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Effects of bluff-body on the thermal performance of micro thermophotovoltaic system based on porous media combustion
摘要： To improve thermophotovoltaic system efficiency, a porous media combustor with a bluff-body as the flame holder was proposed. A two-dimensional numerical simulation of premixed hydrogen/air combustion inside a planar porous media channel with the local thermal non-equilibrium model was conducted. Effects of the bluff-body flame holder on mean wall temperature and system efficiency were examined. By inserting the bluff-body, the blowout limits of the planar porous media combustor for ? = 0.6, 0.8, 1.0, 1.2 are increased by 33%, 19%, 12%, 20%, respectively. Numerical results show that the flame stabilization is dominated by flow and heat recirculation. Further analysis reveals the mechanism of heat transfer on flame stabilization due to three heat recirculation paths. Considering the view factor and the external quantum efficiency, the system efficiency with the bluff-body is increased by 14.72% as compared to the one without the bluff-body at ? = 0.8, vin = 4 m/s.
关键词： Wall temperature,Bluff-body,System efficiency,Micro thermo-photovoltaic system,Porous media combustion,Heat recirculation
更新于2025-09-23 15:19:57
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Numerical and experimental investigation of the energy and exergy performance of solar thermal, photovoltaic and photovoltaic-thermal modules based on roll-bond heat exchangers
摘要： This paper presents numerical and experimental energy and exergy performance assessments of solar thermal (ST), photovoltaic (PV) and photovoltaic/thermal (PV/T) modules based on roll-bond heat exchangers having three different channel geometries: serial, parallel and bionic. The validation of a coupled numerical simulation encompassing the thermo-hydraulic and electrical properties shows that 78% of all the data lies within a ± 10% uncertainty. The thermo-hydraulic simulation shows that the lowest outlet-water temperature inside the absorber is for the case of the bionic absorber (average 44.1 °C vs. 46.5 °C for the serial). This geometry is also beneficial when considering pressure losses, since compared to the parallel configuration (average 778 Pa) the bionic has significantly lower pressure losses (average 385 Pa). The simulation of the electrical properties of PV/T with all three absorber types showed the highest average solar-to-electrical efficiency (14.5%) in the case of the bionic absorber compared to the PV/T with parallel and serial absorbers (14.4% and 14.3%, respectively). Finally, a set of experiments using the ST, PV and PV/T2 (the index 2 denotes a PV/T collector variant with a foil thickness of 0.3 mm, compared to the thickness of 0.4 mm for PV/T1, positioned between the absorber and the PV cells) modules showed that the PV module, coupled with a bionic absorber plate, achieves the highest average electrical (PV – 8.5% vs. PV/T2 – 9.9%) and exergy (ST – 4.4% vs. PV – 9.2% vs. PV/T2 – 12.7%) efficiencies. Only in terms of the thermal efficiency, the PV/T is at a disadvantage to the ST (PV/T2 – 33.5% vs. ST – 61.4%) due to the air gap between the front glass and the absorber of the latter module.
关键词： Simulation,Solar,Roll-bond heat exchanger,Absorber,Exergy,PV/T
更新于2025-09-23 15:19:57
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The effect of preliminary heat treatment on the durability of reaction bonded silicon nitride crucibles for solar cells applications
摘要： Silicon nitride crucibles have the potential to replace silica crucibles and reduce the cost of silicon crystallization because of their reusability potential. Till date, crucibles’ heat treatment before each use is a prerequisite to achieve non-wetting conditions that is needed to facilitate the ingot release and hence enable reusability. Yet, no studies have examined the heat treatment influence on the crucibles’ durability. The present investigation focuses on the crucibles’ heat treatment and its impact on the crucibles’ lifetime. Repeated heat-treatments of silicon nitride crucibles in the air at above 1100 °C leads to crucible fracture. Therefore, this study identifies the cause and the mechanism of such failures by applying different heat treatment procedures in the air. The mass gain and the oxidation rates of the crucibles at different temperatures are measured via Thermogravimetry (TG) and Differential Thermal Analyzer (DTA). The results show that the porosity and phase distribution along the crucible wall thickness, play a key role in the crucible’s behavior during oxidation. Moreover, excessive internal oxidation in the tested crucibles results in severe thermal stresses which cause cracking during cooling.
关键词： B1. Nitrides,A1. Heat treatment,A1. Crucible cracking,A1. Characterization
更新于2025-09-23 15:19:57
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Studies on the formation mechanism of incomplete fusion defects in ultra-narrow gap laser wire filling welding
摘要： Austenitic stainless steel has many excellent properties and it has been extensively used in rail transit trains. Ultra-narrow gap laser wire filling welding is the preferred welding method to connect austenitic stainless steel. However, with this method, it is easy to form defects such as lack of fusion in the welding process. In order to clarify the mechanism of incomplete fusion defects, this article analyzed incomplete fusion defects from the groove design and the welding wire transfer behavior, integrating with high-speed photography and finite element simulation. It is found that the form of narrow gap groove has a close relationship with the formation of fusible defects. Besides, under the condition of globular transfer, all the complicated recoil force, blocking effect of the large droplet on laser energy, the eruption of metal vapor and turbulence of the molten pool caused by large droplet transfer will cause violent disturbance of the molten pool and seriously affect its heat conduction effect. The base metal incompletely melting, the lack of transfer driving force on the droplet and the failure of droplet wetting and spreading on the sidewalls of the groove are the main causes of welding non-fusion defects. Designing reasonable groove, ensuring the stability of wire feeding, adopting liquid bridge transfer mode and appropriately increasing heat input are conducive to reduce the occurrence of incomplete fusion, which is essential to improve the welding quality and enhance the safety of rail vehicles.
关键词： Ultra-narrow gap,Numerical simulation,The heat transfer mechanism,Incomplete fusion
更新于2025-09-23 15:19:57
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Indoor and outdoor characterization of concentrating photovoltaic attached to multi-layered microchannel heat sink
摘要： Concentrating Photovoltaic technology is a promising option in power generation using the photovoltaics compared to the conventional ?at PV system. This study investigates the performance of a high concentrated photovoltaic single solar cell module attached to a multi-layered microchannel heat sink. The system has been tested the ?rst time experimentally both at indoor and outdoor conditions. The indoor characterization of the system investigated the e?ect of varying the number of the layers of the heat sink and the ?ow rate of the ?uid electrically and thermally. The experiments show that varying the number of the heat sink layers from 1-layer to 3-layers increase the maximum electrical generation by 10% and reduces the cell temperature by 3.15 °C under the same ?uid ?ow rate of 30 ml/min. The outdoor experiments show the maximum output electrical generation of the system of 4.60 W and the short circuit current of 1.96 A. The maximum solar cell temperature was maintained below 61 °C where the extracted heat of the system was 12.85 W which represents of 74.9% of the total generated power.
关键词： Heat sink,Concentrating photovoltaic,Thermal regulation,Multi-layered microchannel
更新于2025-09-23 15:19:57
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Prominent Heat Dissipation in Perovskite Light-Emitting Diodes with Reduced Efficiency Droop for Silicon-Based Display
摘要： Solution-processed perovskite light-emitting diodes (LEDs) possess outstanding optoelectronic properties for potential solid-state display applications. However, poor device stability results in significant efficiency droop partly being ascribed to Joule heating when LEDs are operated at high current densities. Herein, we used monocrystal silicon (c-Si) as substrate and charge injection layer to alleviate the thermal affection in perovskite LED (PeLED). By incorporating silicon oxide (SiOx) and poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(4,4’-(N-(4-butylphenyl) (TFB) layer to tune the charge injection balance in c-Si-based device, a PeLED achieves an external quantum efficiency of 2.12% with a current efficiency of 6.06 cd A-1. Benefiting from excellent heat dissipation of c-Si, the PeLEDs display reduced efficiency droop and extended operational lifetime. Furthermore, both electroluminescent (EL) dynamic information display and static pattern displays of c-Si-based PeLED have been successfully demonstrated. These results reveal the feasibility of potential practical c-Si-based PeLEDs with reduced efficiency droop for EL display applications.
关键词： efficiency droop,silicon substrate,perovskite light-emitting diode,display application,heat dissipation
更新于2025-09-23 15:19:57
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Transition regime in the ultrafast laser heating of solids
摘要： Based on the phenomenological theory of heat diffusion, we show that the generated peak temperature Tmax after absorption of a laser pulse strongly depends on the pulse duration. We identify three different heat conduction regimes that can be identified via a simple parameter that depends only on the pulse duration and on material constants. The phenomenological approach is supported by numerical simulations of heat diffusion and measurements of the thermal surface expansion after transient grating excitation with 1 ps and 10 ns optical pulses.
关键词： laser heating,heat diffusion,thermal surface expansion,pulse duration
更新于2025-09-23 15:19:57
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Near-Field Radiative Heat Transfer between Dissimilar Materials Mediated by Coupled Surface Phonon- and Plasmon-Polaritons
摘要： Near-field radiative heat transfer (NFRHT) between dissimilar materials supporting surface polaritons in the infrared is of critical importance for applications such as photonic thermal rectification and near-field thermophotovoltaics. Here, we measure NFRHT between millimeter-size surfaces made of 6H-SiC and doped Si, respectively supporting surface phonon-polaritons (SPhPs) and surface plasmon-polaritons (SPPs) in the infrared, separated by a 150-nm-thick vacuum gap spacing maintained via SiO2 nanopillars. For purpose of comparison, measurements are also performed between two doped Si surfaces. The measured radiative flux is in good agreement with theoretical predictions based on fluctuational electrodynamics. A flux enhancement beyond the blackbody limit of ~ 8.2 is obtained for the SiC-Si sample, which is smaller than the enhancement for the Si-Si sample (~ 12.5) owing to the spectral mismatch of the SiC and Si light lines, and SPhP and SPP resonances. However, due to lower losses in SiC than Si and weaker SPhP-SPP coupling than SPP coupling, the near-field enhancement for the SiC-Si sample exhibits a more pronounced monochromatic behavior with a resonant flux that is ~ 5 times larger than the resonant flux for the Si-Si sample. This work demonstrates that it is possible to modulate NFRHT via surface polariton coupling, and will accelerate the development of energy conversion and thermal management devices capitalizing on the near-field effects of thermal radiation between dissimilar materials.
关键词： radiative flux measurement,doped silicon,near-field radiative heat transfer,dissimilar materials,coupled surface phonon- and plasmon-polaritons,silicon carbide
更新于2025-09-23 15:19:57
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Twoa??dimensional model of heat flow in edgea??emitting laser revisited: A new and more versatile approach
摘要： An analytical, two-dimensional, stationary model of heat flow in edge-emitting laser is revisited. In the work, we show how to use this approach to be able to calculate the temperature of the entire device including the most susceptible for thermal runaway region, namely the vicinity of the joint of mirrors and an active layer. Numerical tools based on our considerations are implemented in Matlab code and available at the software developer's web site. A procedure of investigation of surface recombination at facets with the help of our model combined with mirror temperature measurements is proposed. To get an insight in reasonableness of our theoretical research, we calculated temperature profiles and surface recombination velocities for example devices and successfully confronted them with results found in the literature.
关键词： temperature distribution,catastrophic optical damage,edge-emitting laser,heat conduction equation,thermal analysis,mirror temperature
更新于2025-09-23 15:19:57
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Development of technology for robotic laser welding of thin-walled products from heat-resistant alloys
摘要： The results of testing the modes of robotic laser welding of spatial welded joints of thin-walled products from heat-resistant steels are considered. Comparative studies of the influence of the parameters of various methods of industrial welding on the metallography of the weld and the technological strength of the welded joint are presented. The resistance of welded joints against the formation of crystallization (hot) cracks is evaluated.
关键词： heat-resistant alloys,robotic laser welding,technological strength,metallography,crystallization cracks,thin-walled products
更新于2025-09-23 15:19:57