Pool-boiling Enhancement and Liquid Choking Limits Within and Above a Modulated Porous-layer Coating PDF Download
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Author: Scott Gayton Liter
Publisher:
ISBN:
Category :
Languages : en
Pages : 246
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Author: Scott Gayton Liter
Publisher:
ISBN:
Category :
Languages : en
Pages : 246
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Book Description
Author: Klaus D. Sattler
Publisher: CRC Press
ISBN: 1351649590
Category : Science
Languages : en
Pages : 1133
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Book Description
This comprehensive tutorial guide to silicon nanomaterials spans from fundamental properties, growth mechanisms, and processing of nanosilicon to electronic device, energy conversion and storage, biomedical, and environmental applications. It also presents core knowledge with basic mathematical equations, tables, and graphs in order to provide the reader with the tools necessary to understand the latest technology developments. From low-dimensional structures, quantum dots, and nanowires to hybrid materials, arrays, networks, and biomedical applications, this Sourcebook is a complete resource for anyone working with this materials: Covers fundamental concepts, properties, methods, and practical applications. Focuses on one important type of silicon nanomaterial in every chapter. Discusses formation, properties, and applications for each material. Written in a tutorial style with basic equations and fundamentals included in an extended introduction. Highlights materials that show exceptional properties as well as strong prospects for future applications. Klaus D. Sattler is professor physics at the University of Hawaii, Honolulu, having earned his PhD at the Swiss Federal Institute of Technology (ETH) in Zurich. He was honored with the Walter Schottky Prize from the German Physical Society, and is the editor of the sister work also published by Taylor & Francis, Carbon Nanomaterials Sourcebook, as well as the acclaimed multi-volume Handbook of Nanophysics.
Author: Ephraim M. Sparrow
Publisher: Academic Press
ISBN: 0323850820
Category : Technology & Engineering
Languages : en
Pages : 414
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Book Description
Advances in Heat Transfer, Volume 53 in this long-running serial, highlights new advances in the field, with this new volume presenting interesting chapters written by an international board of authors. Provides the authority and expertise of leading contributors from an international board of authors Presents the latest release in the Advances in Heat Transfer series
Author: Smreeti Dahariya
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Boiling has received considerable attention in the technology advancement of electronics cooling for high-performance computing applications. Two-phase cooling has an advantage over a single-phase cooling in the high heat removal rate with a small thermal gradient due to the latent heat of vaporization. Many surface modifications have been done in the past including surface roughness, mixed wettability and, porous wick copper play a crucial role in the liquid-vapor phase change heat transfer. However, the mechanisms of high-pressure pool-boiling heat transfer enhancement due to surface modifications has not been well studied or understood. The properties of water, such as the latent heat of vaporization, surface tension, the difference in specific volume of liquid and vapor, decrease at high-pressure. High-pressure pool-boiling heat transfer enhancement is studied fundamentally on various engineered surfaces. The boiling tests are performed at a maximum pressure of 90 psig (620.5 kPa) and then compared to results at 0 psig (0 kPa). The results indicate that the pressure influences the boiling performance through changes in bubble dynamics. The bubble departure diameter, bubble departure frequency, and the active nucleation sites change with pressure. The pool-boiling heat transfer enhancement of a Teflon© coated surface is also experimentally tested, using water as the working fluid. The boiling results are compared with a plain surface at two different pressures, 30 and 45 psig. The maximum heat transfer enhancement is found at the low heat fluxes. At high heat fluxes, a negligible effect is observed in HTC. The primary reasons for the HTC enhancement at low heat fluxes are active nucleation sites at low wall superheat and bubble departure size. The Teflon© coated surface promotes nucleation because of the lower surface energy requirement. The boiling results are also obtained for wick surfaces. The wick surfaces are fabricated using a sintering process. The boiling results are compared with a plain surface. The reasons for enhancements in the pool-boiling performance are primarily due to increased bubble generation, higher bubble release frequency, reduced thermal-hydraulic length modulation, and enhanced thermal conductivity due to the sintered wick layer. The analysis suggests that the Rayleigh-critical wavelength decreases by 4.67 % of varying pressure, which may cause the bubble pinning between the gaps of sintered particles and avoids the bubble coalescence. Changes in the pitch distance indicate that a liquid-vapor phase separation happens at the solid/liquid interface, which impacts the heat-transfer performance significantly. Similarly, the role of the high-pressure over the wicking layer is further analyzed and studied. It is found that the critical flow length, [lambda]u reduces by three times with 200 [mu]m particles. The results suggest that the porous wick layer provides a capillary-assist to liquid flow effect, and delays the surface dry out. The surface modification and the pressure amplify the boiling heat transfer performance. All these reasons may contribute to the CHF, and HTC enhancement in the wicking layer at high-pressure.
Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 820
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Author: Arvind Jaikumar
Publisher:
ISBN:
Category : Ebullition
Languages : en
Pages : 158
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Book Description
"Boiling is an efficacious mode of heat transfer and is utilized in various energy conversions, heat exchange systems and in cooling of high energy density electronic components. Fundamental pool boiling mechanisms suggest that liquid rewetting on a heated surface is a key factor in delaying critical heat flux (CHF) for enhancing pool boiling performance. In this study, pool boiling enhancement is achieved by providing improved liquid supply pathways to nucleation sites in open microchannels. A two part study is conducted to enhance pool boiling performance of open microchannels. Micromachined and porous surfaces are identified as enhancement techniques in Part-I and Part-II respectively. The results obtained in part-I showed significant improvement in the pool boiling performance when tested with water and FC-87. In part-II of the study, porous coatings are deposited on the boiling surface of an open parallel microchannel fin tops, channel bottoms and both, and individually investigated for their pool boiling performance. The best performing surface was with porous coatings throughout the geometry and had a CHF of 313 W/cm2 at a wall superheat of 7.5 °C. High speed images for the three surfaces show that bubble nucleation occurred at the location of porous deposits. Furthermore, additional nucleation sites are identified as the main contributing factor in the best performing surface which had an enhancement of 150% in CHF when compared to a plain surface. Efficient liquid recirculation provided by open microchannels also contributed to improved microconvection in the channels."--Abstract.
Author: Sujoy Kumar Saha
Publisher:
ISBN: 9783030207564
Category : Fluid mechanics
Languages : en
Pages : 121
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Book Description
This Brief concerns heat transfer and pressure drop in heat transfer enhancement for boiling and condensation. The authors divide their topic into six areas: abrasive treatment and coatings, combined structured and porous surfaces, basic principles of boiling mechanism, vapor space condensation, convective vaporization, and forced condensation inside tubes. Within this framework, the book examines range of specific phenomena including abrasive treatment, open grooves, 3D cavities, etched surfaces, electroplating, pierced 3D cover sheets, attached wire and screen promoters, non-wetting coatings, oxide and ceramic coatings, porous surfaces, structured surfaces (integral roughness), combined structured and porous surfaces, composite surfaces, single-tube pool boiling tests, theoretical fundamentals like liquid superheat, effect of cavity shape and contact angle on superheat, entrapment of vapor in cavities, nucleation at a surface cavity, effect of dissolved gases, bubble departure diameter, bubble dynamics, boiling hysteresis and orientation effects, basic principles of boiling mechanism, visualization and mechanism of boiling in subsurface tunnels, and Chien and Webb parametric boiling studies.
Author: Melanie Tetreault-Friend
Publisher:
ISBN:
Category :
Languages : en
Pages : 99
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Book Description
Predicting the conditions of critical heat flux (CHF) is of considerable importance for safety and economic reasons in heat transfer units, such as in nuclear power plants. It is greatly advantageous to increase this thermal limit and much effort has been devoted to studying the effects of surface characteristics on it. In particular, recent work carried out by O'Hanley demonstrated the separate effects of surface wettability, porosity, and roughness on CHF, and found that porous hydrophilic surface coatings provided the largest CHF increase, with a 50-60% enhancement over the base case. In the present study, a systematic investigation of the effects that the physical characteristics of the hydrophilic layers have on heat transfer was conducted. Parameters experimentally explored include porous layer thickness, pore size, and void fraction (pore volume fraction). The surface characteristics are created by depositing layer-by-layer (LbL) thin compact coatings made of hydrophilic SiO2 nanoparticles of various sizes. A new coating was developed to reduce the void fraction by using polymers to partially fill the voids in the porous layers. All test surfaces are prepared on indium tin oxide - sapphire heaters and tested in a pool boiling facility at atmospheric pressure in MIT's Thermal-Hydraulics Laboratory. Results indicate that CHF follows a trend with respect to each parameter studied and clear CHF maxima reaching up to 114% enhancement are observed for specific thickness and pore size values. ZnO2 nanofluid-generated coatings are also prepared and their boiling performance is compared to the boiling performance of the engineered LbL coatings. The results highlight the dependence of CHF on capillary wicking and are expected to allow further optimization of the nanoengineered surfaces.
Author: Wendell O. S. Bailey
Publisher:
ISBN:
Category :
Languages : en
Pages : 603
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Author: Camil-Daniel Ghiu
Publisher:
ISBN:
Category : Ebullition
Languages : en
Pages :
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Book Description
A study of pool boiling of a dielectric liquid (PF 5060) from single-layered enhanced structures was conducted. The parameters investigated were the heat flux, the width of the microchannels and the microchannel pitch. The boiling performance of the enhanced structures increases with increase in channel width and decrease in channel pitch. Simple single line curve fits are provided as a practical way of predicting the data over the entire nucleate boiling regime. The influence of confinement on the thermal performance of the enhanced structures was also assessed. The main parameter investigated was the top space (0 mm 3{13 mm). High-speed visualization was used as a tool . For the total confinement (= 0 mm), the heat transfer performance of the enhanced structures was found to depend weakly on the channel width. For>0 mm, the enhancement observed for plain surfaces in the low heat fluxes regime is not present for the present enhanced structure. The maximum heat flux for a prescribed 85 °C surface temperature limit increased with the increase of the top spacing, similar to the plain surfaces case. Two characteristic regimes of pool boiling have been identified and described: isolated flattened bubbles regime and coalesced bubbles regime. A semi-analytical predictive model applicable to pool boiling under confinement is developed. The model requires a limited number of empirical constants and is capable of predicting the experimental heat flux within 30%.
