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Performance modeling and analysis of high-concentration multi-junction photovoltaics using advanced hybrid cooling systems
摘要： This paper presents the performance modeling and analysis of the high-concentration multi-junction photovoltaic cells, using either constant-width one-section or two-stepwise microchannels-jet impingement hybrid cooling system. The performance simulation and analysis of the cells are conducted using a three dimensional-Computational Fluid Dynamics program for various operating parameters, including water flow rate (100–1300 mL/min.), inlet water temperature (10–80 °C), and heat flux (10–90 W/cm2 corresponding to concentration ratios of 250–2250). The thermal and electrical characteristics of the cells are correlated in dimensionless form as functions of the direct normal irradiance and the operating and geometrical parameters of the hybrid cooling systems. The developed high-quality explicit performance model correlations assist in the design, performance prediction, and selection of operation strategy of photovoltaic cells. The results indicated that the generated and net output power is directly proportional to the applied heat flux (concentration ratio) and inversely proportional to the inlet water temperature. Temperature uniformity of the photovoltaic base enhances with the water flow rate, deteriorates with heat flux, and less affected by the inlet temperature, particularly for the two-sections cooling system. The pumping power increases with water flow rate and decreases as both inlet temperature or heat flux increases. Heat transfer characteristics enhance significantly with water flow rate, moderately with inlet water temperature and slightly with heat flux.
关键词： Photovoltaic performance modeling,High-concentration multi-junction photovoltaic,Operating parameters,Microchannels heat sink,Electrical power correlations
更新于2025-09-23 15:21:01
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Fabrication of millimeter-long structures in sapphire using femtosecond infrared laser pulses and selective etching
摘要： This paper analyzes laser and etching parameters to fabricate open and continuous microchannels and stacks of such microchannels in the bulk of crystalline sapphire (??-Al2O3). The structures are produced using a two-step method consisting of laser irradiation and selective etching. Infrared femtosecond laser pulses are focused in the bulk to locally render the crystalline material into amorphous. The amorphous material is, then, selectively etched in hydrofluoric acid. Amorphous sapphire shows a high etching selectivity in comparison to its crystalline state, which makes this material very attractive for a use with this technique. However, some of its properties make the processing challenging, especially during the laser-induced amorphization phase. This paper studies the effect of laser parameters by a step-by-step approach to fabricate long structures (longest dimensions up to millimeters) of different shapes inside the bulk of sapphire. The minimum cross-sectional dimensions of the resulting structures (microchannels) vary from few hundreds of nanometers for the smallest channels to tens of micrometers for the largest stacks of microchannels. The effect of the variation of repetition rate, pulse energy and channel-to-channel distance on the microchannels and stacks of microchannels is studied. SEM micrographs of polished cross-sections are used for performing a quantitative and qualitative analysis of the morphology of the structures after laser irradiation and, subsequently, after selective wet chemical etching.
关键词： Selective etching,Laser processing,Microchannels,Femtosecond laser,Sapphire
更新于2025-09-23 15:21:01
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Self-propelled water droplet movement on a laser-etched radial gradient copper surface
摘要： This paper reports the behavior of water droplets on a topography-based, radial gradient on a metallic surface. The radial gradient was designed to concentrate water in the center region through the spontaneous motion and coalescence of individual droplets on the gradient pattern. In this work, parallel microchannels having a fixed width (~25 μm) and depth (100 μm) but variable spacing were used to impart a net surface tension force to the droplet for actuation. The diameter of the radial gradient (i.e. circular test region) was approximately 18.9 mm (or, ~0.75 in.). The surfaces were fabricated using a 355 nm YVO4 laser system and then characterized using droplet injection (5–38 μL) and spray testing techniques. Injected droplets were observed to move spontaneously away from the hydrophobic outer ring region of the circle towards the hydrophilic center as designed by the gradient. Droplet travel distances as large as 4 mm were measured depending on the droplet volume and injection site location. In application, such a design could be useful for promoting droplet coalescence on a surface and subsequently removal by gravity through the formation of sufficiently large droplets from two or more otherwise small droplets.
关键词： Surface tension gradient,Microchannels,Condensation,Heat exchangers,Radial pattern,Laser etching,Water droplet
更新于2025-09-23 15:21:01
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[ASME ASME 2018 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference - Quebec City, Quebec, Canada (Sunday 26 August 2018)] Volume 4: 23rd Design for Manufacturing and the Life Cycle Conference; 12th International Conference on Micro- and Nanosystems - A Novel Method for Rapid Microfabrication
摘要： We introduce a novel microfabrication method using direct writing of photoresist with an ultrasonic microplotter equipped. First, the photoresist is driven into the pipette through capillary forces. The pipette is then used to directly write microfeatures on a polydimethylsiloxane (PDMS) substrate. The photoresist is cured on a hot-plate and used as a mold for replication. A second layer of PDMS is cast onto the mold. Once cured on a hot-plate, it is peeled off from the mold to obtain the desired microfeatures. We demonstrate that this method can be used for ultra-rapid and cost-effective fabrication of microchannels (39.65 μm wide) without need for clean room facilities.
关键词： Microchannels,PDMS,Rapid microfabrication
更新于2025-09-23 15:21:01
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Laser Direct Structuring of Bioinspired Spine with Backward Microbarbs and Hierarchical Microchannels for Ultrafast Water Transport and Efficient Fog Harvesting
摘要： Achieving effective dropwise capture and ultrafast water transport is essential for fog harvesting. In nature, Cactus uses the conical spine with micro-barbs to effectively capture fog while Sarracenia utilizes the trichome with hierarchical microchannels to quickly transport water. Herein, we combined their advantages to present a novel configuration, spine with barbs and hierarchical channels (SBHC), for simultaneous ultrafast water transport and high-efficient fog harvesting. This bio-inspired SBHC exhibited the fastest water transport ability and the highest fog harvesting efficiency in comparison with spine with hierarchical channels (SHC), spine with barbs and grooves (SBG) and spine with barbs (SB). Based on the fundamental SBHC unit, we further designed and fabricated a 2D spider-web alike fog collector and a 3D cactus alike fog collector using direct laser structuring and Origami techniques. The 2D spider-web and 3D cactus alike fog collectors showed high-efficient fog collection capacity. We envision that this fundamental understanding and rational design strategy can be applied in fog harvesting, heat transfer, liquid manipulation, and microfluidics.
关键词： Direct laser structuring,Water transport,Spine and micro-barbs,Fog harvesting,Hierarchical microchannels
更新于2025-09-23 15:19:57
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Temperature Effect on Capillary Flow Dynamics in 1D Array of Open Nanotextured Microchannels Produced by Femtosecond Laser on Silicon
摘要： Capillary ?ow of water in an array of open nanotextured microgrooves fabricated by femtosecond laser processing of silicon is studied as a function of temperature using high-speed video recording. In a temperature range of 23–80°C, the produced wicking material provides extremely fast liquid ?ow with a maximum velocity of 37 cm/s in the initial spreading stage prior to visco-inertial regime. The capillary performance of the material enhances with increasing temperature in the inertial, visco-inertial, and partially in Washburn ?ow regimes. The classic universal Washburn’s regime is observed at all studied temperatures, giving the evidence of its universality at high temperatures as well. The obtained results are of great signi?cance for creating capillary materials for applications in cooling of electronics, energy harvesting, enhancing the critical heat ?ux of industrial boilers, and Maisotsenko cycle technologies.
关键词： Maisotsenko cycle,cooling of electronics,silicon,open capillary microchannels,microstructures,nanostructures,femtosecond laser processing,capillary flow
更新于2025-09-23 15:19:57
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Effects of Laser Fluence and Pulse Overlap on Machining of Microchannels in Alumina Ceramics Using an Nd:YAG Laser
摘要： The quality of micro-features in various technologies is mostly affected by the choice of the micro-fabrication technique, which in turn results in several limitations with regard to materials, productivity, and cost. Laser beam micro-machining has a distinct edge over other non-traditional methods in terms of material choices, precision, shape complexity, and surface integrity. This study investigates the effect of laser fluence and pulse overlap while developing microchannels in alumina ceramic using an neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. Microchannels 200 μm wide with different depths were machined using different laser peak fluence and pulse overlap (percentage of overlap between successive laser pulses) values. It was found that high pulse overlaps and fluences should be avoided as they give rise to V-shaped microchannels i.e., 100% bottom width errors. The optimal peak fluence range was found to be around 125–130 J/cm2 corresponding to 3–5 μm depth per scan. In addition, channels fabricated with moderate pulse overlap were found to be of good quality compared to low pulse overlaps.
关键词： microchannels,laser,fluence,alumina,micromachining
更新于2025-09-11 14:15:04