Experimental Investigation on Effect of Heterogeneous Wettable Surfaces on Pool Boiling Heat Transfer Performance of Cylindrical Copper Surface PDF Download
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Author: 張耀文
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: 張耀文
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: 莊侑軒
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Rajiv Gupta
Publisher: CRC Press
ISBN: 1000820815
Category : Technology & Engineering
Languages : en
Pages : 793
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Book Description
The role of manufacturing in a country’s economy and societal development has long been established through their wealth generating capabilities. To enhance and widen our knowledge of materials and to increase innovation and responsiveness to ever-increasing international needs, more in-depth studies of functionally graded materials/tailor-made materials, recent advancements in manufacturing processes and new design philosophies are needed at present. The objective of this volume is to bring together experts from academic institutions, industries and research organizations and professional engineers for sharing of knowledge, expertise and experience in the emerging trends related to design, advanced materials processing and characterization, and advanced manufacturing processes.
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: George William Preckshot
Publisher:
ISBN:
Category : Heat
Languages : en
Pages : 62
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Author: Ankit Kalani
Publisher:
ISBN:
Category : Heat sinks (Electronics)
Languages : en
Pages : 170
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"The growing trend in miniaturization of electronics has generated a need for efficient thermal management of these devices. Boiling has the ability to dissipate large quantity of heat while maintaining a small temperature difference. Vapor chamber with pool boiling offers an effective way to provide cooling and maintaining temperature uniformity. The objective of the current work is to investigate pool boiling performance of ethanol and FC-87 on microchannel surfaces. Ethanol is an attractive working fluid due to its better heat transfer performance and higher heat of vaporization compared to refrigerants, and lower boiling point compared to water. The saturation temperature of ethanol can be further reduced to temperatures suitable for electronics cooling by lowering the system pressure. Fluorocarbons are considered to be ideal fluids for electronics cooling due to their low normal boiling point, dielectric and inert nature. FC-87 is selected for the current work. Ethanol is tested at four different absolute pressures, 101.3 kPa, 66.7 kPa, 33.3 kPa and 16.7 kPa using different microchannel surface configurations. Heat dissipation in excess of 900 kW/m2 was obtained while maintaining the wall surface below 85°C at 33 kPa. Flammability, toxicity and temperature overshoot issues need to be addressed before practical implementation of ethanol-based cooling systems in electronics cooling application. FC-87 with microchannel yields average performance when compared to literature. Effect of surface area is identified as the key reason for performance enhancement. A new finned structure is developed, which gave a heat flux value 1.25 MW/m2 at 40°C wall superheat for FC-87 at atmospheric conditions."--Abstract.
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: Shikha Ebrahim
Publisher:
ISBN:
Category :
Languages : en
Pages :
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In this research, minimum film boiling temperature (Tmin) is quantitatively determined as a function of the initial substrate temperature, liquid subcooling, surface thermophysical properties and surface conditions. Since Tmin defines the boundary between the film and transition boiling regimes, its value is significant for the design of an emergency core cooling system following a hypothetical loss-of-coolant accident (LOCA) in a nuclear power plant. When a sufficiently heated surface is plunged in a water pool, a vapor blanket is generated around the test section acting as a heat transfer insulator due to the poor thermal conductivity of the vapor. At temperatures lower than Tmin, the heat transfer is dramatically enhanced owing the collapse of the vapor film allowing direct physical contact between the water and the heated surface. Therefore, it is very important to explore methods and techniques that increase this temperature in order to improve the safety of nuclear reactors. A test facility was designed and constructed to conduct quenching experiments using vertical rods. Seven cylindrical test samples were fabricated with embedded thermocouples inside the cladding material. The thermocouples were connected to a data acquisition system in order to measure the temperature history during the experiments. The temperature and heat flux at the surface were calculated using an inverse heat conduction code along with an advance image processing technique to quantitatively characterize the liquid-vapor interfacial waves, vapor layer thickness, Tmin, quenching temperature, quenching time, and quench front velocity in the film boiling heat transfer regime. Visualization of the boiling behavior was captured by a high-speed camera at a frame rate of 750 frames per second (fps). The thermocouple data and the captured videos were synchronized to couple the behavior of the vapor layer with the thermal behavior of the heated sample. Various characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM) associated with Energy-dispersive X-ray spectroscopy (EDS), and field emission scanning electron were employed to identify the phases, chemical composition, and surface microstructure of the Inconel-600 before and after being used in a 7 x 7 rod bundle facility. Micro- and nanoparticles composed of nickel, chromium, and iron oxides were observed at the surface of the oxidized Inconel samples. It was found that the porous microstructure coupled with the increase in liquid spreading played a significant role in the enhancement of the film boiling heat transfer. Finally, the heat transfer behavior in the film boiling regime was investigated by calculating the heat transfer coefficient and Nusselt number for various cases. The novelty of this research is the coupling between the results of the quenching experiments and the surface characterization analyses that prompted the development of a new correlation for Tmin. This correlation adequately captures the effects of liquid subcooling, porosity of the oxide layer, and system pressure.
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: Stephen Matthew Bajorek
Publisher:
ISBN:
Category : Heat
Languages : en
Pages : 480
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