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Author: Austin Hayes
Publisher:
ISBN:
Category : Ebullition
Languages : en
Pages : 94
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Book Description
"Heat dissipation is vital in industries requiring predictable operating temperatures while also producing large heat fluxes. These industries include electronics and power generation. For electronics, as more devices fit on a smaller area, the heat flux increases dramatically. Pool boiling offers a solution to electronic cooling due to extremely high heat transfer with a low temperature change. Previous research has focused on coatings and precision manufacturing to create microchannels and features for boiling augmentation. However, this is limited to designs for subtractive processes. The use of additive manufacturing (AM) offers a novel way of thinking of design for boiling enhancement. 3-D boiling structures are fabricated out of aluminum using the Vader System's magnetojet printer. Three generations of geometric structures are created: a volcano-with-holes, a miniaturized volcano-with-holes, and a modular volcano-with-holes. These designs are not easily manufactured using standard techniques. As such, three-dimensional bubble dynamics are currently being explored using high speed imaging and particle image velocimetry. By printing a volcano shape with base holes, the liquid and vapor phases are physically separated in a process termed macroscale liquid-vapor pathways. The singular volcano-with-holes chips achieved a maximum heat flux of 217.3 W/cm2 with a maximum heat transfer coefficient (HTC) of 97.2 kW/m2K (81% improvement over plain). By producing four volcanoes on a single chip, the liquid flow length inside the volcano, which acts as the entrance length, is reduced by 50% and the HTC greatly increased. The highest performing miniaturized volcano-with-holes chip reached a maximum heat flux of 223.1W/cm2 with a maximum HTC of 139.1 kW/m2K (150% improvement over plain). Additionally, the highest performing miniaturized chip was printed on top of a microchannel array. This resulted in combined enhancement from both microchannel and bubble dynamics resulting in a maximum heat flux of 228.4 W/cm2 with a HTC of 339.6 kW/m2K (533% improvement over plain). Finally, a modular structure was created to determine the individual influence of conduction and bubble dynamic augmentation on boiling enhancement. The modular designs show an 83% improvement in CHF (202.4 W/cm2) over plain copper chips and a 83% improvement in HTC(139.0 kW/m2K). This indicates boiling enhancement arises from three-dimensional control over bubble dynamics, resulting in macroscale separate liquid-vapor pathways."--Abstract.
Author: Austin Hayes
Publisher:
ISBN:
Category : Ebullition
Languages : en
Pages : 94
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Book Description
"Heat dissipation is vital in industries requiring predictable operating temperatures while also producing large heat fluxes. These industries include electronics and power generation. For electronics, as more devices fit on a smaller area, the heat flux increases dramatically. Pool boiling offers a solution to electronic cooling due to extremely high heat transfer with a low temperature change. Previous research has focused on coatings and precision manufacturing to create microchannels and features for boiling augmentation. However, this is limited to designs for subtractive processes. The use of additive manufacturing (AM) offers a novel way of thinking of design for boiling enhancement. 3-D boiling structures are fabricated out of aluminum using the Vader System's magnetojet printer. Three generations of geometric structures are created: a volcano-with-holes, a miniaturized volcano-with-holes, and a modular volcano-with-holes. These designs are not easily manufactured using standard techniques. As such, three-dimensional bubble dynamics are currently being explored using high speed imaging and particle image velocimetry. By printing a volcano shape with base holes, the liquid and vapor phases are physically separated in a process termed macroscale liquid-vapor pathways. The singular volcano-with-holes chips achieved a maximum heat flux of 217.3 W/cm2 with a maximum heat transfer coefficient (HTC) of 97.2 kW/m2K (81% improvement over plain). By producing four volcanoes on a single chip, the liquid flow length inside the volcano, which acts as the entrance length, is reduced by 50% and the HTC greatly increased. The highest performing miniaturized volcano-with-holes chip reached a maximum heat flux of 223.1W/cm2 with a maximum HTC of 139.1 kW/m2K (150% improvement over plain). Additionally, the highest performing miniaturized chip was printed on top of a microchannel array. This resulted in combined enhancement from both microchannel and bubble dynamics resulting in a maximum heat flux of 228.4 W/cm2 with a HTC of 339.6 kW/m2K (533% improvement over plain). Finally, a modular structure was created to determine the individual influence of conduction and bubble dynamic augmentation on boiling enhancement. The modular designs show an 83% improvement in CHF (202.4 W/cm2) over plain copper chips and a 83% improvement in HTC(139.0 kW/m2K). This indicates boiling enhancement arises from three-dimensional control over bubble dynamics, resulting in macroscale separate liquid-vapor pathways."--Abstract.
Author: Callum McLaughlin
Publisher:
ISBN:
Category : Ebullition
Languages : en
Pages : 44
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Book Description
"Heat generation in electronic hardware has become a major limiting factor in achieving maximum efficiency in modern computer parts. Classically forced flow convection systems are used to remove this heat at high rates but can be costly to implement and can take up space that may be needed for other critical components. In response to this, systems that use fewer parts scale in compact spaces are needed. In these situations, pool boiling as a heat transfer mechanism can excel. Pool boiling removes heat through the evaporation of fluid. On a flat surface pool boiling is chaotic and this random nature may hinder its ability to remove heat as effectively. The surface geometry of a pool boiling system can be altered to direct the flow of generated vapor bubbles to allow for increased heat flow and higher heat transfer performance. By creating paths for the vapor to follow we can induce currents in the flow of cool fluid to the heater surface, creating a faster cycle of vapor production therefore cooling the heated surface at a faster rate. The purpose of this study is to investigate angled chip notches as an alternative to already existing high heat transfer surfaces in pool boiling. These alternative chips may prove cheaper or easier to produce the alternative which may incorporate fine, hard to produce features or post process coatings like sintering and the addition of hydrophobic materials. This study will examine the effect these specifically designed notches have on the interaction between the directed vapor and the liquid pathways they create. By creating notches in the surface of the chip, vapor bubble is given sites to nucleate and form vapor pathways. The angle walls on the one side of the notch will act as a wedge when water being driven toward the notch pushes the nucleating bubble up and out of the notch. Combined with pairing nucleating notches up with another oppositely facing one the vapor bubble is departing earlier then it would have had it not been assisted by these surface elements. With just these paired notches placed in row, an HTC improvement of 158% was recorded, compared to a plain copper surface. With the inclusion of microchannels this improvement was brought up to 161%"--Abstract.
Author: Farhan Mody
Publisher:
ISBN:
Category : Dielectrics
Languages : en
Pages : 75
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Book Description
"The miniaturization trend of transistors and increase in packing density of electronic devices has resulted in high heat flux generation, which has created a need for efficient heat removal systems. The present research is an experimental study of pool boiling using plain copper chip and microchannel chip with boiling surface of 34.5mm x 32mm. Three dielectric fluids, Perfluoro-2-methylpentane (PP1), perfluoro-methyl-cyclopentane (PP1C), and fluorocarbon (FC-87) were used in a closed loop pool boiling system to determine their performance at atmospheric pressure. The pool boiling results have been compared with literature for a boiling surface of 10 mm x 10 mm to study the effect of heater size. To improve the performance of the pool boiling system, we desire high critical heat flux and low surface temperatures. In the current study, we introduced two external structures fitted on the test surfaces for regulating the flow of vapor through specific structures and generating independent liquid-vapor pathways without any deposition and/or chemical surface modifications of the test surface. Firstly, an array of hollow conical structures (HCS) called volcano manifold are printed using additive manufacturing technique. A critical heat flux (CHF) of 28.1 W/cm2, 38.3 W/cm2 and 32.5 W/cm2 was achieved for volcano manifold with plain copper chip using PP1, PP1C and FC87 respectively giving 19%, 33% and 6.5% enhancement in CHF respectively as compared to a plain chip without volcano manifold. Secondly, dual taper manifold having taper angle of 15° is printed using a stereolithography (SLA) additive manufacturing technique. Plain chip with dual taper manifold gave the CHF of 25.6 W/cm2, 31.7 W/cm2 and 32.3 W/cm2 for PP1, PP1C and FC-87, respectively. These results indicate a deterioration in CHF caused by vapor constriction. In addition, the heater size effect was studied by comparing the pool boiling performance of a plain copper boiling surface of 34.5 mm x 32 mm (Large heater) with 10 mm x 10 mm (Small heater) from published literature for all three refrigerants. It was noted that 31%, 66% and 104% increment in maximum heat transfer coefficient was obtained for PP1, PP1C and FC-87 respectively with larger heater over smaller heater at CHF. The geometrical parameters of the enhancement structures were based on published results for water. The results show that the external surface modification techniques require further geometrical parameter optimization as the current designs based on water performance caused vapor constriction effects that caused performance deterioration for dielectric fluids."--Abstract.
Author: Arvind Jaikumar
Publisher:
ISBN:
Category : Ebullition
Languages : en
Pages : 218
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Book Description
"The advent of cloud computing and the complex packaging architecture of next generation electronic devices drives methods for advanced thermal management solutions. Convection based single-phase cooling systems are inefficient due to their large pressure drops, fluid temperature differences and costs, and are incapable of meeting the cooling requirements in the high power density components and systems. Alternatively, phase-change cooling techniques are attractive due to their ability to remove large amounts of heat while maintaining uniform fluid temperatures. Pool boiling heat transfer mechanism centers on the nucleation, growth and departure of a bubble from the heat transfer surface in a stagnant pool of liquid. The pool boiling performance is quantified by the Critical Heat Flux (CHF) and Heat Transfer Coefficients (HTC) which dictate the operating ranges and efficiency of the heat transfer process. In this work, three novel geometries are introduced to modify the nucleation characteristics, liquid pathways and contact line motion on the prime heater surface for a simultaneous increase in CHF and HTC. First, sintered microchannels and nucleating region with feeder channels (NRFC) were developed through the mechanistic concept of separate liquid-vapor pathways and enhanced macroconvection heat transfer. A maximum CHF of 420 W/cm2 at a wall superheat of 1.7 °C with a HTC of 2900 MW/m2°C was achieved with the sintered-channels configuration, while the NRFC reached a CHF of 394 W/cm2 with a HTC of 713 kW/m2°C. Second, the scale effect of liquid wettability, roughness and microlayer evaporation was exploited to facilitate capillary wicking in graphene through interlaced porous copper particles. A CHF of 220 W/cm2 with a HTC of 155 kW/m2°C was achieved using an electrodeposition coating technique. Third, the chemical heterogeneity on nanoscale coatings was shown to increase the contribution from transient conduction mechanisms. A maximum CHF of 226 W/cm2 with a HTC of 107 kW/m2°C was achieved. The enhancement techniques developed here provide a mechanistic tool at the microscale and nanoscale to increase the boiling CHF and HTC."--Abstract.
Author: Hongbin Ma
Publisher: Springer
ISBN: 1493925040
Category : Science
Languages : en
Pages : 441
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Book Description
This book presents the fundamental fluid flow and heat transfer principles occurring in oscillating heat pipes and also provides updated developments and recent innovations in research and applications of heat pipes. Starting with fundamental presentation of heat pipes, the focus is on oscillating motions and its heat transfer enhancement in a two-phase heat transfer system. The book covers thermodynamic analysis, interfacial phenomenon, thin film evaporation, theoretical models of oscillating motion and heat transfer of single phase and two-phase flows, primary factors affecting oscillating motions and heat transfer, neutron imaging study of oscillating motions in an oscillating heat pipes, and nanofluid’s effect on the heat transfer performance in oscillating heat pipes. The importance of thermally-excited oscillating motion combined with phase change heat transfer to a wide variety of applications is emphasized. This book is an essential resource and learning tool for senior undergraduate, graduate students, practicing engineers, researchers, and scientists working in the area of heat pipes. This book also · Includes detailed descriptions on how an oscillating heat pipe is fabricated, tested, and utilized · Covers fundamentals of oscillating flow and heat transfer in an oscillating heat pipe · Provides general presentation of conventional heat pipes
Author: Amir Faghri
Publisher: Academic Press
ISBN:
Category : Multiphase flow
Languages : en
Pages : 1072
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Book Description
Engineering students in a wide variety of engineering disciplines from mechanical and chemical to biomedical and materials engineering must master the principles of transport phenomena as an essential tool in analyzing and designing any system or systems wherein momentum, heat and mass are transferred. This textbook was developed to address that need, with a clear presentation of the fundamentals, ample problem sets to reinforce that knowledge, and tangible examples of how this knowledge is put to use in engineering design. Professional engineers, too, will find this book invaluable as reference for everything from heat exchanger design to chemical processing system design and more. * Develops an understanding of the thermal and physical behavior of multiphase systems with phase change, including microscale and porosity, for practical applications in heat transfer, bioengineering, materials science, nuclear engineering, environmental engineering, process engineering, biotechnology and nanotechnology * Brings all three forms of phase change, i.e., liquid vapor, solid liquid and solid vapor, into one volume and describes them from one perspective in the context of fundamental treatment * Presents the generalized integral and differential transport phenomena equations for multi-component multiphase systems in local instance as well as averaging formulations. The molecular approach is also discussed with the connection between microscopic and molecular approaches * Presents basic principles of analyzing transport phenomena in multiphase systems with emphasis on melting, solidification, sublimation, vapor deposition, condensation, evaporation, boiling and two-phase flow heat transfer at the micro and macro levels * Solid/liquid/vapor interfacial phenomena, including the concepts of surface tension, wetting phenomena, disjoining pressure, contact angle, thin films and capillary phenomena, including interfacial balances for mass, species, momentum, and energy for multi-component and multiphase interfaces are discussed * Ample examples and end-of-chapter problems, with Solutions Manual and PowerPoint presentation available to the instructors
Author: K. C. Mills
Publisher: Woodhead Publishing
ISBN: 9780871707536
Category : Alloys
Languages : en
Pages : 288
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Book Description
Author: Andrea Di Schino
Publisher: MDPI
ISBN: 3039286501
Category : Technology & Engineering
Languages : en
Pages : 260
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Book Description
Stainless steels represent a quite interesting material family, both from a scientific and commercial point of view, following to their excellent combination in terms of strength and ductility together with corrosion resistance. Thanks to such properties, stainless steels have been indispensable for the technological progress during the last century and their annual consumption increased faster than other materials. They find application in all these fields requiring good corrosion resistance together with ability to be worked into complex geometries. Despite to their diffusion as a consolidated materials, many research fields are active regarding the possibility to increase stainless steels mechanical properties and corrosion resistance by grain refinement or by alloying by interstitial elements. At the same time innovations are coming from the manufacturing process of such a family of materials, also including the possibility to manufacture them starting from metals powder for 3D printing. The Special Issue scope embraces interdisciplinary work covering physical metallurgy and processes, reporting about experimental and theoretical progress concerning microstructural evolution during processing, microstructure-properties relations, applications including automotive, energy and structural.
Author: Matthias Worgull
Publisher: William Andrew
ISBN: 0815519745
Category : Technology & Engineering
Languages : en
Pages : 368
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Book Description
This book is an overview of replication technology for micro- and nanostructures, focusing on the techniques and technology of hot embossing, a scaleable and multi-purpose technology for the manufacture of devices such as BioMEMS and microfluidic devices which are expected to revolutionize a wide range of medical and industrial processes over the coming decade.The hot embossing process for replicating microstructures was developed by the Forschungszentrum Karlsruhe (Karlsruhe Institute of Technology) where the author is head of the Nanoreplication Group. Worgull fills a gap in existing information by fully detailing the technology and techniques of hot embossing. He also covers nanoimprinting, a process related to hot embossing, with examples of actual research topics and new applications in nanoreplication. - A practical and theoretical guide to selecting the materials, machinery and processes involved in microreplication using hot embossing techniques - Compares different replication processes such as: micro injection molding, micro thermoforming, micro hot embossing, and nanoimprinting - Details commercially available hot embossing machinery and components like tools and mold inserts
Author:
Publisher: Academic Press
ISBN: 0080575846
Category : Technology & Engineering
Languages : en
Pages : 467
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Book Description
Advances in Heat Transfer
