- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Low-Temperature Graphene Growth by Forced Convection of Plasma-Excited Radicals
摘要： We developed the forced convection (FC)-PECVD method for the synthesis of graphene in which a specially designed blowing plasma source is used at moderate gas pressure (1-10 Torr) and the distribution of reactive radicals reaching the substrate surface can be controlled by forced convection. Self-limiting growth of graphene occurs on copper foil and monolayer graphene growth with few defects is achieved even at low temperature (<400 °C). We also demonstrated the enlargement of growth area using the scalable blowing plasma source. We expect that the FC-PECVD method overcomes the limitations of conventional low-temperature PECVD and provides a breakthrough for the achievement of industrial applications based on graphene.
关键词： low temperature growth,self-limiting growth,Graphene,forced-convection plasma CVD
更新于2025-09-23 15:23:52
-
Direct absorption solar collector with magnetic nanofluid: CFD model and parametric analysis
摘要： Direct absorption collectors (DAC) with nanofluid are among the most promising yet least studied in solar energy technology. There are numerous micro- and macroscopic factors that determine their efficiency. This complicates in situ optimization of DACs using physical prototypes. The present paper describes a multiphase CFD model of the collector, which was validated against two independent experimental datasets. The model was used for a multiparametric numerical analysis, where we altered concentration and size of the nanoparticles, as well as the geometry and inclination of the collector. The optimization resulted in up to 10% improvement in the collector's efficiency. Finally, we considered the process of thermomagnetic convection in the collector using a magnetic nanofluid. This resulted in a 30% increase in the collector performance.
关键词： multiphase,nanofluid,thermomagnetic convection,CFD,direct absorption collector
更新于2025-09-23 15:23:52
-
Thermal performance analysis of a novel linear cavity receiver for parabolic trough solar collectors
摘要： The trough solar thermal power generation system is one of the most mature solar thermal power generation systems. A novel major arc-shaped linear cavity receiver with a lunate channel based on the black cavity effect principle for parabolic trough solar collectors is proposed in this work. The effects of the inclination angle, collecting temperature, surface emissivity and aperture width on the heat loss are thoroughly analyzed with a two-dimensional numerical model coupling natural convection with surface radiation. In addition, the thermal performance of the proposed linear cavity receiver is compared with that of the Solel’s UVAC series evacuated collector tube. The results show that: (1) The natural convection heat loss is significantly affected by the inclination angle, while the radiation heat loss is mainly affected by the surface emissivity and the collecting temperature. (2) The aperture width of the receiver has a great impact on the thermal performance. The larger the aperture width is, the greater the heat losses. However, the aperture width can also affect the optical performance and the manufacturing cost. The reasonable aperture width for this kind of linear cavity receiver is about 50–70 mm with consideration of all these factors. (3) The proposed linear cavity receiver demonstrates comparative or even better thermal performance as traditional evacuated collector tubes, especially in high temperature range. In general, the proposed linear cavity receiver has the comparative shape and size as the traditional evacuated collector tubes. More importantly, it has the advantages of raising the collecting temperature and reducing the production and maintenance costs. Therefore, it can be used to replace the evacuated collector tube which has poor performance due to long-term operation.
关键词： Cavity receiver,Parabolic trough solar collector,Surface radiation,Natural convection,Thermal performance,Linear receiver
更新于2025-09-23 15:23:52
-
Effect of hydrodynamic conditions on the Cu(In,Ga)Se2 thin film growth by electrodeposition
摘要： In this paper, an experimental study about CIGS thin film growth due to hydrodynamic conditions variations on the working electrode surface is reported. Local hydrodynamic conditions were produced by the interaction of the natural convection flow with a non-conducting hemisphere placed on the working electrode surface. The electrodeposition process was made by a single bath with copper, indium, gallium and selenium ions to obtain CIGS thin films. The electrodes in the electrolytic cell were placed vertically. The as-electrodeposited CIGS thin film morphology near the hemisphere had a characteristic growth as a consequence of the local hydrodynamic conditions. CIGS thin film morphology and composition variations due to the wake and boundary layer were identified. With the CIGS film morphology obtained due to the presence of the wake was possible to represent the natural convection flow pattern on the Mo electrode surface. The CIGS thin film composition, inside and outside of the wake and throughout the boundary layer, was characterized. The gallium incorporation to the CIGS film was principally affected. As a consequence of this study, it was found that the atomic percentage of gallium in the CIGS film is related to deposition current density.
关键词： Electrodeposition,CIGS thin film,Natural convection flow
更新于2025-09-23 15:22:29
-
Convection Dynamics Forced by Optical Trapping with a Focused Laser Beam
摘要： Optical trapping dynamics of colloidal particles in solution is essential for understanding laser-induced assembling of molecules and nanomaterials, which contributes to nanofabrication, bioengineering, and microfluidics. In this paper, the importance of the surrounding fluid motion in optical trapping is investigated; that is, we reveal convection fluid dynamics forced by optical trapping with a focused laser beam. The fluid flow in optical trapping is evaluated by both experiments using the particle-image-velocimetry of fluorescent particles in solutions and theoretical consideration based on numerical analysis. A theoretical model consists of Navier?Stokes equations with the Boussinesq approximation that considers the temperature elevation induced by a photothermal effect. Furthermore, the effect of the particle motion induced by the optical force on fluid flow is also included in the analysis by developing a simple one-way homogeneous-type multiphase flow model. From both experimental and theoretical results, it turns out that the fluid flow in optical trapping is caused not only by thermal convection due to the temperature elevation but also by the collective particle motion induced by optical forces. Therefore, the optical forces can induce the large-scale fluid convection, which supports accumulating the target particles to the focal spot.
关键词： thermal convection,fluid dynamics,colloidal particles,photothermal effect,Boussinesq approximation,optical trapping,multiphase flow model,Navier?Stokes equations,particle-image-velocimetry
更新于2025-09-23 15:21:01
-
Influence of Static Magnetic Field on the Microstructure of Nickel-Based Superalloy by Laser-Directed Energy Deposition
摘要： The influence of a static magnetic field on microstructure evolution during laser direct energy deposition was studied. Our results reveal that dendrite spacing increases with increasing magnetic field flux density (MFFD). Moreover, electron backscatter diffraction results reveal that the epitaxial growth was preferred with increasing MFFD. We discuss these findings in terms of the influence of a magnetic field on melt convection and propose that an applied magnetic field effectively limits Marangoni convection.
关键词： microstructure,static magnetic field,laser-directed energy deposition,dendrite spacing,Marangoni convection
更新于2025-09-23 15:21:01
-
Exper?±mental and Numer?±cal Analysis of the Effect of Components on a Double-Sided PCB on LED Junction Temperature and Light Output Using CFD
摘要： In today’s lighting industry, with developing technology and a widened usage area, LEDs have become very popular due to their higher energy efficiency and longer life. In the present study, the effect of electronic components on printed circuits and the radiation level on light output was studied. The performed analysis was validated with an experimental method. For the finite volume method, FloEFD 2019, commercial software, was used. The ambient temperature was assumed to be 23 °C. The value of solar irradiance was taken as 1009 W/cm2. LEDs on a PCB were driven at 70 mA at first and then at 50 mA, and, by exerting power on all electronic components, analyses were performed. Both sides of the PCB were examined, and, in order to achieve efficient heat conduction, the power and distribution of the electronic components on the back side of the LEDs were optimized. With a new electronic circuit design, analyses were performed at 50, 55, 60, 65, and 70 mA. It was determined that the highest light output was achieved at 65 mA and that the distribution of electronic components on a PCB indirectly affects light output through junction temperature (T j).
关键词： Laminar natural convection,Junction temperature,Monte Carlo radiation,LED automotive lamp,Computational fluid dynamics (CFD)
更新于2025-09-23 15:19:57
-
Sub-100 nm 2D nanopatterning on large scale by ultrafast laser energy regulation
摘要： Coupling ultrafast light to surface nanoreliefs leads to periodic patterns achieving record processing scales down to tens of nanometers. Driven by near-field interactions, the promising potential of the spontaneous pattern formation relies on the scale-up manufacturing one-step process. Here, we report the self-assembly of unconventional arrays of nanocavities of 20 nm diameter with a periodicity down to 60 nm upon ultrafast laser irradiation of a nickel surface. In stark contrast to laser-induced surface ripples, which are stochastic and suffer from a lack of regularity, the 2D patterns present an unprecedented uniformity on extreme scales. The onset of nanocavity arrays ordered in a honeycomb lattice is achieved by overcoming the anisotropic polarization response of the surface by a delayed action of cross-polarized laser pulses. The origin of this self-arrangement is identified as a manifestation of Marangoni convection instability in a nanoscale melt layer, destabilized by the laser-induced rarefaction wave.
关键词： nanopatterning,self-assembly,ultrafast laser,Marangoni convection,nanocavities
更新于2025-09-23 15:19:57
-
Optimization of pyroelectric conversion of thermal energy through the PZT ceramic buzzer and natural convection
摘要： The main purpose of this work is to take advantage of the pyroelectric e?ect to produce electricity. We propose the use of the PZT ceramic buzzer, which possesses pyroelectric properties, to convert thermal energy into electrical energy by pyroelectric e?ect. We take advantage of natural convection to create temperature variation from a ?xed thermal source. The amount of power harvested by this technique is su?cient to supply low-power systems. Our experiment consists in subjecting the PZT ceramic buzzer to a temperature variation insured only by natural convection created in an oil bath. In order to verify the existence of thermal ?uctuations and con?rm the e?ciency of our technique, we use thermal imaging which shows that the temperature changes as a function of time. We propose in this paper an optimization of our energy-harvesting system by studying the e?ect of the convection system geometry on the pyroelectric response: the e?ect of volume on the pyroelectric response and the e?ect of the distance between the oil surface and the pyroelectric ceramic. It appears from our study that the harvested power increases when the distance between the buzzer and the ?uid decreases but it increases slightly with the volume of liquid.
关键词： pyroelectric effect,energy harvesting,thermal energy,PZT ceramic buzzer,natural convection
更新于2025-09-23 15:19:57
-
Thermal driven natural convective flows inside the solar chimney flush-mounted with discrete heating sources: Reversal and cooperative flow dynamics
摘要： Fluid flow and heat transfer mechanism in a solar chimney induced by thermal buoyancy within a range of Ra numbers are reported by numerical and experimental investigations. The transport paths followed respectively by air and heat are visualized by streamlines and heatlines. Numerical results demonstrate that the reverse flow not only slows down the volume flow rate but also accelerates backflow presented in the solar chimney when Ra increases beyond a certain value, which makes the solar chimney lost its role of ventilation. In order to suppress the reverse flow and enhance ventilation performance, a solar chimney with multiple discrete sources flush attached the glazing wall is proposed. The effects of the sizes, positions, and numbers of those discrete heat sources on the system heat transfer rate and volume flow rate are discussed. After comparing with conventional solar chimney, the modified solar chimney with discrete heat source of height D0 = 1 and position S0 = 1 could perform better, not only preventing reverse flow but also enhancing the ventilation performance. The results obtained by the lab experimental measurements were agreed well with former numerical simulations. Temperature distributions along the heated wall for different heat input at ambient temperature illustrate the temperatures on the heated wall do not increase linearly and even drop near the top exit. This research could be significant for solar energy utilization and building energy conservation.
关键词： Discrete heat sources.,Solar energy,Reversal flow,Thermal driven natural convection
更新于2025-09-19 17:15:36