.展开更多
Cryogenic magnetic cooling based on the principle of the magnetocaloric effects(MCEs)of magnetic solids has been recognized as an alternative cooling technology due to its significant economic and social benefits.Desi...Cryogenic magnetic cooling based on the principle of the magnetocaloric effects(MCEs)of magnetic solids has been recognized as an alternative cooling technology due to its significant economic and social benefits.Designing novel magnetic materials with good magnetocaloric performance is a prerequisite for practical applications.In this study,three gadolinium-transition metal-based high entropy oxides(HEOs)of Gd(Fe_(1/4)Ni_(1/4)Al_(1/4)Cr_(1/4))O_(3),Gd(Fe_(1/5)Ni_(1/5)Al_(1/5)Cr_(1/5)Co_(1/5))O_(3),and Gd(Fe_(1/6)Ni_(1/6)Al_(1/6)Cr_(1/6)Co_(1/6)Mn_(1/6))O_(3)were designed and systematically characterized regarding their structural and cryogenic magnetic properties.These HEOs were confirmed to crystallize into a single-phase perovskite-type orthorhombic structure with a homogeneous microstructure,reveal a second-order magnetic transition at low temperatures,and exhibit significant cryogenic MCEs.The magnetocaloric performances of the present HEOs,identified by magnetic entropy changes,relative cooling power,and temperature-averaged entropy changes,were com-parable with recently reported candidate materials.The present study indicates potential applications for cryogenic magnetic cooling of the present HEOs and provides meaningful clues for designing and exploring HEOs with good cryogenic magnetocaloric performances.展开更多
文摘 On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State vip House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……
基金Projects 50574094 supported by the National Natural Science Foundation of ChinaCPEUKF06-11 by the Key Laboratory Open Project of Education Ministry of China200600242 by the Science and Technology Innovation Project of Xuzhou
文摘Disassembly and recycling of E-waste creates a series of environmental problems. The selection of a technologically reliable, environmentally friendly, economically affordable and socially acceptable recycling technology for E-waste is a significant question. This study establishes a Monte-Carlo mathematical model of cost minimization, given the constraints of environmentally sound handling of the e-waste, in the context of Crystal Ball risk assessment and evaluation software. By following the streams of the different treatment processes, which consist of various technologies including disassembly, recycling and disposal, the econom-ics of various possibilities were identified and the optimal recycling technology proposed. The key factors of the proposed scenarios were determined by using sensitivity analysis. The results of this study show that, for discarded refrigerators, the operating life span plays the key role. The model supports maintenance and resale of the short lived refrigerators. For the longer lived refrigerators material recycling is recommended by the model. Sensitivity analysis shows that purchase cost, plastic sale price, condenser sale price and disassembly costs are the main effects. This study provides a significant technical support for policy making in E-waste management.
基金supported by the Beijing Commission of Science and Technology(Grant No.Z211100004021012)Special Research Assistant Program of the Chinese Academy of Sciences(Grant No.E3VP021RX4)。
文摘We have successfully developed cryogen-free dilution refrigerators with medium cooling power that can be applied to quantum experiments. Breakthroughs have been made in some key technologies and components of heat switches and dilution units. Our prototype has been running continuously and stably for more than 100 hours below 10 m K, with a minimum temperature of 7.6 m K and a cooling power of 450 μW at 100 m K. At the same time, we have also made progress in the application of dilution refrigerators, such as quantum computing, low-temperature detector, and magnet integration. These indicators and test results indicate good prospects for application in physics, astronomy, and quantum information.
基金the National Natural Science Foundation of China(Grant No.11875034)the Opening Project of Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology.
文摘We investigate the finite-time performance of a quantum endoreversible Carnot engine cycle and its inverse operation-Carnot refrigeration cycle,employing a spin-1/2 system as the working substance.The thermal machine is alternatively driven by a hot boson bath of inverse temperatureβ_(h)and a cold boson bath at inverse temperatureβ_(c)(>βh).While for the engine model the hot bath is constructed to be squeezed,in the refrigeration cycle the cold bath is established to be squeezed,with squeezing parameter r.We obtain the analytical expressions for both efficiency and power in heat engines and for coefficient of performance and cooling rate in refrigerators.We find that,in the high-temperature limit,the efficiency at maximum power is bounded by the analytical valueη_(+)=√sech(2r)(1-η_(C)),and the coefficient of performance at the maximum figure of merit is limited byε_(+)=√sech(2r)(1+ε_(C))/sech(2r)(1+ε_(C))-εC)-1,whereη_(C)=1-β_(h)/β_(c)andε_(C)=β_(h)/(β_(c)-β_(h))are the respective Carnot values of the engines and refrigerators.These analytical results are identical to those obtained from the Carnot engines based on harmonic systems,indicating that the efficiency at maximum power and coefficient at maximum figure of merit are independent of the working substance.
基金the Fundamental Research Fund for the Central Universities,China(No.2011011302)National Natural Science Foundation of China(No.51078068)
文摘The dynamic stability analysis of an irreversible refrigerator working at the minimum power input P for given cooling load R was investigated.An irreversible refrigerator model was established based on coupled differential equations.The global asymptotic stability characteristics were proved by constructing Lyapunov function based on Lyapunov stability theory and analyzed by sketching global phase portraits.The influence of parameters such as initial and operating parameters were studied for different values.It was found that an equilibrium point of nonlinear system was the global stability point,and the temperature of the working fluids converged to the stability value as time t approximated to positive infinite.Besides,numerical integrations were carried out to corroborate the global asymptotic stability properties of the system.Finally,the dynamic stability and the thermodynamic properties of the system were analyzed.It was found that the energetic characteristics and the dynamic stability properties were deteriorated as the dimensionless cooling load R~* and the thermal conductance ratio b increased.
基金supported by the National Natural Science Foundation of China(Grant Nos.51779262,51576207,51306206)the Hubei Province Natural Science Foundation of China(Grant No.2017CFB498)。
文摘In this paper,an irreversible thermionic refrigerator model based on van der Waals heterostructure with various irreversibilities is established by utilizing combination of non-equilibrium thermodynamics and finite time thermodynamics.The basic performance characteristics of the refrigerator are obtained.The effects of key factors,such as bias voltages,Schottky barrier heights and heat leakages,on the performance are studied.Results show that cooling rates and coefficients of performances(COPs)can attain the double maximum with proper modulation of barrier heights and bias voltages.Increasing cross-plane thermal resistance as well as decreasing electrode-reservoir thermal resistance and reservoir-reservoir thermal resistance can enhance the performance of the device.The optimal performance region is the interval between the maximum cooling rate point and the maximum COP point.By modulating the bias voltage,the working state of the device can fall into the optimal performance region.The optimal performance of the refrigerator when using single layer graphene and a few layers graphene as electrode material is also compared.
基金supported by National Natural Science Foundation of China(No.51506152 and No.51777141)the Fundamental Research Funds for the Central Universities(inter-disciplinary program)under the contract No.kx0080020173427。
文摘The regenerative refrigeration is an important reverse work-heat conversion cycle with a theoretical coefficient of performance(COP)identical to the Carnot efficiency.Practical regenerative refrigerators are capable of working down to 4 K and largely fulfill the refrigeration requirement of modern technologies in many fields,especially for space applications.However,the enthalpy flow associated with the pressure dependence,abbreviated as pressure-induced enthalpy flow,brought about by real gas effects degrades the theoretical COP of the refrigerator to below about 30% of the Carnot efficiency at the temperatures of below the critical point.This paper reviews the long history of exploring the real gas effects which dates back to the 1970 s and continues to now.Important explorations of uncovering the loss mechanism and reducing such losses are summarized.The theories that are in accordance with experimental results and simulation results are expounded.We further carry out analyses on the expansion components,including the pulse tube and the clearance gap.Several inferences are made in order to explore the long-lasting puzzles about real gas effects.It is emphasized that the underlying cause of the loss in the regenerator is an indirect effect of the real gas properties.Further study about carrying out a direct verification of the theory is proposed.
基金supported by the National High Technology Research and Development Program of China(2006AA05Z216).
文摘As a novel generation of a rotational gas wave machine,the wave rotor refrigerator(WRR)is an unsteadyflow device used for refrigeration,in whose passages pressured streams directly contact and exchange energy due to the movement of pressure waves.In this paper,the working mechanism and refrigeration principle are inves-tigated based on the one-dimensional unsteadyflow theory.A basic limitation on main structural parameters and operating parameters is deduced and the wave diagram of WRR to guide designing is sketched.The main influential factors are studied through an experiment.In the DUT Gas Wave Refrigeration Studying and Development Center(GWRSDC)lab,the isentropic efficiency can now reach about 65%.The results show that the WRR is a feasible and promising technology in pressured gas refrigeration cases.
基金supported by the National Natural Science Foundation of China(Grant No.51176198)
文摘The pulse tube refrigerator （PTR） is a promising small-scale cryocooler. This paper first briefly introduces the history of the pulse tube refrigerator. It has pointed out that technology improvements and theoretical developments of the pulse tube refrig- erator closely relate with the internal streaming effects. Then the discovering history and classification of the streaming or DC （direct current） flow effect are summarized. It proposes for the first time that the physical significance of the streaming con- tains the driving mechanisms and the transport mechanisms. It demonstrates that the driving mechanisms are the asymmetry of fluid flow and temperature while the transport mechanisms are a loop or vorticity, which transmits nonlinear dissipations. The important advancements have been made over the past two decades all over the world in research of streaming of the pulse tube refrigerator including Gedeon DC flow, Rayleigb streaming, the third type of DC flow and the regenerator circulation. With regard to Gedeon DC flow, theoretical and experimental analyses have been made and different suppression methods are summarized. In the aspect of Rayleigh streaming, it mainly focuses on the analytical solution of the second-order mass flow and the research of tapered pulse tubes. In particular, limited research on the third type of DC flow and regenerator circulation is presented. The experimental measurement techniques of streaming also are summarized. Finally, this paper briefly discusses the key scientific and technical issues of the current research, and foretells the future development trends of streaming research in PTR.
基金Supported by the National Natural Science Foundation of China(No. 50676045)the National High-Tech Research and Devel-opment (863) Program of China (No. 2006AA05Z207)
文摘In recent years, microchannel heat exchangers have begun to be used in refrigeration and air conditioning systems. This paper introduces a microchannel condenser for domestic refrigerators with a theoretical model to evaluate its performance. The model was used to obtain the optimal design parameters for different numbers of tubes and tube lengths. The results show that the needed tube height of the down- ward section decreases with the number of tubes and the tube diameter. Compared with the original con- denser, the present optimal design parameters can reduce the total metal mass by 48.6% for the two wall two side design and by 26% for the two wall one side design. Thus, the present condenser is much better than the condensers usually used in actual domestic refrigerators.
文摘Two international standards,ISO 18501:2025,Performance rating of positive displacement refrigerant compressor,and ISO 18483:2025,Performance rating of centrifugal refrigerant compressor,were released at an event held by GREE and Hefei General Machinery Research Institute Co.,Ltd.in Zhuhai,South China’s Guangdong province on June 12.
基金supported by the National Natural Science Foundation of China(22178190)the National Youth Natural Science Foundation of China(22408195).
文摘Waste heat generation,upgrading,and refrigeration are the fundamental ways to recover and utilize waste heat.Rationalizing the use of refrigerants also contributes to creating energy savings and minimizing carbon emissions.This study evaluates the thermodynamics,economics,and environment of different refrigerants in three waste heat recovery schemes:generate electricity,heat pump,and refrigeration.Based on this,the entropy weight and technique for order preference by similarity to an ideal solution are combined to assess the overall performance of the refrigerants.A thorough analysis reveals that R1234ze(E)could replace R245fa and R123 in the organic Rankine cycle.The best refrigerant for vapor compression refrigeration and high-temperature heat pump systems is R1243zf.In addition,the multi-objective decision analysis shows that the performance difference among the nine selected refrigerants is the total cost,followed by the environmental impact.The approach successfully recognizes the variations between different refrigerants in the same waste heat recovery scheme and gives a thorough evaluation.It sets instructions for the future use of eco-friendly refrigerants and their application of waste heat recovery schemes.
基金Supported by Tangshan Talent Funding Project(A202202005)Dairy Industry Revitalization Major Technological Innovation Project of Hebei Key Research and Development Program(19227516D)High-level Talents Funding Project of Hebei Province(A201803034).
文摘[Objectives]This study was conducted to investigate the influence mechanisms of microbial succession in raw milk under cold storage at different temperatures.[Methods]A raw milk sample was collected from a local large-scale farm in Tangshan and divided into four treatment gradients:a control group(M)rapidly frozen at-80℃,and three experimental groups stored at 4℃(T),6℃(F),and 8℃(Y),respectively.A time series experiment was carried out according to time intervals of 24,48 and 72 h in each experimental group.Traditional microbial culture methods and 16S rRNA high-throughput sequencing were combined to analyze the dynamic changes in microbial abundance and structural variation.[Results]Plate counting revealed significantly lower total bacterial count and psychrotrophic bacteria in the 4℃storage group within 24 h compared with other treatment groups(P<0.01),confirming that maintaining low-temperature cold chain integrity and controlling treatment time(<24 h)can effectively inhibit microbial metabolic activity.16S rRNA sequencing analysis revealed high initial microbial diversity in raw milk,with dominant genera being Lactococcus,Acinetobacter,and Pseudomonas.Low-temperature treatment effectively reduced theαdiversity index of the microbial community.During the later stage of cold storage at 4℃,the relative abundance of Pseudomonas increased to over 90%,making it the dominant bacterial genus.[Conclusions]This study has significant application value for maintaining the quality of milk and dairy products and prolonging their shelf life.
基金the National Natural Science Foundation of China (No. 22306146)the PhD Scientific Research Startup Foundation of Xihua University (No. RX2200002003) for their financial support。
文摘To accomplish on-site separation, preconcentration and cold storage of highly volatile organic compounds(VOCs) from water samples as well as their rapid transportation to laboratory, a high-throughput miniaturized purge-and-trap(μP&T) device integrating semiconductor refrigeration storage was developed in this work. Water samples were poured into the purge vessels and purged with purified air generated by an air pump. The VOCs in water samples were then separated and preconcentrated with sorbent tubes. After their complete separation and preconcentration, the tubes were subsequently preserved in the semiconductor refrigeration unit of the μP&T device. Notably, the high integration, small size, light weight, and low power consumption of the device makes it easy to be hand-carried to the field and transport by drone from remote locations, significantly enhancing the flexibility of field sampling. The performances of the device were evaluated by comparing analytical figures of merit for the detection of four cyclic volatile methylsiloxanes(cVMSs) in water. Compared to conventional collection and preservation methods, our proposed device preserved the VOCs more consistently in the sorbent tubes, with less than 5% loss of all analytes, and maintained stability for at least 20 days at 4℃. As a proof-of-concept,10 municipal wastewater samples were pretreated using this device with recoveries ranging from 82.5% to 99.9% for the target VOCs.
基金supported by the National Natural Science Foundation of China(Nos.52261035,52201223,52371006,52371194)Applied Basic Projects of Yunnan province(No.202101BA070001-233).
文摘Superelastic martensitic transformation(MT)confers a considerable elastocaloric response to shape memory alloys,but the significant hysteretic loss cripples the energy conversion efficiency.In the present work,large elastocaloric effect with high refrigeration efficiency is realized in a polycrystalline Co_(50)V_(35)Ga_(15)Heusler alloy.Experimental results show that the studied alloy undergoes a paramagnetic type MT from L2_(1)cubic austenite to D0_(22)tetragonal martensite with a small thermal hysteresis(ΔT_(hys))of~3 K.By carefully examining the strain rate dependence of superelastic response,it is also found that the stress hysteresis(Δσ_(hys))consists of two components including intrinsic stress hysteresis(Δσ_(hys)^(int.))caused by inherent attribute of MT and extrinsic stress hysteresis(Δσ_(hys)^(ext.))aroused by applied strain rate.Accordingly,we put forward a strain relaxation equation to separate the relative contributions betweenΔσ_(hys)^(int.)andΔσ_(hys)^(ext.)quantitatively,which demonstrates that a smallΔT_(hys)is conducive to substantial decrease inΔσ_(hys)^(int.).Moreover,associated with stress-induced superelastic MT,large reversible adiabatic temperature changes(ΔT_(ad))higher than 11 K are achieved under an applied strain of 6.5%over a temperature range of at least 60 K.With the combination of a large elastocaloric cooling capacity and a low energy dissipation,significant improvements in refrigeration efficiency can be obtained in a wide strain range,being superior to those reported in most of typical elastocaloric materials near room temperature.
基金Project supported by the National Key Research and Development Program of China(2022YFB3505101)the National Science Foundation for Excellent Young Scholars(52222107)+2 种基金the National Science Foundation for Distinguished Young Scholars(51925605)the National Natural Science Foundation of China(52171195)the Projects of Ganjiang Innovation Academy,Chinese Academy of Sciences(E055B002)。
文摘Frustrated lanthanide oxides with dense magnetic lattice and suppressed ordering temperature have potential applications in cryogenic magnetic refrigeration.Herein,the crystal structure,magnetic properties,magnetic phase transition(MPT)together with magnetocaloric effect(MCE)of LnOF(Ln=Gd,Dy,Ho,and Er)compounds were investigated.Crystallographic study shows that these compounds crystallize in the centrosymmetric space group R3m with an ideal triangular lattice.No long-range magnetic ordering is observed above 2 K for LnOF(Ln=Gd,Ho,and Er).However,DyOF compound undergoes an MPT from paramagnetic(PM)to antiferromagnetic(AFM)at the Neel temperature(TN≈4 K).Considerable reversible MCE is observed in these triangular-lattice compounds.Under the magnetic field change(μ0ΔH)of 0-2 T,the maximum values of magnetic entropy change(-ΔSMmax)of them are 6.1,9.4,12.7,and 14.1 J/(kg·K),respectively.Interestingly,the value of ErOF with Ising-like spin is 2.3 times that of GdOF,which provides an approach for exploring magnetic refrigerants with excellent low-field cryogenic magnetocaloric effect.
基金supported by Hainan Provincial Natural Science Foundation of China(No.422CXTD509).
文摘In the organic Rankine cycle,the refrigerant inevitably interacts with the lubricating oil.This study investigates the interaction mechanism between the fourth-generation refrigerant R1336mzz(Z)and the polyol ester(POE)which is a representative component of the lubricating oil,using molecular dynamics simulations.The research focuses on pentaerythritol ester(PEC)with medium to long chain lengths,specifically PEC9.Relevant parameters such as solubility parameters,diffusion coefficients,binding energies,and radial distribution functions were calculated to elucidate the interaction dynamics.The variation in solubility parameters suggests that the miscibility of PEC9 and R1336mzz(Z)diminishes as the number of PEC9 chains increases.Additionally,the compatibility between these two components deteriorates with rising temperature,which is accompanied by a reduction in their binding energy.The simulation results presented in this study offer theoretical insights into the behavior of refrigerant R1336mzz(Z)upon contact with lubricating oil during actual operation,as well as implications for the operational efficiency of the equipment.
基金Project supported by the National Key R&D Program of China(2021YFB3501204)the National Science Fund for Distinguished Young Scholars(51925605)+1 种基金the National Science Foundation for Excellent Young Scholars(52222107)the National Natural Science Foundation of China(52171195,52201036)。
文摘As one of the core components of a magnetic refrigerator,magnetic refrigeration materials are expected to have not only a considerable magnetocaloric effect but also excellent thermal conductivity.The poor thermal conductivity of many competitive oxide-based magnetic refrigerants,exemplified by EuTiO3-based compounds,acts as a major limitation to their practical application.Therefore,improving the thermal conductivity of magnetic refrigeration materials has become a research emphasis of magnetic refrigeration in recent years.In this work,a series of EuTiO_(3)(ETO)/Cu composites with different copper additives was prepared using a solid-phase reaction method by introducing appropriate amounts of copper powder.The influence of the introduction of copper on the phase composition,microstructure,thermal conductivity,and magnetocaloric effect of the composites was systematically investigated.Unexpectedly,the thermal conductivity of the composites is enhanced by up to 260%due to copper addition,accompanied by only a 5%decrease in magnetic entropy change and refrigerating capacity.Copper additive forms localized thermal conductive networks and promotes the densification process,resulting in significantly enhanced thermal conductivity of the composites.This work demonstrates the feasibility of improving the thermal conductivity of oxide-base d magnetic refrigeration materials by introducing highly thermally conductive substances.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52301241 and 52271175)。
文摘The barocaloric effect is considered as one of the most promising refrigeration with the potential to replace traditional gas compression refrigeration.One of the main obstacles to the application of barocaloric materials lies in the requirement for high driving pressures.In this paper,we report on the barocaloric effect of Pb_(3)(VO_(4))_(2),which exhibits a ferroelastic transition from a high-temperature trigonal structure to a low-temperature monoclinic structure at 357 K,accompanied by a substantial volume change.The entropy change induced by hydrostatic pressure can reach up 14 J·kg^(-1)·K^(-1)under a relatively low pressure of 80 MPa.This work is expected to expand the selection range of barocaloric materials.
基金supported by the National Natural Science Foundation of China(No.52171174).The authors acknowledge Dr.Chao Zhang from the Instrumentation Service Center for Physical Sciences at Westlake University for magnetization measurements.
文摘Cryogenic magnetic cooling based on the principle of the magnetocaloric effects(MCEs)of magnetic solids has been recognized as an alternative cooling technology due to its significant economic and social benefits.Designing novel magnetic materials with good magnetocaloric performance is a prerequisite for practical applications.In this study,three gadolinium-transition metal-based high entropy oxides(HEOs)of Gd(Fe_(1/4)Ni_(1/4)Al_(1/4)Cr_(1/4))O_(3),Gd(Fe_(1/5)Ni_(1/5)Al_(1/5)Cr_(1/5)Co_(1/5))O_(3),and Gd(Fe_(1/6)Ni_(1/6)Al_(1/6)Cr_(1/6)Co_(1/6)Mn_(1/6))O_(3)were designed and systematically characterized regarding their structural and cryogenic magnetic properties.These HEOs were confirmed to crystallize into a single-phase perovskite-type orthorhombic structure with a homogeneous microstructure,reveal a second-order magnetic transition at low temperatures,and exhibit significant cryogenic MCEs.The magnetocaloric performances of the present HEOs,identified by magnetic entropy changes,relative cooling power,and temperature-averaged entropy changes,were com-parable with recently reported candidate materials.The present study indicates potential applications for cryogenic magnetic cooling of the present HEOs and provides meaningful clues for designing and exploring HEOs with good cryogenic magnetocaloric performances.
