Download or read book Electrostatic Control and Enhancement of Film Boiling Heat Transfer written by Arjang Shahriari and published by . This book was released on 2018 with total page 416 pages. Available in PDF, EPUB and Kindle. Book excerpt: Boiling heat transfer is severely degraded at high surface temperatures due to the formation of a vapor layer at the surface, commonly known as the Leidenfrost effect. Heat transfer is limited to a critical heat flux (CHF); higher heat fluxes lead to surface dryout and temperature excursions. An externally applied electric field in the vapor layer can significantly enhance boiling heat transfer for electrically conducting or polar liquids. In such liquids, the electric field is concentrated in the vapor layer, and promotes liquid-surface contact, which can significantly enhance boiling heat transfer. This dissertation is a fundamental study of the influence of concentrated interfacial electric fields on film boiling heat transfer for liquids with finite electrical conductivity (like water and organic solvents). This dissertation describes experimental, analytical and numerical studies on various aspects of the physics underlying electrostatic suppression of film boiling. This dissertation also quantifies the heat transfer benefits associated with electrostatic suppression of film boiling. This dissertation is divided into five main studies, which analyze different aspects of electrostatic suppression of the Leidenfrost state. The first part of this dissertation (Chapter 2) describes droplet-based experimental investigations on electrostatic suppression of the Leidenfrost state. It is demonstrated that the Leidenfrost state can be suppressed and surface dryout can be prevented using externally applied electric fields (AC or DC). Elimination of the Leidenfrost state increases heat dissipation capacity by more than one order of magnitude. In preliminary experiments, heat removal capacities exceeding 500 W/cm2 are measured for water, which is five times the CHF of water on common engineering surfaces. A multiphysics analytical model is developed to predict the vapor layer thickness in the Leidenfrost state. The second part of this dissertation (Chapter 3) analyzes the fundamental mechanisms underlying electrostatic suppression of Leidenfrost state. It is shown that the interplay of destabilizing and stabilizing forces determines the minimum (threshold) voltage required to suppress the Leidenfrost state. Detailed linear instability analysis is conducted to investigate the growth of electrostatically-induced perturbations on the liquid-vapor interface in the Leidenfrost state, and predict the threshold voltage required for suppression. The third part of this dissertation (Chapter 4) focuses on suppression of the Leidenfrost state on soft, deformable surfaces, like liquids. It is seen that the nature of electrostatic suppression on a deformable liquid substrate is drastically different from that on a solid substrate. This is due to the existence of an electric field inside the substrate and the deformability of the substrate. A multiphysics analytical model is developed to predict the vapor layer thickness on deformable liquids. The fourth part of this dissertation (Chapter 5) includes experimental studies on suppression of film boiling during high temperature quenching of metals. It is shown that an electric field can fundamentally change the boiling patterns, wherein the stable vapor layer (film boiling) is replaced by intermittent wetting of the surface. This fundamental switch in the heat transfer mode significantly accelerates cooling during quenching. An order of magnitude increase in the cooling rate is observed, with the heat transfer seen approaching saturation at higher voltages. An analytical model is developed to extract voltage dependent heat transfer rates from the measured cooling curve. The fifth part of this dissertation (Chapter 6) develops the concept of using acoustic signature tracking to study electrostatic suppression of film boiling. It is shown that acoustic signature tracking can be the basis for objective measurements of the threshold voltage and frequency required for suppression. Acoustic signature tracking can also detect various boiling patterns associated with electrostatically-assisted quenching. With appropriate calibration, this technique can be used to estimate surface temperatures, heat flux and onset of dryout associated with electrically enhanced boiling. In summary, this dissertation has led to seminal contributions in the field of boiling heat transfer, and essentially opened up a new area of study in the field. This work has shown that electric fields can make the CHF limit irrelevant, and reshape the boiling curve. The present work lays the proposed work is evident in the area of quenching, where electrically tunable cooling offers a new foundations for electrically tunable boiling heat transfer with conducting liquids. The impact of the tool to control the microstructure and mechanical properties of metals.

Download or read book Boiling Heat Transfer Enhancement Over a Copper Tube Via Electrolytic and Electrostatic Effect written by 林和靖 and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Heat Transfer in Stable Film Boiling written by LeRoy Alton Bromley and published by . This book was released on 1949 with total page 40 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electric Fields Additives and Simultaneous Heat and Mass Transfer in Heat Transfer Enhancement written by Sujoy Kumar Saha and published by Springer. This book was released on 2019-07-18 with total page 125 pages. Available in PDF, EPUB and Kindle. Book excerpt: This Brief deals with electrode design and placement, enhancement of both liquid and gas flow, vapor space condensation, in-tube condensation, falling film evaporation, correlations. It further provides a fundamental understanding of boiling and condensation, pool boiling, critical heat flux, convective vaporization, additives for single-phase liquids like solid particles, gas bubbles, suspensions in dilute polymer and surfactant solutions, solid additives and liquid additives for gases, additives for boiling, condensation and absorption, mass transfer resistance in gas phase (condensation with noncondensible gases, evaporation into air, dehumidifying finned tube heat exchangers, water film enhancement of finned tube exchanger), controlling resistance in liquid phase, and significant resistance in both phases. The volume is ideal for professionals and researchers dealing with thermal management in devices.

Download or read book Some Theories and Applications of Electric Field Enhanced Boiling Heat Transfer written by Kwokming James Cheng and published by . This book was released on 1986 with total page 110 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 Model Laws for the Transition from Nucleate to Film Boiling with Forced Convection written by Ottomar Kampfenkel and published by . This book was released on 1978 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book New Surfaces for the Control of Boiling Heat Transfer written by Nicole Lea Aitcheson and published by . This book was released on 2003 with total page 210 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Further Remarks on the Stability of Boiling Heat Transfer written by N. Zuber and published by . This book was released on 1958 with total page 80 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Enhancement of Boiling Heat Transfer in Di electric Fluids written by Robert A. Egger and published by . This book was released on 1991 with total page 83 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Enhanced Convective and Film Boiling Heat Transfer by Surface Gas Injection written by M. R. Duignan and published by . This book was released on 1992 with total page 93 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Improvement of Film Boiling Heat Transfer by Means of Artificial Surface Projections written by James A. Tevepaugh and published by . This book was released on 1979 with total page 129 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Enhanced Convective and Film Boiling Heat Transfer by Surface Gas Injection written by and published by . This book was released on 1992 with total page 107 pages. Available in PDF, EPUB and Kindle. Book excerpt: Heat transfer measurements were made for stable film boiling of water over a horizontal, flat stainless steel plate from the minimum film boiling point temperature, T{sub SURFACE} (approximately)500K, to T{sub SURFACE} (approximately)950K. The pressure at the plate was approximately 1 atmosphere and the temperature of the water pool was maintained at saturation. The data were compared to the Berenson film-boiling model, which was developed for minimum film-boiling-point conditions. The model accurately represented the data near the minimum film-boiling point and at the highest temperatures measured, as long it was corrected for the heat transferred by radiation. On the average, the experimental data lay within {plus minus}7% of the model. Measurements of heat transfer were made without film boiling for nitrogen jetting into an overlying pool of water from nine 1-mm- diameter holes, drilled in the heat transfer plate. The heat flux was maintained constant at approximately 26.4 kW/m2. For water-pool heights of less than 6cm the heat transfer coefficient deceased linearly with a decrease in heights. Above 6cm the heat transfer coefficient was unaffected. For the entire range of gas velocities measured (0 to 8.5 cm/s), the magnitude of the magnitude of the heat transfer coefficient only changed by approximately 20%. The heat transfer data bound the Konsetov model for turbulent pool heat transfer which was developed for vertical heat transfer surfaces. This agreement suggests that surface orientation may not be important when the gas jets do not locally affect the surface heat transfer. Finally, a database was developed for heat transfer from the plate with both film boiling and gas jetting occurring simultaneously, in a pool of water maintained at its saturation temperature. The effect of passing nitrogen through established film boiling is to increase the heat transfer from that surface. 60 refs.

Download or read book Enhanced Convective and Film Boiling Heat Transfer by Surface Gas Injection written by Mark Robert Duignan and published by . This book was released on 1989 with total page 294 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book High flux Heat Transfer Studies written by P. W. McFadden and published by . This book was released on 1959 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt: An analysis was made of stable, laminar, free convection, film boiling from isothermal vertical plates and horizontal cylinders surrounded by a saturated liquid, where radiation was only of minor importance. The mathematical techniques of boundary layer theory were used and the boundary layer equations were reduced to ordinary differential equations by means of a transformation similar to those used in free convection and condensation. The equations were solved for: (1) compressible flow with variable specific heat, (2) variable specific heat and density variations considered only in the evaluation of the buoyant force, and (3) the case of constant properties. Numerical results were obtained for: (1) near critical water at 2800 and 3100 psia with wall to liquid temperature differences of 250, 500, and 1000 deg F; (2) for fluids with Prandtl numbers of 2/3, 1, and 2; and (3) for mercury and methanol film boiling at one atmosphere, considering constant properties. The results obtained by assuming constant properties were compared to: (1) the results obtained by considering variable properties, (2) experimental results, and (3) the comparable case of laminar film condensation. It was shown that the method of considering density variations only in the evaluation of the buoyant force is not valid in film boiling. It was also shown that the constant property solutions for heat transfer did not always agree with solutions obtained considering compressible flow and variable specific heat. An approximate analysis of a non-isothermal wall, including the effects of radiation, was presented. It was shown that for high emissivity walls at high temperature, radiation is the controlling factor in film boiling heat transfer.

Download or read book Enhanced Boiling Heat Transfer written by John R. Thome and published by CRC Press. This book was released on 1990-01-01 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is a comprehensive survey of boiling heat transfer augmentation, one of the most dynamic areas in the field. The text covers fundamental aspects of boiling augmentation and provides an in-depth treatment of enhanced boiling surface applications in industry.

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.