Experimental and Analytical Study of the Effects of Wettability on Nucleation Site Density During Pool Boiling PDF Download

Author: Chunghsiung Wang
Publisher:
ISBN:
Category : Nucleate boiling
Languages : en
Pages : 256

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Book Description

Author: S. Mostafa Ghiaasiaan
Publisher: Cambridge University Press
ISBN: 1316785300
Category : Technology & Engineering
Languages : en
Pages : 1322

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Book Description
Providing a comprehensive introduction to the fundamentals and applications of flow and heat transfer in conventional and miniature systems, this fully enhanced and updated edition covers all the topics essential for graduate courses on two-phase flow, boiling, and condensation. Beginning with a concise review of single-phase flow fundamentals and interfacial phenomena, detailed and clear discussion is provided on a range of topics, including two-phase hydrodynamics and flow regimes, mathematical modeling of gas-liquid two-phase flows, pool and flow boiling, flow and boiling in mini and microchannels, external and internal-flow condensation with and without noncondensables, condensation in small flow passages, and two-phase choked flow. Numerous solved examples and end-of-chapter problems that include many common design problems likely to be encountered by students, make this an essential text for graduate students. With up-to-date detail on the most recent research trends and practical applications, it is also an ideal reference for professionals and researchers in mechanical, nuclear, and chemical engineering.

Author:
Publisher:
ISBN:
Category : Mechanics, Applied
Languages : en
Pages : 354

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Book Description

Author: Yih-Yun Hsu
Publisher:
ISBN:
Category : Ebullition
Languages : en
Pages : 54

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Book Description
The ebullition cycle of nucleate pool boiling from a heating strip was studied through the use of high-speed motion pictures of schlieren and shadowgraph images. The effects of bubble agitation on thermal layer and neighboring bubbles were observed. An over-all model of ebullition based upon experimental observation was proposed that included an analytical method for predicting bubble growth rate and an analysis of the factors that influence the magnitude of the waiting period (time interval between bubbles at a particular site). Thermal-layer thickness, cavity size, and area of influence of a growing bubble are considered. A film supplement is made available. (Author).

Author: V. K. Dhir
Publisher:
ISBN:
Category : Ebullition
Languages : en
Pages : 504

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Author:
Publisher:
ISBN:
Category : Heat
Languages : en
Pages : 632

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Book Description

Author: Nikolay Ivanov Kolev
Publisher: Springer Science & Business Media
ISBN: 3642213723
Category : Technology & Engineering
Languages : en
Pages : 683

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Book Description
Multi-phase flows are part of our natural environment such as tornadoes, typhoons, air and water pollution and volcanic activities as well as part of industrial technology such as power plants, combustion engines, propulsion systems, or chemical and biological industry. The industrial use of multi-phase systems requires analytical and numerical strategies for predicting their behavior. .In its fourth extended edition the successful monograph package “Multiphase Flow Daynmics” contains theory, methods and practical experience for describing complex transient multi-phase processes in arbitrary geometrical configurations, providing a systematic presentation of the theory and practice of numerical multi-phase fluid dynamics. In the present third volume methods for describing of the thermal interactions in multiphase dynamics are provided. In addition a large number of valuable experiments is collected and predicted using the methods introduced in this monograph. In this way the accuracy of the methods is revealed to the reader. This fourth edition includes various updates, extensions, improvements and corrections. "The literature in the field of multiphase flows is numerous. Therefore, it is very important to have a comprehensive and systematic overview including useful numerical methods. The volumes have the character of a handbook and accomplish this function excellently. The models are described in detail and a great number of comprehensive examples and some cases useful for testing numerical solutions are included. These two volumes are very useful for scientists and practicing engineers in the fields of technical thermodynamics, chemical engineering, fluid mechanics, and for mathematicians with interest in technical problems. Besides, they can give a good overview of the dynamically developing, complex field of knowledge to students. This monograph is highly recommended,” BERND PLATZER, ZAAM In the present third volume methods for describing of the thermal interactions in multiphase dynamics are provided. In addition a large number of valuable experiments is collected and predicted using the methods introduced in this monograph. In this way the accuracy of the methods is revealed to the reader. This fourth edition includes various updates, extensions, improvements and corrections. "The literature in the field of multiphase flows is numerous. Therefore, it is very important to have a comprehensive and systematic overview including useful numerical methods. The volumes have the character of a handbook and accomplish this function excellently. The models are described in detail and a great number of comprehensive examples and some cases useful for testing numerical solutions are included. These two volumes are very useful for scientists and practicing engineers in the fields of technical thermodynamics, chemical engineering, fluid mechanics, and for mathematicians with interest in technical problems. Besides, they can give a good overview of the dynamically developing, complex field of knowledge to students. This monograph is highly recommended,” BERND PLATZER, ZAAM

Author: S.G. Kandlikar
Publisher: Routledge
ISBN: 1351442198
Category : Science
Languages : en
Pages : 786

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Book Description
Provides a comprehensive coverage of the basic phenomena. It contains twenty-five chapters which cover different aspects of boiling and condensation. First the specific topic or phenomenon is described, followed by a brief survey of previous work, a phenomenological model based on current understanding, and finally a set of recommended design equa

Author: Shailesh Malla
Publisher:
ISBN:
Category : Heat
Languages : en
Pages : 124

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Book Description
The present work consists of two major studies. The first study investigates the effects of surface energy or wettability on nucleate pool boiling and the second study investigates the thin-film evaporative cooling for near junction thermal management. For the first study, effects of surface energy or wettability on critical heat flux (CHF) and boiling heat transfer (BHT) of smooth heated surfaces was studied in saturated pool boiling of water at 1 atm. For this purpose hydrophilic and hydrophobic surfaces were created on one side of 1cm x 1cm double-side polished silicon substrates. A resistive heating layer was applied on the opposite side of each substrate. The surface energies of the created surfaces were characterized by measuring the static contact angles of water sessile drops. To provide a wide range of surface energies, surfaces were made of Teflon (hydrophobic), bare silicon (hydrophilic) and aluminum oxide (most hydrophilic). The measured contact angles on these surfaces were ~108, ~57 and ~13 degrees respectively. The results of pool boiling tests on these surfaces clearly illustrate the connection between surface energy and CHF. CHF was shown to linearly decrease with contact angle increase, from ~125 W/cm2 on aluminum oxide (most hydrophilic) to nearly one tenth of this value on Teflon (hydrophobic). The most hydrophilic surface also produced increasingly better BHT than plain silicon and Teflon as heat flux increased. However, below ~5 W/cm2 the hydrophobic surface demonstrated better heat transfer due to earlier onset of nucleate boiling, reducing surface superheats by up to ~5 degrees relative to the other two surfaces. Above ~5 W/cm2 the BHT of the hydrophobic surface rapidly deteriorated as superheat increased towards the value at CHF. To further understand the effect of surface energy on pool boiling performance, the growth and departure of bubbles from single nucleating sites on each surface were analyzed from high-speed video recordings. A distinct bubble behavior was observed in the hydrophobic surface where bubble growth and departure period was extremely long compared to plain silicon and aluminum oxide surfaces. This study also investigated the performance of thin-film evaporative cooling for near-junction thermal management. A liquid delivery system capable of delivering water in small volumes ranging 20~75 nl at frequencies of up to 600 Hz was established. On one side of the silicon chip, a resistive heating layer of 2 mm x 2 mm was fabricated to emulate the high heat flux hot-spot, and on the other side a superhydrophilic nanoporous coating (SHNC) was applied over an area of 1 cm x 1 cm. With the aid of the nanoporous coating, delivered droplets spread into thin films of thicknesses less than 10[mu]m. With this system, evaporative tests were conducted in ambient in an effort to maximize dryout heat flux and evaporative heat transfer coefficient. During the tests, heat flux at the hot spot was varied to values above 1000 W/cm2. Water was delivered at either given constant frequency (constant mass flow rate) or at programmed variations of frequency (variable mass flow rate), for a given nanoliter dose volume. Heat flux and hot spot surface temperatures were recorded upon reaching steady state at each applied heat flux increment. Relative to bare silicon surface, dryout heat flux of the SHNC surface was found to increase by ~5 times at 500~600 Hz. Tests were also conducted at various system pressures and temperatures in a micro-gap to emulate the actual embedded thermal management system. The micro-gap was made by positioning a top cover plate 500 [mu]m above the test surface. System temperature did not influence the hotspot temperature. This was due to the formation of near saturation temperature inside the micro-gap for all cases as a result of vapor accumulation. Increase in system pressure increased the hotspot temperature. At 1500 W/cm2, hotspot temperature increased by 6 C and 24 C by increasing the system pressure by 7.32 and 14.7 psi respectively. This was due to increase in saturation point as a result of increase in pressure. On the SHNC surface a mixed mode of heat transfer comprising of thin-film boiling and thin-film evaporation was observed particularly at moderate heat flux (~700 W/cm2). To further enhance the heat transfer coefficient, aluminum microporous coating was developed that increased the number of nucleation sites for thin-film boiling and also maintained the wettability for thin-film evaporation at higher heat fluxes. Test results showed a marginal improvement in dry-out heat flux compared to SHNC, however, significant reduction was achieved in hot-spot temperature at all heat flux levels. A net reduction of ~ 58oC was obtained at ~1600 W/cm2 by using aluminum based microporous coating.

Author: John R Thome
Publisher: World Scientific
ISBN: 9813227427
Category : Technology & Engineering
Languages : en
Pages : 1460

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Book Description
Set III of this encyclopedia is a new addition to the previous Sets I and II. It contains 26 invited chapters from international specialists on the topics of numerical modeling of two-phase flows and evaporation, fundamentals of evaporation and condensation in microchannels and macrochannels, development and testing of micro two-phase cooling systems for electronics, and various special topics (surface wetting effects, microfin tubes, two-phase flow vibration across tube bundles). The chapters are written both by renowned university researchers and by well-known engineers from leading corporate research laboratories. Numerous 'must read' chapters cover the fundamentals of research and engineering practice on boiling, condensation and two-phase flows, two-phase heat transfer equipment, electronics cooling systems, case studies and so forth. Set III constitutes a 'must have' reference together with Sets I and II for thermal engineering researchers and practitioners.