- 标题
- 摘要
- 关键词
- 实验方案
- 产品
过滤筛选
- 2019
- 2018
- Heat Trap
- outgassing
- lifetime
- Carbon nanotubes
- current stability
- cathode
- thermionic emission
- photovoltaic
- monocrystalline
- Heat mapping
- Nanomaterials and Technology
- Electrical Engineering and Automation
- University of British Columbia
- Univesitas Budi Luhur
- Institut Teknologi Sepuluh Nopember
-
Laser hardening of copper-iron pseudoalloy
摘要： The purpose of the study is to improve the performance characteristics of powder pseudo-alloy materials using surface heat treatment. Such materials have unique properties, for example, self-lubrication under dry friction conditions, high thermal conductivity coefficient, and high electro-erosion resistance. The disadvantage of powder pseudo-alloys is their relatively low strength. The paper considers the method of surface hardening by high-energy treatment - laser radiation. The paper describes the method of experimental research, describes the method of obtaining powder material, its chemical composition, shows the equipment used. The results of studies of the microstructure and microhardness of the surface layer of steel-copper powder pseudo-alloy after laser heat treatment (LHT) of a continuous-wave fiber laser with a maximum power of 1 kW are given, LHT modes are indicated, the influence of LHT parameters on the characteristics of the hardened layer is evaluated. It is revealed that the partial melting region in which melting occurs in the volumes of the fusible component (copper) in the initial structure and contacting segments of steel matrix is formed in the material in addition to the total melting zone. Then the quenching zone from the solid state follows, in which the maximal hardness up to 1000 HV is attained for best samples in the volume of martensite, which is formed in perlite colonies of the initial steel–copper material.
关键词： Steel–copper pseudoalloy,Microhardness,Abrasive wear,Laser heat treatment,Powder metallurgy,Microstructure
更新于2025-09-23 15:19:57
-
Recent Problems of Heat-Transfer Simulation in Technological Processes of Selective Laser Melting and Fusion
摘要： The thermal processes arising upon the implementation of the additive technologies of selective laser melting and the fusion of metals and alloys are analyzed. An adequate description of the heat transfer upon the implementation of additive technological processes associated with high-intensity local heating by a moving laser beam and the phase transitions generated by a semifinished powder product, crystallization, and the concomitant effects in the growing element is the key to gaining insight into the microstructure and the efficient properties of the obtained material and the prevention of residual deformation (shrinkage) of the item. Currently, the main causes of unpredictable production defects are deviations of the shape of the final item from the preset geometry and high-amplitude residual stresses, which can initiate destruction of the item under loads significantly lower than those calculated, as well as the occurrence of the microscopic defects (pores, layer interfaces, etc.) are. The development of mathematical models that, on the one hand, are sufficiently accurate to predict the listed phenomena and, on the other hand, allow practical implementation in engineering calculations is the basis for the further development of the laser-melting and fusion of metal materials. At the same time, analysis of the current state of the problem shows that development of efficient numerical methods providing acceptable computational costs while maintaining accuracy is the key element in the practical implementation of the models. A method based on multiscale, interconnected modeling of the mechanical and the thermal state of the growing body—at the local level in the melt pool domain, at the intermediate level in the vicinity of the melt pool and the adjacent layers, and at the level of the entire product as a whole—seems to be efficient; here, the computing process at the global level can be based on a combination of the finite-element method (indisputable in practice) and analytical calculations providing local refinement of the solution.
关键词： numerical methods,heat-transfer simulation,microstructure,residual deformation,mathematical models,fusion,thermal processes,selective laser melting,additive technologies
更新于2025-09-23 15:19:57
-
Multiple epitaxial lift-off of stacked GaAs solar cells for low-cost photovoltaic applications
摘要： This paper presents a multilayer peeling from a stacked cell structure as an approach for the cost reduction of III–V solar cells. We demonstrate the separation of two-layer stacked GaAs solar cells with Al(Ga)As release layers on the GaAs substrate into individual layers without cracks. The cells in each layer peeled from the stacked structure show equivalent device performances. Thermal cycling tests with repeated heating to 85 °C and cooling to ?40 °C show that the flexible GaAs thin-film cell exhibits a high durability against temperature changes. Further, a damp heat test conducted at 85 °C and 85% humidity indicates that the cell has long-term stability. These results suggest that the flexible GaAs thin-film cells fabricated by peeling from stacked structures have a high reliability and prove that the separation of the stacked cell structures into individual layers is effective in fabricating low-cost III–V solar cells.
关键词： epitaxial lift-off,cost reduction,damp heat test,photovoltaic applications,thermal cycling,GaAs solar cells
更新于2025-09-23 15:19:57
-
Size- and Surface-Dependent Photoresponses of Solution-Processed Aluminum Nanoparticles
摘要： Plasmonic aluminum nanoparticles have emerged as an exciting new materials platform due to the high natural abundance of aluminum, their ability to be synthesized in the solution phase, and the potential of these materials to be used for photocatalysis and sensing. However, the photothermal properties of solution-processed aluminum nanoparticles, in particular, how phonon energy transfer depends on the particle size and surface properties, are critical for practical applications and are currently unexplored. Here we use transient absorption spectroscopy, in combination with simulations of phonon and thermal energy dissipation, to investigate the photoresponses of aluminum nanoparticles of various diameters (54, 85, 121, and 144 nm) suspended in 2-propanol. Fast thermal-transfer rates to the solvent (170?280 ps) are observed for particles of all sizes and are facilitated by native oxide coverage, as veri?ed by a two-interface thermal energy-transfer model. Size-dependent phonon “breathing”/vibrational modes are also observed as oscillations in the total cross-section. We ?nd that both the oscillation frequency and the damping rate increase as the diameter of the particles decreases. On the basis of the results of ?nite element calculations, we attribute the damping strength and oscillation period observed to a combination of the noncrystalline nature of the native oxide shell and the presence of surface-bound ligands, both of which increase the vibrational mode damping rates relative to bare Al and Al particles with a bare crystalline oxide shell. These insights should guide future work on controlling energy transfer through the use of size and surface tuning in sustainable aluminum nanomaterial systems for applications in catalysis and sensing.
关键词： aluminum,phonons,surface effects,transient absorption,heat transfer,localized surface plasmon resonances
更新于2025-09-23 15:19:57
-
Photon-Assisted Heat Generation by Electric Current in a Quantum Dot Attached to Ferromagnetic Leads
摘要： Heat generated by electric current in a quantum dot device contacting a phonon bath is studied using the non-equilibrium Green function technique. Spin-polarized current is generated owing to the Zeeman splitting of the dot level. The current’s strength and the spin polarization are further manipulated by changing the frequency of an applied photon field and the ferromagnetism on the leads. We find that the associated heat by this spin-polarized current emerges even if the bias voltage is smaller than the phonon energy quanta and obvious negative differential of the heat generation develops when the photon frequency exceeds that of the phonon. It is also found that both the strength and the resonant peaks’ position of the heat generation can be tuned by changing the value and the arrangement configurations of the magnetic moments of the two leads, and then provides an effective method to generate large spin-polarized current with weak heat. Such a result may be useful in designing low energy consumption spintronic devices.
关键词： quantum dot,heat generation,ferromagnetic leads,photon-assisted tunneling,spin-polarized current
更新于2025-09-23 15:19:57
-
Thermal management of high-power LED based on thermoelectric cooler and nanofluid-cooled microchannel heat sink
摘要： Effective thermal management for light-emitting diodes (LEDs) is critical, as temperature significantly affects their lifetime and performance. In this study, a system combining a thermoelectric cooler (TEC) and a microchannel heat sink (MHS) is investigated experimentally for thermal management of high-power LEDs. Nanofluids and water are used as coolant. The LED substrate temperature (Ts) is measured at various TEC powers, nanofluid concentrations, ambient temperatures of LED (Ta), and ambient temperatures of the fluid radiator (Ta,f). The effective thermal resistance (Rs-fa) of the LED substrate to the ambient of the fluid radiator is analyzed. Correlations of Ts and Rs-fa are obtained. Results show that the Ts is lowest when the TEC works at its rated power, and Ts is lower than Ta at Ta ≥ 55 °C. Using nanofluids instead of water as coolant reduces the Ts by up to 18.5 °C and decreases the thermal resistance by as much as 42.4%. The MHS heat transfer capacity is increased by 38.6%. The Ta,f exhibites greater influence on Ts compared to Ta. Results show that favorable performance of the thermal management of the high-power LED is obtained by the proposed nanofluid-cooled TEC-MHS system, particularly at high ambient temperature of LED.
关键词： Thermal management,Nanofluid,LED,Thermoelectric cooler,Thermal resistance,Microchannel heat sink
更新于2025-09-23 15:19:57
-
Intensification of the Plant Products Drying Process by Improving Solar Dryer Design
摘要： The article presents the rationale for production of dried fruits and vegetables using a solar drying unit. To intensify the drying process, convection of drying agent ?ow in the proposed drying chamber is studied using Navier–Stokes equations. Numerical methods are used for solving equations describing the process of convective heat transfer. As a result, graphical interpretations of isolines of drying agent ?ow are obtained and location of passive zones in the dryer chamber are identi?ed. Uniformity of the temperature zones in the chamber is ensured by supplying additional drying agent into the passive zones. Temperature values at various levels of the drying chamber are experimentally obtained. Results for drying cut-up mass of vegetables and fruits are presented.
关键词： solar drying,passive zones,convective heat transfer,Navier–Stokes equations,temperature uniformity
更新于2025-09-23 15:19:57
-
Enhanced heat capacity of binary nitrate eutectic salt-silica nanofluid for solar energy storage
摘要： In concentrating solar power plants, the heat capacity of thermal storage media is a key factor that affects the cost of electricity generation. This work investigated the effective specific heat capacity of binary nitrate eutectic salts seeded with silica nanoparticles, using both experimental measurements and molecular dynamics simulations. The effects of the mass concentration (0–2.0 wt%) and average size (10, 20, and 30 nm) of the nanoparticles on the specific heat capacity value of nanofluids were analyzed. The results show that specific heat capacity increases when adding 10 nm silica nanoparticles up to 1.0 wt%, and then it decreases at higher concentrations. At this optimal mass concentration, the 20 nm nanoparticles displayed a maximum enhancement in the average specific heat capacity (by ~26.7%). The simulation results provided information about the different energy components in the system. The rate of potential energy change versus nanoparticle mass concentration was found to be maximized at 1.0 wt% concentration, which agrees with the experimental measurements. The potential energy components in the simulation system indicate that the change of Coulombic energy contributes the most to the variation of specific heat capacity.
关键词： Molten salt based nanofluids,Molecular dynamics simulation,Solar energy storage,Specific heat capacity
更新于2025-09-23 15:19:57
-
Photoinduced Regulation of the Heat Resistance in Polymer Networks with Diarylethene-Conjugated Reversible Covalent Cross-Links
摘要： A cross-linker with a diarylethene-conjugated Diels?Alder adduct (DAE/DA) was synthesized and applied in a radical polymerization system to afford polymer networks whose dynamic nature can be changed reversibly by photo-irradiation. Free-radical polymerization of hexyl methacrylate and the DAE/DA-based cross-linker furnished an insoluble and transparent poly(hexyl methacrylate) network with DAE/DA moieties at their cross-linking points, which undergo de-cross-linking via a thermally induced retro-DA reaction upon heating. The photoregulation of such a thermal de-cross-linking reaction in DAE/DA-based polymer networks was demonstrated by swelling experiments and tensile tests, revealing drastic changes in the heat resistance and mechanical properties upon exposure to UV?vis irradiation.
关键词： heat resistance,mechanical properties,polymer networks,diarylethene,photo-irradiation,Diels?Alder adduct
更新于2025-09-23 15:19:57
-
Transient thermoelastic response in a cracked strip of functionally graded materials via generalized fractional heat conduction
摘要： This work is devoted to analyzing a thermal shock problem of an elastic strip made of functionally graded materials containing a crack parallel to the free surface based on a generalized fractional heat conduction theory. The embedded crack is assumed to be insulated. The Fourier transform and the Laplace transform are employed to solve a mixed initial-boundary value problem associated with a time-fractional partial differential equation. Temperature and thermal stresses in the Laplace transform domain are evaluated by solving a system of singular integral equations. Numerical results of the thermoelastic fields in the time domain are given by applying a numerical inversion of the Laplace transform. The temperature jump between the upper and lower crack faces and the thermal stress intensity factors at the crack tips are illustrated graphically, and phase lags of heat flux, fractional orders, and gradient index play different roles in controlling heat transfer process. A comparison of the temperature jump and thermal stress intensity factors between the non-Fourier model and classical Fourier model is made. Numerical results show that wave-like behavior and memory effects are two significant features of the fractional Cattaneo heat conduction, which does not occur for the classical Fourier heat conduction.
关键词： functionally graded materials,thermal stress,crack,time-fractional heat conduction,phase lag of heat flux
更新于2025-09-19 17:15:36