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Effect of shielding gas flow on welding process of laser-arc hybrid welding and MIG welding
摘要： The influence of shielding gas on welding process of laser-arc hybrid welding (LAHW) and metal inert-gas welding (MIG) was investigated by the computational fluid dynamics analysis (CFD) and high-speed photography. The results show that the process stability of MIG under high gas flow rate is poorer than that of LAHW. And the force of gas flow Fg can hinder the droplet transfer, whether MIG or LAHW. But the vaporization-induced recoil force Fv in LAHW helps to reduce this kind of hindrance and keep the process stability. Next, it can be found that the shielded gas flow mode in the main welding area cannot be changed significantly by increasing the shielding gas flow rate, while high gas flow rate can increase the area of high argon concentration and benefit the spread of molten metal.
关键词： Welding process,Computational fluid dynamics analysis,Laser-arc hybrid welding,MIG welding
更新于2025-11-28 14:24:20
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Run-to-run control of PECVD systems: Application to a multiscale three-dimensional CFD model of silicon thin film deposition
摘要： Deposition of amorphous silicon thin films via plasma-enhanced chemical vapor deposition (PECVD) and batch-to-batch operation under run-to-run control of the associated chambered reactor are presented in this work using a recently developed multiscale, three-dimensional in space, computational fluid dynamics model. Macroscopic reactor scale behaviors are linked to the microscopic growth of amorphous silicon thin films using a dynamic boundary which is updated at each time step of the transient in-batch simulations. This novel workflow is distributed across 64 parallel computation nodes in order to reduce the significant computational demands of batch-to-batch operation and to allow for the application and evaluation in both radial and azimuthal directions across the wafer of a benchmark, run-to-run based control strategy. Using 10 successive batch deposition cycles, the exponentially weighted moving average algorithm, an industrial standard, is demonstrated to drive all wafer regions to within 1% of the desired thickness set-point in both radial and azimuthal directions across the wafer surface. This is the first demonstration of run-to-run control in reducing azimuthal film nonuniformity. Additionally, thin film uniformity is shown to be improved for poorly optimized PECVD geometries by manipulating the substrate temperature alone, without the need for re-tooling of the equipment.
关键词： thin film silicon solar cells,parallel computing,multiscale modeling,computational fluid dynamics,run-to-run control,thin film growth
更新于2025-09-23 15:21:21
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Performance evaluation and optimization of the cooling system of a hybrid thermionic-photovoltaic converter
摘要： Hybrid thermionic-photovoltaic (TIPV) converters are efficient and clean solutions for the direct conversion of thermal energy to electricity, taking advantage of both the photovoltaic and thermionic phenomena. An important hurdle for their efficient operation is the overheating of the PV cell integrated within the TIPV anode, due to partial conversion of the emitted electron and photon fluxes to thermal heat. This obstacle needs to be overcome with an efficient, yet practical, cooler. In this work, a copper plate heat spreader is experimentally tested for TIPV cathode temperatures up to 1450 °C, whilst its performance is also assessed using a validated CFD model for temperatures up to ~2000 °C. A multi-parametric analysis is conducted testing two coolants: i) a water/ethylene glycol mixture at various temperatures (?5–40 °C) and mass flow rates (0.05–0.4 kg·s?1), and, ii) cryogenic liquid nitrogen at a temperature of ?196 °C and mass flow rate of 0.074 kg·s?1. Numerical results reveal that with water/ethylene mixture the PV can withstand heat fluxes up to 360 W·cm?2, without its temperature exceeding 100 °C. For higher thermal fluxes (360–600 W·cm?2), cryogenic liquid nitrogen is found to prevent the PV overheating and, therefore, is an attractive coolant; however, it poses safety concerns due to its possible boiling. Finally, two additional cooling system designs are proposed, a heat sink with straight fins and another with copper pipes, which offer higher heat transfer areas, but are more difficult to manufacture, than the copper plate heat spreader.
关键词： Ultra-high power density,Copper plate heat spreader,Cooling system design optimization,Electronic device,Computational fluid dynamics (CFD)
更新于2025-09-23 15:21:01
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Numerical studies of metal particle behaviors inside the selective laser melting (SLM) chamber through computational fluid dynamics (CFD)
摘要： The flow behavior of the shielding gas has been a key factor to improve the quality of products manufactured by the selective laser melting (SLM) technology as it is a major mechanism to remove the ejected metal particles away from the working plane. In this study, to obtain a proper flow field, computational fluid dynamics (CFD) with the application of the Taguchi method was employed to investigate the flow field across the working chamber, with the variations in the geometries of the blowing nozzle, the widths of the suction tunnel, the suction-to-plane distances, and the Reynolds numbers of the blowing flow. The simulation was first verified with experimental measurements. The ejecting motions of the metal powders were also taken into consideration to study the interactions between the shielding gas and the ejected particles. The results demonstrated that axis switching as well as the suction-to-plane distance are the important factors for improving the particle removal efficiency during the SLM operation.
关键词： Selective laser melting,Computational fluid dynamics,Particle removal efficiency,3-D printing,Axis switching,Taguchi method
更新于2025-09-23 15:21:01
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Wind load analysis of a new linear Fresnel receiver assembly design
摘要： A linear Fresnel collector includes a low-profile reflector array and a receiver assembly with one or more absorber tubes and an optional secondary reflector. This combined optical system concentrates sunlight and converts it into thermal energy. The design of a receiver assembly is critical to the performance of a linear Fresnel collector. A position deviation of a few centimeters for the receiver assembly can result in notably reduced performance, thus leading to a direct loss in revenue associated with thermal power production. Wind load is one of the most significant environmental factors that can alter the optical—and therefore thermal—performance of a solar power system due to displacements after installation. At the same time, an over-designed receiver assembly may add unnecessary construction cost to a typically high-cost-constrained system. Thus, wind load analysis is particularly important when considering optimal engineering design of a receiver assembly and its supporting structure to cost-effectively mitigate the impacts of wind. In this study, a detailed computational fluid dynamics (CFD) model is adopted to derive the wind load of a commercial linear Fresnel receiver assembly. This wind load is then used as a reference to optimize the detailed engineering design. The CFD model is first carefully developed and benchmarked within a critical regime toward turbulence. The drag force, lift force, and vortex-shedding frequencies are derived at both the operating and survival wind-speed limits for target project deployment locations. The wind load analysis results provide a valuable reference for future engineering design and prototyping.
关键词： wind load analysis,receiver assembly,linear Fresnel collector,vortex-shedding frequencies,drag force,computational fluid dynamics,lift force
更新于2025-09-23 15:21:01
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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
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Solar gain mitigation in ventilated tiled roofs by using phase change materials
摘要： Several passive cooling design techniques are known for reducing solar heat gain through building envelope in summer season. These include the use of phase change materials (PCM), which has received an increased attention over the last years, and the strategy of increasing the above-sheathing ventilation (ASV) in ventilated roofs. However, few studies combine both technologies to maximise the building resilience in hot season. The effect of including a PCM layer into a ventilated roof is numerically analysed here in two different configurations: firstly, laid on the roof deck (PCM1 case) and, secondly, suspended in the middle of the ASV channel (PCM2 case). A computational fluid dynamics model was implemented to simulate airflow and heat transfer around and through the building envelope, under 3 days of extreme hot conditions in summer with high temperatures and low wind speed. Results showed slight differences in terms of mean temperatures at the different roof layers, although temperature fluctuations at deck in the PCM1 case were smaller than half of those estimated for the benchmark case. However, PCM2 configuration achieved a daily reduction of about 10 Wh/m2 (18%) in building energy load with respect to the benchmark case, whilst PCM1 got only 4% due to the lower ventilation at night time. Therefore, a suspended PCM layer in the ASV channel would be a better measure in terms of energy performance than laid on the deck surface, although this last option significantly decreases thermal stress of the insulation layer.
关键词： passive cooling technique,ventilated pitched roof,computational fluid dynamics,phase change material
更新于2025-09-23 15:19:57
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Theoretical and Numerical Study of a Photovoltaic System with Active Fluid Cooling by a Fully-Coupled 3D Thermal and Electric Model
摘要： The paper deals with the three-dimensional theoretical and numerical investigation of the electrical performance of a Photovoltaic System (PV) with active fluid cooling (PVFC) in order to increase its efficiency in converting solar radiation into electricity. The paper represents a refinement of a previous study by the authors in which a one-dimensional theoretical model was presented to evaluate the best compromise, in terms of fluid flow rate, of net power gain in a cooled PV system. The PV system includes 20 modules cooled by a fluid circulating on the bottom, the piping network, and the circulating pump. The fully coupled thermal and electrical model was developed in a three-dimensional geometry and the results were discussed with respect to the one-dimensional approximation and to experimental tests. Numerical simulations show that a competitive mechanism between the power gain due to the cell temperature reduction and the power consumption of the pump exists, and that a best compromise, in terms of fluid flow rate, can be found. The optimum flow rate can be automatically calculated by using a semi-analytical approach in which irradiance and ambient temperature of the site are known and the piping network losses are fully characterized.
关键词： thermal–electrical model,solar energy,photovoltaic modules,active cooling,computational fluid dynamics (CFD)
更新于2025-09-16 10:30:52
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Effect of plasmonic lens distribution on flight characteristics in rotational near-field photolithography
摘要： Rotational near-?eld photolithography exposes photoresists by exciting surface plasmon polaritons to realize nanopatterns with ultrahigh-resolution beyond the di?raction limit. This feature enables broad application prospects in the micro-nanomanufacturing ?eld. The lithography ?ight head, carrying a plasmonic lens (PL), with an approximately 10 nm spacer from the substrate, is the core of the system for e?ective etching. This paper investigates the ?ight state of a PL-loaded lithography head on the air ?lm, based on computational ?uid dynamics analysis. We found that the in?uence of the PL on the ?ight height produces an edge e?ect. This means that a PL fabricated on the edge region can signi?cantly a?ect the ?ight height of the head. By processing the PL at a distance of 10 μm from the edge of the slider tail block, a steady 37 nm linewidth depth pattern was ?nally realized, using a rotational near-?eld photolithography system.
关键词： edge effect,rotational near-field photolithography,flight characteristics,plasmonic lens,computational fluid dynamics
更新于2025-09-12 10:27:22
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Thermo-fluid-metallurgical modelling of the selective laser melting process chain
摘要： The entire process chain of selective laser melting of Ti-6Al-4V is analysed. First, a thermo-fluid dynamical model is used to investigate the temperature profile during the process and estimate the size and shape of the melt pool. The inclusion of the Marangoni effect improves upon previous work by showing the liquid velocity in the melt pool. Next, this information allows us to estimate the morphology of the grains of a part produced by selective laser melting. Finally, a cellular automata is used to model the microstructural evolution during a uniform heat treatment at the beta transus temperature. It is shown that the model shows good agreement with earlier experimental results.
关键词： selective laser melting,Ti6Al4V,computational fluid dynamics,thermal modelling,microstructural modelling
更新于2025-09-12 10:27:22