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Статті в журналах з теми "Radiative thermal diodes":
1
Tan, Yixuan, Baoan Liu, Sheng Shen, and Zongfu Yu. "Enhancing radiative energy transfer through thermal extraction." Nanophotonics 5, no. 1 (June 1, 2016): 22–30. http://dx.doi.org/10.1515/nanoph-2016-0008.
Анотація:
Abstract Thermal radiation plays an increasingly important role in many emerging energy technologies, such as thermophotovoltaics, passive radiative cooling and wearable cooling clothes [1]. One of the fundamental constraints in thermal radiation is the Stefan-Boltzmann law, which limits the maximum power of far-field radiation to P0 = σT4S, where σ is the Boltzmann constant, S and T are the area and the temperature of the emitter, respectively (Fig. 1a). In order to overcome this limit, it has been shown that near-field radiations could have an energy density that is orders of magnitude greater than the Stefan-Boltzmann law [2-7]. Unfortunately, such near-field radiation transfer is spatially confined and cannot carry radiative heat to the far field. Recently, a new concept of thermal extraction was proposed [8] to enhance far-field thermal emission, which, conceptually, operates on a principle similar to oil immersion lenses and light extraction in light-emitting diodes using solid immersion lens to increase light output [62].Thermal extraction allows a blackbody to radiate more energy to the far field than the apparent limit of the Stefan-Boltzmann law without breaking the second law of thermodynamics.Thermal extraction works by using a specially designed thermal extractor to convert and guide the near-field energy to the far field, as shown in Fig. 1b. The same blackbody as shown in Fig. 1a is placed closely below the thermal extractor with a spacing smaller than the thermal wavelength. The near-field coupling transfers radiative energy with a density greater than σT4. The thermal extractor, made from transparent and high-index or structured materials, does not emit or absorb any radiation. It transforms the near-field energy and sends it toward the far field. As a result, the total amount of far-field radiative heat dissipated by the same blackbody is greatly enhanced above SσT4, where S is the area of the emitter. This paper will review the progress in thermal extraction. It is organized as follows. In Section 1, we will discuss the theory of thermal extraction [8]. In Section 2, we review an experimental implementation based on natural materials as the thermal extractor [8]. Lastly, in Section 3, we review the experiment that uses structured metamaterials as thermal extractors to enhance optical density of states and far-field emission [9].
2
Kasali, Suraju Olawale, Jose Ordonez-Miranda, and Karl Joulain. "Optimization of the rectification factor of radiative thermal diodes based on two phase-change materials." International Journal of Heat and Mass Transfer 154 (June 2020): 119739. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2020.119739.
3
Lin, Yuan-Chih, Marco Bettinelli, Suchinder K. Sharma, Britta Redlich, Adolfo Speghini, and Maths Karlsson. "Unraveling the impact of different thermal quenching routes on the luminescence efficiency of the Y3Al5O12:Ce3+ phosphor for white light emitting diodes." Journal of Materials Chemistry C 8, no. 40 (2020): 14015–27. http://dx.doi.org/10.1039/d0tc03821k.
4
Shen, Dongyang, Chengzhao Luo, Ronghong Zheng, Qinyi Li, and Yu Chen. "Improvement of photoluminescence intensity and film morphology of perovskite by Ionic liquids additive." E3S Web of Conferences 257 (2021): 03066. http://dx.doi.org/10.1051/e3sconf/202125703066.
Анотація:
Metal halide perovskites have received much attention for their application in light-emitting diodes (LEDs) and solar cells in the past several years. Among them, 2D and quasi-2D perovskite with organic long-chain cations introduced have drawn significant attention. However, while improving wet and thermal stability, as the grain size becomes smaller, more defects introduced at the grain boundary and surface, resulting in the increase of non-radiative recombination is becoming the main problem which should be faced by 2D/quasi-2D perovskite materials. Here, we report a new strategy employing ionic liquid named 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide(EMB).By adding a small amount of ionic liquid to the precursor, the defect was effectively passivated and the photoluminescence intensity was increased by 11 times and the fluorescent lifetime was increased by about 1.5 times. The flatness of the prepared perovskite thin films has also been effectively improved.
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Patel, Ruchita R., G. K. Solanki, N. N. Gosai, and Rahul B. Patel. "DVT Grown GeSe Single Crystals and their Thermal Parameters in N2." Advanced Materials Research 665 (February 2013): 8–14. http://dx.doi.org/10.4028/www.scientific.net/amr.665.8.
Анотація:
Most of the applications of semiconductors involve either photon absorption to form free carriers (photodetectors or solar cells) or the formation of photons by free carrier recombination (light emittiing diodes or lasers). Both kinds of applications require high quality single crystals having desirable dimensions, devoid of defects, grain boundaries, or impurities that act as electron scatterers, traps and non radiative recombination centers. As a consequence of the requirement of high quality, fabrication and growth conditions for the semiconductors must be carefully controlled for most applications. Hence single crystals of GeSe were grown by Direct Vapor Transport (DVT) technique, in a two zone horizontal furnace with temperature difference of 50 K between growth and source zones. The material crystallizes in the form of shining gray and platelets like crystals at the end of growth cycles. Thermogravimetric analysis (TGA) has been used for many years to evaluate thermal stability of material as it will determine the range of stable operation for a device made up out of these materials under investigation. Thermal characteristics of GeSe crystals were studied employing thermoanalytical techniques, viz. TGA and DTA. Thermal analysis experiments were carried out with constant heating rate of 10 °C/ min in N2. The objective of this study is to determine activation energy and other kinetic parameters of GeSe crystals. Broido and Coats-Redfern (C-R) methods are used to evaluate different kinetic parameters of GeSe crystals viz. activation energy, entropy, enthalpy, Gibbs mean free energy etc.
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Zhou, Zhiguang, Enas Sakr, Yubo Sun, and Peter Bermel. "Solar thermophotovoltaics: reshaping the solar spectrum." Nanophotonics 5, no. 1 (June 1, 2016): 1–21. http://dx.doi.org/10.1515/nanoph-2016-0011.
Анотація:
Abstract Recently, there has been increasing interest in utilizing solar thermophotovoltaics (STPV) to convert sunlight into electricity, given their potential to exceed the Shockley-Queisser limit. Encouragingly, there have also been several recent demonstrations of improved system-level efficiency as high as 6.2%. In this work, we review prior work in the field, with particular emphasis on the role of several key principles in their experimental operation, performance, and reliability. In particular, for the problem of designing selective solar absorbers, we consider the trade-off between solar absorption and thermal losses, particularly radiative and convective mechanisms. For the selective thermal emitters, we consider the tradeoff between emission at critical wavelengths and parasitic losses. Then for the thermophotovoltaic (TPV) diodes, we consider the trade-off between increasing the potential short-circuit current, and maintaining a reasonable opencircuit voltage. This treatment parallels the historic development of the field, but also connects early insights with recent developments in adjacent fields.With these various components connecting in multiple ways, a system-level end-to-end modeling approach is necessary for a comprehensive understanding and appropriate improvement of STPV systems. This approach will ultimately allow researchers to design STPV systems capable of exceeding recently demonstrated efficiency values.
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Sheikhi, Moheb, Yijun Dai, Mei Cui, Liang Li, Jianzhe Liu, Wenan Lan, Rongrong Jiang, Wei Guo, Kuan W. A. Chee, and Jichun Ye. "On the Luminescence Properties and Surface Passivation Mechanism of III- and N-Polar Nanopillar Ultraviolet Multiple-Quantum-Well Light Emitting Diodes." Micromachines 11, no. 6 (June 5, 2020): 572. http://dx.doi.org/10.3390/mi11060572.
Анотація:
The non-centrosymmetricity of III-nitride wurtzite crystals enables metal or nitrogen polarity with dramatically different surface energies and optical properties. In this work, III-polar and N-polar nanostructured ultraviolet multiple quantum wells (UV-MQWs) were fabricated by nanosphere lithography and reactive ion etching. The influence of KOH etching and rapid thermal annealing treatments on the luminescence behaviors were carefully investigated, showing a maximum enhancement factor of 2.4 in emission intensity for III-polar nanopillars, but no significant improvement for N-polar nanopillars. The discrepancy in optical behaviors between III- and N-polar nanopillar MQWs stems from carrier localization in III-polar surface, as indium compositional inhomogeneity is discovered by cathodoluminescence mapping, and a defect-insensitive emission property is observed. Therefore, non-radiative recombination centers such as threading dislocations or point defects are unlikely to influence the optical property even after post-fabrication surface treatment. This work lays solid foundation for future study on the effects of surface treatment on III- and N-polar nanostructured light-emitting-diodes and provides a promising route for the design of nanostructure photonic devices.
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Huang, Yaren, Benedikt Lechner, and Gerhard Wachutka. "Comparative Numerical Analysis of the Robustness of Si and SiC PiN Diodes Against Cosmic Radiation-Induced Failure." Materials Science Forum 1004 (July 2020): 1088–96. http://dx.doi.org/10.4028/www.scientific.net/msf.1004.1088.
Анотація:
This work aims at extending the predictive simulation technique for cosmic ray-induced failure analysis from Si PiN diodes [1] to SiC PiN diodes. Accurate 3D cylindrical-symmetric transient simulations were performed with a minimum mesh size of 20nm at the center track of the impinging ion and a maximum time step of 0.1ps during the development of the ion-induced transient current. We made a comparative study between a SiC PiN diode and a Si PiN diode with the same blocking voltage of 1.5kV, using the same heavy ion transportation models. In the simulation, we observed different ion-induced current transients, differing not only in the peak value of the current, but also in its duration. Due to different physical mechanisms, the dependence of the ion-induced current on the reverse pre-bias voltage and the numerical mesh adaptations are also different. Eventually, we brieflydiscuss electro-thermal simulations, which indicate once more that the ion-induced transient current in the SiC PiN diodes under consideration is primarily drift current and involves only negligible impact ionization.
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Karimov, A. V., A. Z. Rakhmatov, O. A. Abdulkhaev, U. H. Aripova, A. Yu Khidirnazarova, and Sh M. Kuliyev. "Controlling voltage drops in silicon diodes by electron irradiation and thermal treatment." Технология и конструирование в электронной аппаратуре, no. 4 (2018): 33–37. http://dx.doi.org/10.15222/tkea2018.4.33.
Анотація:
High-frequency limiting rectifier diodes are used in power sources for rectifying alternating current, in protective elements of radio-electronic equipment, and in switching devices. They are the basis of energy-saving devices, meeting the high requirements for power limit and performance. The main task in the manufacturing process of high-frequency diodes is to ensure the low leakage current and the optimum value of the forward voltage drop which can be compared with the contact potential difference of the p–n junction. This paper is devoted to studying the effect of radiation exposure and subsequent heat treatment on the current-voltage and capacitance characteristics of high-frequency silicon diodes. The authors studied p+–p–n–n+ diodes made of n-type KEF-4 (ÊÝÔ-4) silicon wafers with an initial thickness of 235 µm. Radiation processing was performed using an ELU-6 (ÝËÓ-6) linear electron accelerator. The integral flux of “fast” electrons ranged from 1,0∙1015 to 2,6∙1017 cm–2, energy was 1.5 MeV, density was 1,7∙1011 — 5,5∙1013 cm–2∙s –1. Heat treatment was performed for 5 hours at a temperature of 90°C in a special chamber. The studies have shown that heat treatment lead to a shift of the forward current-voltage characteristic to a region of lower voltages (i.e., a given current can be reached at a lower voltage); at low current values, however, the voltage drop may increase after heat treatment. Reverse current decreased fivefold, resulting in a decrease in power output. At the same time, the temporal characteristics of the diode could also be improved by reducing the capacitance (to one order of magnitude)
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Kaur, C., S. Chaurasia, A. A. Pisal, A. K. Rossall, D. S. Munda, A. Venkateswara Rao, and M. N. Deo. "X-ray and ion emission studies from subnanosecond laser-irradiated SiO2 aerogel foam targets." Laser and Particle Beams 35, no. 3 (August 10, 2017): 505–12. http://dx.doi.org/10.1017/s0263034617000489.
Анотація:
AbstractIn this experiment, a comparative study of ion and X-ray emission from both a SiO2 aerogel foam and a quartz target is performed. The experiment is performed using Nd:glass laser system operated at laser energy up to 15 J with a pulse duration of 500 ps with focusable intensity of 1013–1014 W/cm2 on target. X-ray fluxes in different spectral ranges (soft and hard) are measured by using X-ray diodes covered with Al filters of thickness 5 µm (0.9–1.56 keV) and 20 µm (3.4–16 keV). A 2.5 times enhancement in soft X-ray flux (0.9–1.56 keV) and a decrease of 1.8 times in hard X rays (3.4–16 keV) for 50 mg/cc SiO2 aerogel foam is observed compared with the solid quartz. A decrease in the flux of the K-shell line emission spectrum of soft X rays is noticed in the case of the foam targets. The high-resolution K-shell spectra (He-like) of Si ions in both the cases are analyzed for the determination of plasma parameters by comparing with FLYCHK simulations. The estimated plasma temperature and density are Tc = 180 eV, ne = 7 × 1020 cm−3 and Tc = 190 eV, ne = 4 × 1020 cm−3 for quartz and SiO2 aerogel foam, respectively. To measure the evolution of the plasma moving away from the targets, four identical ion collectors are placed at different angles (22.5, 30, 45, and 67.5°) from target normal. The angular distribution of the thermal ions are scaled as cosnθ with respect to target normal, where n = 3.8 and 4.8 for the foam and quartz, respectively. The experimental plasma volume measured from the ion collectors and shadowgraphy images are verified by a two-dimensional Eulerian radiative–hydrodynamic simulation (POLLUX code).
Дисертації з теми "Radiative thermal diodes":
1
Kasali, Suraju Olawale. "Thermal diodes based on phase-change materials." Thesis, Poitiers, 2021. http://www.theses.fr/2021POIT2254.
Анотація:
Nous étudions dans cette thèse la rectification thermique de diodes thermiques radiatives ou conductive constituées de matériaux à changement de phase.Cette thèse est divisée en trois parties. Dans les premières parties, nous modélisons comparativement les performances d’une diode thermique conductive sphérique et cylindrique constitués de VO2 présentant un transition de phase et des matériaux n’en présentant pas. Des expressions analytiques aux bornes des diodes sont dérivées. Des flux thermiques, des facteurs de rectifications ainsi que les profils de température à l’intérieur de la diode sont obtenus. Nos résul-tats montrent que les différentes géométries de diodes ont un impact significatif sur les profils de température et les flux thermiques, mais moins un sur les facteurs de rectification. Dans ce travail, nous avons obtenu des facteurs de rectification maximaux allant jusqu’à 20.8% et 20.7%, qui sont supérieurs à celui prédit pour une diode plane constituée de VO2. Nous montrons également que des facteurs de rectification similaires à ceux obtenus avec le VO2 dans les géométries sphériques et cylindriques peuvent être atteints avec des matériaux à changement de phase dont le contraste de conductivité est plus important que dans le cas du VO2. Dans la deuxième partie, nous étudions la rectification de diodes thermiques constituées de deux matériaux à changement de phase. Avec, l’idée de générer un facteur de redressement plus élevé que dans le cas d’une diode thermique conductive ne comprenant qu’un matériau à changement de phase unique. Là encore, le travail a conduit à l’établissement d’expressions explicites pour les profils de température, les flux thermiques et le facteur de rectification. Nous avons obtenu un facteur de rectification optimal de 60% avec une variation de température de 250 K couvrant les transitions métal-isolant des deux matériaux. Dans la troisième partie de notre travail, nous avons modélisé et optimisé la rectification thermique de diodes thermiques planes, cylindriques et sphériques radiatives à base de deux matériaux à changement de phase. Nous savons calculer et analyser les facteurs de rectification de ces trois diodes et obtenu les facteurs de rectification optimaux respectifs pour les trois géométries 82%, 86% et 90.5%. Nos résultats montrent que la géométrie sphérique est la meilleure pour optimiser la rectification des courants thermiques radiatifs. De plus, des facteurs de rectification potentiellement supérieurs à ceux prédits ici peuvent être réalisés en utilisant deux matériaux à changement de phase avec des contrastes d’émissivités plus élevés que ceux proposés ici. Ces résultats analytiques et graphiques fournissent un guide utile pour optimiser les facteurs de rectification des diodes thermiques conductives et radiatifs basées sur des matériaux à changement de phase de géométries différentesThe thermal rectification of conductive and radiative thermal diodes based on phase-change materials, whose thermal conductivities and effective emissivities significant change within a narrow range of temperatures, is theoretically studied and optimized in different geometries. This thesis is divided into three parts. In the first part, we comparatively model the performance of a spherical and cylindrical conductive thermal diodes operating with vanadium dioxide (VO2) and non-phase-change materials, and derive analytical expressions for the heat flows, temperature profiles and optimal rectification factors for both diodes. Our results show that different diode geometries have a significant impact on the temperature profiles and heat flows, but less one on the rectification factors. We obtain maximum rectification factors of up to 20.8% and 20.7%, which are higher than the one predicted for a plane diode based on VO2. In addition, it is shown that higher rectification factors could be generated by using materials whose thermal conductivity contrast is higher than that of VO2. In the second part, on the other hand, we theoretically study the thermal rectification of a conductive thermal diode based on the combined effect of two phase-change materials. Herein, the idea is to generate rectification factors higher than that of a conductive thermal diode operating with a single phase-change material. This is achieved by deriving explicit expressions for the temperature profiles, heat fluxes and rectification factor. We obtain an optimal rectification factor of 60% with a temperature variation of 250 K spanning the metal-insulator transitions of VO2 and polyethylene. This enhancement of the rectification factor leads us to the third part of our work, where we model and optimize the thermal rectification of a plane, cylindrical and spherical radiative thermal diodes based on the utilization of two phase-change materials. We analyze the rectification factors of these three diodes and obtain the following optimal rectification factors of 82%, 86% and 90.5%, respectively. The spherical geometry is thus the best shape to optimize the rectification of radiative heat currents. In addition, potential rectification factors greater than the one predicted here can be realized by utilizing two phase-change materials with higher emissivities contrasts than the one proposed here. Our analytical and graphical results provide a useful guide for optimizing the rectification factors of conductive and radiative thermal diodes based on phase-change materials with different geometries
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Lin, Chung-Han. "The Effects of Thermal, Strain, and Neutron Irradiation on Defect Formation in AlGaN/GaN High Electron Mobility Transistors and GaN Schottky Diodes." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1371466261.
Частини книг з теми "Radiative thermal diodes":
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Berger, X., M. Schneider, J. C. Deval, F. Kieno, C. N. Awanou, and I. Donet. "THERMAL COMFORT IN HOT DRY COUNTRIES : RADIATIVE COOLING BY “DIODE” ROOF." In Passive and Low Energy Ecotechniques, 960–67. Elsevier, 1985. http://dx.doi.org/10.1016/b978-0-08-031644-4.50081-3.
Тези доповідей конференцій з теми "Radiative thermal diodes":
1
Etor, David, Linzi E. Dodd, David Wood, and Claudio Balocco. "High-frequency metal-insulator-metal (MIM) diodes for thermal radiation harvesting." In 2015 40th International Conference on Infrared, Millimeter, and Terahertz waves (IRMMW-THz). IEEE, 2015. http://dx.doi.org/10.1109/irmmw-thz.2015.7327649.
2
Storey, Thomas, Robin Rackerby, Heather Dillon, and Lydia Gingerich. "Thermal Performance of Domestic Replacement A19 LED Lighting Products." In ASME 2016 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/imece2016-67974.
Анотація:
In an effort to create a Light Emitting Diode (LED) lighting system that is as efficient as possible, the heat dissipation system must be accurately measured for proper design and operation. Because LED lighting technology is new, little optimization has been performed on typical cooling system required for most A19 replacement products. This paper describes the research process for evaluating the thermal performance of over 15 LED lighting products and compares their performance to traditional lighting sources, namely incandescent and compact fluorescent (CFL). This process uses radiation and convection to model typical cooling mechanisms for domestic A19 type replacement LED products. The A19 products selected for this investigation had input wattages ranging between 7 to 60 Watts, with outputs ranging from 450 to 1100 lumens. The average LED tested dissipated 43% (± 5%) of the total heat generated in the lighting product through the heat exchanger. The best thermal performance was observed in an LED product that dissipated approximately 58% of the total product heat through the heat exchanger. Results indicate that significant improvements to the current LED heat exchanger designs are possible, which will help lower the cost of future LED products, improve performance, and reduce the environmental footprint of the products.
3
Merced, Emmanuelle, Rafmag Cabrera, Noraica Da´vila, Nelson Sepu´lveda, and Fe´lix E. Ferna´ndez. "Characterization of VO2-Coated SiO2 Micromechanical Bridges Heated by Light Radiation." In ASME 2011 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. ASMEDC, 2011. http://dx.doi.org/10.1115/smasis2011-4963.
Анотація:
This letter reports the resistivity variations for a VO2 thin film on silicon dioxide (SiO2) micromechanical bridges when the coating’s insulator-to-metal transition (IMT) is thermally induced by optical radiation with a 635 nm laser diode or by conduction using a heater. The coating’s resistivity and temperature coefficient of resistance (TCR) were calculated as a function of temperature through heating-cooling cycles. A resistivity change of nearly three orders of magnitude through the IMT was observed, and the results obtained for the two different heating methods were compared. A peak TCR of −85%/°C during the heating process and −80.8%/°C during cooling were measured.
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Perkins, John F., Richard H. Hopkins, Charles D. Brandt, Anant K. Agarwal, Suresh Seshadri, and Richard R. Siergiej. "SiC High Temperature Electronics for Next Generation Aircraft Controls Systems." In ASME 1996 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1996. http://dx.doi.org/10.1115/96-gt-106.
Анотація:
Several organizations, including Westinghouse, CREE, and ATM, as well as researchers in Japan and Europe, are working to develop SiC power devices for reliable, high power and high temperature environments in military, industrial, utility, and automotive applications. Other organizations, such as NASA Lewis and several universities, are also doing important basic work on basic SiC technology development. It has been recognized for two decades that the superior properties of SiC lead to range of devices with higher power, greater temperature tolerance, and significantly more radiation hardness than silicon or GaAs. This combination of superior thermal and electrical properties results in SiC devices that can operate at up to ten times the power density of Si devices for a given volume. Recent research has focused on the development of vertical metal oxide semiconductor field effect transistor (VMOSFET) power device technology, and complementary high speed, temperature-tolerant rectifier-diodes for power applications. We are also evaluating applications for field control thyristors (FCT) and MOS turn-off thyristors (MTO). The technical issues to be resolved for these devices are also common to other power device structures. The present paper reviews the relative benefits of various power devices structures, with emphasis on how the special properties of SiC enhance the desirability of specific device configurations as compared to the Si-based versions of these devices. Progress in SiC material quality and recent power device research will be reviewed, and the potential for SiC-based devices to operate at much higher temperatures than Si-based devices, or with enhanced reliability at higher temperatures will be stressed. We have already demonstrated 1000V breakdown, current densities of 1 kA/cm2, and measurements up to 400°C in small diodes. The extension of this work will enable the implementation of highly distributed aircraft power control systems, as well as actuator and signal conditioning electronics for next generation engine sensors, by permitting electronic circuits, sensors and smart actuators to be mounted on or at the engine.
5
Petroski, James. "Understanding Longitudinal Fin Heat Sink Orientation Sensitivity for Light Emitting Diode (LED) Lighting Applications." In ASME 2003 International Electronic Packaging Technical Conference and Exhibition. ASMEDC, 2003. http://dx.doi.org/10.1115/ipack2003-35055.
Анотація:
Light Emitting Diodes (LEDs) have progressed in recent years from emitting indicator level lighting to emitting enough light for illumination applications. This has opened a new field for LED applications, resulting in significant advantages over conventional light sources and creating some application challenges unique to LEDs. Conventional lighting methods provide little guidance for LED thermal problems since these usually involve a very high temperature source, such as a filament or an arc, and radiant heat transfer dissipates the thermal energy. LED junction temperatures are limited to much lower values and hence the heat transfer system cannot depend upon radiant energy transfer. This means the cooling methods for lighting now shift from primarily radiation to conduction and natural convection, and this paradigm shift lighting designers must recognize when moving to LEDs. In this paper, the development of a LED-based spot module heat sink in a free convective cooling system is discussed. The rationale for choosing a cylindrical tube, longitudinal fin (CTLF) heat sink is shown, as is the performance of five different configurations of the heat sink in various orientations. The requirement for using heat sinks in various orientations comes from lighting applications, where the light may be installed in various directions, such as vertical up, vertical down, horizontal, or at almost any other angle. Heat sink test results are plotted for Nussult number versus standard and modified channel Rayleigh number, showing a similar correlation to the parallel plate heat sinks investigated first by Elenbaas. A different correlation for the isolated-plate limit section is proposed for CTLF heat sinks, as well as a proposed area of operation on these Nu-Ra curves for orientation-insensitive heat sinks. Finally, explanations for the different levels of sensitivities observed in different areas of the Nu-Ra curves are offered.
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Lall, Pradeep, Hao Zhang, and Rahul Lall. "Design and Development of Biometric Sensor Wearable Band Using Flexible Electronics." In ASME 2017 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems collocated with the ASME 2017 Conference on Information Storage and Processing Systems. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/ipack2017-74232.
Анотація:
Flexible electronics have a myriad of potential applications in fields such as healthcare, soldier situational awareness, soldier rehabilitation, sports performance, and textile manufacturing among other areas. The primary benefits that flexible electronics provide to both the producers and consumers are their light weight, low power consumption, efficiency, low cost of production, flexibility, and scalability. In comparison to rigid electronics, these systems would be subjected to a greater amount of mechanical and thermal stress in real-time due to their ability to be flexed, rolled, folded, and stretched. Environmental conditions such as bending, mechanical shock, water immersion, sweat, UV radiation, and temperature exposure could degrade the performance of these embedded electronic systems. At this time, there is a lack of suitable test standards and reliability data about flexible electronics manufacturing, assembly, and real-time use. In this paper, a fully flexible medical electronics system was built in full dimension to study the assembly and operation-related failure mechanisms of flexible and wearable electronics. The fabricated flexible electronics system measures pulse and muscle activity, and then transmits this data to a paired mobile device. The pulse rate was measured using an LED and a photo diode, while an electromyography (EMG) sensor was used to measure muscle activity. After collecting the data, the microcontroller sends it to a Bluetooth module, which can in turn transmit this information to a paired mobile device. Through experimentation with the fabricated flexible electronics device, unexpected degradation and quality issues were observed. In flexible PCBs, the space between the IC lead could not be isolated by the solder mask because of its large feature size and as a result, increases the risk of shortage between IC leads when subjected to mechanical stress. In addition, during the assembly process, high reflow temperature was found to subject a huge thermal stress on the connections between the solder pad and copper trace. Proper support of the solder pad should be designed to compensate the thermal stress during the reflow process, and prevent the copper joint on top of the board from being damaged. A set of guidelines for flexible medical electronics and an implementable reliability test standard can, therefore, be established for medical device manufacturers based on these reliability assessments.
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Lippmann, Wolfgang, Marion Herrmann, Carmen Hille, and Antonio Hurtado. "Laser Joining of Ceramics: A Contribution to High Temperature Range Application of Ceramic Components." In 16th International Conference on Nuclear Engineering. ASMEDC, 2008. http://dx.doi.org/10.1115/icone16-48409.
Анотація:
Non-oxide ceramics, such as silicon carbide (SiC) and silicon nitride (Si3N4), have excellent properties that make the materials interesting for application also in the nuclear sector. Due to their exceptional resistance to high temperatures, aggressive and abrasive media as well as nuclear radiation, the materials seem to be particularly suitable for developments in such fields as high-temperature reactors ((V)HTR) and peripheral systems (e.g. for hydrogen production). To simplify and thus to enable the technical application of these high-tech ceramics, the Dresden University of Technology has developed a laser beam joining process. This opens up many possibilities, e.g., to encase HTR fuel elements (as well as spheres and composites) in SiC, to encapsulate highly radioactive waste in SiC or to build a highly efficient heat transformer using high-temperature energy from VHT reactors. The progress made in laser beam technology in the last few years is a major element that has contributed to the developments achieved to date. Research has been focused mainly on the following three areas: (1) optimization of the laser parameters in combination with the advancement of oxide brazing fillers, (2) transfer of the basic technology to other high-tech ceramics like oxide ceramics, and (3) application of the laser process to develop electrically conductive joints. The possibility to laser join also Al2O3 and ZrO2 ceramics has created the opportunity to produce full ceramic sensors for (V)HTR specific applications at low cost. This requires adaptation of laser technology to the special properties of oxide ceramics. These are markedly less resistant to thermally induced stress than non-oxide ceramics, placing high requirements on laser process control. Another peculiarity is the property of oxide ceramics to be partly transparent to the laser wavelengths emitted by diode lasers (808 nm and 940 nm), with the result that the ceramic material is not heated primarily at the surface but inside its volume. This produces joint seams inside ceramic components even without any excessive thermal stress. The R&D work has made it possible to produce novel sensors for the high-temperature range that are also highly resistant to aggressive media. It is considered a further advantage that this joining technology has no special requirements regarding the process atmosphere such as vacuum or inert gas, which ensures that the process lends itself well to automation.
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Shang, Fu-Min, Yi-Fang Dong, Jian-Hong Liu, and Deng-Ying Liu. "Experimental Investigation on the Heat Transferring of Nanofluid in Self-Exciting Mode Oscillating-Flow Heat." In ASME 2016 5th International Conference on Micro/Nanoscale Heat and Mass Transfer. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/mnhmt2016-6400.
Анотація:
In this article, the heat transferring property of the copper-water nanofluids in self-exciting mode oscillating flow heat pipe under different laser heating power is experimented, as well as is compared with that of the distilled water medium in self-exciting mode oscillating flow heat pipe under same heating condition. The objective of this article is to provide the heat transfer characteristics of Cu-H2O nanofluids in self-exciting mode oscillating-flow heat pipe under different laser heating input, and to compare with the heat transfer characteristics of the same heat pipe with distilled water as working fluids. The SEMOS HP used in this experiment is made of brass tube with 2mm interior diameter, which is consisted of 8 straight tubes with 4 turns’ evaporation section and 12 turns’ condensation section. The heat resource for the evaporation zone is eight channel quantum pitfall diode array semi-conductor laser heater with 940nm radiation wave length, while the radiation power of each channel is changeable within 0–50W and the facular size is 1×30mm2. The condensation section is set in a cooling water tank in which water is from another higher tank. The actual transferring rate could be calculated by the flow rate of the cooling water and the change of the temperature. The change of the temperature of the heat pipe wall is measured by those thermo-couple fixed in different section in the heat pipe and data is collected by a data acquisition. In the heat pipe the fluid filling rate is 43%, the pressure is 2.5×10−3Pa, and the heat pipe inclination angle is 55° while the size of the brass particle in the nanofluids is less than 60nm and volume proportion is 0.5%. In this paper, the particularity of heat transfer rate of the SEMOS heat pipe with Cu-H2O fluid has been experimentally confirmed by changing the proportion of working fluid and Cu nonsocial particles in the heat pipe. By comparing the experimental result of these two different medium in the SEMOS HP, it is shown that the heat transferring rate with brass-water nanofluids as medium is much better than that with distilled water as medium under same volume proportion.
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Hille, Carmen, Wolfgang Lippmann, Marion Herrmann, and Antonio Hurtado. "Non-Oxide Ceramics: Chances for Application in Nuclear Hydrogen Production." In 16th International Conference on Nuclear Engineering. ASMEDC, 2008. http://dx.doi.org/10.1115/icone16-48408.
Анотація:
Research and development are increasingly focusing on the provision and utilization of heat in the high-temperature range above 900 °C, in particular under the aspect of resource-saving energy technologies. On the one hand, the exploitation of the high-temperature range helps to improve the efficiency of energy conversion processes; on the other hand, the provision of high-temperature heat makes it possible to utilize innovative thermochemical processes, which in turn represent environmentally compatible processes. An example to be quoted here is the thermally induced production of hydrogen by the iodine-sulfur process. The high temperatures alone place extremely high requirements on the materials to be used so that metallic materials soon reach their limits of application. If additionally chemically aggressive process media are used, as in the iodine-sulfur process, basically only ceramic materials can be considered as construction materials. In this application, notably silicon carbide (SiC) is favored owing to its excellent high-temperature properties. The possible technical fields of application of such high-performance ceramics can be broadly extended provided that suitable, highly efficient joining methods are available for these ceramics. In addition to its use as a constructional ceramic, SiC can principally also be used as a functional ceramic. For this purpose, the basic ceramic is modified with different additives, providing it with electrical properties that permit its application as a full ceramic heat conductor or sensor. In this case, it also holds true that a suitable joining method for making electrically conductive joints will extend the fields of application considerably. Laser-based joining technologies are being developed for both applications at the Dresden University of Technology. The research work presented here notably focuses on laser joining of electrically conductive SiC ceramics. In addition to a CO2 laser, a diode laser has been used. Basically, electrical connection has been made in two ways. In the first variants, graphite pins are inserted into the joining zone as electrically conductive bridges. In an alternative concept, the oxidic glass filler itself is made electrically conductive with additives. Like that a full ceramic heating conductor joined by means of laser radiation has been tested. The temperature resistance and functionality of the laser-joined heating conductor could be fully demonstrated.
Звіти організацій з теми "Radiative thermal diodes":
1
Lipson, Michal. Thermal Diodes Based on Near-Field Radiation. Fort Belvoir, VA: Defense Technical Information Center, October 2015. http://dx.doi.org/10.21236/ada622487.