Letteratura scientifica selezionata sul tema "Sub-K coolers"
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Articoli di riviste sul tema "Sub-K coolers":
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Gupta, Sandeep K., Aijaz A. Dar, Thayalan Rajeshkumar, Subramaniam Kuppuswamy, Stuart K. Langley, Keith S. Murray, Gopalan Rajaraman e Ramaswamy Murugavel. "Discrete {GdIII4M} (M = GdIII or CoII) pentanuclear complexes: a new class of metal-organophosphate molecular coolers". Dalton Transactions 44, n. 13 (2015): 5961–65. http://dx.doi.org/10.1039/c4dt03655g.
Abstract (sommario):
A higher magnetic entropy change is observed for the homometallic {GdIII5} complex (25.8 J kg−1 K−1) as compared to the heterometallic {GdIII4CoII} complex (20.3 J kg−1 K−1).
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Lei, Yongqing, Biao Zhong, Tao Yang, Xuelu Duan, Meng Xia, Chaoyu Wang, Jiajin Xu, Ziheng Zhang, Jingxin Ding e Jianping Yin. "Laser cooling of Yb3+:LuLiF4 crystal below cryogenic temperature to 121 K". Applied Physics Letters 120, n. 23 (6 giugno 2022): 231101. http://dx.doi.org/10.1063/5.0094705.
Abstract (sommario):
Optical cooling techniques of solid-state refrigerators, especially those toward the cryogenic temperature range, have attracted considerable attention in the fields of space exploration, precise measurement, material sciences, and so forth. Here, we report the laser cooling of the 7.5% Yb3+-doped LuLiF4 crystal down to 121 K reaching NIST's designated range of cryogenic temperatures (<123 K). Further results based on the cooling window indicate a promising cooling limit of 59 K, provided with enhancement in pump absorbance and heat load management of the sample. Our work, therefore, can motivate an all-solid-state optical refrigeration application beyond the liquid nitrogen boiling point, thus bringing great opportunity to realize cryogenic coolers and radiation-balanced lasers in miniaturized systems.
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Lee, Jongmin, Wenmei Liu, Hannah Löffler e Pierre Boillat. "New Characterizations for PEFC Under Sub-Zero Temperature". ECS Meeting Abstracts MA2023-02, n. 37 (22 dicembre 2023): 1791. http://dx.doi.org/10.1149/ma2023-02371791mtgabs.
Abstract (sommario):
The operation of fuel cells at sub-zero temperature results in direct deposition of ice or production of supercooled water that freezes upon interacting with nucleation seeds. Ice formation can lead to irreversible mechanical damages in membrane electrode assembly (MEA), particularly at interfaces, which is detrimental to the performance and safety of fuel cells. The mitigation strategies are focused on temperature elevation, including assisted heating, catalytic heating, and starvation (low potential) heating; however, these are associated with parasitic loss that reduces overall efficiency of the system. An alternative method is to develop porous media that are capable of ensuring oxygen transport pathways in the presence of ice or retaining supercooled water without phase transition until the cell reaches above 0ºC. The development of ice-resistant porous media for sub-zero operation is hindered by limitations on material characterization and performance evaluation techniques. The most common characterization technique is differential scanning calorimetry (DSC), by which water-saturated porous media is subjected to rapid temperature cycles to measure melting and freezing peaks. The DSC is a well-established and convenient technique that is suitable for statistical analysis; however, the sample size is limited to the mm-scale, and water must be injected in hydrophobic media prior to the DSC measurement where water saturation level and morphology are unpredictable. In situ testing of novel materials are performed on single cell hardware, in which the temperature is controlled by circulating a coolant through endplates or cooling channels that are placed several mm to cm away from an MEA. Such pseudo-active cooling system results in a significant difference (and delay) between the coolant and cell temperatures, influenced by heat production due to cell operation as well as freezing/melting. On the other hand, free heating operation starting from sub-zero is not desirable, since product heat is dissipated to current collectors and endplates that have much greater mass per active area in comparison to stack. As a result, most of sub-zero tests are performed on isothermal condition. Our previous works [1,2] introduced a unique single fuel cell hardware featuring temperature control and heat flux measurement (TCHM) system. Thermoelectric coolers and tangential gradient heat flux sensors enable a precise control of temperature in the MEA and detection of freezing and melting events during the cell operation. We have advanced the TCHM controlling software and integrated them on the custom fuel cell test bench. In this work, two novel techniques are introduced for sub-zero application for fuel cell porous media: (1) advanced calorimetry and (2) non-isothermal cold start. The advantages of our advanced calorimetry include testing of a large sample area up to 12cm2 and control of water quantity in a gas diffusion layer (GDL). Through neutron imaging, we validated capillary water injection method in the GDL and reduced saturation level with drying gas purging. Using techniques, we analyzed the effect of GDL structures and hydrophobicity on repeated freezing-thaw cycle to assist design of ice-resistant material. Additionally, we successfully implemented non-isothermal cold-start at -20 ºC in addition to isothermal condition, as seen in Figure 1. After the calibration of the TCHM units, the heating load was emulated to match that of the stack, corresponding to the heating rate between 10-15 K/min. The methods introduced in this study are expected to make a significant contribution towards the development of GDLs and catalyst layers that suppress ice formation and related mechanical damages. In particular, the non-isothermal cold-start provides a flexible, precise temperature control in the MEA, which can bridge the gap between the single cell and stack testing. Reference [1] J. Lee, E.R. Carreon-Ruiz, M. Siegwart, P. Boillat, Segmentation for Preventing Ice Propagation in Operating Fuel Cells, Meet. Abstr. MA2021-02 (2021) 1066. https://doi.org/10.1149/MA2021-02361066mtgabs. [2] M. Siegwart, F. Huang, M. Cochet, T.J. Schmidt, J. Zhang, P. Boillat, Spatially Resolved Analysis of Freezing during Isothermal PEFC Cold Starts with Time-of-Flight Neutron Imaging, Journal of The Electrochemical Society. 167 (2020) 064510. https://doi.org/10.1149/1945-7111/ab7d91. Figure 1
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Matsuki, Yoh, Takeshi Kobayashi, Jun Fukazawa, Frédéric A. Perras, Marek Pruski e Toshimichi Fujiwara. "Efficiency analysis of helium-cooled MAS DNP: case studies of surface-modified nanoparticles and homogeneous small-molecule solutions". Physical Chemistry Chemical Physics 23, n. 8 (2021): 4919–26. http://dx.doi.org/10.1039/d0cp05658h.
Abstract (sommario):
DNP enhancement, paramagnet-induced quenching/depolarization and build-up times are studied in a heterogeneous catalyst between 30 and 100 K. He-cooled MAS DNP at 30 K provides up to 100-fold better time performance than N2-cooled MAS DNP at 90 K.
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Belkhodja, Y., J. Loreau, A. van der Avoird, Y. Berger e P. Asselin. "Intermolecular dynamics of NH3-rare gas complexes in the ν2 umbrella region of NH3 investigated by rovibrational laser jet-cooled spectroscopy and ab initio calculations". Physical Chemistry Chemical Physics 23, n. 18 (2021): 10864–74. http://dx.doi.org/10.1039/d1cp00316j.
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Xi, Xiaotong, Biao Yang, Zhaozhao Gao, Liubiao Chen, Yuan Zhou e Junjie Wang. "Experimental study on a helium-4 sorption cryocooler". IOP Conference Series: Materials Science and Engineering 1240, n. 1 (1 maggio 2022): 012022. http://dx.doi.org/10.1088/1757-899x/1240/1/012022.
Abstract (sommario):
Abstract The sorption cooler is one of the commonly used Sub-Kelvin temperature refrigeration technologies, used in space exploration and ground experiments to provide a low temperature below 1 K. In this paper, a sorption cooler using helium-4 as the working gas has been developed. At a heat sink temperature of 3 K, the lowest no-load temperature of the developed sorption cooler is 843 mK and the hold time below 1 K is 4 hours. The effects of different sorption pump temperatures and sorption pump cooling rates on the refrigeration performance were studied through experiments. The test results show that during the condensation process, when the temperature of the sorption pump is higher than 45 K, the pump temperature has little effect on the liquefaction efficiency, and speeding up the cooling rate of the sorption pump is conducive to obtaining a lower refrigeration temperature.
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Sistani, M., M. S. Seifner, M. G. Bartmann, J. Smoliner, A. Lugstein e S. Barth. "Electrical characterization and examination of temperature-induced degradation of metastable Ge0.81Sn0.19 nanowires". Nanoscale 10, n. 41 (2018): 19443–49. http://dx.doi.org/10.1039/c8nr05296d.
Abstract (sommario):
Electrical characterization of Ge0.81Sn0.19 nanowires has been performed revealing high electrical conductivity and semiconductor behaviour when cooled to 10 K. The impact on slightly elevated temperatures on the device stability of this metastable material is described.
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Vaghela, Hitensinh, Ketan Choukekar, Pratik Patel, Vinit Shukla, Anuj Garg, Srinivasa Muralidhara, Vikas Gaur, Shk Madeenavalli e Bikash Dash. "Augmentation scheme of 80 K helium test facility to 65 K using sub-cooled liquid nitrogen". Indian Journal of Cryogenics 45, n. 1 (2020): 90–96. http://dx.doi.org/10.5958/2349-2120.2020.00015.1.
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Zhang, Lili, Yongzhang Cui, Wenlong Mao, Xiangzhuo Sheng e Guanmin Zhang. "The Condensation Characteristics of Propane in Binary and Ternary Mixtures on a Vertical Plate". Energies 16, n. 16 (8 agosto 2023): 5873. http://dx.doi.org/10.3390/en16165873.
Abstract (sommario):
Natural gas is one of the most common forms of energy in our daily life, and it is composed of multicomponent hydrocarbon gas mixtures (mainly of methane, ethane and propane). It is of great significant to reveal the condensation mechanism of multicomponent mixtures for the development and utilization of natural gas. A numerical model was adopted to analyze the heat and mass transfer characteristics of propane condensation in binary and ternary gas mixtures on a vertical cold plate. Multicomponent diffusion equations and the volume of fluid method (VOF) are used to describe the in-phase and inter-phase transportation. The conditions of different wall sub-cooled temperatures (temperature difference between the wall and saturated gas mixture) and the inlet molar fraction of methane/ethane are discussed. The numerical results show that ethane gas is more likely to accumulate near the wall compared with the lighter methane gas. The thermal resistance in the gas boundary layer is one hundred times higher than that of the liquid film, revealing the importance of diffusion resistance. The heat transfer coefficients increased about 11% (at ΔT = 10 K) and 7% (at ΔT = 40 K), as the molar fraction of ethane increased from 0 to 40%. Meanwhile, the condensation heat transfer coefficient decreased by 53~56% as the wall sub-cooled temperature increased from 10 K to 40 K.
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Kováč, P., L. Kopera, T. Melišek, M. Búran, I. Hušek, D. Berek e J. Kováč. "Water ice-cooled MgB2 coil made by wind and react process". Superconductor Science and Technology 35, n. 5 (17 marzo 2022): 055001. http://dx.doi.org/10.1088/1361-6668/ac521c.
Abstract (sommario):
Abstract A wind and react (W&R) coil of inner diameter 53 mm has been made from multi-core MgB2/Nb/CuNi wire manufactured by the internal magnesium diffusion (IMD) process. The W&R coil is wound from non-insulated rectangular wire of 1 mm2 with only 5 µm thick stainless steel foil used for interlayer insulation. The transport current performance of the coil and short wire samples was measured in a liquid He bath at external magnetic fields of 4.5–8.5 T and also in self-field conditions in sub-cooled water ice at temperatures between 33 K and 38 K. The presented MgB2 coil exhibits stable behavior at water ice cooling, and its high space factor allows a high current density of winding in comparison to the data from the already published MgB2 coils. The presented results demonstrate that MgB2 windings can be used safely in He-free conditions inside sub-cooled water ice, and this technique can be further optimized and used for future MgB2 coils.
Tesi sul tema "Sub-K coolers":
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Sauvage, Valentin. "Development of a Closed-Cycle Dilution Refrigerator for future cosmological missions". Electronic Thesis or Diss., université Paris-Saclay, 2023. http://www.theses.fr/2023UPASP035.
Abstract (sommario):
Le développement d'un réfrigérateur à dilution à cycle fermé pour l'étude du fond diffus cosmologique permettrait de faire progresser de manière significative la cosmologie expérimentale. Ce type de réfrigérateur permet de refroidir en continu les détecteurs à des températures extrêmement basses (100 mK) en utilisant de l'³He et de l'⁴He. Contrairement à son prédécesseur, le réfrigérateur à dilution à cycle ouvert utilisé lors de la mission spatiale Planck-HFI, la conception à cycle fermé permet de répéter indéfiniment le processus de refroidissement. Cela ne limite plus la durée de la mission à la quantité d'hélium embarquée. Le mélange ³He -⁴He, produisant la puissance de refroidissement, est séparé en deux composants ³He et ⁴He, et réinjecté dans le système. Cela permet de répondre aux besoins des missions futures : plus de puissance de refroidissement (OCDR < 0.2 μW, CCDR > 2 μW), une durée d'observation plus longue (OCDR < 2.5 ans, CCDR > 3 ans) avec la même stabilité en température (20 nK.Hz⁻⁰•⁵).Le CCDR doit être amélioré pour fonctionner dans un environnement de microgravité. Le mélange est injecté dans le bouilleur, où l'éponge (un matériau poreux) sépare la phase liquide de la phase gazeuse. Le circulateur va pomper la phase gazeuse (principalement de l'3He). L'⁴He superfluide est extrait de la phase liquide par la pompe à pression fontaine. Les deux isotopes sont ensuite réinjectés dans le système, perpétuant ainsi la production de puissance froide. Diverses expériences ont démontré son bon fonctionnement dans un environnement de laboratoire, faisant du CCDR une technologie TRL ₄. Pour une application spatiale, le CCDR doit atteindre le TRL ₅. Le développement d'un modèle d'ingénierie (EM) permettra de démontrer le bon fonctionnement du CCDR dans un environnement significatif. Cette thèse rend compte de l'avancement de ce développement. Un modèle structurel et thermique (STM) a été conçu pour accueillir les multiples composants du CCDR dans un volume et une masse restreints. Ce STM, un hexapode, supportera les vibrations d'un lancement de fusée tout en limitant les échanges thermiques entre les différents étages de température. Une sélection rigoureuse des matériaux a été effectuée pour optimiser la rigidité de la structure en fonction du flux thermique atteignant l'étage le plus froidDeveloping a Closed-Cycle Dilution Refrigerator for cosmic microwave background (CMB) study would significantly advance experimental cosmology. This type of refrigerator allows the detectors to be cooled continuously at extremely low temperatures (100 mK) using ³He and ⁴He. Unlike its predecessor, the Open-Cycle Dilution Refrigerator used for on the space mission Planck-HFI, the closed-cycle design allows for the cooling process to be repeated indefinitely. This does not limit the mission's duration to the quantity of embarked helium anymore. The ³He -⁴He mixture, producing the cooling power, is separated into the two components ³He and ⁴He, and re injected into the system. This ensures meeting the needs of future missions: more cooling power (OCDR < 0.2 μW, CCDR > 2 μW), longer observation time (OCDR < 2.5 years, CCDR > 3 years) with the same temperature stability (20 nK.Hz⁻⁰•⁵).The CCDR needs development to operate in a microgravity environment. The ³He -⁴He mixture is injected inside the still, where the porous sponge will separate the liquid phase from the gaseous phase. The circulator will pump the gaseous phase (mainly ³He). The superfluid ⁴He is extracted from the liquid phase by the fountain pump. Both isotopes are then re-injected into the system, perpetuating the cooling-power generation. Various experiments demonstrated its proper operation in a laboratory environment, making the CCDR a TRL ₄ technology. For a space application, the CCDR has to reach TRL ₅. Developing an Engineering Model will demonstrate the CCDR's proper operation in a relevant environment. This thesis reports on the progress in this development. A Structural and Thermal Model (STM) has been designed to host the multiple CCDR components in a restricted volume and mass. This STM, a hexapod, will handle the vibrations from a rocket launch while limiting the thermal exchanges between the various temperature stages. A rigorous material selection has been performed to optimize the structure stiffness regarding the thermal flux reaching the coldest stage
Libri sul tema "Sub-K coolers":
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T, Anderson David, e United States. National Aeronautics and Space Administration., a cura di. An intense slit discharge source of jet-cooled molecular ions and radicals (T[sub rot] < 30 K). [Washington, DC: National Aeronautics and Space Administration, 1996.
Atti di convegni sul tema "Sub-K coolers":
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Damle, Pankaj, e Tejesh Chawda. "Use of Ferritic SS444 in Exhaust Gas Cooling for Gasoline Engine". In International Conference on Automotive Materials and Manufacturing AMM 2023. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 2023. http://dx.doi.org/10.4271/2023-28-1328.
Abstract (sommario):
<div class="section abstract"><div class="htmlview paragraph">With the introduction of CAFÉ norms (Corporate Average Fuel Economy or Efficiency) in automobile industries, gasoline engines must improve their fuel economy by reducing overall CO<sub>2</sub> footprints. To fulfil this demand many OEMs have adopted the use of exhaust gas circulation coolers (EGR)</div><div class="htmlview paragraph">Most of the gasoline engines are having exhaust gas temperatures ranging from 650-850°C, these gases could also be highly corrosive in nature. It’s very important to select the right grade of stainless steel which should have high corrosion resistance and oxidation properties. It should also withstand high temperatures and should have low sensitization at high temperatures.</div><div class="htmlview paragraph">Most of grades stainless steel offers high resistance against corrosion, high temperature properties. But good sensitization at high temperature is not always associated with all grades of steel.</div><div class="htmlview paragraph">To compare corrosion resistivity, PREN number (Pitting Resistance Equivalent Number) plays important role. Highest the PREN number highest is the resistance to corrosion. Based on initial screening SS316L and SS444 grade are selected to undergo various test to demonstrate and compare corrosion, oxidation, and sensitization properties.</div><div class="htmlview paragraph">These materials have gone under various tests like condensate corrosion test as per VDA 230-214 K-1.2 standard, for 1000 hours. After each test, material microstructure properties have been analysed and results are compared. This technical paper includes advantage of material grade in terms of austenitic vs ferritic, manufacturing process, joining process (weldability or brazing), cost and the application where is it most suitable to use.</div></div>
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Chen, Xiaohu, Jiao Li, Yun Long, Yuzhang Wang, Shilie Weng e Savas Yavuzkurt. "A Conjugate Heat Transfer and Thermal Stress Analysis of Film-Cooled Superalloy With Thermal Barrier Coating". In ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/gt2020-16241.
Abstract (sommario):
Abstract A conjugate heat transfer study is carried out to obtain temperature and thermal stress field of a film-cooled superalloy with multi-layer thermal barrier coatings (TBCs). The aim is to understand the effects of the blowing ratio and ceramic top coating (TC) thickness on temperature and thermal stress which have an influence on component reliability and life. Results reveal that the distribution of film cooling effectiveness gets more uniform as TC thickness decrease because thick TC with low thermal conductivity prevents heat conduction in the axial and spanwise directions. In the upstream of the film cooling hole, the cooling effect is enhanced nonlinearly with the increase of the blowing ratio since the flow separation in the cooling tube affects the heat transfer enhancement. The insulation performance is improved by about 10 K for every 0.1D increase in TC thickness and the cooling effect is improved by about 20 K when the blowing ratio is increased from 0.5 to 1.0 at the leading edge of the film-cooling tube. The influence of jet lift-off and hotgas entrainment on the insulation effect is greater than TC thickness. The stress is concentrated at the leading edge of the film cooling hole and interfaces of TBCs. The maximum Von-Mises stress (761 MPa) on the interfaces is not at the leading or trailing sides of the film-cooling tube, it is about ± 45° from the centerline of the BC/SUB interface. The debonding stress at TC/BC interface and BC/SUB interface are about 26 MPa and 175 MPa respectively. The normal stress near the film-cooling tube on the BC/SUB interface is 5 – 7 times the one at TC/BC interface. Therefore, the interface crack is more likely to initiate at the BC/SUB interface, and the crack may keep growing and cause the spalling of TBC.
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Carlsson, Johan, Kamil Tucek e Hartmut Wider. "Investigations of Alternative Steam Generator Location and Flatter Core Geometry for Lead-Cooled Fast Reactors". In 14th International Conference on Nuclear Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/icone14-89316.
Abstract (sommario):
This paper concerns two independent safety investigations on critical and sub-critical heavy liquid metal cooled fast reactors using simple flow paths. The first investigation applies to locating the steam generators in the risers instead of the down-comers of a simple flow path designed sub-critical reactor of 600 MWth power. This was compared to a similar design, but with the steam generators located in the downcomers. The transients investigated were Total-Loss-of-Power and unprotected Loss-Of-Flow. It is shown that this reactor peaks at 1041 K after 29 hours during a Total-Loss-Of-Power accident. The difference between locating the steam generators in the risers and the downcomers is insignificant for this accident type. During an unprotected Loss-Of-Flow accident at full power, the core outlet temperature stabilizes at 1010 K, which is 337 K above nominal outlet temperature. The second investigation concerns a 1426 MWth critical reactor where the influence of the core height versus the core outlet temperature is studied during an unprotected Loss-Of-Flow and Total-Loss-Of-Power accident. A pancake type core geometry of 1.0 m height and 5.8 m diameter, is compared to a compact core of 2 m height and 4.5 m diameter. Moderators, like BeO and hydrides, and their influence on safety coefficients and burnup swings are also presented. Both cores incinerate transuranics from spent LWR fuel with minor actinde fraction of 5%. We show that LFRs can be designed both to breed and burn transuranics from LWRs. It is shown that the hydrides lead to the most favorable reactivity feedbacks, but the poorest reactivity swing. The computational fluid dynamics code STAR-CD was used for all thermal hydraulic calculations, and the MCNP and MCB for neutronics, and burn-up calculations.
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Joshi, Shailesh N., Matthew J. Rau, Ercan M. Dede e Suresh V. Garimella. "An Experimental Study of a Multi-Device Jet Impingement Cooler With Phase Change Using HFE-7100". In ASME 2013 Heat Transfer Summer Conference collocated with the ASME 2013 7th International Conference on Energy Sustainability and the ASME 2013 11th International Conference on Fuel Cell Science, Engineering and Technology. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/ht2013-17059.
Abstract (sommario):
Jet impingement cooling with phase change has shown the potential to meet the increased cooling capacity demands of high-power-density (of order 100 W/cm2) automotive electronics components. In addition to improved heat transfer, phase change cooling has the potential benefit of providing a relatively isothermal cooling surface. In the present study, two-phase jet impingement cooling of multiple electronic devices is investigated, where the fluorinated dielectric fluid HFE-7100 is used as the working fluid. Four different types of jet arrays, namely, a single round jet with orifice diameter of 3.75 mm, and three different 5 × 5 arrays of round jets with orifice diameters of 0.5 mm, 0.6 mm and 0.75 mm, were tested and compared for both heat transfer and pressure drop. The experimental Reynolds number at the orifice ranged from 1860 to 9300. The results show that for the same orifice pressure drop, the single jet reached CHF at approximately 60 W/cm2, while the 5 × 5 array (d = 0.75 mm) safely reached heat fluxes exceeding 65 W/cm2 without reaching CHF. Additionally, the experimental results show that the multi-device cooler design causes an unintended rise in pressure inside the test section and a subsequent increase in sub-cooling from 10 K to 23.3 K.
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Bloch, Gregor, Christina Jochum, Tobias Schechtl e Thomas Sattelmayer. "Subcooled Flow Boiling in a Rectangular Channel With Added Turbulence and Longitudinal Vortices". In 2012 20th International Conference on Nuclear Engineering and the ASME 2012 Power Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/icone20-power2012-54533.
Abstract (sommario):
Experiments are conducted to analyze the influence of turbulence and secondary flows on heat transfer and CHF in sub-cooled flow boiling. Inserts creating turbulence and stationary vortices are placed below a vertical channel with a heated wall and upward flow direction with flow velocities up to 1.2 m/s. The boiling chamber is of square shape with inner dimensions of 40 × 40 mm2. Boiling regimes range from onset of nucleate boiling up to fully developed film boiling. Influence of the inserts is measured for varying flow velocities and subcooling from 4 K to 27 K. Flow parameters are measured with Particle Image Velocimetry (PIV). A decay of nearly isotropic turbulence within only few diameters is observed, while stationary swirls exhibit longer penetration depths. Boiling experiments are conducted with unsteady heating with a low boiling hydrocarbon (dodekafluoromethylpentanone) as working fluid. Results from boiling experiments show a positive influence of the inserts on the boiling process, increasing with higher subcooling and flow velocities.
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Bethardy, G. A., Jungsug Go e David S. Perry. "Experimental evidence for distinct classes of coupling mechanism in intramolecular vibrational redistribution". In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1991. http://dx.doi.org/10.1364/oam.1991.thq3.
Abstract (sommario):
Sub-Doppler infrared absorption spectra of jet- cooled 1-butyne and trans-ethanol exhibit contrasting patterns of molecular eigenstates. In the presence of intramolecular vibration energy redistribution, frequency resolved spectra reveal that transitions to zero order upper state, v, J, K a , K c levels are fragmented into clumps of molecular eigenstates. The number and frequencies of these discrete features contain information about the nature of the intramolecular coupling. In the methyl C-H stretch of ethanol at 2990 cm-1 between J = 0 to 2, the number of coupled states increases sharply and is comparable to the rovibrational state density. In contrast, the actetylenic and methyl C-H stretches of 1-butyne at 3333 cm-1, respectively, exhibit coupling that is approximately independent of J and coupled state densities comparable to the purely vibrational state density. It is therefore concluded that a rotationally mediated coupling mechanism such as Coriolis or centrifugal coupling is involved in ethanol whereas only anharmonic coupling is apparent in 1-butyne.
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Sakurai, Hisashi, Yasuo Koizumi e Hiroyasu Ohtake. "Critical Heat Flux by High Velocity Liquid Flow in Narrow Rectangular Channel". In ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-67945.
Abstract (sommario):
Experiments of critical heat flux of extremely thin-fast plate jet film sub-cooled flow were conducted. The extremely thin-fast film-type jet of sub-cooled water was erupted into a stagnant pool. The heat transfer is augmented by the fast jet flow on the heat transfer surface. Vapor generated on the surface is easily taken away from the surface by the fast jet flow and leaves upward from the surface. The static head of water in the pool depress down the fast film-type jet flow on to the heat transfer surface and may collapse the vapor film that is formed between the heat transfer surface and the fast film flow. All these combine to have the possibility to improve the critical heat flux. In the experiments, the liquid sub-cooling was in the range of 30 ∼ 70 K. The thickness of the jet film was 0.2 mm and 0.5 mm. The width of the jet film was 2 mm. The velocity of the erupting jet film was 5.0 ∼ 32 m/s. The heat transfer surface was 2.0 × 2.0 mm heated electrically. The heat transfer surface was placed on the bottom of the pool. The fast-thin film jet was erupted on the bottom of the pool parallel to the heat transfer surface. Bubble behavior generated on the heat transfer surface was recorded by a high speed video camera at 10,000 frames/s. The highest critical heat flux obtained up to now is 3.2 × 107 W/m2. The analytical model of the critical heat flux for the present flow system will be presented.
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Shang, Zhi, e Yufeng Yao. "CFD Investigation of Heat Transfer in Supercritical Water-Cooled Flow Through 3×3 Fuel Rod Bundles". In 16th International Conference on Nuclear Engineering. ASMEDC, 2008. http://dx.doi.org/10.1115/icone16-48055.
Abstract (sommario):
CFD investigation of heat transfer in supercritical water-cooled flow through fuel rod bundles has been carried out, using commercial software STAR-CD 4.02 with specific ad hoc user routines for modeling physical property of supercritical water. The configuration considered is a typical core assembly of 3×3 fuel rod (round tube) bundles inside solid square box, as seen in the nuclear reactor. After priori mesh convergence studies, investigations are focused on key characteristics of flow and heat transfer performance, notably the wall temperature distributions, the mass flux and the secondary flow patterns in the cross-section. It is found that the rod wall temperature distributions exhibit highly non-uniform feature near the domain exit with very high wall temperatures: about 625°C observed on the corner rod and about 562.5°C on the border rod, respectively. It is believed that the appearance of the extremely wall temperature may be related to the non-uniform distributions of mass flux in the cross-section of the bundles as the low mass flux co-existing with the high wall temperature. Further analysis of the secondary flow in the cross-section reveals wider spectrum of vortex flow structures, more complicated than previously noted by the sub-channel analysis. To verify the influence of turbulence models on the secondary flow, both linear and non-linear k-ε models are applied and results are quite similar. This finding indicates that the cause of the secondary (cross) flow might not be solely due to the anisotropic property of turbulence as suggested by other researchers. The present 3D CFD study provides more complete database of 3×3 rod bundle flows and will be useful to improve the industry practice of applying the sub-channel analysis.
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Lee, P. Y. C., e W. H. Leong. "Validation of a Thermal Spreading/Constriction Resistance Model for a Convectively Cooled Plate With an Applied Heat Flux". In ASME 2008 Heat Transfer Summer Conference collocated with the Fluids Engineering, Energy Sustainability, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/ht2008-56243.
Abstract (sommario):
A thermal resistance model of a two-dimensional boundary value problem (BVP) that is commonly found in engineering/experimental heat transfer is presented. The problem consists of two different convectively cooled sub-sections along one boundary, and a heat flux distribution imposed on a portion of another (opposite) boundary, coupled with adiabatic conditions (Neumann boundary conditions) along the remaining boundaries under steady-state conditions. In solving this BVP, the solution technique is highlighted. Consistent with theory, the solution to this problem depends on two Biot numbers, dimensionless heat flux and other dimensionless geometric parameters related to the problem. The present solution is an exact general solution to an existing two-dimensional problem found in literature, and as a special case, the general solution reduces exactly to the existing solution. Also, the present model is validated by comparing the present solution with measured data, and in terms of a temperature difference between two locations on the plate, the analytical solution is well within the experimental error of 0.03 K.
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Picard, B., A. L.-Blais, M. Picard e D. Rancourt. "Power-Density vs Efficiency Trade-Off for a Recuperated Inside-Out Ceramic Turbine (ICT)". In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-91017.
Abstract (sommario):
Abstract Recuperated cycles can significantly increase the efficiency of small gas turbines that are today operating with low pressure ratios and uncooled or lightly cooled turbine blades. However, for mass-driven applications such as aeroengines, the efficiency benefit is typically outweighed by the increased weight associated with the heat exchanger (HX). Increase in specific power could overcome this penalty by reducing the mass flow through the system and therefore its weight and size. To do so, the Turbine Inlet Temperature (TIT) must be increased by ∼250 K over state-of-the-art small gas turbines. The Inside-out Ceramic Turbine (ICT) propose a new path to increase TIT of small turbines, where blade cooling schemes are impractical and costly. This new architecture increases the achievable TIT by using ceramic blades loaded in compression under centrifugal loads supported by an air-cooled rotating composite rim. This paper provides a system-level evaluation of the power-density to efficiency trade-off for the sub-megawatt class turbines using the ICT configuration. The numerical simulation includes 3 submodels to provide cycle efficiency and mass estimates for various cycle and HX design: (1) a station-based thermodynamic model; (2) a 1D-FEM HX model for a straight counterflow recuperator; and (3) a system-level mass model of the recuperated engine configured for a turboprop or turboshaft. At a TIT of 1550 K, the optimal ICT configuration provides a power density of 3 kW/kg and 40% thermal efficiency, which is 4 times lighter than recuperated turbines at 1300 K for the same efficiency level. Further increase in TIT to 1800 K would reach current state-of-the-art turboprop power densities (up to 5 kW/kg) while still achieving over 40% thermal efficiency or — for applications where power density can be traded for efficiency — up to 50% thermal efficiency while maintaining low pressure ratios and associated simplicity.