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Thermophotonic cooling with light-emitting diodes
摘要： The currently ubiquitous light-emitting diodes (LEDs) have revolutionized the lighting industry. Contrary to common belief, however, LEDs are much more than just simple electricity-to-light converters. They are solid-state thermodynamic machines, theoretically capable of continuous and near-reversible energy conversion between electrical, thermal and optical energy. For over 50 years, the possibility of exploiting LEDs as efficient solid-state coolers has remained largely out of reach due to the high-material-quality requirements and commercial focus on light emission. Recent promising advances in electroluminescent cooling by LEDs, however, suggest that the remaining challenges in the area may be surmountable and practical cooling could be feasible. This Perspective discusses recent achievements in electroluminescent cooling, outlining the expected promise, the remaining challenges and their potential solutions.
关键词： solid-state thermodynamic machines,light-emitting diodes,electroluminescent cooling,LEDs,thermophotonic cooling
更新于2025-09-23 15:19:57
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Towards Sympathetic Cooling of Highly Charged Ions by Laser-Cooled Ca+ Ions
摘要： The long-term goal of the Penning trap system for the heavy ion accelerator named RAON in Korea is to obtain an order of magnitude higher mass accuracy for short-lived rare isotopes. For that purpose, we are developing a sympathetic cooler for highly charged ions by exploiting laser-cooled Ca+ ions. We installed a prototype octagon chamber with a calcium atom source, a Paul trap, and a helical resonator for the high-voltage RF supply. The laser system is composed of three extended cavity diode lasers (423, 397, 866 nm) plus one UV diode laser (375 nm). The optical frequency stabilization setup is made up of a wavelength meter, a multichannel fiber switch and a PXI system with an 8-channel analog output module. After having obtained a resonant ionization signal from the calcium atomic beam, we applied the RF voltage to the trap electrodes and illuminated the cooling lasers at the center of the trap. We successfully observed a laser-cooled ion bunch and a linearly aligned ion string by using imaging optics and an electron multiplying charge coupled device (EMCCD) camera. In addition to the experimental effort, we performed a simulation study for cooling 132Sn10+ ions inside a laser-cooled 40Ca+ Coulomb crystal by using a parallel computation technique.
关键词： Ion trap,Sympathetic cooling,Laser cooling
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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Production Tools Made by Additive Manufacturing Through Laser-based Powder Bed Fusion; Herstellung von Produktionswerkzeugen mittels additiver Fertigung durch laserbasiertes Pulverbettschmelzen;
摘要： This paper deals with the design and production of stamping tools and dies for sheet metal components and injection molds for plastic components. Laser-based Powder Bed Fusion (LPBF) is the additive manufacturing method used in this investigation. Solid and topology optimized stamping tools and dies 3D-printed in DIN 1.2709 (maraging steel) by LPBF are approved/certified for stamping of up to 2-mm thick hot-dip galvanized DP600 (dual-phase steel sheet). The punch in a working station in a progressive die used for stamping of 1-mm thick hot-dip galvanized DP600 is 3D-printed in DIN 1.2709, both with a honeycomb inner structure and after topology optimization, with successful results. 3D printing results in a significant lead time reduction and improved tool material efficiency. The cost of 3D-printed stamping tools and dies is higher than the cost of those made conventionally. The core (inserts) of an injection mold is 3D-printed in DIN 1.2709, conformal cooling optimized and 3D-printed in Uddeholm AM Corrax, and compared with the same core made conventionally. The cooling and cycle time can be improved, if the injection molding core (inserts) is optimized and 3D-printed in Uddeholm AM Corrax. This paper accounts for the results obtained in the above-mentioned investigations.
关键词： Design,Injection molding,Tools,Stamping,Powder bed fusion,Optimization,Topology,Metal,Additive manufacturing,Cooling
更新于2025-09-23 15:19:57
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Assessment of laser power and scan speed influence on microstructural features and consolidation of AISI H13 tool steel processed by additive manufacturing
摘要： Additive manufacturing can produce parts with complex geometries in fewer steps than conventional processing, which leads to cost reduction and a higher quality of goods. One potential application is the production of molds and dies with conformal cooling for injection molding, die casting, and forging. AISI H13 tool steel is typically used in these applications because of its high hardness at elevated temperatures, high wear resistance, and good toughness. However, available data on the processing of H13 steel by additive manufacturing are still scarce. Thus, this study focused on the processability of H13 tool steel by powder bed fusion and its microstructural characterization. Laser power (97-216 W) and scan speed (300-700 mm/s) were varied, and the consolidation of parts, common defects, solidification structure, microstructure, and hardness were evaluated. Over the range of processing parameters, microstructural features were mostly identical, consisting of a predominantly cellular solidification structure. Cellular/dendritic solidification structure displayed C, Cr, and V segregation toward cell walls. The thermal cycle resulted in alternating layers of heat-affected zones, which varied somewhat in hardness and microstructure. Retained austenite was correlated to the solidification structure and displayed a preferential orientation with {001}//build direction. Density and porosity maps were obtained by helium gas pycnometry and light optical microscopy, respectively, and, along with linear crack density, were used to determine appropriate processing parameters for H13 tool steel. Thermal diffusivity, thermal conductivity, and thermal capacity were measured to determine dimensionless processing parameters, which were then compared to others reported in the literature.
关键词： retained austenite,powder bed fusion,additive manufacturing,conformal cooling,processing parameters
更新于2025-09-23 15:19:57
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Study on mechanical and metallurgical properties of fiber laser welded Nb-1% Zr-0.1% C alloy
摘要： Laser welding of Nb-1% Zr-0.1% C was attempted in butt-welding configuration using top and bottom sided inert gas shielding. The precautionary measure during welding was to limit the reactivity of niobium alloy in ambient atmosphere. The ranges of input parameters, that is, laser power (P), welding speed (V) and beam diameter (D) for full penetration welding were attempted by carrying out bead-on-plate (BOP) experiments. The selection of the combination of process parameters was such that the formed weld area could be minimized without hampering the depth of penetration. Bead-geometry, hardness and tensile strength were quantified to study the influence of input process parameters during laser welding. Base metal had an average hardness of 108 VHN and the average hardness of fusion zone (FZ) was found to lie between 278 and 546 VHN. The steeper increment in microhardness value of the FZ could be due to the grain refinement, dissolution of precipitates and formation of brittle intermetallic phases of carbide and oxides, which were evident by the result of energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) phase analysis. The weld joint that failed in the weld zone exhibited the brittle failure, and ductile mode was achieved in the joint, where failure occurs at base metal. The range of elongation in laser welded joints varied in between 1.97 and 5.73 mm. The reduction of tensile strength and ductility of the joints could be due to marginal enhancement of microhardness and increment of brittle phase density in fusion zone, as were evident from XRD phase analysis. The main focus of the present work was intended towards the establishment of laser welding as an alternative technique for fabrication of reactive niobium alloy in ambient atmosphere.
关键词： Cooling rate,Laser welding,Grain refinement,Niobium alloy,Mechanical properties,Nb-1% Zr-0.1% C
更新于2025-09-23 15:19:57
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Strongly Correlated Quantum Gas Prepared by Direct Laser Cooling
摘要： We create a one-dimensional strongly correlated quantum gas of 133Cs atoms with attractive interactions by direct laser cooling in 300 ms. After compressing and cooling the optically trapped atoms to the vibrational ground state along two tightly confined directions, the emergence of a non-Gaussian time-of-flight distribution along the third, weakly confined direction reveals that the system enters a quantum degenerate regime. We observe a reduction of two- and three-body spatial correlations and infer that the atoms are directly cooled into a highly correlated excited metastable state, known as a super-Tonks-Girardeau gas.
关键词： super-Tonks-Girardeau gas,quantum gas,strongly correlated,laser cooling
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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Characterization of form-stable phase-change material for solar photovoltaic cooling
摘要： Solar PV panel cooling is essential to achieve maximum efficiency of PV modules. Phase-change material (PCM) is one of the prominent options to cool the panel and reduce the temperature, since PCMs have low thermal conductivity. Expanded graphite particles are used to enrich the structure and stability as well as to increase the thermal properties. In the present research work, polyethylene glycol (PEG) 1000 is used as a base material and expanded graphite for inclusive particle. A novel form-stable PEG1000/EG composite PCM mixture is prepared, using impregnation and dispersion method. Expanded graphite and PEG1000/EG sample phase compositions are investigated, using X-ray diffraction technique. No new peak is identified in the composite PCM sample. The surface morphology and structure of EG and PEG1000/EG are investigated, using scanning electron microscopy (SEM). Chemical stability analysis is done by Fourier-transform infrared spectroscopy. Thermal properties of the prepared composite PCMs are analysed by differential scanning calorimetry, thermogravimetric analysis (TGA) and KD2 pro analyser. Results show that addition of EG in various propositions (5%, 10% and 15%) enhances the thermal conductivity of PCM samples from 0.3654 to 1.7866 W mK?1, while melting point and latent heat of fusion of PCM samples are getting reduced. TGA thermographs are used to investigate the thermal stability of the composite PCM samples. TGA curves show that loss of mass happens above the operating temperature, and it is varied with different mass ratios of EG. Characterization of the prepared composite PCM samples is compared and found that PEG1000-85%/EG-15% is the best form-stable PCM, suitable for cooling the solar PV panel as well as to improve the electrical efficiency coupled with a decrease of temperature in the range of 35 °C to 40 °C.
关键词： PEG1000 PCM material,Solar PV cooling,Expanded graphite,Thermal storage,DSC,Characterization
更新于2025-09-23 15:19:57
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A new approach for photovoltaic module cooling technique evaluation and comparison using the temperature dependent photovoltaic power ratio
摘要： Many photovoltaic module cooling techniques are available to reduce the solar cell temperature, resulting in enhanced e?ciency. Although the power of the photovoltaic module is usually reported as a measure for the performance of the cooling technique, the performance assessment and comparison among di?erent coolers become di?cult if di?erent photovoltaic module’s reference power is being utilized. The existing method requires calculations to be done repeatedly to obtain the photovoltaic module’s power, for any given value of the reference power. In order to compare the performance of the coolers, the use of the same reference power is needed, resulting in a lengthy process. Hence, a new assessment method is proposed, based on the temperature dependent photovoltaic module’s power ratio that is de?ned and derived. The new method identi?es the relevant parameters that are essential for measuring the performance of the cooler such as the power of a photovoltaic module with a cooler and the reference power at photovoltaic module’s standard test conditions. The outcome is that the calculation of the unknown power for di?erent reference power can be instantly obtained and the performance comparison among di?erent coolers become simple without going through the lengthy process as it is in the case of the existing method. It is shown that the proposed method has the same results as the existing method which is experimentally validated. This is evidence to support the new method which may have potential to be applied by photovoltaic module cooling techniques designers.
关键词： Photovoltaic power ratio,Comparison,Cooling techniques,Photovoltaic module,Evaluation,Photovoltaic e?ciency
更新于2025-09-23 15:19:57