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Energy transport analysis in a Ga <sub/>0.84</sub> In <sub/>0.16</sub> N/GaN heterostructure using microscopic Raman images employing simultaneous coaxial irradiation of two lasers
摘要： Anisotropic heat transport in a Ga0.84In0.16N/GaN-heterostructure on a sapphire substrate is observed from microscopic Raman images obtained by utilizing coaxial irradiation of two laser beams, one for heating (325 nm) in the GaInN layer and the other for signal probing (325 nm or 532 nm). The increase in temperatures of the GaInN layer and the underlying GaN layer is probed by the 325-nm and 532-nm lasers, respectively, by analyzing the shift in the Raman peak energy of the higher energy branch of E2 modes. The result reveals that energy diffuses across a considerable length in the GaInN layer, whereas the energy transport in the perpendicular direction to the GaN layer is blocked in the vicinity of mis?t dislocations on the heterointerface. This simultaneous irradiation of two lasers for heat generation and probing is effective in the microscopic analysis of energy transport through heterointerfaces.
关键词： coaxial laser irradiation,heat transport,Raman imaging,GaInN/GaN heterostructure
更新于2025-09-23 15:19:57
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Effect of temperature on the performance of perovskite solar cells
摘要： The poor stability of perovskite solar cells is a crucial obstacle for its commercial applications. Here, we investigate the thermal stability of the mixed cation organic–inorganic lead halide perovskites (FAPbI3)1?xMAPb(Br3?yCly)x films and devices in air atmosphere. The results show that with the increase of heat treatment from 25 to 250 °C, the MA-perovskite decomposed into PbI2 firstly and the efficiency of corresponding solar cells reduced linearly. For the perovskite film, the increased heat treatment temperature can bring the redshift of the absorption edge leading to the decrease of band gap from 1.569 to 1.508 eV and increase of defect density from 3.87 × 1017 cm?3 to 9.03 × 1017 cm?3. However, a proper heat treatment time (10 min) at certain temperature (85 °C) can passivate defects effectively and improve the efficiency to 16.50%, realizing a 15% relative improvement of average efficiency. This work reveals a detailed thermal decomposition behavior of perovskite material and solar cells, which may provide insights into the stability of perovskite solar cells.
关键词： defect passivation,heat treatment,perovskite solar cells,thermal stability,mixed cation organic–inorganic lead halide perovskites
更新于2025-09-23 15:19:57
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Performance analysis of photovoltaic-thermal air collectors combined with a water to air heat exchanger for renewed air conditioning in building
摘要： In this work, a new solar system that includes photovoltaic-thermal (PVT) air collectors coupled to a water-to-air heat exchanger is investigated. The considered system generates sufficient energy for cooling and heating of the ambient air injected in a 300 m2 tertiary building and saves its total energy consumption. Therefore, it allows the minimization of greenhouse gas emissions of the building. A numerical model is developed to ensure comfortable temperatures during summer and winter, including days with the highest energy needs. The results show that the proposed system can generate the required heating and cooling needs using an airflow rate equal to 0.25 kg/s and a PVT area of 17 m2. It was found that the coupling of the PVT air collectors with a water to air heat exchanger minimizes the total required area for heating by ~ 33%. Moreover, the PV module’s efficiency was enhanced by 2.0% in winter and 5.1% in summer. The thermal energy saved for heating, thermal energy saved for cooling and the electrical energy saved are, respectively, equal to 15.30 kWh/day, 24.79 kWh/day, and 3.14 kWh/day. This represents an average emission reduction of 11.4 kg CO2 per day.
关键词： Water to air heat exchanger,Energy saving,Thermal comfort in buildings,Photovoltaic air collectors,Renewable energies,Greenhouse gas emissions
更新于2025-09-23 15:19:57
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The hybrid Photovoltaic-Thermal double-pass solar system for drying applications
摘要： In this paper, is devoted to evaluating the performance of the double-pass hybrid Photovoltaic-Thermal (PVT) solar system proposed for drying purposes theoretically and experimentally as well as the system is designed, fabricate and modeled in order to simulate the productivity of this system. The hot air extracted from the PVT collector can be used as a heat source for the drying application. The critical parameter such as temperature distribution, useful heat gain, electrical power, and thermal efficiency are computed using MATLAB 2015b program built for this purpose. Results show that the higher output fluid temperature was 63°C at a lesser mass flow rate which 0.017 kg/s and the maximum efficiencies of electrical, thermal and overall at a higher mass flow rate which reached 12.65%, 56.73%, and 85% respectively at mass flow rate 0.031 kg/s. In addition, the optimum electrical power and thermal energy reached 50.57 W and 389.37 W at 0.031 kg/s.
关键词： dryer,performance,photovoltaic cell,heat gain,thermal collector
更新于2025-09-23 15:19:57
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Design of Thermophysical Properties Test System by Laser Point Heat Source Method
摘要： Laser is widely used in material thermophysical properties testing because of its good test accuracy and test efficiency. However, due to the high market price of laser flash devices, their promotion space is limited. Based on the unsteady heat transfer model of a laser point heat source, the enantiomorphous heat source theory was introduced to modify the influence of an adiabatic boundary on the temperature rise of a measuring point. The thermal conductivity and thermal diffusivity of isotropic materials were calculated by numerical analysis combined with computer programming. A thermophysical property test system was developed, and the thermophysical properties of blast furnace firebrick, marble, and diatomite brick were studied. The results showed that the maximum repeatable accuracy error was 4.75%, and the maximum relative deviation from the reference value was 2.04%. The effective test range of the device was that the thermal conductivity was less than 3 W∕(m ? K). Compared with the laser flash method, the device does not require high test-time accuracy and data collection instantaneity in terms of test principles. Therefore, the device can use a general-level laser generator, temperature sensor, timer, data collector, and so on, and the hardware cost is greatly reduced.
关键词： thermophysical properties,thermal diffusivity,test system,thermal conductivity,laser point heat source
更新于2025-09-23 15:19:57
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Study on Nitrogen-Doped Graphene Ink and Its Effects on the Heat Dissipation for the LED Lamps
摘要： This study explored the application of nitrogen-doped graphene (NDG) ink to the coating of light-emitting diode (LED) lamps for the thermal management. Unlike the general solutions of graphene, the NDG ink used in this study was tuned with high electrical resistance and quietly suitable for the application of the LED lamp coating, which prevented the short circuit problem; besides, the NDG ink also provided a high heat dissipation effect to improve the performance of the LED lamp. The investigation of adhesion and resistance for the NDG ink were conducted by the cross-cut test and the four-point probe resistance measurement, respectively. Three types of LED lamps including the original lamp, fin-removed lamp, and NDG-ink coated (NGC) lamp were tested for the actual operating temperature distribution by K-type thermal couples and for the lumens by the integrating sphere. The results showed that the heat dissipation of the NGC lamp was better than that of the original lamp. In addition, the inspections for the properties of NDG powder were also performed by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and Raman spectroscopy. According to the inspectional results, the NDG powder had a percentage of nitrogen of about 3.8% by XPS, a surface roughness Rq of 0.9 nm by AFM, and over ten layers by Raman analysis. It showed that the NDG powder in this study belonged to the type of multi-layer graphene.
关键词： integrating sphere,heat dissipation,nitrogen-doped graphene,LED
更新于2025-09-23 15:19:57
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Sequences of Sub-Microsecond Laser Pulses for Material Processing: Modeling of Coupled Gas Dynamics and Heat Transfer
摘要： Multipulse laser processing of materials is promising because of the additional possibilities to control the thickness of the treated and the heat-affected zones and the energy efficiency. To study the physics of mutual interaction of pulses at high repetition rate, a model is proposed where heat transfer in the target and gas-dynamics of vapor and ambient gas are coupled by the gas-dynamic boundary conditions of evaporation/condensation. Numerical calculations are accomplished for a substrate of an austenitic steel subjected to a 300 ns single pulse of CO2 laser and a sequence of the similar pulses with lower intensity and 10 μs inter-pulse separation assuring approximately the same thermal impact on the target. It is revealed that the pulses of the sequence interact due to heat accumulation in the target but they cannot interact through the gas phase. Evaporation is considerably more intensive at the single-pulse processing. The vapor is slightly ionized and absorbs the infrared laser radiation by inverse bremsstrahlung. The estimated absorption coefficient and the optical thickness of the vapor domain are considerably greater for the single-pulse regime. The absorption initiates optical breakdown and the ignition of plasma shielding the target from laser radiation. The multipulse laser processing can be applied to avoid plasma ignition.
关键词： laser evaporation,multipulse laser processing,laser plasma,heat transfer,gas dynamics
更新于2025-09-23 15:19:57
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One-Step Femtosecond Laser Stealth Dicing of Quartz
摘要： We report on a one-step method for cutting 250-μm-thick quartz plates using highly focused ultrashort laser pulses with a duration of 200 fs and a wavelength of 1030 nm. We show that the repetition rate, the scan speed, the pulse overlap and the pulse energy directly influence the cutting process and quality. Therefore, a suitable choice of these parameters was necessary to get single-pass stealth dicing with neat and flat cut edges. The mechanism behind the stealth dicing process was ascribed to tensile stresses generated by the relaxation of the compressive stresses originated in the laser beam focal volume during irradiation in the bulk material. Such stresses produced micro-fractures whose controlled propagation along the laser beam path led to cutting of the samples.
关键词： ultrashort laser pulses,stealth dicing,transparent materials,heat accumulation,quartz
更新于2025-09-23 15:19:57
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Investigation on the effect of power and velocity of laser beam welding on the butt weld joint on TRIP steel
摘要： In this study, the characterization of laser weld joint on transformation-induced plasticity (TRIP) steel sheets coupled with Nd:YAG laser welding was investigated, and the influence of welding conditions like angle of weld, power of laser, and welding speed on the strength of the joint was measured. The microstructure, tensile behavior, and microhardness of TRIP laser-welded sheets were examined in detail. The power was maintained constant, i.e., 1800 W, and by relatively varying the velocity from 25 to 30 mm/s, the strength of the joint increased drastically to 11%. In contrast, by varying the power, the effect of velocity was reduced; however, the point performance was enormously stable. Finally, the microhardness behavior of the heat-affected zone and fusion zone was investigated and discussed.
关键词： butt weld joint,heat treatment,TRIP steel,Nd:YAG laser,laser welding
更新于2025-09-23 15:19:57
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Laser Powder Bed Fusion of Precipitation-Hardened Martensitic Stainless Steels: A Review
摘要： Martensitic stainless steels are widely used in industries due to their high strength and good corrosion resistance performance. Precipitation-hardened (PH) martensitic stainless steels feature very high strength compared with other stainless steels, around 3-4 times the strength of austenitic stainless steels such as 304 and 316. However, the poor workability due to the high strength and hardness induced by precipitation hardening limits the extensive utilization of PH stainless steels as structural components of complex shapes. Laser powder bed fusion (L-PBF) is an attractive additive manufacturing technology, which not only exhibits the advantages of producing complex and precise parts with a short lead time, but also avoids or reduces the subsequent machining process. In this review, the microstructures of martensitic stainless steels in the as-built state, as well as the effects of process parameters, building atmosphere, and heat treatments on the microstructures, are reviewed. Then, the characteristics of defects in the as-built state and the causes are specifically analyzed. Afterward, the effect of process parameters and heat treatment conditions on mechanical properties are summarized and reviewed. Finally, the remaining issues and suggestions on future research on L-PBF of martensitic precipitation-hardened stainless steels are put forward.
关键词： 17–4 stainless steel,heat treatment,microstructure,precipitation-hardened stainless steels,ferrite,selective laser melting,building atmosphere,defects,laser powder bed fusion
更新于2025-09-23 15:19:57