This study investigates the physical properties of the rare earth XFes(X=Sm,Dy,or Nd)materials.Our analysis encompasses these compounds'structural,electronic,thermodynamic,and optical characteristics using density...This study investigates the physical properties of the rare earth XFes(X=Sm,Dy,or Nd)materials.Our analysis encompasses these compounds'structural,electronic,thermodynamic,and optical characteristics using density functional theory(DFT)as implemented in the Wien2k software package.The GGA+SOC+U method was employed to determine the exchange-correlation potential.Our results show that the XFes materials exhibit metallic behavior and exhibit ferromagnetic(FM)phases.Notably,our optical analysis reveals a strong absorption response in the UV region,with characteristic absorption curves and peak intensities varying across the different materials.We also investigated the thermodynamic properties of the materials,finding that the entropy increases exponentially with temperature as the materials transition from a ground state to a more disordered and amorphous state.Our thermodynamic results show that the Debye temperature decreases for all three materials,with DyFes exhibiting the highest Debye temperature at 0 K(307 K),followed by NdFes(298 K),and then SmFes(288 K).This indicates that each material has a unique thermal energy barrier to overcome before vibrations occur.As the temperature increases,the Debye temperature decreases,reflecting a decrease in the thermal energy required to induce vibrations.The differences in Debye temperature values between the three materials may suggest differences in their lattice structures or phonon properties,highlighting the importance of understanding these thermal properties for developing new materials and technologies.展开更多
A conventional solid-state process was used to synthesize the double perovskite materials HoRCoMnO_(6)(R=Ho,Gd,Eu,Nd).The structural properties of the compounds were investigated using X-ray powder diffraction(XRD).Th...A conventional solid-state process was used to synthesize the double perovskite materials HoRCoMnO_(6)(R=Ho,Gd,Eu,Nd).The structural properties of the compounds were investigated using X-ray powder diffraction(XRD).The results revealed that Ho_(2)CoMnO_(6) crystallizes in a monoclinic structure with the P2_(1)/n space group.In contrast,the other compounds HoRCoMnO_(6)(R=Gd,Eu,or Nd) exhibit an orthorhombic structure with the Pnma space group.As a result,the average crystallite size also changes as a function of rare-earth element doping.This investigation reveals that the magnetic properties of the compounds studied are significantly dependent on the doping elements.The Curie temperature T_C,for example,increases from 80 to 118℃ with the ionic radii of rare earths increasing.Furthermore,the study of the magnetocaloric effect(MCE) shows that the maximum of the entropy variation(-ΔS_(M)^(max)) increases from 4.97 to 6.06 J/(kg·K) under a magnetic field of 5 T with substitution by rare-earth ions.To examine the efficiency of MCE materials,the relative cooling power(RCP) was evaluated and is found to increase with increment of rare-earth radius till 406.69 J/kg for Nd.The mean entropy variation with tempe rature(TEC) was also studied.Due to their significant magnetocaloric performance,HoRCoMnO_(6)(noted as HRCMO) compounds(with R=Ho,Gd,Eu or Nd) could be good candidates for low-temperature magnetic cooling applications.展开更多
We report on the structural,magnetic,and magnetocaloric properties of EuRhO_(3) powders.The oxidation states of Eu and Rh ions were studied using X-ray photoelectron spectroscopy(XPS).It is found that the Eu ions are ...We report on the structural,magnetic,and magnetocaloric properties of EuRhO_(3) powders.The oxidation states of Eu and Rh ions were studied using X-ray photoelectron spectroscopy(XPS).It is found that the Eu ions are mainly in the divalent oxidation state while the Rh ions have+4 state.EuRhO_(3) powders are found to be antiferromagnetic with a second order magnetic transition at Neel temperature(T_(N)=2.9 K).Analysis of the magnetic susceptibility versus temperature data in terms of the Curie=Weiss law:(χ=C/(T-θ_(W))) for T>T_(N),yields θ_(W)=-3.1 K and effective magne tic moment μ_(ff)^(exp),which is close to the theoretical value μ_(eff)^(theo).The magnetic entropy change(-Δ_(SM)),was determined by em ploying the thermodynam ic Maxwell's relation.At μ_0H=5 T and near T_(N),ΔS_(M)^(Max) and relative cooling power(RCP) exhibit large values of 33.7 J/(kg·K) and 238 J/kg,respectively.The large magnitude of-Δ_(SM) and RCP show that the EuRhO_(3) compound could be a potential candidate to be used in cryogenic magnetic refrigeration.展开更多
In this paper,experimental and numerical studies of heat transfer in a test local of side H=0.8 m heated from below are presented and compared.All the walls,the rest of the floor and the ceiling are made from plywood ...In this paper,experimental and numerical studies of heat transfer in a test local of side H=0.8 m heated from below are presented and compared.All the walls,the rest of the floor and the ceiling are made from plywood and polystyrene in sandwich form(3 mmplywood-3 cm polystyrene-3 mmplywood)just on one of the vertical walls contained a glazed door(2 H/3×0.15 m).This local is heated during two heating cycles by a square plate of iron the width L=0.6 H,which represents the heat source,its temperature T_(h) is controlled.The plate is heated for two cycles by an adjustable set-point heat source placed just down the center of it.For each cycle,the heat source is switched“on”for 6 h and switched“off”for 6 h.The outdoor air temperature is kept constant at a low temperature T_(c)<T_(h).All measurements are carried out with k-type thermocouples and with flux meters.Results will be qualitatively presented for two cycles of heating in terms of temperatures and heat flux densitiesϕfor various positions of the test local.The temperature evolution of the center and the profile of the temperature along the vertical centerline are compared by two dimensions simulation using the lattice Boltzmann method.The comparison shows a good agreement with a difference that does not exceed±1℃.展开更多
Creating sustainable cities is the only way to live in a clean environment,and this problem can be solved by using bio-sourced and recycled materials.For this purpose,the authors contribute to the valuation of sheep w...Creating sustainable cities is the only way to live in a clean environment,and this problem can be solved by using bio-sourced and recycled materials.For this purpose,the authors contribute to the valuation of sheep wool waste as an eco-friendly material to be used in insulation.The paper investigates the thermal,hygrothermal,and biological aspects of sheep wool by testing a traditional treatment.The biological method of aerobic mesophilicflora has been applied.Fluorescence X was used to determine the chemical composition of the materials used.Also,thermal characterization has been conducted.The thermal conductivity is above 0.046(W·m^(-1)·K^(-1))and the thermal diffusivity is 1.56.10^(-6) m^(2)·s^(-1).Besides,the energy efficiency of using sheep wool in buildings was studied.Furthermore,its humidity behavior was evaluated in different aspects in both winter and summer.Results of biological analyses show the efficiency of the treatment by removing the majority of the microorgan-isms:the value of yeast and mildew was reduced from 38.10^(2) to 2.10^(2)(UFC·g^(-1)).In addition to that,sheep wool permits obtaining a low thermal transmittance on the scale of the walls and low cooling needs on the scale of the building with a gain of 45%and 52%,respectively.展开更多
The development of bio-sourced materials is essential to ensuring sustainable construction;it is considered a locomotive of the green economy.Furthermore,it is an abundant material in our country,to which very little ...The development of bio-sourced materials is essential to ensuring sustainable construction;it is considered a locomotive of the green economy.Furthermore,it is an abundant material in our country,to which very little attention is being given.This work aims to valorize the waste of the trunks of banana trees to be used in construction.Firstly,the physicochemical properties of the fiber,such as the percentage of crystallization and its morphology,have been determined by X-ray diffraction tests and scanning electron microscopy to confirm the potential and the impact of the mode of drying on the quality of the banana fibers,with the purpose to promote the use of this material in construction.Secondly,the results obtained with the gypsum matrix allowed us to note a preponderant improvement in the composite’s thermal properties thanks to the variation of the banana fiber additive.Thirdly,the impact of the nature of the banana fiber distribution(either fiber mixed in matrix or fiber series model)on the flexural and compressive strengths of the composites was studied.The results obtained indicate that the insulation gain reaches up to 40%.It depends on the volume fraction and type of distribution of the banana fibers.However,the thermal inertia of the composites developed,represented by thermal diffusivity and thermal effusivity,was studied.Results indicate a gain of 40%and 25%,respectively,in terms of thermal diffusivity and thermal effusivity of the developed composites compared to plaster alone.Concerning the mechanical properties,the flexural strength depends on the percentage of the volume fraction of banana fibers used,and it can reach 20%more than the flexural strength of plaster;nevertheless,there is a significant loss in terms of the compressive strength of the studied composites.The results obtained are confirmed by the microstructure of the fiber banana.In fact,the morphology of the banana fibers was improved by the drying process.It reduces the amorphous area and improves the cellulosic crystalline surfaces,which assures good adhesion between the fiber and the matrix plaster.Finally,the dimensionless coefficient analysis was done to judge the optimal proportion of the banana fiber additive and to recommend its use even on false ceilings or walls.展开更多
This study scrutinizes the thermomechanical dynamics of 3D-printed hydrofoil blades utilizing a carbon and glass bead-reinforced thermoplastic polymer.Comparative analyses underscore the pivotal role of polymer reinfo...This study scrutinizes the thermomechanical dynamics of 3D-printed hydrofoil blades utilizing a carbon and glass bead-reinforced thermoplastic polymer.Comparative analyses underscore the pivotal role of polymer reinforcement in augmenting mechanical strength and mitigating deformation and residual stress.The investigation elucidates the expeditious and cost-efficient manufacturing potential of low-cost Fused Filament Fabrication(FFF)printers for small-scale blades,revealing exemplary mechanical performance with nominal deflection and warping in the PA12-CB/GB printed blade.A comprehensive juxtaposition between Selective Laser Sintering(SLS)and FFF printing methods favors SLS due to its isotropic properties,notwithstanding remediable warping.Emphasizing the rigorous marine environment,the study cautions against the anisotropic properties of FFF-printed blades,despite their low mechanical warping.These discernments contribute to hydrofoil design optimization through numerical analysis,shedding light on additive manufacturing’s potential for small blades in renewable energy,while underscoring the imperative for further research to advance these techniques.展开更多
文摘This study investigates the physical properties of the rare earth XFes(X=Sm,Dy,or Nd)materials.Our analysis encompasses these compounds'structural,electronic,thermodynamic,and optical characteristics using density functional theory(DFT)as implemented in the Wien2k software package.The GGA+SOC+U method was employed to determine the exchange-correlation potential.Our results show that the XFes materials exhibit metallic behavior and exhibit ferromagnetic(FM)phases.Notably,our optical analysis reveals a strong absorption response in the UV region,with characteristic absorption curves and peak intensities varying across the different materials.We also investigated the thermodynamic properties of the materials,finding that the entropy increases exponentially with temperature as the materials transition from a ground state to a more disordered and amorphous state.Our thermodynamic results show that the Debye temperature decreases for all three materials,with DyFes exhibiting the highest Debye temperature at 0 K(307 K),followed by NdFes(298 K),and then SmFes(288 K).This indicates that each material has a unique thermal energy barrier to overcome before vibrations occur.As the temperature increases,the Debye temperature decreases,reflecting a decrease in the thermal energy required to induce vibrations.The differences in Debye temperature values between the three materials may suggest differences in their lattice structures or phonon properties,highlighting the importance of understanding these thermal properties for developing new materials and technologies.
文摘A conventional solid-state process was used to synthesize the double perovskite materials HoRCoMnO_(6)(R=Ho,Gd,Eu,Nd).The structural properties of the compounds were investigated using X-ray powder diffraction(XRD).The results revealed that Ho_(2)CoMnO_(6) crystallizes in a monoclinic structure with the P2_(1)/n space group.In contrast,the other compounds HoRCoMnO_(6)(R=Gd,Eu,or Nd) exhibit an orthorhombic structure with the Pnma space group.As a result,the average crystallite size also changes as a function of rare-earth element doping.This investigation reveals that the magnetic properties of the compounds studied are significantly dependent on the doping elements.The Curie temperature T_C,for example,increases from 80 to 118℃ with the ionic radii of rare earths increasing.Furthermore,the study of the magnetocaloric effect(MCE) shows that the maximum of the entropy variation(-ΔS_(M)^(max)) increases from 4.97 to 6.06 J/(kg·K) under a magnetic field of 5 T with substitution by rare-earth ions.To examine the efficiency of MCE materials,the relative cooling power(RCP) was evaluated and is found to increase with increment of rare-earth radius till 406.69 J/kg for Nd.The mean entropy variation with tempe rature(TEC) was also studied.Due to their significant magnetocaloric performance,HoRCoMnO_(6)(noted as HRCMO) compounds(with R=Ho,Gd,Eu or Nd) could be good candidates for low-temperature magnetic cooling applications.
文摘We report on the structural,magnetic,and magnetocaloric properties of EuRhO_(3) powders.The oxidation states of Eu and Rh ions were studied using X-ray photoelectron spectroscopy(XPS).It is found that the Eu ions are mainly in the divalent oxidation state while the Rh ions have+4 state.EuRhO_(3) powders are found to be antiferromagnetic with a second order magnetic transition at Neel temperature(T_(N)=2.9 K).Analysis of the magnetic susceptibility versus temperature data in terms of the Curie=Weiss law:(χ=C/(T-θ_(W))) for T>T_(N),yields θ_(W)=-3.1 K and effective magne tic moment μ_(ff)^(exp),which is close to the theoretical value μ_(eff)^(theo).The magnetic entropy change(-Δ_(SM)),was determined by em ploying the thermodynam ic Maxwell's relation.At μ_0H=5 T and near T_(N),ΔS_(M)^(Max) and relative cooling power(RCP) exhibit large values of 33.7 J/(kg·K) and 238 J/kg,respectively.The large magnitude of-Δ_(SM) and RCP show that the EuRhO_(3) compound could be a potential candidate to be used in cryogenic magnetic refrigeration.
文摘In this paper,experimental and numerical studies of heat transfer in a test local of side H=0.8 m heated from below are presented and compared.All the walls,the rest of the floor and the ceiling are made from plywood and polystyrene in sandwich form(3 mmplywood-3 cm polystyrene-3 mmplywood)just on one of the vertical walls contained a glazed door(2 H/3×0.15 m).This local is heated during two heating cycles by a square plate of iron the width L=0.6 H,which represents the heat source,its temperature T_(h) is controlled.The plate is heated for two cycles by an adjustable set-point heat source placed just down the center of it.For each cycle,the heat source is switched“on”for 6 h and switched“off”for 6 h.The outdoor air temperature is kept constant at a low temperature T_(c)<T_(h).All measurements are carried out with k-type thermocouples and with flux meters.Results will be qualitatively presented for two cycles of heating in terms of temperatures and heat flux densitiesϕfor various positions of the test local.The temperature evolution of the center and the profile of the temperature along the vertical centerline are compared by two dimensions simulation using the lattice Boltzmann method.The comparison shows a good agreement with a difference that does not exceed±1℃.
文摘Creating sustainable cities is the only way to live in a clean environment,and this problem can be solved by using bio-sourced and recycled materials.For this purpose,the authors contribute to the valuation of sheep wool waste as an eco-friendly material to be used in insulation.The paper investigates the thermal,hygrothermal,and biological aspects of sheep wool by testing a traditional treatment.The biological method of aerobic mesophilicflora has been applied.Fluorescence X was used to determine the chemical composition of the materials used.Also,thermal characterization has been conducted.The thermal conductivity is above 0.046(W·m^(-1)·K^(-1))and the thermal diffusivity is 1.56.10^(-6) m^(2)·s^(-1).Besides,the energy efficiency of using sheep wool in buildings was studied.Furthermore,its humidity behavior was evaluated in different aspects in both winter and summer.Results of biological analyses show the efficiency of the treatment by removing the majority of the microorgan-isms:the value of yeast and mildew was reduced from 38.10^(2) to 2.10^(2)(UFC·g^(-1)).In addition to that,sheep wool permits obtaining a low thermal transmittance on the scale of the walls and low cooling needs on the scale of the building with a gain of 45%and 52%,respectively.
文摘The development of bio-sourced materials is essential to ensuring sustainable construction;it is considered a locomotive of the green economy.Furthermore,it is an abundant material in our country,to which very little attention is being given.This work aims to valorize the waste of the trunks of banana trees to be used in construction.Firstly,the physicochemical properties of the fiber,such as the percentage of crystallization and its morphology,have been determined by X-ray diffraction tests and scanning electron microscopy to confirm the potential and the impact of the mode of drying on the quality of the banana fibers,with the purpose to promote the use of this material in construction.Secondly,the results obtained with the gypsum matrix allowed us to note a preponderant improvement in the composite’s thermal properties thanks to the variation of the banana fiber additive.Thirdly,the impact of the nature of the banana fiber distribution(either fiber mixed in matrix or fiber series model)on the flexural and compressive strengths of the composites was studied.The results obtained indicate that the insulation gain reaches up to 40%.It depends on the volume fraction and type of distribution of the banana fibers.However,the thermal inertia of the composites developed,represented by thermal diffusivity and thermal effusivity,was studied.Results indicate a gain of 40%and 25%,respectively,in terms of thermal diffusivity and thermal effusivity of the developed composites compared to plaster alone.Concerning the mechanical properties,the flexural strength depends on the percentage of the volume fraction of banana fibers used,and it can reach 20%more than the flexural strength of plaster;nevertheless,there is a significant loss in terms of the compressive strength of the studied composites.The results obtained are confirmed by the microstructure of the fiber banana.In fact,the morphology of the banana fibers was improved by the drying process.It reduces the amorphous area and improves the cellulosic crystalline surfaces,which assures good adhesion between the fiber and the matrix plaster.Finally,the dimensionless coefficient analysis was done to judge the optimal proportion of the banana fiber additive and to recommend its use even on false ceilings or walls.
文摘This study scrutinizes the thermomechanical dynamics of 3D-printed hydrofoil blades utilizing a carbon and glass bead-reinforced thermoplastic polymer.Comparative analyses underscore the pivotal role of polymer reinforcement in augmenting mechanical strength and mitigating deformation and residual stress.The investigation elucidates the expeditious and cost-efficient manufacturing potential of low-cost Fused Filament Fabrication(FFF)printers for small-scale blades,revealing exemplary mechanical performance with nominal deflection and warping in the PA12-CB/GB printed blade.A comprehensive juxtaposition between Selective Laser Sintering(SLS)and FFF printing methods favors SLS due to its isotropic properties,notwithstanding remediable warping.Emphasizing the rigorous marine environment,the study cautions against the anisotropic properties of FFF-printed blades,despite their low mechanical warping.These discernments contribute to hydrofoil design optimization through numerical analysis,shedding light on additive manufacturing’s potential for small blades in renewable energy,while underscoring the imperative for further research to advance these techniques.
