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A novel computational supplement to an IR-thermography based non-destructive test of electrofusion polyethylene joints
摘要： Electrofusion Polyethylene (PE) joints are important elements of the gas distribution networks. Unfortunately they are prone to leakage if not tested thoroughly. Our team has recently proposed a novel noncontact and IR thermal non-destructive test for these PE joints. That is, to induce a controlled heat pulse within the joint via its internal wire, and compare its thermal response with other experimental reference cases. Two gaps exist in this method due to the lack of access to a mathematical model. Firstly the pulsing duration at different initial temperatures are only determined by trial and errors. Secondly, preparing experimental reference thermal images at different joint conditions is considerably costly. Therefore, here we rigorously simulate this pulsing process to tackle both abovementioned shortcomings. We experimentally validate our simulation and report the appropriate pulsing durations between 300 K and 320 K initial temperatures. Moreover, we successfully screen a contaminated joint nondestructively.
关键词： Non destructive testing,Dynamic heat transfer,Non-contact IR test,Electrofusion polyethylene joint,IR thermal imaging
更新于2025-09-23 15:21:01
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Thermal design for the package of high-power single-emitter laser diodes
摘要： An analytical three-dimensional thermal model is employed to perform the thermal design for the package of high-power single-emitter laser diodes. Thermal design curves for the heat sink and submount are presented in detail, for laser diodes subjected to several convective heat transfer conditions on the bottom of the heat sink. An effective heat spreading angle is proposed to characterize thermal design for the heat sink. A differential heat spreading angle is proposed to clearly manifest heat flow in the packages. Full width and length at 90% energy are introduced to reveal the requirement of submount width and length, respectively. The impact of coefficient of thermal expansion (CTE)-matched sandwiched submount on total heat dissipation is studied. Special discussion is presented for a commercial F-Mount laser diode, and it is found that current heat sink design leads to a 27.4% increase in thermal resistance relative to a free lateral diffusion package.
关键词： Thermal resistance,Heat spreading angle,Submount,Heat sink,Thermal design,High-power laser diodes
更新于2025-09-23 15:19:57
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Metastable Behavior on Cesium Fluoridea??Treated Cu(In <sub/> 1a?? <i>x</i> </sub> ,Ga <sub/><i>x</i> </sub> )Se <sub/>2</sub> Solar Cells
摘要： Metastable behavior of cesium fluoride (CsF)-treated Cu(In1–x,Gax)Se2 (CIGS) solar cells is investigated under heat-light soaking (HLS) and heat-soaking (HS) treatments. HLS increases open-circuit voltage, fill factor, efficiency, and net carrier concentration and decreases short-circuit current density, whereas heat-soaking treatment acts oppositely. The performance of a CsF postdeposition treatment to CIGS thin film in selenium vapor, and closer to stoichiometry copper content, did not mitigate the open-circuit voltage improvement after HLS. These results argue the traditional concept of the VSe–VCu divacancy complex for the total beneficial effect of HLS in alkali-treated CIGS solar cells. The metastable behavior observed in the CsF-treated devices due to the HLS and HS treatments is explained by the specific behavior of alkali-containing new compounds at the surface and/or the migration of alkali metals at the surface and bulk regions.
关键词： heat soaking,heat-light soaking,metastable behavior,high efficiency,CsF-postdeposition treatment
更新于2025-09-23 15:19:57
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Estimation of the performance limits of a concentrator solar cell coupled with a micro heat sink based on a finite element simulation
摘要： Concentrated photovoltaic (CPV) technology makes use of cheap optical elements to amplify the irradiance and focus it on small-sized solar cells enabling the extraction of higher amounts of electricity. However, increasing the solar concentration raises the temperature of the PV cell which can deter its performance and can also cause its failure. To combat this issue both active and passive cooling mechanisms are utilized for different types of CPV systems. In this study, we determine the limits of passive cooling systems and establish when an active cooling system is needed based on the recommended operating temperature of the solar cell. We investigate the temperature characteristics of the solar cells bonded to three different substrate materials under different solar concentrations. Results showed that cell temperature is linearly dependent on the concentration ratio and ambient temperature independent of the substrate material. Further, the integration of a micro-finned heatsink results in higher heat dissipation by 25.32%, 23.13%, and 22.24% in comparison with a flat plate heatsink for Direct Bonded Copper (DBC), Insulated Metal Substrate (IMS), and Silicon Wafer (Si wafer) substrates respectively. The low thermal resistance of the IMS substrate compared to the DBC and the Si wafer substrates result in the best thermal performance in terms of maintaining the cell temperature < 80 °C and allowing a wider range of high concentration ratio.
关键词： Concentration Ratio,Passive cooling,micro fin heat-sink,finite element,Concentrating Photovoltaic,flat-plate heat-sink
更新于2025-09-23 15:19:57
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Comparative analysis of different cooling fin types for countering LED luminaires' heat problems
摘要： A significant problem with high-power LED luminaires is heat. Aluminum heat sinks have been extensively used as a solution. The most common method for heat sinks that increases surface area uses fins. In the present study, pin- and plate-fins were compared and it was observed that, in equal surface areas, better cooling was achieved by pin-fins. Thus, the study’s concentration narrowed to pin-fins and the results of different pin-fins were compared. Simulations of a sample group were conducted by using different numbers of fins, and the number of fins giving the lowest Tmax value (the highest junction point temperature) was accepted to be optimum for each group; then the optimum values were compared among the different groups. Keeping the base width of fins constant, optimum values were obtained for the same number of fins when the fin height was changed. However, keeping fin height constant, surface areas of optimum values and measured Tmax values were very close to one another other, even if the base width of fins was changed. The results have practical significance in designing high-power LED luminaires.
关键词： LED cooling,fin height,junction point temperature,base width,High-power LED luminaire,plate-fin heat sink,pin-fin heat sink
更新于2025-09-23 15:19:57
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Performance enhancement of graphene-coated micro heat pipes for light-emitting diode cooling
摘要： The rate of water transport through graphene nanocapillaries is profoundly enhanced compared to that in microscale capillaries due to the prevalence of exceptionally high capillary pressures and large slip lengths. As an inaugural study, we integrate graphene nanocapillaries into a micro heat pipe (MHP) for enhanced light-emitting diode (LED) cooling. With the use of graphene nanocapillaries, the ultrafast water transport synergically enhances the water circulation and evaporation process in the microfluidic device. The graphene-coated MHP achieves more than 45% enhancement in the overall performance compared to the uncoated counterpart. In turn, the experiments demonstrate a drastic reduction of LED’s operating temperature (more than 25 °C) which translates into a significantly prolonged lifespan of LED. The molecular dynamics simulations reveal that the oxygenated functional groups attached on graphene further increase the capillary pressure (~1000 bar) and effective velocity (~20 m/s) of the nanoconfined water, compared to those (~500 bar and ~10 m/s) in a pristine graphene nanochannel. The ultrafast water transport in graphene nanocapillary is justified. This study provides a holistic analysis and important insight into the phenomenon of ultrafast water transport in graphene nanocapillaries that exhibits an enormous potential in thermal energy management applications for LED cooling.
关键词： Electronics cooling,Micro heat pipe,Graphene nanocapillaries,Ultrafast water transport
更新于2025-09-23 15:19:57
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Application of Atom Probe Tomography to Complex Microstructures of Laser Additively Manufactured Samples
摘要： Additive Manufacturing (AM) technologies have gained increasing interest across multiple industrial sectors ranging from biomedical to aerospace. AM is not only used for prototyping, but also for tooling as well as for final part production. The computer-controlled, layer-by-layer building up process allows for increased design freedom enabling to produce almost any shape. Additional benefits are potential resource efficiency, increased product customization and lightweight design. Two prominent metal-based laser AM (LAM) techniques are laser powder bed fusion (LPBF) and laser metal deposition (LMD). In LPBF, a focused laser beam is scanned over a bed filled with metal powder to locally melt and fuse the powder to produce fully dense metal parts. The next layer of powder is then distributed and the laser scans again. LMD is a nozzle-based AM process in which a focused laser beam creates a melt pool in the build’s surface. Metallic powder is then injected into the melt pool through a nozzle. The 3D part is built by moving the nozzle/laser assembly forward track by track and layer by layer. Material produced by LAM exhibits a unique thermal history: initially, the material is cooled rapidly from the liquid state in the meltpool. Subsequently, the material experiences a cyclic reheating, the so-called intrinsic heat treatment (IHT), as neighboring tracks and further layers are deposited during the LAM process. Consequences of this thermal history are very complex, sometimes hierarchical microstructures with inhomogeneities at scales ranging from nanometers up millimeters. Fully understanding and characterizing these microstructures is challenging and requires the combination of methods spanning a similar range: from light optical microscopy (LOM) to electron microscopy to atom probe tomography (APT). Here we present examples how APT can deliver valuable information on complex microstructures to better understand the IHT, rapid solidification as well as phase separation in different metallic alloys. Here I will discuss examples in steel, Al- and Ni-based superalloys, and high entropy alloys (HEA).
关键词： Laser Additive Manufacturing,Additive Manufacturing,Phase Separation,Microstructures,Atom Probe Tomography,Rapid Solidification,Intrinsic Heat Treatment
更新于2025-09-23 15:19:57
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Multi-physics modelling of molten pool development and track formation in multi-track, multi-layer and multi-material selective laser melting
摘要： Selective laser melting (SLM) is a promising powder-based additive manufacturing technology due to its capability to fabricate metallic components with complex geometries. While most previous investigations focus on printing with a single material, recent industry-orientated studies indicate the need for multi-material SLM in several high-value manufacturing sectors including medical devices, aerospace and automotive industries. However, understanding the underlying physics in multi-material SLM remains challenging due to the di?culties of experimental observation. In this paper, an integrated modelling framework for multi-track, multi-layer and multi-material SLM is developed to advance the in-depth understanding of this process. The main novelty is in modelling the molten pool evolvement and track morphology of multiple materials deposited on the same and across different layers. Discrete element method (DEM) is employed to reproduce the powder deposition process of multiple materials in different deposition patterns, with particle size distribution imported from a particle size analyser. Various phenomena including balling effect, keyhole depression, and lack of fusion between layers are investigated with different laser energy inputs. As a result of the different thermal properties, several process parameters including energy density and hatch spacing are optimised for different powder materials to obtain a continuous track pro?le and improved scanning e?ciency. The interface between two layers of different materials is visualised by simulation; it was found that the phase migration at the interface is related to the convection ?ow inside the molten pool, which contributes to the mixing of the two materials and elemental diffusion. This study signi?cantly contributes to the challenging area of multi-material additive manufacturing by providing a greater in-depth understanding of the SLM process from multi-material powder deposition to laser interaction with powders across multiple scanning tracks and different building layers than can be achieved by experimentation alone.
关键词： Additive manufacturing,Discrete element method (DEM),Computational ?uid dynamics (CFD),Heat transfer,Multi-material,Selective laser melting (SLM)
更新于2025-09-23 15:19:57
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Process studies on copper laser beam welding over gap by using disc laser at green wavelength
摘要： The increasing demand for the substitution of the internal combustion engine vehicles to the battery electric vehicles requires beside battery cells high performance power electronic devices such as power control units (PCU). However, a combined requirement of high junction temperature stability and a large joint area of the interconnection on the PCU is a challenge for the conventional joining method such as soldering and wire bonding process. The Laser Impulse Metal Bonding (LIMBO) process enables a high temperature stable weld joint and large joint area. During the LIMBO process only minimized thermal stress is induced into the underlying substrate by a spatial separation between both joining partners in an overlap configuration with a gap. Hence, an energetic separation between the melting and joining phase is given. In this paper, the LIMBO process is firstly investigated with the disc laser at wavelength λ = 515 nm. Due to the enhanced absorptivity of the laser beam at this wavelength on copper material, the process duration of the LIMBO process is about the half compared to the LIMBO process with wavelength λ = 1064 nm.
关键词： Shadow projection,Green laser beam,Heat conduction welding mode,Laser beam micro joining,LIMBO
更新于2025-09-23 15:19:57
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Correlation between laser energetic parameters and magnetic properties of GO laminations under surface treatments with long, short or ultra-short pulsed lasers
摘要： Electromagnetic components mostly incorporate soft magnetic materials used as flux multipliers. Hence, any reduction in iron loss of the magnetic core yields in saving energy. Among the techniques, the local laser treatment is a non-contact method applied for 180° domain refinement (Patri et al. [1]). The present study reassessed the impact of laser treatment on the magnetic properties of grain oriented silicon steels. Various laser pulse widths are used: an ultra-short pulse laser mainly adapted to the ablation process and a long and short pulse durations used for both irradiation and scribing processes [2]. The power loss is measured with a Single Sheet Tester (150 × 150 mm2). Each type of treatment resulted in a power loss reduction of 15–35% at peak induction 1.5 T and frequency 50 Hz. However, only the scribing and the ablation improved also the apparent permeability. In this work, the laser energy parameters are used to estimate the laser impact on the heat affected zone, the groove depth, the induced thermal stress, and on the internal properties of a magnetic behavioral model: static permeability and dynamic magnetization property [3].
关键词： Groove depth,Heat affected zone,GO laminations,Induced thermal stress,Laser treatment,Magnetic properties
更新于2025-09-23 15:19:57