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Enhancement Of Pool Boiling Heat Transfer Using Thermally Conductive Microporous Coating Techniques
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Book Synopsis Enhancement of Pool Boiling Heat Transfer Using Thermally-conductive Microporous Coating Techniques by : Joo Han Kim
Download or read book Enhancement of Pool Boiling Heat Transfer Using Thermally-conductive Microporous Coating Techniques written by Joo Han Kim and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The present research is an experimental study of the enhancement of boiling heat transfer using microporous coating techniques. The current research is divided into four major phases. During the first phase, the effects of different metal particle sizes in the coating compound for thermally non-conductive microporous coating on pool boiling performance of refrigerants and water are investigated. The test surfaces were solid copper blocks with 1-cm2 base at atmospheric pressure in saturated FC-72, R-123, and water. Results showed that the surface treatment by non-conductive microporous coating significantly enhanced both nucleate boiling and critical heat flux of FC-72 and R-123. However, the enhancement of boiling performance for water was merely shown. In the second phase, thermally conductive microporous coatings to enhance boiling performance of water were developed. The first phase motivated efforts to fabricate microporous coatings with conducting binder options. The second phase was stemmed from an effort to combine the advantages of both a mixture batch type (inexpensive & easy process) and sintering/machining method (low thermal resistance of conduction). Two categories of surface treatment processes were considered in the current research. The first can be achieved by a chemical process, Multi-Staged Electroplating (MSE), which uses electricity in a chemical bath to deposit a microporous structure on the surface. The second is a soldering process, Multi-Temperature Soldering Process (MTSP), which binds the metal particles to generate optimum microporous cavities. Scanning Electron Microscope (SEM) and optical microscope images were obtained for thermally conductive microporous coated surfaces. During the third phase, the pool boiling performance of developed MSE and MTSP from second phase was confirmed for water. Results showed that the MSE and MTSP augmented the boiling performance not only for refrigerants but also for water significantly compared to non-conductive microporous coatings. Further investigation for possible future industrial applications of microporous coatings, such as indirect cooling for electronic chips, nanofluids for high power generation industries, and freezing problem of water, were conducted in the final phase.
Book Synopsis Enhancement of Pool Boiling and Evaporative Heat Transfer Using High Temperature Thermally Conductive Microporous Coatings by : Ajay Gurung
Download or read book Enhancement of Pool Boiling and Evaporative Heat Transfer Using High Temperature Thermally Conductive Microporous Coatings written by Ajay Gurung and published by . This book was released on 2015 with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt: The present research is an experimental study of the enhancement of pool boiling and evaporative heat transfer using high temperature thermally conductive microporous coatings. Two major types of coatings were investigated: one that is based on copper powders on copper substrate and the other on aluminum powders on aluminum substrate. Both coatings were easy to fabricate with low costs compared to conventional sintering and plasma spraying techniques, yet have high bonding strength and some of them can operate at temperatures up to 670 °C. Multiple coating options were fabricated and tested in pool boiling of water in order to optimize the coating. These coating options consisted of variations of coating composition ratio, coating thickness and powder sizes. Average powder sizes ranged from 5 micron to 110 micron, and coating thicknesses from 75 micron to 340 micron, applied on flat 1x1cm2 test heaters. The heaters were tested in the horizontal, upward-facing orientation in saturated conditions at atmospheric pressure and under increasing heat flux. Pool boiling results revealed an optimum composition, powder size and thickness for each coating types. The maximum enhancement in boiling heat transfer coefficient obtained from copper microporous coatings was up to 8.7 times relative to a plain copper test surface and nearly doubled the critical heat flux while aluminum microporous coatings enhanced boiling heat transfer coefficient by 3.5 times compared to plain aluminum surface without any further enhancement in CHF. This enhancement was ascribed to the numerous microcavities of optimum shape and size formed within the porous matrix of the coating. The detail microstructures of the coatings from the top surface as well as cross-sections are also presented through optical microscope and SEM images. The optimized aluminum coatings were also explored on fluids other than water such as acetone and HFE-7100 for their boiling heat transfer enhancement. Furthermore, the same coatings were applied on evaporative spray and jetimpingement tests using water to broaden the application of aluminum microporous coatings in evaporative cooling technology.
Book Synopsis Hydrodynamic Aspects of Boiling Heat Transfer by : N. Zuber
Download or read book Hydrodynamic Aspects of Boiling Heat Transfer written by N. Zuber and published by . This book was released on 1959 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Enhancement of Pool Boiling Heat Transfer Using a Combination of Open Microchannels and Microporous Surfaces by : Chinmay Patil
Download or read book Enhancement of Pool Boiling Heat Transfer Using a Combination of Open Microchannels and Microporous Surfaces written by Chinmay Patil and published by . This book was released on 2014 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Enhancement of Pool Boiling Critical Heat Flux in Dielectric Liquids by : Mehmet Arik
Download or read book Enhancement of Pool Boiling Critical Heat Flux in Dielectric Liquids written by Mehmet Arik and published by . This book was released on 2001 with total page 462 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Handbook of Thermal Science and Engineering by :
Download or read book Handbook of Thermal Science and Engineering written by and published by Springer. This book was released on 2018-07-31 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This Handbook provides researchers, faculty, design engineers in industrial R&D, and practicing engineers in the field concise treatments of advanced and more-recently established topics in thermal science and engineering, with an important emphasis on micro- and nanosystems, not covered in earlier references on applied thermal science, heat transfer or relevant aspects of mechanical/chemical engineering. Major sections address new developments in heat transfer, transport phenomena, single- and multiphase flows with energy transfer, thermal-bioengineering, thermal radiation, combined mode heat transfer, coupled heat and mass transfer, and energy systems. Energy transport at the macro-scale and micro/nano-scales is also included. The internationally recognized team of authors adopt a consistent and systematic approach and writing style, including ample cross reference among topics, offering readers a user-friendly knowledgebase greater than the sum of its parts, perfect for frequent consultation. The Handbook of Thermal Science and Engineering is ideal for academic and professional readers in the traditional and emerging areas of mechanical engineering, chemical engineering, aerospace engineering, bioengineering, electronics fabrication, energy, and manufacturing concerned with the influence thermal phenomena.
Book Synopsis Bioinspired Engineering of Thermal Materials by : Tao Deng
Download or read book Bioinspired Engineering of Thermal Materials written by Tao Deng and published by John Wiley & Sons. This book was released on 2018-06-11 with total page 274 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive overview and summary of recent achievements and the latest trends in bioinspired thermal materials. Following an introduction to different thermal materials and their effective heat transfer to other materials, the text discusses heat detection materials that are inspired by biological systems, such as fire beetles and butterflies. There then follow descriptions of materials with thermal management functionality, including those for evaporation and condensation, heat transfer and thermal insulation materials, as modeled on snake skins, polar bears and fire-resistant trees. A discussion of thermoresponsive materials with thermally switchable surfaces and controllable nanochannels as well as those with high thermal conductivity and piezoelectric sensors is rounded off by a look toward future trends in the bioinspired engineering of thermal materials. Straightforward and well structured, this is an essential reference for newcomers as well as experienced researchers in this exciting field.
Book Synopsis Multiscale Mechanistic Approach to Enhance Pool Boiling Performance for High Heat Flux Applications by : Arvind Jaikumar
Download or read book Multiscale Mechanistic Approach to Enhance Pool Boiling Performance for High Heat Flux Applications written by Arvind Jaikumar and published by . This book was released on 2017 with total page 218 pages. Available in PDF, EPUB and Kindle. Book excerpt: "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.
Book Synopsis Electronics Cooling by : S. M. Sohel Murshed
Download or read book Electronics Cooling written by S. M. Sohel Murshed and published by BoD – Books on Demand. This book was released on 2016-06-15 with total page 184 pages. Available in PDF, EPUB and Kindle. Book excerpt: Featuring contributions from the renowned researchers and academicians in the field, this book covers key conventional and emerging cooling techniques and coolants for electronics cooling. It includes following thematic topics: - Cooling approaches and coolants - Boiling and phase change-based technologies - Heat pipes-based cooling - Microchannels cooling systems - Heat loop cooling technology - Nanofluids as coolants - Theoretical development for the junction temperature of package chips. This book is intended to be a reference source and guide to researchers, engineers, postgraduate students, and academicians in the fields of thermal management and cooling technologies as well as for people in the electronics and semiconductors industries.
Book Synopsis Enhanced Pool Boiling Heat Transfer by Flow Modulation and Contact Line Augmentation Over Cylindrical Tubes by : Indranil M. Joshi
Download or read book Enhanced Pool Boiling Heat Transfer by Flow Modulation and Contact Line Augmentation Over Cylindrical Tubes written by Indranil M. Joshi and published by . This book was released on 2017 with total page 71 pages. Available in PDF, EPUB and Kindle. Book excerpt: "The miniaturization trend in electronics has spurred the development of efficient thermal management solutions. Single phase techniques are reliable but are limited by large fluid temperature differences and pressure drop. Two phase cooling has very little pressure drop with large heat absorption capacity. Boiling stands out as one of the most effective methods of heat dissipation which utilizes phase change. However, the design of two-phase systems is limited by the critical heat flux condition where a vapor layer prevents the liquid from contacting the heater surface. The current research study is directed towards increasing the CHF and maintaining low wall superheats to design efficient heat removal systems. In this study, different surface modification techniques are studied with an aim to identify various mechanisms that affect the heat transfer. Different surface enhancements in the form of Circumferential rectangular microchannels(CRM) and fin are used over cylindrical surface. Cylindrical tube with outer diameter of 15 mm was used for testing with water as working fluid. Tubular surface with fin attached performed the best yielding the CHF of 115 W/cm2 at wall superheat of 18oC which translated to an enhancement of 76%. The best performance of 110 W/cm2 at 9 oC without reaching CHF was obtained amongst CRM. Different mechanisms were identified by analyzing the results from pool boiling experiments. Area enhancement and contact line substantially affected the heat transfer performance in CRM. Area enhancement increased performance by providing additional area for heat transfer. Contact line region has higher heat flux. Single bubble growing over multiple grooves has increased contact line density which increases heat transfer performance. Increment in CHF was obtained by employing any one of these surface enhancements. High speed imaging enabled to analyze the behavior of bubble after nucleation on the fin surface thus deciphering the flow modulation over the cylindrical surface. Presence of bubble diverter at the bottom surface ensured higher evaporative momentum force towards the cylindrical surface. This displaced nucleating bubble at the bottom away from the fin, enabling liquid to rewet the surface. This allowed the formation of separate liquid vapor pathways which resulted in increased performance."--Abstract.
Book Synopsis Recent Advances in Mechanical Engineering by : K.M. Pandey
Download or read book Recent Advances in Mechanical Engineering written by K.M. Pandey and published by Springer Nature. This book was released on 2021-01-10 with total page 949 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents the select proceedings of the International Conference on Recent Advancements in Mechanical Engineering (ICRAME 2020). It provides a comprehensive overview of the various technical challenges faced, their systematic investigation, contemporary developments, and future perspectives in the domain of mechanical engineering. The book covers a wide array of topics including fluid flow techniques, compressible flows, waste management and waste disposal, bio-fuels, renewable energy, cryogenic applications, computing in applied mechanics, product design, dynamics and control of structures, fracture and failure mechanics, solid mechanics, finite element analysis, tribology, nano-mechanics and MEMS, robotics, supply chain management and logistics, intelligent manufacturing system, rapid prototyping and reverse engineering, quality control and reliability, conventional and non-conventional machining, and ergonomics. This book can be useful for students and researchers interested in mechanical engineering and its allied fields.
Book Synopsis Exploring the Limits of Boiling and Evaporative Heat Transfer Using Micro/Nano Structures by : Ming-Chang Lu
Download or read book Exploring the Limits of Boiling and Evaporative Heat Transfer Using Micro/Nano Structures written by Ming-Chang Lu and published by . This book was released on 2010 with total page 218 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation presents a study exploring the limits of phase-change heat transfer with the aim of enhancing critical heat flux (CHF) in pool boiling and enhancing thermal conductance in heat pipes. The state-of-the-art values of the CHF in pool boiling and the thermal conductance in heat pipes are about two orders of magnitudes smaller than the limits predicted by kinetic theory. Consequently, there seems to be plenty of room for improvement. Pool boiling refers to boiling at a surface immersed in an extensive motionless pool of liquid. Its process includes heterogeneous nucleation, growth, mergence and detachment of vapor bubbles on a heating surface. It is generally agreed that the high heat transfer coefficient of boiling could be explained by the concept of single-phase forced convection, i.e., the motion of bubbles agitating surrounding liquid is similar to the process in single-phase forced convection. The occurrence of CHF results from a formation of a vapor film on the heater surface, which reduces the thermal conductance drastically and causes a huge temperature rise on the surface. Over the past few decades, researchers were struggling to identify the exact mechanism causing CHF. General observations are that both surface properties and pool hydrodynamics could affect the values of CHF. Nanowire array-coated surfaces having a large capillary force are employed to enhance the CHF. It has been shown that CHFs on the nanowire array-coated surface could be doubled compared to the values on a plain surface. The obtained CHF of 224 ± 6.60 W/cm̂2 on the nanowire-array coated surface is one of the highest values reported in the boiling heat transfer. To further enhance CHF, the mechanisms that govern CHF have been systematically explored. Experimental results show that the CHF on the nanowire array-coated surface are not limited by the capillary force. Instead, the CHF are dependent on the heater size. Corresponding experiments on plain surfaces with various heater sizes also exhibits similar heater-size dependence. The CHFs on nanowire array-coated surfaces and plain surfaces are consistent with the predictions of the hydrodynamic theory while a higher CHF is obtained on the nanowire array-coated surface as compared to the plain Si surface. This suggests that the CHFs are a result of the pool hydrodynamics while surface properties modify the corresponding hydrodynamic limits. A heat pipe is a device that transports thermal energy in a very small temperature difference and thereby producing a very large thermal conductance. It relies on evaporation of liquid at the heated end of the pipe, flow of vapor between the heated and cooled end, condensation at the other end, and capillary-driven liquid flow through a porous wick between the condenser and the evaporation. The large latent heat involved in evaporation and condensation leads to very large heat flows for a small temperature drop along the heat pipe. Despite the large thermal conductance, their operation is limited by such factors as capillary limit, boiling limit, sonic limit and entrainment limit, etc. Among these operational limits, capillary and boiling limits are most frequently encountered. The capillary limit determines the maximum flow rate provided by the capillary force of the wick structure whereas boiling limit is referred to a condition that liquid supply is blocked by vapor bubbles in the wick. Consequently, the wick structure is the key component in a heat pipe, which determines the maximum capillary force and the dominant thermal resistance. In a heat pipe using evaporation as the dominant heat transfer mechanism, a thin liquid film (̃ a few microns) extended from the solid structure in the wick causes the dominant thermal resistance. Therefore, if one reduces the pore size of a porous media, the thermal conductance could be enhanced by increasing the surface area of the thin liquid film. On the other hand, the classical thermodynamics depicts that the superheat required for evaporation is inversely proportional to the equilibrium radius of the meniscus. Consequently, enhancing thermal conductance via increasing the thin film area is contradictory to the effect of evaporation suppression for small pores. A hierarchical wick structure with multiple length scales that enhances dry-out heat flux and thermal conductance simultaneously in heat pipes was demonstrated. This hierarchical wick structure is composed of a large microchannel array to reduce flow resistance and small pin-fin arrays to provide a large capillary force. The enhancement of thermal conductance is achieved via a large number of pin-fins for increasing the total thin film area. A thermal conductance defined by the slope of the curve of ̃16.28 ± 1.33 W/cm̂2-K and a dry-out heat flux of 228.85 ± 10.73 W/cm̂2 were achieved by this design. Further, vapor transport resistance is minimized within the aligned-multi-scale wick structure. As a result, this wick does not pose a boiling limit. Artificial cavities were created in the wick structure to take the advantage of the high heat transfer coefficient of boiling heat transfer. The wick with artificial cavities successfully triggers boiling at a lower wall temperature resulting in a conductance of 9.02 ± 0.04 W/cm̂2-K compared to an evaporation mode of 3.54 ± 0.01 W/cm̂2-K. For a given heat flux, the wick with cavities effectively reduce wall temperature compared to a wick without cavities. Our experimental results display an enhancement of thermal conductance by using boiling heat transfer. This opens up a new direction for further enhancing thermal conductance in heat pipes by circumventing the limit in the evaporative heat transfer regime, in which further increase in surface area will eventually result in evaporation suppression in small pores.
Book Synopsis Enhancement of Pool Boiling Heat Transfer in Confined Space by : Chia-Hsiang Hsu
Download or read book Enhancement of Pool Boiling Heat Transfer in Confined Space written by Chia-Hsiang Hsu and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Pool boiling is an effective method used in many technical applications for a long time. Its highly efficient heat transfer performance results from not only the convection effect but also the phase change process in pool boiling. Pool boiling enhancement has been studied in the past decade. However, the mechanisms of pool boiling has not yet been fully understood because of the many parameters that affect its behavior including the latent heat of vaporization, nucleation density, bubble and fluid motion, interaction at the interface, and the physical properties of surface. Among the current studies, bubble departure rate is viewed as one of the dominant factors that affect heat transfer. This research considers the effect of bubble confinement on pool boiling. In the study, confinement was achieved by placing a flat plate over heated surface. The flat plate has a hole in the middle, and there is a gap between the flat plate and the heater. The diameters of hole are 2 mm, 3 mm, and 4 mm; the gap distances are 2.3 mm, 3.6 mm, and 5 mm. The heater consists of an indium-tin-oxide layer deposited on a silicon wafer. An IR camera and high speed cameras are used to acquire the surface temperature distribution and bubble image. By controlling the plate hole size and the gap distance, the effect of confinement on heat transfer performance can be evaluated. Moreover, heat transfer performance of pool boiling with three-2mm-holes plate was investigated and compared with that of single-2mm-hole plate with the smallest gap size. At the lower heat flux values, heat transfer enhancement in confined space was experimentally observed. Surface temperature can be reduced by 4 °C at most. Results indicate that higher bubble departure rate and coalescence effect might be the dominant factor for improving heat transfer performance in a confined space caused by induced shear flow. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/152843
Book Synopsis AN EXPERIMENTAL INVESTIGATION OF THE EFFECTS OF SURFACE CONDITIONS ON POOL-BOILING HEAT TRANSFER FOR VARIOUS MATERIALS. by : Shikha Ebrahim
Download or read book AN EXPERIMENTAL INVESTIGATION OF THE EFFECTS OF SURFACE CONDITIONS ON POOL-BOILING HEAT TRANSFER FOR VARIOUS MATERIALS. written by Shikha Ebrahim and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Boiling Enhancement on Engineered Surfaces by : Md Mahamudur Rahman
Download or read book Boiling Enhancement on Engineered Surfaces written by Md Mahamudur Rahman and published by . This book was released on 2016 with total page 382 pages. Available in PDF, EPUB and Kindle. Book excerpt: The realization of next generation technologies to enhance boiling heat transfer is of critical importance due to its impact on energy, the environmental, and water resources, as well as thermal management needs of high-power electronics. Recent studies have shown that high surface area coatings comprised of micro and nano scale structures can be used to substantially increase performance during boiling. While exciting results have been reported in the literature, there is little understanding, and even less consensus, on the fundamental underlying mechanisms by which structured coatings enhance boiling. Additionally, the fabrication schemes used in the lab setting to create these structures are not scalable to large areas, complex geometries, or materials traditionally used in heat transfer applications. The focus of the Ph.D. dissertation research is on: (1) a detailed characterization of the effects of structured surfaces on boiling performance, including the role of capillary wicking, as well as the effects of surface morphology, material, and length scales; (2) scalable nanomanufacturing of structured coatings using nanoscale biological templates, and (3) the realization of novel surfaces for boiling enhancement that are resistant to degradation. The Tobacco mosaic virus (TMV) has been used as a nanoscale building block to create nanostructured and hierarchically structured surfaces with a wide variety of morphologies. Utilizing a simple technique for characterizing surface wicking, an experimentally validated model relating the maximum heat flux from a boiling surface to its inherent "wickability" has been shown for the first time. For structured superhydrophillic surfaces with characteristic lengths much smaller than the inherent flow structures (~ 1mm), capillary wicking through surface structures is the single factor determining the critical heat flux (CHF). Separately, it has been shown that hierarchically structured surfaces with length scales comparable to the flow yield more complicated enhancement mechanisms with each length scale contributing differently. Nanoscale structures enhance CHF, while micro-to-milli scale structures enhance nucleation and therefore heat transfer coefficient (HTC). The combination of the two has been show to enhance CHF and HTC by over 238% and 540% respectively. TMV biotemplating has been leveraged not only for fundamental studies of boiling enhancement but also demonstrated here for the scalable nanomanufacturing of structured coatings. Biotemplating has been used to conformally coat a variety of materials using a cheap and sustainable room-temperature solution-based procedure. Repeatable boiling heat transfer enhancements of over 200% have been demonstrated on aluminum, silicon, copper, and stainless steel surface. Such solution-based techniques are easily extended to complex surfaces and large areas using in-situ depositions for retrofittings existing systems and rejuvenating surfaces that have fouled and degraded. Finally, the use of engineered thermal gradients across surfaces comprised of heterogeneous materials has been demonstrated. By promoting ordered pathways between nucleating bubbles and replenishing liquid, engineered thermal gradients have been shown to be as effective as structured surfaces in boiling enhancement, yet inherently resistant to foiling. These planar "bi-conductive" surfaces have been characterized and their geometries optimized based on analysis of the bubble departure phenomena and surface tension effects.
Book Synopsis Handbook of Single-Phase Convective Heat Transfer by : Sadik Kakaç
Download or read book Handbook of Single-Phase Convective Heat Transfer written by Sadik Kakaç and published by Wiley-Interscience. This book was released on 1987-11-03 with total page 1268 pages. Available in PDF, EPUB and Kindle. Book excerpt: Very Good,No Highlights or Markup,all pages are intact.
