Soil backfilling and compaction are often involved in urban construction projects like the burying of power cables.The thermal conductance of backfill soil is therefore of great interest.To investigate the thermal con...Soil backfilling and compaction are often involved in urban construction projects like the burying of power cables.The thermal conductance of backfill soil is therefore of great interest.To investigate the thermal conductivity variation of compacted backfill soil,10 typical soils sampled in Zhejiang Province of China with moisture contents of 0%–25%were fully compacted according to the Proctor compaction test method and then subjected to thermal conductivity measurement using the thermal probe method at 20℃.The particle size distribution and the chemical composition of the soil samples were characterized to analyze their effects on thermal conductivity.The results showed that the maximum thermal conductivity of fully compacted soils generally exceeds 1.9 W/(m·K)and is 20%–50%higher than that of uncompacted soils.With increasing moisture content,soil thermal conductivity and dry bulk density first increase and then remain unchanged or decrease slowly;the critical moisture content is greater than 20%in most cases.Overall,the critical moisture content of soils with large particle size is lower than that of those with small particle size.Quartz has the highest thermal conductivity in the soil solid phase,and the mass percentage of quartz for most soils in this study is more than 50%,while that for yellow soil is less than 30%,which leads to the thermal conductivity of the former being nearly twice as great as that of the latter in most circumstances.Based on regression analysis,with moisture content and dry bulk density as the independent parameters,the prediction formulae for the thermal conductivity of two categories of compacted backfill soils are proposed for practical applications.展开更多
A conduction heat transfer process is enhanced by filling prescribed quantity and optimized-shaped high thermal conductivity materials to the substrate. Numerical simulations and analyses are performed on a volume to ...A conduction heat transfer process is enhanced by filling prescribed quantity and optimized-shaped high thermal conductivity materials to the substrate. Numerical simulations and analyses are performed on a volume to point conduction problem based on the principle of minimum entropy generation. In the optimization, the arrangement of high thermal conductivity materials is variable, the quantity of high thermal-conductivity material is constrained, and the objective is to obtain the maximum heat conduction rate as the entropy is the minimum.A novel algorithm of thermal conductivity discretization is proposed based on large quantity of calculations.Compared with other algorithms in literature, the average temperature in the substrate by the new algorithm is lower, while the highest temperature in the substrate is in a reasonable range. Thus the new algorithm is feasible. The optimization of volume to point heat conduction is carried out in a rectangular model with radiation boundary condition and constant surface temperature boundary condition. The results demonstrate that the algorithm of thermal conductivity discretization is applicable for volume to point heat conduction problems.展开更多
High-temperature radiative cooling is essential for solar absorbers,as it mitigates efficiency degradation resulting from thermal accumulation.While porous structures have proven effective in enhancing absorber perfor...High-temperature radiative cooling is essential for solar absorbers,as it mitigates efficiency degradation resulting from thermal accumulation.While porous structures have proven effective in enhancing absorber performance,practical manufacturing processes and prolonged operational wear inevitably introduce surface roughness and structural deviations,which profoundly impact radiative properties.This study constructs a ZnS/Ag solar absorber model with surface roughness and employs the finite-difference time-domain method to investigate how characteristic length,surface roughness,porosity,pore shape factor,and taper influence its radiative properties in the 3μm-5μm band at 750 K.Results show optimal absorption at a 1μm characteristic length with a 36.72%improvement compared to the model with l=0.25μm,increased absorption with higher porosity with a 69.29%improvement at 0.6 compared to the non-porous structure,lower circularity with a 19.03%improvement for C=0.89 compared to C=1.00,while surface roughness with a 61.24%improvement at RMS=0.031 compared to RMS=0 and taper with a 38.29%improvement at β=20°compared to β=0°also exert significant effects.This work provides engineering design guidelines for high-efficiency,low-cost absorbers.展开更多
In order to meet the growing global energy demand and fulfill energy conservation and emission reduction goals, the efficient utilization of solar energy is becoming increasingly critical. However, the effects of high...In order to meet the growing global energy demand and fulfill energy conservation and emission reduction goals, the efficient utilization of solar energy is becoming increasingly critical. However, the effects of high temperatures on solar absorption are rarely considered in practical research. Therefore, this study presents a porous zinc and silver sulfide solar absorber with high-temperature radiative cooling capabilities. The solar absorption rate and radiative cooling efficiency in the high-temperature range(636 K–1060 K) are computed using the finite-difference time-domain method. Furthermore, the impact of parameters such as characteristic length, porosity, incident angle, and pore shape factor on both the absorption rate and efficiency of the solar absorber is analyzed. The mechanism is further examined from the perspective of microscopic thermal radiation. The results show that, in the high-temperature range, the solar absorption rate increases with higher porosity and incident angles, reaching its peak when the characteristic length is 1 μm. These findings highlight the significant potential of the solar absorber for efficient solar energy harvesting in photo-thermal conversion applications within a specific high-temperature range.展开更多
Shape and quantity of helical baffles have great impact on the shell-side performance of helical baffled heat exchangers （HBHE）. In this work, three physical models of HBHE with baffles of different shape （trisecti...Shape and quantity of helical baffles have great impact on the shell-side performance of helical baffled heat exchangers （HBHE）. In this work, three physical models of HBHE with baffles of different shape （trisection, quadrant and sextant sector） were investigated. Numerical simulations were performed on HBHE at three helix an- gles （10°, 25° and 40°） by the software ANSYS CFX. Analyses of numerical results indicate that the sextant HBHE shows relatively better fluid flow performance because the leakage flow in the triangle area is evidently reduced and the fluid streamline appears much closer to an ideal spiral flow, while the trisection and quadrant HBHE show more scattered and disordered streamline distributions. The convective heat transfer coefficient and pressure drop in three types of HBHE were presented. Further investigations on the shell side performance with different helical baf- fles were implemented by the field synergy theory. Both theoretical and numerical analyses gave support on the re- lations between helical baffle shape and shell-side performance. This paper may provide useful reference for the selection of baffle shade and auantitv in HBHE.展开更多
Valve-regulated-lead-acid (VRLA) battery charging performed in high-temperature environments is extremely risky under overcharge conditions, and may lead to a subsequent thermal runaway. A new pressure-controlled char...Valve-regulated-lead-acid (VRLA) battery charging performed in high-temperature environments is extremely risky under overcharge conditions, and may lead to a subsequent thermal runaway. A new pressure-controlled charging method was adopted and the charging characteristics of the pressure-controlled VRLA battery in high-temperature environments were ex-perimentally studied. The concept was tested in a large temperature gradient to obtain more details about the effects of users' accustomed charging and discharging modes on battery capacity. The premature capacity loss (PCL) phenomenon under high temperature exposure was analyzed. The results showed that the capacity loss could be recovered by charging using a large current.展开更多
TiNb_(2)O_(7) is an advanced anode material for high-energy density lithium-ion batteries(LIBs) due to its considerable specific capacity and satisfactory safety.However,its rate capability is limited by its poor ioni...TiNb_(2)O_(7) is an advanced anode material for high-energy density lithium-ion batteries(LIBs) due to its considerable specific capacity and satisfactory safety.However,its rate capability is limited by its poor ionic conductivity and electronic conductivity.To solve this problem,TiNb_(2)O_(7) with W^(6+) doping was synthesized by a convenient solid-state method.The doping of W^(6+) will lead to arranging cation mixing and charge compensation.The cation rearrangement creates a new Li-conductive environment for lithiation,resulting in a low-energy barrier and the fast Li^(+)storage/diffusion.The results show that the Li^(+)diffusion coefficient of W_(0.06)Ti_(0.91)Nb_(2)O_(7) is increased by 9.96 times greater than that of TiNb_(2)O_(7).Besides,as the calculation proves,due to the partial reduction of the Nb^(5+)and Ti^(4+) caused by charge compensation,W^(6+)doping results in low charge transfer resistance and excellent electronic conductivity.Moreover,W^(6+) doping accounts for a high pseudocapacitive contribution.At the scan rate of 1 mV·s^(-1),the pseudocapacitive contribution for TiNb_(2)O_(7) is 78%,while that for W_(0.06)Ti_(0.91)Nb_(2)O_(7) increases to 83%.The reversible specific capacity of W_(0.06)Ti_(0.91)Nb_(2)O_(7) after 600 cycles is maintained at 148.90mAh·g^(-1) with a loss of only 16.37% at 10.0C.Also,it delivers a commendable capacity of 161.99 mAh·g^(-1) at20.0C.Even at 30.0C,it still retains a satisfactory capacity of 147.22 mAh·g^(-1),much higher than TiNb_(2)O_(7)(97.49mAh·g^(-1)).Our present study provides ideas for the development of electrode materials for lithium-ion batteries.展开更多
This paper focuses on the heat transfer performance of semi-open heat pipe which is a new type of heat pipe. After analyzing its condensation heat transfer mechanisms theoretically, several semi-open heat pipes in dif...This paper focuses on the heat transfer performance of semi-open heat pipe which is a new type of heat pipe. After analyzing its condensation heat transfer mechanisms theoretically, several semi-open heat pipes in different length ratios and upper hole diameters are studied experimentally and compared with the same dimensions closed heat pipes. Experimental results show that the heat transfer performance of semi-open heat pipe becomes better by increasing heat transfer rate. At the first transitional point, the heat transfer performance of semi-open heat pipe approaches the level of the closed heat pipe. It is suitable to choose upper small hole about 1 mm in diameter and length ratio larger than 0.6 for the semi-open heat pipe.展开更多
Because of potential high energy densities,microfluidic fuel cells can serve as micro-scale power sources.Because microfluidic fuel cells typically operate in the co-laminar flow regime to enable a membrane-less desig...Because of potential high energy densities,microfluidic fuel cells can serve as micro-scale power sources.Because microfluidic fuel cells typically operate in the co-laminar flow regime to enable a membrane-less design,they generally suffer from severe mass transfer limitations with respect to diffusion transport.To address this issue,a novel channel design that integrates slanted groove micro-mixers on the side walls of the channel is proposed.Numerical modeling on the design of groove micro-mixers and grooveless design demonstrates a mass transfer enhancement that has a 115%higher limiting current density and well-controlled convective mixing between the oxidant and the fuel streams with the use of slanted groove micro-mixers.Moreover,the growth of the thickness of the depletion boundary layer is found to be terminated within approximately 2 mm from the channel entrance,which is distinct from the constantly growing pattern in the grooveless design.In addition,a simplified mass transfer model capable of modeling the mass transfer prFocess with the presence of the transverse secondary flow is developed.Further,a dimensionless correlation is derived to analyze the effects of the design parameters on the limiting current density.The present theoretical study paves the way towards an optimal design of a microfluidic fuel cell integrating groove micro-mixers.展开更多
The charging characteristics of the valve-regulated lead acid(VRLA) battery driven by solar energy were experimentally studied through the pressure-control method in this paper.The aims of the research were to increas...The charging characteristics of the valve-regulated lead acid(VRLA) battery driven by solar energy were experimentally studied through the pressure-control method in this paper.The aims of the research were to increase charging efficiency to make the most of solar energy and to improve charging quality to prolong life of battery.The charging process of a 12 V 12 A·h VRLA battery has been tested under the mode of a stand-alone photovoltaic(PV) system.Results show that the pressure-control method can effectively control PV charging of the VRLA battery and make the best of PV cells through the maximum power point tracking(MPPT).The damage of VRLA battery by excess oxygen accumulation can be avoided through the inner pressure control of VRLA battery.Parameters such as solar radiation intensity,charging power,inner pressure of the battery,and charging current and voltage during the charging process were measured and analyzed.展开更多
In the high-humidity, hot-summer-cold-winter(HSCW) zone of China, the moisture buffering effect in the envelope is found to be significant in optimum insulation thickness. However, few studies have considered the effe...In the high-humidity, hot-summer-cold-winter(HSCW) zone of China, the moisture buffering effect in the envelope is found to be significant in optimum insulation thickness. However, few studies have considered the effects of indoor moisture buffering on the optimum insulation thickness and energy consumption. In this study, we considered the energy load of an exterior wall under moisture transfer from the outdoor to the indoor environment. An optimum insulation thickness was obtained by integrating the P1-P2model. A residential building was selected for the case study to verify the proposed method. Finally, a comparison was made with two other widely used methods, namely the transient heat transfer model(TH) and the coupled heat and moisture transfer model(CHM). The results indicated that the indoor moisture buffering effect on the optimum insulation thickness is 2.54 times greater than the moisture buffering effect in the envelope, and the two moisture buffering effects make opposing contributions to the optimum insulation thickness. Therefore, when TH or CHM was used without considering the indoor moisture buffering effect, the optimum insulation thickness of the southern wall under one air change per hour(1 ACH) and 100% normal heat source may be overestimated by 2.13% to 3. 59%, and the annual energy load on a single wall may be underestimated by 10.10% to 11.44%. The decrease of airtightness and the increase of indoor heat sources may result in a slight reduction of optimum insulation thickness. This study will enable professionals to consider the effects of moisture buffering on the design of insulation thickness.展开更多
The reversibility and stability of aqueous Zn metal batteries(AZMBs)are largely limited by Zn dendrites and interfacial parasitic reactions.Herein,we propose a parallel modulation strategy to boost the reversibility o...The reversibility and stability of aqueous Zn metal batteries(AZMBs)are largely limited by Zn dendrites and interfacial parasitic reactions.Herein,we propose a parallel modulation strategy to boost the reversibility of the Zn anode by introducing N,N,N',N'-tetramethylchloroformamidinium hexafluorophosphate(TCFH)as an additive in the electrolyte.TCFH is composed of PF6-and TN+with opposite charges.PF6-can spontaneously induce the in-situ generation of ZnF_(2)solid electrolyte interface(SEI)on the anode,which can improve the transport kinetics of Zn^(2+)at the interface,thus promoting the rapid and uniform deposition of Zn as well as inhibiting the growth of dendrites.In addition,TN+is enriched at the anode surface during Zn deposition through the anchoring effect,which brings a reconfiguration of the ion/molecule distribution.The anchored-TN+reduces the concentrations of H_(2)O and SO_(4)^(2-),sufficiently restraining the parasitic reaction.Thanks to the dual-phase interface engineering constructed of PF6-and TN+in parallel,the symmetric cell with the proposed electrolyte survives long cycling stability over750 h at 20 mA cm^(-2),10 mAh cm^(-2).This study offers a distinct viewpoint to the multidimensional optimization of Zn anodes for high-performance AZMBs.展开更多
This study reports a new model of an air standard Dual-Miller cycle(DMC)with two polytropic processes and heat transfer loss.The two reversible adiabatic processes which could not be realized in practice are replaced ...This study reports a new model of an air standard Dual-Miller cycle(DMC)with two polytropic processes and heat transfer loss.The two reversible adiabatic processes which could not be realized in practice are replaced with two polytropic processes in order to more accurately reflect the practical working performance.The heat transfer loss is taken into account.The expressions of power output,thermal efficiency,entropy generation rate(EGR)and ecological function are addressed using finite-time thermodynamic theory.Through numerical calculations,the influences of compression ratio,cut-off ratio and polytropic exponent on the performance are thermodynamically analyzed.The model can be simplified to other cycle models under specific conditions,which means the results have an certain universality and may be helpful in the design of practical heat engines.It is shown that the entropy generation minimization does not always lead to the best system performance.展开更多
Compared with endoreversible heat engine with pure heat transfer and endoreversible isothermal chemical engine with pure mass transfer,endoreversible non-isothermal chemical engine(ENICE)is a more reasonable model of ...Compared with endoreversible heat engine with pure heat transfer and endoreversible isothermal chemical engine with pure mass transfer,endoreversible non-isothermal chemical engine(ENICE)is a more reasonable model of practical mass exchanger,solid device and chemo-electric systems.There exists heat and mass transfer(HMT)simultaneously between working fluid and chemical potential reservoir in ENICE.There is coupled HMT effect that in ENICE should be considered.There are two ways to consider this coupled effect.One is based on Onsager equations,and another is based on Lewis analogy.For the mathematical and physical description of the above HMT process,the model using Onsager equations are more appropriate in the linear HMT region not far from the equilibrium state,while that based on Lewis analogy is more appropriate in nonlinear HMT region far from the equilibrium state.Different from the previous research on the power optimization of ENICEs with Onsager equations,this paper optimizes power and efficiency of ENICE based on Lewis analogy.HMT processes are assumed to obey Newtonian heat transfer law(q∝ΔT,and T is temperature)and Fick's diffusive mass transfer law(g∝Δc,and c is concentration),respectively.Analytical results of power output and corresponding vector efficiency(η_(T)andη_(μ))of ENICE are obtained,which provide important parallel results with those based on Onsager equations.They include special cases for endoreversible Carnot heat engine with q∝ΔT and endoreversible isothermal chemical engine with g∝Δc.Adopting Lewis analogy in the modelling of ENICEs with simultaneous HMT is an important work.It provides important analytical and numerical results different from those with Onsager equations obtained previously and enriches the research contents of FTT.The research results in this paper have a certain guiding significance for the optimal designs of single irreversible NICEs,multistage NICE systems,practical mass exchangers,solid devices,chemo-electric systems,and so on.展开更多
The research on the output rate performance limit of the multi-stage energy conversion system based on modern optimal control theory is one of the hot spots of finite time thermodynamics.The existing research mainly f...The research on the output rate performance limit of the multi-stage energy conversion system based on modern optimal control theory is one of the hot spots of finite time thermodynamics.The existing research mainly focuses on the multi-stage heat engine system with pure heat transfer and the multi-stage isothermal chemical engine(ICE)system with pure mass transfer,while the multi-stage non ICE system with heat and mass transfer coupling is less involved.A multistage endoreversible non-isothermal chemical engine(ENICE)system with a finite high-chemical-potential(HCP)source(driving fluid)and an infinite low-chemical-potential sink(environment)is researched.The multistage continuous system is treated as infinitesimal ENICEs located continuously.Each infinitesimal ENICE is assumed to be a single-stage ENICE with stationary reservoirs.Extending single-stage results,the maximum power output(MPO)of the multistage system is obtained.Heat and mass transfer processes between the reservoir and working fluid are assumed to obey Onsager equations.For the fixed initial time,fixed initial fluid temperature,and fixed initial concentration of key component(CKC)in the HCP source,continuous and discrete models of the multistage system are optimized.With given initial reservoir temperature,initial CKC,and total process time,the MPO of the multistage ENICE system is optimized with fixed and free final temperature and final concentration.If the final concentration and final temperature are free,there are optimal final temperature and optimal final concentration for the multistage ENICE system to achieve MPO;meanwhile,there are low limit values for final fluid temperature and final concentration.Special cases for multistage endoreversible Carnot heat engines and ICE systems are further obtained.For the model in this paper,the minimum entropy generation objective is not equivalent to MPO objective.展开更多
The Alpha Magnetic Spectrometer(AMS) is an instrument for the international scientific experiment,composed of six detectors and 650 micro-electronics.The objective of AMS experiment is to search for dark matter and an...The Alpha Magnetic Spectrometer(AMS) is an instrument for the international scientific experiment,composed of six detectors and 650 micro-electronics.The objective of AMS experiment is to search for dark matter and anti-matter in space.In this paper,the thermal control system for AMS cryocoolers is designed,analyzed and experimentally studied.Using loop heat pipes(LHPs) as the main heat dissipation component,the thermal control system has sufficient heat dissipation capability to prevent the cryocoolers from over temperature(+40℃) in hot environment,meanwhile to ensure temperatures of the cryocoolers higher than their lower limit(-20℃) in cold environment.Experiment results show that the thermal control system for AMS cryocoolers functions stably satisfying design specification.展开更多
Since its installation on the International Space Station(ISS)in mid-May 2011,the Alpha Magnetic Spectrometer(AMS)has spent over two years on orbit,fully operational,collecting an enormous amount of data including the...Since its installation on the International Space Station(ISS)in mid-May 2011,the Alpha Magnetic Spectrometer(AMS)has spent over two years on orbit,fully operational,collecting an enormous amount of data including the temperatures from the on-board 1118 sensors for thermal control.A large database is continuously updated and analyzed to understand the thermal behavior of the experiment in the space environment and its interaction with the ISS.This paper specifies the design,building,analysis and testing of the thermal control system and its various components for an overview of the AMS thermal control system and its space environment.Also given are some examples of analysis and correlation of the space environmental and ISS parameters with the thermal behaviors of various AMS components.展开更多
A model of quantum thermoacoustic refrigeration micro-cycle(QTARMC)is established in which heat leakage is considered.A single particle contained in a one-dimensional harmonic potential well is studied,and the system ...A model of quantum thermoacoustic refrigeration micro-cycle(QTARMC)is established in which heat leakage is considered.A single particle contained in a one-dimensional harmonic potential well is studied,and the system consists of countless replicas.Each particle is confined in its own potential well,whose occupation probabilities can be expressed by the thermal equilibrium Gibbs distributions.Based on the Schrodinger equation,the expressions of coefficient of performance(COP)and cooling rate for the refrigerator are obtained.Effects of heat leakage on the optimal performance are discussed.The optimal performance region of the refrigeration cycle is obtained by the using ofΩobjective function.The results obtained can enrich the thermoacoustic theory and expand the application of quantum thermodynamics.展开更多
基金supported by the National Key Research and Development Program of China(No.2019YFC1805701)。
文摘Soil backfilling and compaction are often involved in urban construction projects like the burying of power cables.The thermal conductance of backfill soil is therefore of great interest.To investigate the thermal conductivity variation of compacted backfill soil,10 typical soils sampled in Zhejiang Province of China with moisture contents of 0%–25%were fully compacted according to the Proctor compaction test method and then subjected to thermal conductivity measurement using the thermal probe method at 20℃.The particle size distribution and the chemical composition of the soil samples were characterized to analyze their effects on thermal conductivity.The results showed that the maximum thermal conductivity of fully compacted soils generally exceeds 1.9 W/(m·K)and is 20%–50%higher than that of uncompacted soils.With increasing moisture content,soil thermal conductivity and dry bulk density first increase and then remain unchanged or decrease slowly;the critical moisture content is greater than 20%in most cases.Overall,the critical moisture content of soils with large particle size is lower than that of those with small particle size.Quartz has the highest thermal conductivity in the soil solid phase,and the mass percentage of quartz for most soils in this study is more than 50%,while that for yellow soil is less than 30%,which leads to the thermal conductivity of the former being nearly twice as great as that of the latter in most circumstances.Based on regression analysis,with moisture content and dry bulk density as the independent parameters,the prediction formulae for the thermal conductivity of two categories of compacted backfill soils are proposed for practical applications.
基金Supported by the National Key Basic Research Program of China(2013CB228305)
文摘A conduction heat transfer process is enhanced by filling prescribed quantity and optimized-shaped high thermal conductivity materials to the substrate. Numerical simulations and analyses are performed on a volume to point conduction problem based on the principle of minimum entropy generation. In the optimization, the arrangement of high thermal conductivity materials is variable, the quantity of high thermal-conductivity material is constrained, and the objective is to obtain the maximum heat conduction rate as the entropy is the minimum.A novel algorithm of thermal conductivity discretization is proposed based on large quantity of calculations.Compared with other algorithms in literature, the average temperature in the substrate by the new algorithm is lower, while the highest temperature in the substrate is in a reasonable range. Thus the new algorithm is feasible. The optimization of volume to point heat conduction is carried out in a rectangular model with radiation boundary condition and constant surface temperature boundary condition. The results demonstrate that the algorithm of thermal conductivity discretization is applicable for volume to point heat conduction problems.
基金funded by the National Natural Science Foundation of China,grant number 52406102,received by Haiyan YuShandong Provincial Natural Science Foundation,grant number ZR2023QE258,received by Haiyan Yu.
文摘High-temperature radiative cooling is essential for solar absorbers,as it mitigates efficiency degradation resulting from thermal accumulation.While porous structures have proven effective in enhancing absorber performance,practical manufacturing processes and prolonged operational wear inevitably introduce surface roughness and structural deviations,which profoundly impact radiative properties.This study constructs a ZnS/Ag solar absorber model with surface roughness and employs the finite-difference time-domain method to investigate how characteristic length,surface roughness,porosity,pore shape factor,and taper influence its radiative properties in the 3μm-5μm band at 750 K.Results show optimal absorption at a 1μm characteristic length with a 36.72%improvement compared to the model with l=0.25μm,increased absorption with higher porosity with a 69.29%improvement at 0.6 compared to the non-porous structure,lower circularity with a 19.03%improvement for C=0.89 compared to C=1.00,while surface roughness with a 61.24%improvement at RMS=0.031 compared to RMS=0 and taper with a 38.29%improvement at β=20°compared to β=0°also exert significant effects.This work provides engineering design guidelines for high-efficiency,low-cost absorbers.
基金Project supported by the National Natural Science Foundation of China (Grant No. 52406102)Shandong Provincial Natural Science Foundation (Grant No. ZR2023QE258)。
文摘In order to meet the growing global energy demand and fulfill energy conservation and emission reduction goals, the efficient utilization of solar energy is becoming increasingly critical. However, the effects of high temperatures on solar absorption are rarely considered in practical research. Therefore, this study presents a porous zinc and silver sulfide solar absorber with high-temperature radiative cooling capabilities. The solar absorption rate and radiative cooling efficiency in the high-temperature range(636 K–1060 K) are computed using the finite-difference time-domain method. Furthermore, the impact of parameters such as characteristic length, porosity, incident angle, and pore shape factor on both the absorption rate and efficiency of the solar absorber is analyzed. The mechanism is further examined from the perspective of microscopic thermal radiation. The results show that, in the high-temperature range, the solar absorption rate increases with higher porosity and incident angles, reaching its peak when the characteristic length is 1 μm. These findings highlight the significant potential of the solar absorber for efficient solar energy harvesting in photo-thermal conversion applications within a specific high-temperature range.
基金Supported by the National Natural Science Foundation of China(51106090)the National Key Basic Research Program of China(2013CB228305)the Independent Innovation Foundation of Shandong University(2012TS190)
文摘Shape and quantity of helical baffles have great impact on the shell-side performance of helical baffled heat exchangers （HBHE）. In this work, three physical models of HBHE with baffles of different shape （trisection, quadrant and sextant sector） were investigated. Numerical simulations were performed on HBHE at three helix an- gles （10°, 25° and 40°） by the software ANSYS CFX. Analyses of numerical results indicate that the sextant HBHE shows relatively better fluid flow performance because the leakage flow in the triangle area is evidently reduced and the fluid streamline appears much closer to an ideal spiral flow, while the trisection and quadrant HBHE show more scattered and disordered streamline distributions. The convective heat transfer coefficient and pressure drop in three types of HBHE were presented. Further investigations on the shell side performance with different helical baf- fles were implemented by the field synergy theory. Both theoretical and numerical analyses gave support on the re- lations between helical baffle shape and shell-side performance. This paper may provide useful reference for the selection of baffle shade and auantitv in HBHE.
文摘Valve-regulated-lead-acid (VRLA) battery charging performed in high-temperature environments is extremely risky under overcharge conditions, and may lead to a subsequent thermal runaway. A new pressure-controlled charging method was adopted and the charging characteristics of the pressure-controlled VRLA battery in high-temperature environments were ex-perimentally studied. The concept was tested in a large temperature gradient to obtain more details about the effects of users' accustomed charging and discharging modes on battery capacity. The premature capacity loss (PCL) phenomenon under high temperature exposure was analyzed. The results showed that the capacity loss could be recovered by charging using a large current.
基金financially supported by the National Natural Science Foundation of China (Nos. 52274299, 52004103 and 51974137)the Postdoctoral Science Foundation of China (Nos. 2021M691321 and 2020M671361)the Postdoctoral Science Foundation of Jiangsu Province (No. 2020Z090)。
文摘TiNb_(2)O_(7) is an advanced anode material for high-energy density lithium-ion batteries(LIBs) due to its considerable specific capacity and satisfactory safety.However,its rate capability is limited by its poor ionic conductivity and electronic conductivity.To solve this problem,TiNb_(2)O_(7) with W^(6+) doping was synthesized by a convenient solid-state method.The doping of W^(6+) will lead to arranging cation mixing and charge compensation.The cation rearrangement creates a new Li-conductive environment for lithiation,resulting in a low-energy barrier and the fast Li^(+)storage/diffusion.The results show that the Li^(+)diffusion coefficient of W_(0.06)Ti_(0.91)Nb_(2)O_(7) is increased by 9.96 times greater than that of TiNb_(2)O_(7).Besides,as the calculation proves,due to the partial reduction of the Nb^(5+)and Ti^(4+) caused by charge compensation,W^(6+)doping results in low charge transfer resistance and excellent electronic conductivity.Moreover,W^(6+) doping accounts for a high pseudocapacitive contribution.At the scan rate of 1 mV·s^(-1),the pseudocapacitive contribution for TiNb_(2)O_(7) is 78%,while that for W_(0.06)Ti_(0.91)Nb_(2)O_(7) increases to 83%.The reversible specific capacity of W_(0.06)Ti_(0.91)Nb_(2)O_(7) after 600 cycles is maintained at 148.90mAh·g^(-1) with a loss of only 16.37% at 10.0C.Also,it delivers a commendable capacity of 161.99 mAh·g^(-1) at20.0C.Even at 30.0C,it still retains a satisfactory capacity of 147.22 mAh·g^(-1),much higher than TiNb_(2)O_(7)(97.49mAh·g^(-1)).Our present study provides ideas for the development of electrode materials for lithium-ion batteries.
文摘This paper focuses on the heat transfer performance of semi-open heat pipe which is a new type of heat pipe. After analyzing its condensation heat transfer mechanisms theoretically, several semi-open heat pipes in different length ratios and upper hole diameters are studied experimentally and compared with the same dimensions closed heat pipes. Experimental results show that the heat transfer performance of semi-open heat pipe becomes better by increasing heat transfer rate. At the first transitional point, the heat transfer performance of semi-open heat pipe approaches the level of the closed heat pipe. It is suitable to choose upper small hole about 1 mm in diameter and length ratio larger than 0.6 for the semi-open heat pipe.
基金supported by the National Natural Science Foundation of China(No.51606164).
文摘Because of potential high energy densities,microfluidic fuel cells can serve as micro-scale power sources.Because microfluidic fuel cells typically operate in the co-laminar flow regime to enable a membrane-less design,they generally suffer from severe mass transfer limitations with respect to diffusion transport.To address this issue,a novel channel design that integrates slanted groove micro-mixers on the side walls of the channel is proposed.Numerical modeling on the design of groove micro-mixers and grooveless design demonstrates a mass transfer enhancement that has a 115%higher limiting current density and well-controlled convective mixing between the oxidant and the fuel streams with the use of slanted groove micro-mixers.Moreover,the growth of the thickness of the depletion boundary layer is found to be terminated within approximately 2 mm from the channel entrance,which is distinct from the constantly growing pattern in the grooveless design.In addition,a simplified mass transfer model capable of modeling the mass transfer prFocess with the presence of the transverse secondary flow is developed.Further,a dimensionless correlation is derived to analyze the effects of the design parameters on the limiting current density.The present theoretical study paves the way towards an optimal design of a microfluidic fuel cell integrating groove micro-mixers.
文摘The charging characteristics of the valve-regulated lead acid(VRLA) battery driven by solar energy were experimentally studied through the pressure-control method in this paper.The aims of the research were to increase charging efficiency to make the most of solar energy and to improve charging quality to prolong life of battery.The charging process of a 12 V 12 A·h VRLA battery has been tested under the mode of a stand-alone photovoltaic(PV) system.Results show that the pressure-control method can effectively control PV charging of the VRLA battery and make the best of PV cells through the maximum power point tracking(MPPT).The damage of VRLA battery by excess oxygen accumulation can be avoided through the inner pressure control of VRLA battery.Parameters such as solar radiation intensity,charging power,inner pressure of the battery,and charging current and voltage during the charging process were measured and analyzed.
基金supported by the National Natural Science Foundation of China (Nos. 51978623 and 52076189)。
文摘In the high-humidity, hot-summer-cold-winter(HSCW) zone of China, the moisture buffering effect in the envelope is found to be significant in optimum insulation thickness. However, few studies have considered the effects of indoor moisture buffering on the optimum insulation thickness and energy consumption. In this study, we considered the energy load of an exterior wall under moisture transfer from the outdoor to the indoor environment. An optimum insulation thickness was obtained by integrating the P1-P2model. A residential building was selected for the case study to verify the proposed method. Finally, a comparison was made with two other widely used methods, namely the transient heat transfer model(TH) and the coupled heat and moisture transfer model(CHM). The results indicated that the indoor moisture buffering effect on the optimum insulation thickness is 2.54 times greater than the moisture buffering effect in the envelope, and the two moisture buffering effects make opposing contributions to the optimum insulation thickness. Therefore, when TH or CHM was used without considering the indoor moisture buffering effect, the optimum insulation thickness of the southern wall under one air change per hour(1 ACH) and 100% normal heat source may be overestimated by 2.13% to 3. 59%, and the annual energy load on a single wall may be underestimated by 10.10% to 11.44%. The decrease of airtightness and the increase of indoor heat sources may result in a slight reduction of optimum insulation thickness. This study will enable professionals to consider the effects of moisture buffering on the design of insulation thickness.
基金financially supported by the National Natural Science Foundation of China(52172159)the Postdoctoral Fellowship Program of CPSF(GZB20230631).
文摘The reversibility and stability of aqueous Zn metal batteries(AZMBs)are largely limited by Zn dendrites and interfacial parasitic reactions.Herein,we propose a parallel modulation strategy to boost the reversibility of the Zn anode by introducing N,N,N',N'-tetramethylchloroformamidinium hexafluorophosphate(TCFH)as an additive in the electrolyte.TCFH is composed of PF6-and TN+with opposite charges.PF6-can spontaneously induce the in-situ generation of ZnF_(2)solid electrolyte interface(SEI)on the anode,which can improve the transport kinetics of Zn^(2+)at the interface,thus promoting the rapid and uniform deposition of Zn as well as inhibiting the growth of dendrites.In addition,TN+is enriched at the anode surface during Zn deposition through the anchoring effect,which brings a reconfiguration of the ion/molecule distribution.The anchored-TN+reduces the concentrations of H_(2)O and SO_(4)^(2-),sufficiently restraining the parasitic reaction.Thanks to the dual-phase interface engineering constructed of PF6-and TN+in parallel,the symmetric cell with the proposed electrolyte survives long cycling stability over750 h at 20 mA cm^(-2),10 mAh cm^(-2).This study offers a distinct viewpoint to the multidimensional optimization of Zn anodes for high-performance AZMBs.
基金supported by the National Natural Science Foundation of China(Grant No.51576207)
文摘This study reports a new model of an air standard Dual-Miller cycle(DMC)with two polytropic processes and heat transfer loss.The two reversible adiabatic processes which could not be realized in practice are replaced with two polytropic processes in order to more accurately reflect the practical working performance.The heat transfer loss is taken into account.The expressions of power output,thermal efficiency,entropy generation rate(EGR)and ecological function are addressed using finite-time thermodynamic theory.Through numerical calculations,the influences of compression ratio,cut-off ratio and polytropic exponent on the performance are thermodynamically analyzed.The model can be simplified to other cycle models under specific conditions,which means the results have an certain universality and may be helpful in the design of practical heat engines.It is shown that the entropy generation minimization does not always lead to the best system performance.
基金supported by the National Natural Science Foundation of China(Grant Nos.51976235 and 52171317)。
文摘Compared with endoreversible heat engine with pure heat transfer and endoreversible isothermal chemical engine with pure mass transfer,endoreversible non-isothermal chemical engine(ENICE)is a more reasonable model of practical mass exchanger,solid device and chemo-electric systems.There exists heat and mass transfer(HMT)simultaneously between working fluid and chemical potential reservoir in ENICE.There is coupled HMT effect that in ENICE should be considered.There are two ways to consider this coupled effect.One is based on Onsager equations,and another is based on Lewis analogy.For the mathematical and physical description of the above HMT process,the model using Onsager equations are more appropriate in the linear HMT region not far from the equilibrium state,while that based on Lewis analogy is more appropriate in nonlinear HMT region far from the equilibrium state.Different from the previous research on the power optimization of ENICEs with Onsager equations,this paper optimizes power and efficiency of ENICE based on Lewis analogy.HMT processes are assumed to obey Newtonian heat transfer law(q∝ΔT,and T is temperature)and Fick's diffusive mass transfer law(g∝Δc,and c is concentration),respectively.Analytical results of power output and corresponding vector efficiency(η_(T)andη_(μ))of ENICE are obtained,which provide important parallel results with those based on Onsager equations.They include special cases for endoreversible Carnot heat engine with q∝ΔT and endoreversible isothermal chemical engine with g∝Δc.Adopting Lewis analogy in the modelling of ENICEs with simultaneous HMT is an important work.It provides important analytical and numerical results different from those with Onsager equations obtained previously and enriches the research contents of FTT.The research results in this paper have a certain guiding significance for the optimal designs of single irreversible NICEs,multistage NICE systems,practical mass exchangers,solid devices,chemo-electric systems,and so on.
基金supported by the National Natural Science Foundation of China(Grant Nos.51976235 and 52171317)。
文摘The research on the output rate performance limit of the multi-stage energy conversion system based on modern optimal control theory is one of the hot spots of finite time thermodynamics.The existing research mainly focuses on the multi-stage heat engine system with pure heat transfer and the multi-stage isothermal chemical engine(ICE)system with pure mass transfer,while the multi-stage non ICE system with heat and mass transfer coupling is less involved.A multistage endoreversible non-isothermal chemical engine(ENICE)system with a finite high-chemical-potential(HCP)source(driving fluid)and an infinite low-chemical-potential sink(environment)is researched.The multistage continuous system is treated as infinitesimal ENICEs located continuously.Each infinitesimal ENICE is assumed to be a single-stage ENICE with stationary reservoirs.Extending single-stage results,the maximum power output(MPO)of the multistage system is obtained.Heat and mass transfer processes between the reservoir and working fluid are assumed to obey Onsager equations.For the fixed initial time,fixed initial fluid temperature,and fixed initial concentration of key component(CKC)in the HCP source,continuous and discrete models of the multistage system are optimized.With given initial reservoir temperature,initial CKC,and total process time,the MPO of the multistage ENICE system is optimized with fixed and free final temperature and final concentration.If the final concentration and final temperature are free,there are optimal final temperature and optimal final concentration for the multistage ENICE system to achieve MPO;meanwhile,there are low limit values for final fluid temperature and final concentration.Special cases for multistage endoreversible Carnot heat engines and ICE systems are further obtained.For the model in this paper,the minimum entropy generation objective is not equivalent to MPO objective.
基金supported by the Major Project of Technology Transfer of Shandong Province (2009ZHZX1A1105)
文摘The Alpha Magnetic Spectrometer(AMS) is an instrument for the international scientific experiment,composed of six detectors and 650 micro-electronics.The objective of AMS experiment is to search for dark matter and anti-matter in space.In this paper,the thermal control system for AMS cryocoolers is designed,analyzed and experimentally studied.Using loop heat pipes(LHPs) as the main heat dissipation component,the thermal control system has sufficient heat dissipation capability to prevent the cryocoolers from over temperature(+40℃) in hot environment,meanwhile to ensure temperatures of the cryocoolers higher than their lower limit(-20℃) in cold environment.Experiment results show that the thermal control system for AMS cryocoolers functions stably satisfying design specification.
基金supported by the National Natural Science Foundation of China(No.51378482)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,Ministry of Education of Chinathe Foundation of Zhejiang CWPC&BR Heavy Industry Co.,Ltd.,China
文摘Since its installation on the International Space Station(ISS)in mid-May 2011,the Alpha Magnetic Spectrometer(AMS)has spent over two years on orbit,fully operational,collecting an enormous amount of data including the temperatures from the on-board 1118 sensors for thermal control.A large database is continuously updated and analyzed to understand the thermal behavior of the experiment in the space environment and its interaction with the ISS.This paper specifies the design,building,analysis and testing of the thermal control system and its various components for an overview of the AMS thermal control system and its space environment.Also given are some examples of analysis and correlation of the space environmental and ISS parameters with the thermal behaviors of various AMS components.
基金Project(51176143)supported by the National Natural Science Foundation of ChinaProject(K201919)supported by the Scientific Research Foundation of Wuhan Institute of TechnologyChina。
文摘A model of quantum thermoacoustic refrigeration micro-cycle(QTARMC)is established in which heat leakage is considered.A single particle contained in a one-dimensional harmonic potential well is studied,and the system consists of countless replicas.Each particle is confined in its own potential well,whose occupation probabilities can be expressed by the thermal equilibrium Gibbs distributions.Based on the Schrodinger equation,the expressions of coefficient of performance(COP)and cooling rate for the refrigerator are obtained.Effects of heat leakage on the optimal performance are discussed.The optimal performance region of the refrigeration cycle is obtained by the using ofΩobjective function.The results obtained can enrich the thermoacoustic theory and expand the application of quantum thermodynamics.
