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Enhancement Of Pool Boiling Heat Transfer And Control Of Bubble Motion In Microgravity Using Electric Fields Bcoel
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Book Synopsis Enhancement of Pool Boiling Heat Transfer and Control of Bubble Motion in Microgravity Using Electric Fields (BCOEL) by :
Download or read book Enhancement of Pool Boiling Heat Transfer and Control of Bubble Motion in Microgravity Using Electric Fields (BCOEL) written by and published by . This book was released on 2001 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 Bubble Dynamics and Boiling Heat Transfer by : Samuel Siedel
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.
Book Synopsis Electrohydrodynamic Pool Boiling Heat Transfer in Microgravity by : Charles Akira Murakami
Download or read book Electrohydrodynamic Pool Boiling Heat Transfer in Microgravity written by Charles Akira Murakami and published by . This book was released on 2004 with total page 116 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Bubble Dynamics and Heat Transfer in Pool Boiling on Wires at Different Gravity by : Jian-Fu Zhao
Download or read book Bubble Dynamics and Heat Transfer in Pool Boiling on Wires at Different Gravity written by Jian-Fu Zhao and published by . This book was released on 2011 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: A series of experimental studies on bubble dynamical behaviors and heat transfer in pool boiling on thin wires in different gravity conditions have been performed in the past years, including experiments in long-term microgravity aboard the 22nd Chinese recoverable satellite RS-22, in short-term microgravity in the drop tower Beijing, and in normal gravity on the ground. Steady pool boiling of degassed R113 on thin platinum wires has been studied using a temperature-controlled heating method. A voltage-controlled heating method has also been used in normal gravity. A slight enhancement of nucleate boiling heat transfer is observed in microgravity, while dramatic changes of bubble behaviors are very evident. Considering the influence of the Marangoni effects, the different characteristics of bubble behaviors in microgravity have been explained. A new bubble departure model including the influence of the Marangoni effects has also been proposed, which can predict the whole observation both in microgravity and in normal gravity. The value of CHF (critical heat flux) in microgravity is lower than that in normal gravity, but it can be predicted well by the Lienhard-Dhir correlation, although the dimensionless radius, or the square root of the Bond number, in the present case is far beyond its initial application range. A further revisit on the scaling of CHF with heater radius in normal gravity, which is focused on the case of a small Bond number, has also been performed in our laboratory using different kinds of working fluids at different subcooling conditions. Interactions between the influences of the subcooling and heater radius will be important for the case of a small Bond number. In addition to the Bond number, there may exist some other parameters, which may be material-dependent, that play important roles in the CHF phenomenon with a small Bond number.
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 Pool Boiling Heat Transfer by : Dong Soo Jung
Download or read book Pool Boiling Heat Transfer written by Dong Soo Jung and published by . This book was released on 1984 with total page 246 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Zero- and Reduced-gravity Simulation on a Magnetic-colloid Pool-boiling System by : S. Stephen Papell
Download or read book Zero- and Reduced-gravity Simulation on a Magnetic-colloid Pool-boiling System written by S. Stephen Papell and published by . This book was released on 1966 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Experimental Study of Nucleate Boiling Bubble Dynamics and Heat Transfer Enhancement on Printed Bi-functional Surfaces by : Michele David
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.
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 Photonically Enhanced and Controlled Pool Boiling Heat Transfer by : Nicholas Robert Glavin
Download or read book Photonically Enhanced and Controlled Pool Boiling Heat Transfer written by Nicholas Robert Glavin and published by . This book was released on 2012 with total page 109 pages. Available in PDF, EPUB and Kindle. Book excerpt: The high cooling requirements from modern day electronic devices have given rise to a need for alternative heat dissipation methods. State of the art liquid to vapor phase change cooling schemes provide a cooling rate orders of magnitude higher than current single phase systems. Boiling studies have long been performed with the goal to enhance critical boiling parameters such as heat transfer coefficient (HTC) and critical heat flux (CHF) by altering surface morphology. More recently, the desire for active control of boiling processes has been realized due to transient and dynamic changes in system cooling requirements. A means of controlling the boiling process by manipulating surface energy through light excitation can provide the necessary adaptive heat transfer properties. In this study, photonically controlled pool boiling studies are conducted on copper, titanium dioxide, and carbon nanotube (CNT) samples. A significant variance in both HTC and CHF upon light excitation is observed in all samples, with different physical and chemical mechanisms for the change in surface energy. Copper boiling samples were induced to a 35% decrease in CHF condition after several minutes using photonic energy via formation of hydrophobic nanoclusters of copper oxide. Photoactive titanium dioxide and CNT experiments showed a 16.8% decrease and 14.5% increase in HTC, respectively, upon light exposure. Small scale contact angle tests, scanning electron microscopy (SEM), and x-ray photoelectron spectroscopy (XPS) on irradiated samples provide an insight into surface changes due to boiling and ultraviolet (UV) light exposure. In addition to photonically enhanced and controlled heat transfer experiments, a new technique for measuring liquid-solid contact during boiling using electrochemical impedance spectroscopy (EIS) is discussed.
Book Synopsis Effects of Electric Fields on Pool Boiling Heat Transfer by : Yonghui Xu
Download or read book Effects of Electric Fields on Pool Boiling Heat Transfer written by Yonghui Xu and published by . This book was released on 1995 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Influence of Liquid Height on Pool Boiling Heat Transfer by : Maharshi Y. Shukla
Download or read book Influence of Liquid Height on Pool Boiling Heat Transfer written by Maharshi Y. Shukla and published by . This book was released on 2020 with total page 56 pages. Available in PDF, EPUB and Kindle. Book excerpt: "As technology advances due to continuous research, devices are becoming more compact, efficient, and powerful. Therefore, heat rejection from such devices becomes ever so critical to maximizing their potential. Compared to other heat extraction methods, boiling provides one of the highest heat transfer coefficients. The heat extraction due to the boiling process is limited to the Critical Heat Flux (CHF). At CHF, an insulating layer of escaping bubbles forms upon the surface to prevent boiling continuity. Subsequently, the surface temperature increases uncontrollably, leading to a system failure. Hence, the elevation of CHF is critical to boiling enhancement. Improvements to the heat transfer process can be made with either surface manipulation or liquid manipulation. Based on previous studies, it is found that the removal of bubbles from the heater surface is critical to enhancing performance. Therefore, it is hypothesized that if a bubble can be encouraged to reach liquid-gas the interface quickly, gains in the boiling performance can be achieved. Due to the vapor bubble's movement in liquid bulk, it becomes critical to understand the influence of liquid height on pool boiling for enhancement. While pool boiling enhancement using heating surface modification is extensively studied and documented, there is a research gap between understanding the effect of liquid height at high heat fluxes. Thus, this study tries to evaluate the influence of liquid height on pool boiling performance at higher heat fluxes and identify the underlying bubble movement mechanism. It is observed that as CHF increases with liquid height. Moreover, it is observed that bubble movement is more effortless at low liquid height resulting in higher HTC. On the other hand, larger liquid height provides improved rewetting of the surface resulting in higher CHF. Upon analysis of high-speed recording of the escaping bubbles, it was observed that the maximum heat transfer coefficient is observed when the liquid height is about four times the height of the departing bubble diameter."--Abstract.
Book Synopsis Experimental Study of Pool Boiling Heat Transfer Enhancement Over Microchanneled Surfaces by : Dwight Cooke
Download or read book Experimental Study of Pool Boiling Heat Transfer Enhancement Over Microchanneled Surfaces written by Dwight Cooke and published by . This book was released on 2011 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Pool boiling is of interest in heat transfer applications because of its potential for removing large amount of heat resulting from the latent heat of evaporation and little pressure drop penalty for circulating coolant through the system. However, the heat transfer performance of pool boiling systems is still not comparable to the cooling ability provided by enhanced microchannels operating under single-phase conditions. This investigation focuses on the bubble dynamics and heat transfer on plain and structured microchanneled surfaces under various heat fluxes in an effort to understand the underlying heat transfer mechanism through the use of a high speed camera. In a preliminary study, silicon chips have been tested in the nucleate boiling regime, and beneficial microchannel geometries have been identified. It is determined that heat transfer enhancement occurs because of (i) an increase in surface area and (ii) an improvement in the heat transfer mechanism through the channels functioning as liquid conduits for three side heating. The range for channel size in which the greatest enhancement occurs has been identified as being 200 - 400 [micron] width and 300 - 500 [micron] depth. The second study has been investigated with copper chips, with improvements to the test setup for accurate measurement of surface temperature. Ten chips, in addition to a plain chip have been evaluated for heat transfer performance. It has been determined that surfaces with many, small hydraulic diameter channels enhance the heat transfer as well as surfaces with wide and deep channels. The best performing chip had a record heat transfer coefficient of 269 kW/m2K. The large heat fluxes of over 240 W/cm2 were attained without reaching the critical heat flux condition, because of the open channels on the surface acting as conduits for liquid supply to the nucleation sites. The microchannels prevent surface dryout and critical heat flux (CHF), while the channel width controls the size of the departing bubbles."--Abstract.
Book Synopsis Experimental Investigation of Nucleate Boiling Bubble Dynamics in Normal and Zero Gravities by : Thomas H. Cochran
Download or read book Experimental Investigation of Nucleate Boiling Bubble Dynamics in Normal and Zero Gravities written by Thomas H. Cochran and published by . This book was released on 1968 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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.
