Effect of Heterogeneous Wettable Inclined Interlace Structures on Pool Boiling Performance of Cylindrical Copper Surfaces PDF Download
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Author: 莊侑軒
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Category :
Languages : en
Pages :
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Author: 莊侑軒
Publisher:
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Category :
Languages : en
Pages :
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Author: 張耀文
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ISBN:
Category :
Languages : en
Pages :
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Author: Adam Ryon Girard
Publisher:
ISBN:
Category : Contact angle
Languages : en
Pages : 468
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The current study aims to investigate the effect of wettability on the Boiling Heat Transfer Coefficient (BHTC) and Critical Heat Flux (CHF) in both pool and flow boiling of water. In this study, hot alkali solutions were utilized to promote cupric and cuprous oxide growth on copper surfaces, with thicknesses on the order of a couple of micrometers. This growth exhibited micro and nano-scale structures, resulting in differing levels of wettability and roughness while maintaining the effusivity of the bare copper surface. Teflon® was utilized to modify the surface energy of these surfaces, creating a range of wettability with apparent contact angles spanning from ~0° to ~160°. Pool boiling tests were conducted with these surfaces using saturated water at 1 atm on 1×1 cm2 square blocks, heated via resistance heaters. Flow boiling tests were conducted using both 1×1 cm2 square and 1×3 cm2 rectangular heaters, for slightly subcooled (1.5–3.5°) conditions over the velocity range of 0.3 to 0.9 m/s. This study showed that for both Pool and Flow boiling, the BHTC has an inverse relationship to wettability; the BHTC decreases as wettability increases. Furthermore, it was shown that this dependency between BHTC and wettability is more significant than the relationship between BHTC and surface roughness. The CHF was found to increase with increased wettability, roughness and mass flux. Based on the results of this study and published data, it is postulated that there exists a true hydrodynamic CHF limit for pool boiling with water on flat surfaces independent of heater material, near 2,000 kW/m2, representing an 80% increase in the limit suggested by Zuber. This study recommends this topic be explored with more focused research, and also suggests future boiling surface characterizations be performed in terms of both surface roughness as well as apparent contact angle to aid in the creation of a robust boiling dataset.
Author: Aniket M. Rishi
Publisher:
ISBN:
Category : Ebullition
Languages : en
Pages : 194
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"The miniaturization of electronic devices requires advanced thermal management techniques. The two-phase heat transfer process offers more effective and sustainable approach compared to the presently used single-phase cooling techniques. The boiling heat transfer is a two-phase cooling technique, that dissipates a high heat flux while maintaining the low surface temperature thereby, offering an efficient heat transfer mechanism compared to the single-phase process. Furthermore, the surface enhancement techniques such as micro/nano porous coatings help to maintain the low surface temperature thus improving the overall heat transfer performance. Electrodeposition is a simple technique that enhances this performance by creating the porous structure on the surface. This research focuses on developing an enhanced microscale structures on plain copper surfaces to improve the pool boiling performance. Additionally, the longevity (or the long-term stability) and aging of these enhanced structures, and their effects on the pool-boiling performance is also investigated. Initially the pool boiling performance of enhanced surfaces is studied. The enhanced surfaces were prepared using electrodeposition of copper and graphene oxide. Later, the effects of repetitive boiling on the morphology of the surfaces were examined using various characterization techniques such as Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), and Fourier Transform Infrared (FTIR). The chips coated with electrodeposition method rendered a high pool boiling performance for GS-4 (2.5% GO-Cu electrodeposited chip) with CHF of 220 W/cm2 at wall superheat of 14°C, giving ~76% improvement in CHF compared to plain copper chip. While, copper on copper electrodeposited chip, deposited with a different technique, performed better in both CHF and aging. CHF of 192 W/cm2 at wall superheat of 18.8°C was achieved for copper electrodeposited chip, giving ~30% enhancement compared to literature and ~54% enhancement when compared to plain copper chip. Moreover, surface characterization techniques including Scanning Electron Microscope (SEM) with Energy- Dispersive X-Ray Spectroscopy (EDS), Fourier Transform Infrared (FTIR), and X-Ray Diffraction (XRD) were employed to study the morphologies, elemental species, and to confirm the presence of graphene and graphene oxide on the test surfaces."--Abstract.
Author: Nanxi Li
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Boiling is a very effective way of heat transfer due to the latent heat of vaporization. Large amount of heat can be removed as bubbles form and leave the heated surface. Boiling heat transfer has lots of applications both in our daily lives and in the industry. The performance of boiling can be described with two important parameters, i.e. the heat transfer coefficient (HTC) and the critical heat flux (CHF). Enhancing the performance of boiling will greatly increase the efficiency of thermal systems, decrease the size of heat exchangers, and improve the safety of thermal facilities. Boiling heat transfer is an extremely complex process. After over a century of research, the mechanism for the HTC and CHF enhancement is still elusive. Previous research has demonstrated that fluid properties, system pressures, surface properties, and heater properties etc. have huge impact on the performance of boiling. Numerous methods, both active and passive, have been developed to enhance boiling heat transfer. In this work, the effect of pressure was investigated on a plain copper substrate from atmospheric pressure to 45 psig. Boiling heat transfer performance enhancement was then investigated on Teflon© coated copper surfaces, and graphene oxide coated copper surfaces under various system pressures. It was found that both HTC and CHF increases with the system pressure on all three types of surfaces. Enhancement of HTC on the Teflon© coated copper surface is contributed by the decrease in wettability. It is also hypothesized that the enhancement in both HTC and CHF on the graphene oxide coated surface is due to pinning from micro and nanostructures in the graphene oxide coating or non-homogeneous wettability. Condensation and freezing experiments were conducted on engineered surfaces in order to further characterize the pinning effect of non-homogeneous wettability and micro/nano structure of the surface.
Author: Felix Liu
Publisher:
ISBN:
Category : Ebullition
Languages : en
Pages : 146
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"Miniaturization in microelectronics demands effective thermal management from high energy density devices. While current cooling solutions employ single-phase heat transfer, they are often limited by high fluid temperature differences and pressure drops. Alternatively, two-phase cooling schemes offers attractive solutions to dissipate high heat fluxes at small temperature differences. Specifically, pool boiling has the potential to dissipate high heat fluxes without using pumps and other complex header configurations. Two performance criterion that govern the heat transfer in pool boiling systems are the (i) Critical Heat Flux (CHF), and the (ii) Heat Transfer Coefficient. The CHF is the upper limit in nucleate boiling, while the Heat Transfer Coefficient dictates the efficiency of the process. The current thesis work relates to increasing the aforementioned parameters through copper porous coatings. In this work, copper substrates were coated with 3M copper powders using a drop coating and screen printing technique. Substrate bonding was achieved by sintering at elevated temperatures. The coated substrates were characterized using Scanning Electron Microscopy and Laser Confocal Microscopy which revealed the different geometrical parameters (pore sizes and coating thickness etc.) associated with the coatings. Pool boiling tests were conducted with distilled and degassed water at atmospheric pressure. A highest Critical Heat Flux (CHF) of 303 W/cm2 was obtained on a test sample corresponding to a coating thickness of 447 μm. This translated to a CHF enhancement of ~135 % when compared to a plain copper surface. The effect of coating thickness on pool boiling performance was studied. High speed visualization was conducted on the test samples to identify underlying boiling mechanisms. The effect of additional nucleation sites, and wickability were evaluated in this study. The experimental observations were supplemented with analytical equations available in literature to identify driving mechanisms with the thin and thick porous coatings."--Abstract.
Author: N. Zuber
Publisher:
ISBN:
Category : Heat
Languages : en
Pages : 216
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Author:
Publisher: Academic Press
ISBN: 0080575846
Category : Technology & Engineering
Languages : en
Pages : 467
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Advances in Heat Transfer
Author: Mehdi Afshari
Publisher: Woodhead Publishing
ISBN: 0081009119
Category : Technology & Engineering
Languages : en
Pages : 650
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Electrospun Nanofibers covers advances in the electrospinning process including characterization, testing and modeling of electrospun nanofibers, and electrospinning for particular fiber types and applications. Electrospun Nanofibers offers systematic and comprehensive coverage for academic researchers, industry professionals, and postgraduate students working in the field of fiber science. Electrospinning is the most commercially successful process for the production of nanofibers and rising demand is driving research and development in this field. Rapid progress is being made both in terms of the electrospinning process and in the production of nanofibers with superior chemical and physical properties. Electrospinning is becoming more efficient and more specialized in order to produce particular fiber types such as bicomponent and composite fibers, patterned and 3D nanofibers, carbon nanofibers and nanotubes, and nanofibers derived from chitosan. - Provides systematic and comprehensive coverage of the manufacture, properties, and applications of nanofibers - Covers recent developments in nanofibers materials including electrospinning of bicomponent, chitosan, carbon, and conductive fibers - Brings together expertise from academia and industry to provide comprehensive, up-to-date information on nanofiber research and development - Offers systematic and comprehensive coverage for academic researchers, industry professionals, and postgraduate students working in the field of fiber science
Author: Ramasamy Marappa Gounder
Publisher:
ISBN: 1839684097
Category :
Languages : en
Pages : 274
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