Download or read book Experiments in Pool Boiling Heat Transfer and Nucleation Dynamics of High Pressure Refrigerants written by Daniel Joo and published by . This book was released on 2006 with total page 71 pages. Available in PDF, EPUB and Kindle. Book excerpt: A high pressure pool boiling experiment of pressurized R134a is designed and built, utilizing thermochromatic liquid crystal techniques. Liquid crystals thermo-chromatography uses encapsulated liquid crystals that are sensitive to temperature. When exposed to hot temperatures the crystal reflect a blue/violet color, and when exposed to cooler temperatures it reflects a red/orange color. The color value or hue is proportional to its temperature. Using this technique this experiment is capable of studying the physics and thermodynamics of refrigerants under nucleate pool boiling.

Download or read book High pressure Pool boiling Heat Transfer Enhancement and Mechanism on Engineered Surfaces written by Smreeti Dahariya and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Handbook of Phase Change written by S.G. Kandlikar and published by Routledge. This book was released on 2019-01-22 with total page 786 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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

Download or read book Experimental Study of Nucleate Boiling Bubble Dynamics and Heat Transfer Enhancement on Printed Bi functional Surfaces written by Michele David and published by . This book was released on 2016 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt: Boiling heat transfer is studied for its ability to dissipate high fluxes and achieve heat transfer coefficients two orders of magnitude greater than single-phase heat transfer systems. Heater surface enhancement with increased surface area, varied geometry, wettability contrast and micro/nano-structures can further enhance boiling heat transfer performance through bubble nucleation augmentation. Bubble nucleation control, growth and departure dynamics is important in understanding boiling phenomena and enhancing nucleate boiling heat transfer performance. Bi-functional surfaces for enhanced boiling heat transfer were fabricated and studied through investigation of bubble dynamics and pool boiling experiments. For the fabrication of the surface, hydrophobic polymer dot arrays are first printed on a substrate, followed by hydrophilic ZnO nanostructure deposition via microreactor-assisted nanomaterial deposition (MAND) processing. Wettability contrast between the hydrophobic polymer dot arrays and aqueous ZnO solution allows for the fabrication of surfaces with distinct wettability regions. Bi-functional surfaces with various configurations were fabricated and their bubble dynamics were examined at elevated heat flux, revealing various nucleate boiling phenomena. In particular, aligned and patterned bubbles with a tunable departure frequency and diameter were demonstrated in a boiling experiment for the first time. A pool boiling experimental facility has been designed and built to investigate nucleate pool boiling in water at atmospheric pressure. Resulting boiling curves of enhanced surfaces showed up to 3X enhancement in heat transfer coefficients at the same surface superheat using bi-functional surfaces, compared to a bare stainless steel surface. The surfaces show promising results for energy savings in two-phase change applications.

Download or read book Experiments on the Mechanism of Saturated Nucleate Pool Boiling Heat Transfer written by Bruce David Marcus and published by . This book was released on 1963 with total page 444 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Experimental Study of Sodium Pool Boiling Heat Transfer written by R. C. Noyes and published by . This book was released on 1962 with total page 42 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Bubble Dynamics and Boiling Heat Transfer written by Samuel Siedel and published by . This book was released on 2013 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since boiling heat transfer affords a very effective means to transfer heat, it is implemented in numerous technologies and industries ranging from large power generation plants to micro-electronic thermal management. Although having been a subject of research for several decades, an accurate prediction of boiling heat transfer is still challenging due to the complexity of the coupled mechanisms involved. It appears that the boiling heat transfer coefficient is intimately related to bubble dynamics (i.e. bubble nucleation, growth and detachment) as well as factors such as nucleation site density and interaction between neighbouring and successive bubbles. In order to contribute to the understanding of the boiling phenomenon, an experimental investigation of saturated pool boiling from a single or two neighbouring artificial nucleation sites on a polished copper surface has been performed. The bubble growth dynamics has been characterized for different wall superheats and a experimental growth law has been established. The interaction between successive bubbles from the same nucleation site has been studied, showing the bubble shape oscillations that can be caused by these interactions. The forces acting on a growing bubble has been reviewed, and a complete momentum balance has been made for all stages of bubble growth. The curvature along the interface has been measured, and indications concerning the mechanism of bubble detachment have been suggested. The rise of bubble after detachment has been investigated, and the maximum velocity reached before a change of direction has been estimated and compared to existing models from the literature. The interaction between bubbles growing side by side has been studied: the generation and propagation of a wave front during the coalescence of two bubbles has been highlighted. As boiling heat transfer enhancement techniques are being imagined and developed, this study also focuses on the electrohydrodynamic enhancement technique. Boiling experiments have been performed in the presence of electric fields, and their effects on heat transfer and bubble dynamics have been characterized. Although the volume of the bubbles at detachment and the relationship between the bubble frequency and the wall superheat were not affected, the bubble growth curve was modified. The bubbles were elongated in the direction of the electric field, and this elongation was estimated and compared to other studies from the literature. The rising velocity of the bubble was reduced in the presence of electric field, and the behaviour of bubbles growing side by side was modified, the electric field causing the bubbles to repeal each other. These results, obtained in a fully controlled environment, provide compelling evidence that electric fields can be implemented to alter the bubble dynamics and subsequently heat transfer rates during boiling of dielectric fluids.

Download or read book Boiling of Water at Low Pressure written by Karolina Wojtasik and published by . This book was released on 2021 with total page 136 pages. Available in PDF, EPUB and Kindle. Book excerpt: Boiling process is a common heat transfer mode used in various applications, among which air-conditioning and refrigeration. Recently, there has been a sparkling interest in the development of efficient cooling technologies which utilize environmentally-friendly refrigerants. Water could be one of them, but it requires to operate under low pressure. Close to the triple point, the physics of boiling significantly differs from atmospheric pressure. Although the knowledge on subatmospheric boiling is slowly growing, many of its aspects remain unknown. In order to extend the fundamental knowledge concerning the boiling process, several experimental activities were carried out. Initially, the experiments were conducted on a polished surface with single cavity, and then on a rough surface with multiple nucleation sites. Boiling took place on a heated wall equipped with a novel heat flux sensor, under various vapor pressures. The height of liquid in the experimental reservoir was also varied: the induced static pressure creates a significant liquid subcooling that was shown to strongly affect the boiling behavior. The analysis of the dynamics of isolated bubbles allowed to discover three types of bubbles and explain their associated thermal phenomena. Statistical methods were applied for boiling on a rough surface because of the random character of this process. Along with camera visualization, these methods allowed to distinguish four distinct boiling regimes, whose conditions of occurrence were summarized owing to an original boiling regime map. To enhance the phase change heat transfer at low pressure, an alternative option to boiling could be to spray multiple droplets on the heated wall. There is lack of knowledge concerning evaporation process at subatmospheric conditions. For that purpose, the last experiments were focused on the evaporation of a drop or a layer of liquid from a horizontal surface. It allowed to describe the various thermal processes occurring during evaporation phenomenon.

Download or read book An Analytical and Experimental Study of the Thermal Boundary Layer and Ebullition Cycle in Nucleate Boiling written by Yih-Yun Hsu and published by . This book was released on 1961 with total page 54 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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).

Download or read book Experimental and Analytical Study of the Effects of Wettability on Nucleation Site Density During Pool Boiling written by Chunghsiung Wang and published by . This book was released on 1992 with total page 256 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effect of Surface Conditions on Nucleate Pool Boiling of Refrigerant 1l written by Abbas M. Sinnarwalla and published by . This book was released on 1970 with total page 100 pages. Available in PDF, EPUB and Kindle. Book excerpt: "The purpose of this investigation was to determine the effect of surface conditions on the heat transfer for nucleate pool boiling from flat horizontal surfaces. Experiments were carried out using Refrigerant-1l at atmospheric pressure as the test fluid with Inconel-600 as the heater material. The heat transfer coefficient was determined for mirror finished, chemically etched, glass beaded and sandpaper roughened heater surfaces over heat flux ranging for 0 to 18000 BTU/HR SQ FT. At a given heat flux, the heat transfer coefficient was found to be the lowest for mirror finished surface and the highest for sandpaper roughened surface"--Abstract, leaf ii.

Download or read book Heat Transfer and Fluid Flow in Minichannels and Microchannels written by Satish Kandlikar and published by Elsevier. This book was released on 2006 with total page 492 pages. Available in PDF, EPUB and Kindle. Book excerpt: &Quot;This book explores flow through passages with hydraulic diameters from about 1 [mu]m to 3 mm, covering the range of minichannels and microchannels. Design equations along with solved examples and practice problems are also included to serve the needs of practicing engineers and students in a graduate course."--BOOK JACKET.

Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1975 with total page 952 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Experimental Studies of Nucleation Phenomena and Heat Transfer During Fast Transient Pool Boiling in Water and Organic Fluids written by Waljahat Hussain Salman and published by . This book was released on 1994 with total page 405 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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.

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:

Download or read book Heat Pipes and Solid Sorption Transformations written by L.L Vasiliev and published by CRC Press. This book was released on 2013-05-08 with total page 539 pages. Available in PDF, EPUB and Kindle. Book excerpt: Developing clean energy and utilizing waste energy has become increasingly vital. Research targeting the advancement of thermally powered adsorption cooling technologies has progressed in the past few decades, and the awareness of fuel cells and thermally activated (heat pipe heat exchangers) adsorption systems using natural refrigerants and/or alternatives to hydrofluorocarbon-based refrigerants is becoming ever more important. Heat Pipes and Solid Sorption Transformations: Fundamentals and Practical Applications concentrates on state-of-the-art adsorption research and technologies for relevant applications based on the use of efficient heat transfer devices—heat pipe and two-phase thermosyphons—with the objectives of energy efficiency and sustainability. This book also discusses heat pipe thermal control as it relates to spacecraft applications. The first few chapters of Heat Pipes and Solid Sorption Transformations: Fundamentals and Practical Applications focus on heating and cooling, the principles of adsorption, adsorption dynamics, and the availability of three-phase boundaries. Other chapters cover successful heat pipe applications and heat-pipe-based thermal control of fuel cells, solid sorption transformers, and electronic components and air-condition devices. The final chapters summarize the achievements in the field of heat and mass transfer study in heat pipes with variable properties such as gas loaded heat pipes. Several configurations of thermosyphons are showcased, with suggested applications. A number of examples of equipment using the thermosyphon technology are presented and, in the final chapter, the concept of flow boiling and flow condensation heat transfer in micochannels is analyzed in detail.