Dissertations / Theses on the topic 'Subcooled Boiling Flow'
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Cao, Yang. "STUDY ON BUBBLE BEHAVIORS IN SUBCOOLED FLOW BOILING." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215532.
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Stumm, Brian J. "An investigation on bubble departure in subcooled flow boiling /." Online version of thesis, 1993. http://hdl.handle.net/1850/11186.
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Prodanovic, Vladan. "Bubble behaviour in subcooled flow boiling at low pressures and flow rates." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ61160.pdf.
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Samaroo, Randy. "The effects of geometric, flow, and boiling parameters on bubble growth and behavior in subcooled flow boiling." Thesis, The City College of New York, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10159915.
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Air bubble injection and subcooled flow boiling experiments have been performed to investigate the liquid flow field and bubble nucleation, growth, and departure, in part to contribute to the DOE Nuclear HUB project, Consortium for Advanced Simulation of Light Water Reactors (CASL). The main objective was to obtain quantitative data and compartmentalize the many different interconnected aspects of the boiling process — from the channel geometry, to liquid and gas interactions, to underlying heat transfer mechanisms.
The air bubble injection experiments were performed in annular and rectangular geometries and yielded data on bubble formation and departure from a small hole on the inner tube surface, subsequent motion and deformation of the detached bubbles, and interactions with laminar or turbulent water flow. Instantaneous and ensemble- average liquid velocity profiles have been obtained using a Particle Image Velocimetry technique and a high speed video camera. Reynolds numbers for these works ranged from 1,300 to 7,700.
Boiling experiments have been performed with subcooled water at atmospheric pres- sure in the same annular channel geometry as the air injection experiments. A second flow loop with a slightly larger annular channel was constructed to perform further boiling experiments at elevated pressures up to 10 bar. High speed video and PIV measurements of turbulent velocity profiles in the presence of small vapor bubbles on the heated rod are presented. The liquid Reynolds number for this set of experiments ranged from 5,460 to 86,000. It was observed that as the vapor bubbles are very small compared to the injected air bubbles, further experiments were performed using a microscopic objective to obtain higher spatial resolution for velocity fields near the heated wall. Multiple correlations for the bubble liftoff diameter, liftoff time and bub- ble history number were evaluated against a number of experimental datasets from previous works, resulting in a new proposed correlations that account for fluid prop- erties that vary with pressure, heat flux, and variations in geometry.
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Richenderfer, Andrew Jonathan. "Experimental study of heat flux partitioning in pressurized subcooled flow boiling." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/119033.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 133-137).
Understanding of subcooled flow boiling and the critical heat flux (CHF) is of the utmost importance for both safety and profitability of pressurized water nuclear reactors since they are major factors in the determination of the reactor power rating. Motivated by the emergence of a new wall boiling model by Gilman [3] and previous experimental insights from Phillips [12], a first-of-a-kind experimental investigation of pressurized steady-state subcooled flow boiling was conducted using state-ofthe- art diagnostics to gain a unique insight of the relevant mechanisms, including the partitioning of the wall heat flux. Conditions up to 10 bar pressure, 2000 kg/m²s mass flux and 20 K subcooling were explored. High-speed infrared thermometry tools were developed and used to measure the local time-dependent 2-D temperature and heat flux distributions on the boiling surface. These distributions were analyzed to determine fundamental boiling heat transfer parameters such as the nucleation site density, growth and wait times, nucleation frequency, departure diameter as well as the partitioning of the wall heat flux. While established mechanistic models can capture the trends of growth time and wait time with relatively good accuracy, this work reveals current models do not accurately predict the activation and interaction of nucleation sites on the boiling surface. This is a major roadblock, since boiling curves and CHF values obtained in nominally identical environments can be significantly different depending upon the nucleation site density which in turn is determined by the surface properties. The role of evaporation in the partitioning of the heat flux increases monotonically as the average heat flux increases, up to a maximum value of 70%, and is the dominant mechanism at high heat fluxes. At low and intermediate heat fluxes single-phase heat transfer is the dominant mechanism. Traditional heat partitioning models fail to capture these physics, but newer models with a comprehensive and physically consistent framework show promise in predicting the wall heat transfer. The data and understanding produced by this work will be essential for the development and validation of these modeling tools.
by Andrew Jonathan Richenderfer.
Ph. D.
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Tow, Emily Winona. "Bubble behavior in subcooled flow boiling on surfaces of variable wettability." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/75682.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 59).
Flow boiling is important in energy conversion and thermal management due to its potential for very high heat fluxes. By improving understanding of the conditions leading to bubble departure, surfaces can be designed that increase heat transfer coefficients in flow boiling. Bubbles were visualized during subcooled nucleate flow boiling of water on a surface of variable wettability. Images obtained from the videos were analyzed to find parameters influencing bubble size at departure. A model was developed relating the dimensions of the bubble at departure to its upstream and downstream contact angles based on a rigid-body force balance between momentum and surface tension and assuming a skewed truncated spherical bubble shape. Both experimental and theoretical results predict that bubble width and height decrease with increasing flow speed and that the width increases with the equilibrium contact angle. The model also predicts that the width and height increase with the amount of contact angle hysteresis and that the height increases with equilibrium contact angle, though neither of these trends were clearly demonstrated by the data. Several directions for future research are proposed, including modifications to the model to account for deviations of the bubbles from the assumed geometry and research into the parameters controlling contact angle hysteresis of bubbles in a flow. Additionally, observations support that surfaces with periodically-varying contact angle may prevent film formation and increase the heat transfer coefficients in both film and pool boiling.
by Emily W. Tow.
S.B.
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Coyle, Carolyn Patricia. "Synthesis of CRUD and its effects on pool and subcooled flow boiling." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/103652.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 127-132).
This work is dedicated to studying the effects of synthetic CRUD (Chalk River Unidentified Deposits) on pool and subcooled flow boiling parameters. Previous pool boiling studies have demonstrated the potential of porous, hydrophilic surfaces to lead to more efficient boiling. CRUD is a naturally occurring porous, hydrophilic layer that forms on fuel rods during reactor operation. As such, CRUD deposition may have large effects on critical heat flux (CHF) and heat transfer coefficient (HTC). An investigation of such effects was conducted as part of the CASL project by creating well-defined and characterized synthetic CRUD with parameters representative of reactor CRUD on indium tin oxide-sapphire heaters. The effects of synthetic CRUD on boiling heat transfer were then experimentally studied, focusing on heat transfer coefficient (HTC), critical heat flux (CHF), nucleation site density, bubble departure frequency, and bubble departure diameter. These heaters were tested in pool and flow boiling facilities in MIT's Reactor Hydraulics Laboratory. Synthetic CRUD was created using layer-by-layer deposition of 100 nm silica nanoparticles to form porous, hydrophilic thick films. Photolithography was used to manufacture posts that were then dissolved to create characteristic boiling chimneys. Features such as thickness, wettability, pore size, and chimney diameter and pitch were verified to be representative of reactor CRUD. Silica nanoparticles were used as a surrogate for reactor CRUD nanoparticle materials (iron and nickel oxides) since they create more stable films. To ensure accurate modeling, independent of material, 10 nm silica nanoparticle and 10 nm iron oxide nanoparticle boiling tests were conducted and found to be similiar. During testing, IR thermography and high-speed video (HSV) are used to obtain two dimensional temperature profiles of the active heater area to quantify properties such as HTC, nucleation site density, bubble departure frequency, and bubble departure diameter. The bubble parameters follow expected trends with mass flux and heat flux. IR/HSV flow data (Chapter 6) has shown that HTC increases with the presence of chimneys, increasing thickness and increasing chimney diameter. However the HTC is relatively unaffected by the chimney pitch and is decreased by the presence of an LbL layer. The boiling curves and CHF data obtained from pool boiling experiments with iron oxide and silica oxide nanoparticles with and without chimneys also confirm these trends. The largest HTC is observed in the case of uncoated heaters, followed by heaters with chimneys, with heaters with an LbL layer without chimneys having the lowest HTC. From pool boiling data, the benefit of a CRUD layer is observed in the enhancement of CHF. The flow boiling trends are further supported by the combination of measured basic bubble parameters according to the heat flux partitioning model. The statistical significance of these trends varies with mass flux. The data generated here may inform advanced models of boiling heat transfer and/or validate existing models.
by Carolyn Patricia Coyle.
S.M.
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Chong, Jen Haw. "Modelling of subcooled flow boiling in a rectangular micro-channel heat sink." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/51313/.
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Attaching micro-channel heat sinks operating under flow boiling conditions on heat sources of electronic components is an efficient cooling technique which still requires further improvements of designs. When developing this system, the efficient heat transfer performance is essential, however, this development often entangles with difficulties. The difficulties arise as existing prediction approaches are underdeveloped and inadequate to perform the accurate prediction in wide ranges of operating conditions. This inadequacy persists due to incomplete discoveries of involved mechanisms that involve fluid and dynamics for the heat transfer during the flow boiling. Also, the mechanisms involved in the flow boiling process are complicated, hindering the development of more reliable approaches. By addressing this issue, this study explores and investigates the relating mechanisms. The mechanisms of fluids during the flow boiling of subcooled liquids in micro-channel heat sinks immediately before and during the nucleation of first bubbles were explored in this study. This study then addressed the mechanisms of heat transfer enhancement of flow boiling. Later, this study repeated with different substrate materials of micro-channel heat sinks and working fluids. This study serves the purpose to better understand the involved mechanisms during the flow boiling of subcooled liquids in micro-channel heat sinks for the development of more reliable approaches to predict the heat transfer. This study regarding the mechanisms during the flow boiling in micro-channel heat sinks implemented the numerical model associated with the Volume of Fluid (VOF) in which corresponding governing equations were solved using a computational fluid dynamics (CFD). In this model, computational domains of micro-channel heat sinks in three dimensions that include the sub-domains of solids and fluid were created to consider the conjugate heat transfer for better estimation of data. The data collected in this study were from operating parameters of heat flux, mass flux, and inlet temperature of the micro-channel at 500-3197 kW/m2, 115-389 kg/m2 s, and 23-53°C, respectively. The micro-channel heat sinks operated at the atmospheric pressure, and the corresponding substrate materials chosen were steel, silicon, aluminium and copper, and working fluids selected were water and ethanol. The numerical results agree well with the experimental data from the previous study. The results show that although the bubble nucleation is absent, the heat transfer mechanisms in micro-channels possesses the nucleate boiling characteristic involving the transient conduction with the existence of the phase change process. The heat transfer mechanisms from the phase change process with the incomplete evaporation induce the ascending and descending flows and liquid-vapour mixture on the heating surfaces. From the results, four different modes of heat transfer mechanisms from the phase change process associated with ascending and descending flows and liquid vapour mixture become apparent. The ascending and descending flows on the heating surfaces appear with local increases of pressure gradients near to the heating surfaces facilitating the heat transfer enhancement due to phase change. On the other hand, the liquid-vapour mixture produced from the phase change process impeding the heat transfer. In overall, the heat transfer enhancement due to the phase change at the side surfaces in the micro-channel is more extensive as compared to the bottom surface for each condition tested in this study. Meanwhile, the amount of the liquid-vapour mixture accumulating on the bottom surface is more massive as compared to the side surfaces, leading to the impedance of the heat transfer. These heat transfer mechanisms also persist during flow boiling in micro-channels. The heat transfer enhancement due to phase change from the side and bottom surfaces also varies when employing different operating conditions before and during flow boiling. This study provides better insights for researchers and designers in industries regarding the local mechanisms for the heat transfer during the flow boiling in micro-channel heat sinks. These understandings assist the researchers to develop the more reliable prediction methods to design new and better heat transfer performance of micro-channel heat sinks and avoid repeating experiments which are costly and tedious in procedures.
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Cartwright, Michael D. "Experimental and analytical investigation of the bubble nucleation characteristics in subcooled flow /." Online version ot thesis, 1995. http://hdl.handle.net/1850/12048.
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Najibi, Seyed Hesam. "Heat transfer and heat transfer fouling during subcooled flow boiling for electrolyte solutions." Thesis, University of Surrey, 1997. http://epubs.surrey.ac.uk/773/.
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Mizo, Viktor R. "Investigation of inertia controlled bubble departure mechanism in subcooled flow boiling using high speed photography /." Online version of thesis, 1995. http://hdl.handle.net/1850/12084.
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Kim, Sung Joong Ph D. Massachusetts Institute of Technology. "Subcooled flow boiling heat transfer and critical heat flux in water-based nanofluids at low pressure." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53274.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 285-290).
A nanofluid is a colloidal suspension of nano-scale particles in water, or other base fluids. Previous pool boiling studies have shown that nanofluids can improve the critical heat flux (CHF) by as much as 200%. In this study, subcooled flow boiling heat transfer and CHF experiments were performed with low concentrations of alumina, zinc oxide, and diamond nanoparticles in water (< 0.1 % by volume) at atmospheric pressure. It was found that for comparable test conditions the values of the nanofluid and water heat transfer coefficient (HTC) are similar (within ±20%). The HTC increased with mass flux and heat flux for water and nanofluids alike, as expected in flow boiling. The CHF tests were conducted at 0.1 MPa and at three different mass fluxes (1500, 2000, 2500 kg/m2s) under subcooled conditions. The maximum CHF enhancement was 53%, 53% and 38% for alumina, zinc oxide and diamond, respectively, always obtained at the highest mass flux. The measurement uncertainty of the CHF was less than 6.2%. A post-mortem analysis of the boiling surface reveals that its morphology is altered by deposition of the particles during nanofluids boiling. A confocal-microscopy-based examination of the test section revealed nanoparticles deposition not only changes the number of micro-cavities on the surface, but also the surface wettability. A simple model was used to estimate the ensuing nucleation site density changes, but no definitive correlation between the nucleation site density and the heat transfer coefficient data could be found.
(cont.) Wettability of the surface was substantially increased for heater coupons boiled in alumina and zinc oxide nanofluids, and such wettability increase seems to correlate reasonably well with the observed marked CHF enhancement for the respective nanofluids. Interpretation of the experimental data was conducted in light of the governing surface parameters and existing models. It was found that no single parameter could explain the observed HTC or CHF phenomena. The existing models were limited in studying the surface effects, suggesting that more accurate models incorporating surface effects need to be developed. Finally, the research activities performed in this thesis help identify the research gaps and indicate future research directions.
by Sung Joon Kim.
Ph.D.
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Kommajosyula, Ravikishore. "Development and assessment of a physics-based model for subcooled flow boiling with application to CFD." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129051.
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Thesis: Ph. D. in Mechanical Engineering and Computation, Massachusetts Institute of Technology, Department of Mechanical Engineering, 2020Cataloged from student-submitted PDF of thesis.
Includes bibliographical references (pages 113-119).
Boiling is an extremely efficient mode of heat transfer and is the preferred heat removal mechanism in power systems in general and, more recently, in electronics cooling. Physics-based models that describe boiling heat transfer, when coupled with Computational Fluid Dynamics (CFD), can be an invaluable tool to increase the performance of such systems. Existing modeling approaches do not incorporate all relevant heat transfer mechanisms at the wall, limiting their predictive capability and general applicability. These shortcomings restrict the application of CFD in the design process. For the nuclear industry, this means having to rely on expensive experimental campaigns to develop and license new reactor designs. A second-generation mechanistic heat flux partitioning framework developed in our group provides an enhanced physical description of flow boiling.
It introduces several mechanisms not accounted for in previous formulations, such as 1) bubbles sliding on the heater surface, 2) interaction of nucleation sites and 3) microlayer evaporation. The framework requires describing the complete bubble ebullition cycle, including bubble nucleation, growth, and departure through closure models, which are currently lacking. This thesis extends the framework into a closed-formulation by developing closure models that adequately represent the underlying physics. New models for predicting the bubble departure diameter and frequency are developed based on insights gathered from experiments and direct numerical simulations. An assessment against existing approaches to model boiling heat transfer demonstrates the model's ability to predict over 80% of the boiling curves within a 20% error, while also capturing the correct trends with flow conditions.
The model implementation in a commercial CFD software is demonstrated using data from the Bartolomei experiment. The extendability of the model to novel heater surfaces is further demonstrated for a sapphire heater substrate, where fewer cavities for nucleation shift the boiling curves to considerably higher wall superheats. This mechanistic representation of boiling heat transfer has the potential to support predictive design with optimal boiling heat transfer for improved system efficiency, with the specific objective to accelerate the development of novel nuclear fuel concepts.
by Ravikishore Kommajosyula.
Ph. D. in Mechanical Engineering and Computation
Ph.D.inMechanicalEngineeringandComputation Massachusetts Institute of Technology, Department of Mechanical Engineering
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Becht, Charles. "Onset of Flow Instability in Uniformly Heated, Narrow, Rectangular Channels." Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16187.
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The primary purpose of this investigation was to experimentally determine the effect of operational parameters on the onset of flow instability (OFI) in narrow, uniformly heated, vertical, rectangular channels. The geometry investigated was a 9.0 cm long rectangular channel with a 1.0mm by 1.3cm cross section. This geometry closely matches the coolant channel geometry in an accelerator target. Nitrogen-saturated subcooled water was used as the coolant, with mass fluxes ranging from 250 to 1336 kg/m^2 s, and an inlet temperature of 26ºC for the OFI experiments. The exit pressures investigated ranged from 275kPa to 620kPa, while the heat flux ranged from 0.729 to 2.236 MW/m^2. The primary data collected from these experiments were used to develop two correlations for the heat flux and mass flux at OFI.
Wall temperature data were also collected in order to develop a Nusselt number correlation for the single-phase regime. This correlation is valid for the Reynolds number range of 6x103 to 1.7x104. The data obtained in this investigation will aid designers of high-power-density systems establish design limits to prevent over heating and possible damage due to the onset of flow instability.
The data obtained in this investigation will aid designers of high-power-density systems establish design limits to prevent over heating and possible damage due to the onset of flow instability.
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Phillips, Bren Andrew. "Experimental investigation of subcooled flow boiling using synchronized high speed video, infrared thermography, and particle image velocimetry." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92060.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2014.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages [133]-138).
Subcooled flow boiling of water was experimentally investigated using high-speed video (HSV), infrared (IR) thermography, and particle image velocimetry (PIV) to generate a unique database of synchronized data. HSV allowed measurement of the bubble departure diameter. IR thermography allowed measurement of wall superheat (local distribution and surface-averaged values), heat transfer coefficient, nucleation site density, and bubble frequency. Particle image velocimetry allowed for the measurement of velocity profiles in the liquid phase for single bubble nucleation events. The tests were performed at pressures of 1.05, 1.5, and 2.0 bar and at subcoolings of 5, 10, and 15 °C. The mass flux values explored were 150-1250 kg/m2/s. The heat flux values explored were 100-1600 kW/m2. As expected, the heat transfer coefficients increased with increasing mass flux in the single-phase convection and partial boiling regions, and converged to a fully-developed boiling curve for high heat fluxes. The bubble departure diameter decreased with increasing mass flux and decreasing heat flux; in accordance with Sugrue's model. The nucleation site density increased with increasing superheat and decreasing mass flux, as predicted by Kocamustafaogullari and Ishii's model. The nucleation site density models under-predicted the nucleation site density for a given wall superheat. Wait time and frequency models did not reproduce the data accurately, and underestimated wait time by an order of magnitude. A new mechanistic model for calculating the wait time was developed that split the wall heat flux into the component that is transferred to the fluid, and the component that is transferred as sensible heat into the heater wall. Significant localized cooling was observed underneath bubbles sliding along the wall after departure from a nucleation site, an effect which should be considered in advanced models of subcooled flow boiling. The sliding bubble thermal effects were found to be insensitive to system conditions and were limited by the thermal conduction within the substrate. Bubble growth front velocities, and regions of flow influence of departing bubbles were measured with PIV. The database generated in this project can be used to inspire or validate mechanistic models and/or CFD simulations of subcooled flow boiling heat transfer.
by Bren Andrew Phillips.
Ph. D.
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Franz, Benjamin [Verfasser], Peter [Akademischer Betreuer] Stephan, and Catherine [Akademischer Betreuer] Colin. "Numerical simulation of bubble growth in subcooled pool and flow boiling under microgravity conditions / Benjamin Franz ; Peter Stephan, Catherine Colin." Darmstadt : Universitäts- und Landesbibliothek, 2021. http://d-nb.info/1237050197/34.
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Sugrue, Rosemary M. "The effects of orientation angle, subcooling, heat flux, mass flux, and pressure on bubble growth and detachment in subcooled flow boiling." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/76974.
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Thesis (S.M. and S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 119-122).
The effects of orientation angle, subcooling, heat flux, mass flux, and pressure on bubble growth and detachment in subcooled flow boiling were studied using a high-speed video camera in conjunction with a two-phase flow loop that can accommodate a wide range of flow conditions. Specifically, orientation angles of 0' (downward-facing horizontal), 30°, 45°, 60°, and 90° (vertical); mass flux values of 250, 300, 350, and 400 kg/m²s, with corresponding Froude numbers in the range of 0.42 to 1.06; pressures of 101 (atmospheric), 202, and 505 kPa; two values of subcooling (10°C to 20°C); and two heat fluxes (0.05 to 0.10 MW/m²) were explored. The combination of the test section design, high-speed video camera, and LED lighting results in high accuracy (order of 20 microns) in the determination of bubble departure diameter. The data indicate that bubble departure diameter increases with increasing heat flux, decreasing mass flux, decreasing levels of subcooling, and decreasing pressure. Also, bubble departure diameter increases with decreasing orientation angle, i.e. the largest bubbles are found to detach from a downward-facing horizontal surface. The mechanistic bubble departure model of Klausner et al. and its recent modification by Yun et al. were found to correctly predict all the observed parametric trends, but with large average errors and standard deviation: 35.7+/-24.3% for Klausner's and 16.6±11.6% for Yun's. Since the cube of the bubble departure diameter is used in subcooled flow boiling heat transfer models, such large errors are clearly unacceptable, and underscore the need for more accurate bubble departure diameter models to be used in CFD.
by Rosemary M. Sugrue.
S.M.and S.B.
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Bloch, Gregor [Verfasser], Thomas [Akademischer Betreuer] [Gutachter] Sattelmayer, and Horst-Michael [Gutachter] Prasser. "An Experimental Study on Vertical Subcooled Flow Boiling Under the Influence of Turbulence and Secondary Flows / Gregor Bloch ; Gutachter: Thomas Sattelmayer, Horst-Michael Prasser ; Betreuer: Thomas Sattelmayer." München : Universitätsbibliothek der TU München, 2016. http://d-nb.info/1120013798/34.
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Bruder, Moritz [Verfasser], Thomas [Akademischer Betreuer] Sattelmayer, Thomas [Gutachter] Sattelmayer, and Andrea [Gutachter] Luke. "Experimental Study on the Identification of Heat Transfer Characteristics for Subcooled Flow Boiling of Novec 649 / Moritz Bruder ; Gutachter: Thomas Sattelmayer, Andrea Luke ; Betreuer: Thomas Sattelmayer." München : Universitätsbibliothek der TU München, 2019. http://d-nb.info/1203799497/34.
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Nop, Raksmy. "Experimental investigation and modeling of the transient flow boiling crisis of water at moderate pressure and high subcooling." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST046.
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Lors d’une insertion accidentelle de réactivité dans un réacteur nucléaire expérimental, la puissance du cœur peut augmenter de manière exponentielle, avec un temps caractéristique allant de quelques millisecondes à quelques centaines de millisecondes. À cause des effets neutroniques et thermohydrauliques, le système peut atteindre les conditions de crise d’ébullition à même d’engendrer une réaction explosive. Bien que la crise d’ébullition ait été largement étudiée en conditions de chauffage stationnaires, ce n’est pas le cas pour les transitoires notamment de type excursions de puissance. Le but de ce travail est donc de comprendre et de prédire la crise d'ébullition sous l’effet d’un chauffage transitoire rapide de l'eau sous fortes sous-saturations à pression modérée. Des campagnes expérimentales ont été réalisées pour étudier la crise d’ébullition dans de telles conditions au moyen de vidéos et de thermographie IR hautement résolues en temps et en espace. L’analyse de ces données a permis de déterminer la dépendance du flux critique en transitoire rapide en fonction des différents paramètres d’intérêt (temps caractéristique d’excursion de puissance, vitesse d’écoulement, sous-saturation, pression, largeur du canal, longueur de chauffe). De plus, une analyse approfondie de ces données a permis de mettre en évidence les mécanismes sous-jacents à la crise d’ébullition dans ces conditions. En convection forcée et avec de fortes sous-saturations, les bulles générées en paroi présentent un comportement pulsant. Ce phénomène assure un transfert de chaleur efficace depuis la paroi vers le fluide environnant. Le déclenchement de la crise d’ébullition se produit lorsqu’une fine couche de fluide adjacente à la paroi atteint les conditions de saturation. Un modèle développé à partir de ces observations met en évidence deux paramètres adimensionnés utiles pour décrire la nature transitoire du processus ainsi que pour identifier le mode de refroidissement dominant. Grâce à la connaissance du flux critique en régime permanent, le modèle permet d’estimer de manière conservative le flux critique en fonction de la période d’excursion de puissance et du sous-refroidissement. Ce modèle est maintenant prêt à être implémenté dans des codes de simulation pour l’étude des transitoires accidentelsIn case of a reactivity insertion accident in an experimental nuclear reactor, heat generation in the core can grow exponentially in time, with a power escalation period ranging from a few to a few hundreds of milliseconds. Due to neutronic and thermohydraulic effects, boiling crisis may arise, possibly leading to an explosive reaction. If the boiling Crisis has been widely investigated in steady-state conditions, this has not been the case for transient heat inputs. The aim of the present work is to understand and to predict the transient flow boiling crisis in the conditions of moderate pressure and high subcooling. To this end, an experimental campaign has been realized making use of space and time highly resolved videos and IR thermography covering a wide range of experimental parameters. The analysis of the massive amount of data produced by these experiments gives a better insight on the dependency of the transient Critical Heat Flux to the different parameters of interest (power escalation period, flow velocity, subcooling, pressure, channel width, heating length). Moreover, their fine analysis enables to highlight the underlying mechanisms. For conditions of forced flow and high subcooling, the bubbles generated at the wall present a pulsating behavior. This specific process leads to an efficient heat transfer from the wall to the neighboring fluid. Boiling crisis is stated to occur when a thin layer of liquid contacting the wall reaches the saturation temperature. Starting from these observations, a model is developed which brings to light two non-dimensional parameters useful to describe the transient nature of the process and the dominant cooling processes. With the knowledge of the steady-state CHF, the model permits to conservatively estimate the value of the Critical Heat Flux for any power escalation period and subcooling. This model is now ready for implementation into simulation codes to investigate nuclear accidental transients
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Schneider, Clemens. "Experimentelle Untersuchungen zum Blasensieden bei unterkühlten Strömungen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-185332.
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Die vorliegende Dissertationsschrift beinhaltet die Ergebnisse der Untersuchung von loka-len und globalen Prozessen der Wärmeübertragung beim unterkühlten Strömungssieden. Sie ist an der Schnittstelle zwischen Reaktorsicherheitsforschung und der experimentellen Thermofluiddynamik für Phasenübergänge einzuordnen.
In technischen Anwendungen zur effizienten Übertragung großer Wärmemengen spielt der Prozess des Siedens eine wichtige Rolle. Dieser Vorgang bewirkt einen starken Anstieg des Wärmetransportes von der beizten Wand an das Fluid bei vergleichsweise geringem Anstieg der Wandtemperatur. Der maximal übertragbare Wärmestrom beim Sieden wird begrenzt durch die sogenannte kritische Wärmestromdichte, deren Überschreitung zum thermomechanischen Versagen der beheizten Komponente führen kann.
Aufgrund der Komplexität dieser Prozesse ist es trotz intensiver Arbeiten in den letzten Jahrzehnten noch nicht gelungen, diese Vorgänge detailliert zu modellieren. Eine Weiter-entwicklung der Modelle zur realistischen Beschreibung des unterkühlten Strömungssie-dens erfordert neuartige Untersuchungen, welche eine genaue Klassifizierung der partiellen Wärmeübergänge des Blasensiedens ermöglichen.
Die Analyse partieller Wärmetransportgrößen beim unterkühlten Strömungssieden sowie der Einfluss variierender thermohydraulischer Randbedingungen ist Schwerpunkt dieser Arbeit. In der entwickelten Versuchsanlage erfolgt die Erfassung der Siedevorgänge bei Strömungsgeschwindigkeiten von 0,1 – 2 m/s und Eintrittstemperaturen von 60 - 98 °C.
Mit Hilfe empfindlicher Temperaturmessungen in einem elektrisch beheizten Kapillarrohr innerhalb des Strömungskanals werden die globalen Vorgänge beim Übergang von Kon-vektion zum Sieden erfasst. Durch eine modellbasierte Bestimmung der Oberflächentem-peratur lassen sich Phänomene nachweisen, welche bisher weitestgehend unbeachtet ge-blieben sind. Die transparente Versuchsstrecke ermöglicht eine Erfassung der lokalen Sie-devorgänge mit optisch und zeitlich hochauflösenden Messverfahren. Durch die Entwick-lung neuer Algorithmen der digitalen Bildverarbeitung wurde eine umfangreiche, kenngrö-ßenorientierte Auswertung der in großem Umfang entstandenen Datenmengen realisiert.
Der Einsatz transparenter und elektrisch leitfähiger Beschichtungen ermöglicht die mikro-skopische Erfassung des Blasenwachstums in weiten thermohydraulischen Parameterberei-chen. Mit erweiterten Bildverarbeitungsalgorithmen erfolgt die detaillierte und dynamische Bewertung des Blasenwachstumsverhaltens. Die statistische Auswertung der Verläufe er-möglicht die Ableitung eines Blasenwachstumsmodells für unterkühltes Strömungssieden.
In einer weiteren Versuchsanordnung werden die lokalen Wärmetransportvorgänge bei der Ablösung quasistatisch gewachsener Blasen mit Hilfe der Infrarot-Thermographie be-stimmt. Dadurch können erstmalig die aus der lokalen Abkühlung der beheizten Oberfläche durch Blasenablösung resultierenden Wärmeströme unter Vernachlässigung der Bla-senbildung experimentell quantifiziert werden. Weiterhin können die bisher theoretisch beschriebenen Driftströmungen beim Aufstieg der Blase experimentell nachgewiesen wer-den. Die ermittelten Größen und Zusammenhänge tragen zur Weiterentwicklung und zum Abbau von Unsicherheiten bei der Modellierung von Wärmetransportvorgängen beim unterkühlten Strömungssieden bei.
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Glassman, Brian. "Spray Cooling for Land, Sea, Air and Space Based Applications, A Fluid Managment System for Multiple Nozzle Spray Cooling and a Guide to High Heat Flux Heater Design." Master's thesis, University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3521.
Full textAbstract:
This thesis is divided into four distinct chapters all linked by the topic of spray cooling. Chapter one gives a detailed categorization of future and current spray cooling applications, and reviews the major advantages and disadvantages that spray cooling has over other high heat flux cooling techniques. Chapter two outlines the developmental goals of spray cooling, which are to increase the output of a current system and to enable new technologies to be technically feasible. Furthermore, this chapter outlines in detail the impact that land, air, sea, and space environments have on the cooling system and what technologies could be enabled in each environment with the aid of spray cooling. In particular, the heat exchanger, condenser and radiator are analyzed in their corresponding environments. Chapter three presents an experimental investigation of a fluid management system for a large area multiple nozzle spray cooler. A fluid management or suction system was used to control the liquid film layer thickness needed for effective heat transfer. An array of sixteen pressure atomized spray nozzles along with an imbedded fluid suction system was constructed. Two surfaces were spray tested one being a clear grooved Plexiglas plate used for visualization and the other being a bottom heated grooved 4.5 x 4.5 cm2 copper plate used to determine the heat flux. The suction system utilized an array of thin copper tubes to extract excess liquid from the cooled surface. Pure water was ejected from two spray nozzle configurations at flow rates of 0.7 L/min to 1 L/min per nozzle. It was found that the fluid management system provided fluid removal efficiencies of 98% with a 4-nozzle array, and 90% with the full 16-nozzle array for the downward spraying orientation. The corresponding heat fluxes for the 16 nozzle configuration were found with and without the aid of the fluid management system. It was found that the fluid management system increased heat fluxes on the average of 30 W/cm2 at similar values of superheat. Unfortunately, the effectiveness of this array at removing heat at full levels of suction is approximately 50% & 40% of a single nozzle at respective 10[degrees]C & 15[degrees]C values of superheat. The heat transfer data more closely resembled convective pooling boiling. Thus, it was concluded that the poor heat transfer was due to flooding occurring which made the heat transfer mechanism mainly forced convective boiling and not spray cooling. Finally, Chapter four gives a detailed guide for the design and construction of a high heat flux heater for experimental uses where accurate measurements of surface temperatures and heat fluxes are extremely important. The heater designs presented allow for different testing applications; however, an emphasis is placed on heaters designed for use with spray cooling.M.S.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering
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Rabhi, Achref. "Numerical Modelling of Subcooled Nucleate Boiling for Thermal Management Solutions Using OpenFOAM." Licentiate thesis, Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-53307.
Full textAbstract:
Two-phase cooling solutions employing subcooled nucleate boiling flows e.g. thermosyphons, have gained a special interest during the last few decades. This interest stems from their enhanced ability to remove extremely high heat fluxes, while keeping a uniform surface temperature. Consequently, modelling and predicting boiling flows is very important, in order to optimise the two-phase cooling operation and to increase the involved heat transfer coefficients. In this work, a subcooled boiling model is implemented in the open-source code OpenFOAM to improve and extend its existing solver reactingTwoPhaseEulerFoam dedicated to model boiling flows. These flows are modelled using Computational Fluid Dynamics (CFD) following the Eulerian two-fluid approach. The simulations are used to evaluate and analyse the existing Active Nucleation Site Density (ANSD) models in the literature. Based on this evaluation, the accuracy of the CFD simulations using existing boiling sub-models is determined, and features leading to improve this accuracy are highlighted. In addition, the CFD simulations are used to perform a sensitivity analysis of the interfacial forces acting on bubbles during boiling flows. Finally, CFD simulation data is employed to study the Onset of Nucleate Boiling (ONB) and to propose a new model for this boiling sub-model, with an improved prediction accuracy and extended validity range. It is shown in this work that predictions associated with existing boiling sub-models are not accurate, and such sub-models need to take into account several convective boiling quantities to improve their accuracy. These quantities are the thermophysical properties of the involved materials, liquid and vapour thermodynamic properties and the heated surface micro-structure properties. Regarding the interfacial momentum transfer, it is shown that all the interfacial forces have considerable effects on boiling, except the lift force, which can be neglected without influencing the simulations' output. The new proposed ONB model takes into account convective boiling features, and it able to predict the ONB with a very good accuracy with a standard deviation of 2.7% or 0.1 K. This new ONB model is valid for a wide range of inlet Reynolds numbers, covering both regimes, laminar and turbulent, and a wide range of inlet subcoolings and applied heat fluxes.
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Wenzel, Ulrich. "Saturated pool boiling and subcooled flow boiling of mixtures at atmospheric pressure." 1992. http://hdl.handle.net/2292/2190.
Full textAbstract:
An experimental and theoretical investigation of heat transfer to liquid mixtures has been performed using binary and ternary mixtures of acetone, isopropanol and water. Two data-bases were established which contain measurements of the heat transfer coefficient under saturated pool boiling and subcooled flow boiling conditions. A third database comprises measurements of heat transfer and pressure drop in a plate heat exchanger. The performance of two heat transfer enhancement techniques, namely the coating of the heat transfer surface with teflon and a perforated brass foil, was studied under saturated pool boiling conditions. A model was developed, which can be used to predict the heat transfer coefficient. The model is based on the additive superposition of convective and boiling heat transfer coefficients. It is applicable for heat transfer to mixtures and single component fluids under saturated and subcooled boiling conditions. The empirical parameters in the correlations used in the model were not altered to fit the measurements of this study. The predictions of the model were compared to the experimental data, which covers the convective heat transfer regime, the transition region and the fully developed nucleate boiling regime. It was found that the best agreement between predicted an measured values was achieved, if the linear mixing law was used to calculate the ideal heat transfer coefficient rather than the correlations by Stephan-Preußer or Stephan-Abdelsalam. The heat transfer coefficient under saturated pool boiling conditions could be predicted with an accuracy of 12.6 %. A comparison between over 2000 measured heat transfer coefficients under subcooled flow boiling conditions in an annulus and the predictions of the model showed good agreement with a mean error of 10.3 %. The accuracy of the model was found to be independent of the fluid velocity and composition, as well as of the magnitude and mechanism of heat transfer. The heat flux in a plate heat exchanger could be predicted with a mean error of 6.9 % for a wide range of fluid velocities, subcoolings and compositions. The heat transfer coefficient on the test liquid side of the exchanger could be predicted with a mean error of 10 %. The heat transfer model was used for a theoretical study of the heat transfer to mixtures boiling on a finned surface. It was found that the fin geometry and thermal conductivity have a distinct influence on the local and mean heat transfer coefficients. The results indicate that the application of fins is more effective for boiling of mixtures than for boiling of single component liquids.
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Ming-Tsai, Huang, and 黃明才. "Subcooled Flow Boiling in Serpentine Enhanced Tubes with Refrigerants." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/29870363335409583026.
Full text
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Estrada, Perez Carlos E. "Experimental Two-Phase Flow Characterization of Subcooled Boiling in a Rectangular Channel." 2009. http://hdl.handle.net/1969.1/ETD-TAMU-2009-05-699.
Full textAbstract:
On the efforts to provide a reliable source of experimental information on turbulent
subcooled boiling ow, time resolved Particle Tracking Velocimetry (PTV) experiments
were carried out using HFE-301 refrigerant ow through a vertical rectangular
channel with one heated wall. Measurements were performed at liquid Reynolds numbers
of 3309, 9929 and 16549 over a wall heat flux range of 0.0 to 64.0 kW=m2. From
the PTV measurements, liquid two dimensional turbulence statistics are available,
such as: instantaneous 2-D velocity fields, time-averaged axial and normal velocities,
axial and normal turbulence intensities, and Reynolds stresses. The present results
agree with previous works and provide new information due to the 2-D nature of
the technique, for instance, this work shows that by increasing heat ux, the boiling
bubbles influence on the liquid phase is portrayed as a persistent increase of axial
velocity on regions close to the heater wall. This persistent increase on the axial
velocity reaches a maximum value attributed to the terminal bubble velocity. These
new observed phenomena must be considered for the development and improvement
of two-phase ow turbulence models. To this end, an extensive error analysis was also
performed with emphasis on the applicability of the PTV measurement technique on
optically inhomogeneous flows. The error quantification exhibited negligible optically
induced errors for the current conditions, making the data acquired in this work a
vast and reliable source.
27
Franz, Benjamin. "Numerical simulation of bubble growth in subcooled pool and flow boiling under microgravity conditions." Phd thesis, 2021. https://tuprints.ulb.tu-darmstadt.de/19063/1/Dissertationsschrift_Veroeffentlichung_Benjamin_Franz.pdf.
Full textAbstract:
Nucleate boiling is a process, that allows heat transfer characterized by high heat flows at low temperature differences. It is therefore employed in a wide range of industrial applications from the chemical industry over power generation to cooling. It is also a promising method for the cooling e.g. of electronic devices in space applications.
Until today, the design of heat exchangers, which employ nucleate boiling, relies on purely empirical correlations. The heat transfer correlations obtained under 1-g conditions cannot be employed for the design of heat exchangers operating in space. Heat and fluid flow mechanisms under microgravity conditions are not sufficiently understood, e.g. typical time and length scales during boiling in microgravity are larger compared to those under 1-g conditions. The latter is in turn promising for the experimental investigation of the boiling process in general and to draw conclusions for boiling under 1-g conditions. The objective is to find physically based correlations for the boiling process in general and to make the process more predictable.
In order to obtain deeper insight into the mechanisms dominating the boiling process in microgravity, a benchmark experiment was designed for operation aboard the International Space Station ISS. For the present thesis, CFD simulations of the boiling process are performed additional to that experiment. The numerical model employed uses the VOF method to cover the two-phase flow and includes models for the treatment of phase change, contact line evaporation and transient heat transfer between the wall and the fluid. It is further developed to account for specific design features of the reproduced experiment.
3-D simulations of multiple growing and moving vapor bubbles in a laminar, subcooled shear flow inside the boiling cell are conducted. Parameter studies are performed to investigate the impact of flow velocity, input heat flux, pre-heating time and subcooling on the hydrodynamics and heat transfer around vapor bubbles. Selected material properties of the fluid and the solid are varied, as well. In a second study simulations of bubble growth and detachment at the cavity, which serves as nucleation site in the experiment, are carried out.
For intermediate values of the above mentioned experimental parameters, vapor bubbles grow to an equilibrium volume determined by evaporation at the bubble foot and condensation to the subcooled bulk. Contact line evaporation shows a significantly higher share in the overall evaporation heat flow, than it does in studies conducted under 1-g conditions. A high input heat flux, a long pre-heating time and a low subcooling provoke a highly complex flow pattern of bubbles, which rapidly emerge after one another and coalesce, letting the initial bubble grow beyond its equilibrium volume. This causes a decreasing heat transfer coefficient. A choice of parameters, which causes a high number of small, distant vapor bubbles, appears advantageous for optimized heat transfer.
The cavity simulations show, that the influence of the nucleation process on the flow and temperature field outside the cavity cannot be ignored. Furthermore, for the correlation between detachment diameter of a vapor bubble from a cavity and flow velocity a non-dimensional approach is developed.
The present work shows both the advantages as well as the challenges of the employed numerical model to reproduce the according experimental setup. The impact of system parameters and material properties on bubble growth and heat transfer performance is examined and recommendations on the choice of parameters are given.
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Chen, Pei-Ting, and 陳蓓亭. "The Experimental Analysis of Subcooled and Saturated Flow Boiling for Dielectric Fluid FC-72 in Horizontal Microchannels." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/19874834702206286728.
Full textAbstract:
碩士國立交通大學
機械工程系
90
This thesis experimentally investigated the boiling curve, heat transfer characteristics and critical heat flux of dielectric liquid FC-72 in horizontal microchannels. The experiments were carried out for mass flux at 320﹑425﹑530 and 635㎏/㎡s, and subcooled temperature at 3℃﹑6℃and 10℃.The resuls showed that the fluid inlet subcooled temperature has much more effects than mass flux on heat transfer characteristics in the regime of nucleate boiling. The lower subcooled temperature had the better heat transfer performance. On the contrary, in the saturated state, the measured results were far different from those in the subcooled state. The heat transfer coefficients increased with mass flux, except only at low mass flux 320 ㎏/㎡s where higher heat transfer coefficients were found. In this experiment, the critical heat flux was mainly affected by subcooled temperature, not mass flux. A modified correlation of heat transfer coefficients of subcooled flow boiling was developed,which could predict the heat transfer coefficient for this experiment within 15% band of deviation.
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Chiang, Lian-Jien, and 江連金. "Experimental Study of Saturated and Subcooled Flow Boiling Heat Transfer of R-134a in Plate Heat Exchanger." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/84217994950559692547.
Full textAbstract:
碩士國立交通大學
機械工程系
88
The saturated and subcooled flow boiling heat transfer of refrigerant R-134a in a plate heat exchanger are measured in this study. Besides, the associated bubble characteristics in the plate heat exchanger are also inspected by visualizing the boiling flow. Two vertical counterflow channels are formed in the exchanger by three plates of commercial geometry with a corrugated sinusoidal shape of a chevron angle of 60°. Upflow boiling of refrigerant R-134a in one channel receives heat from the downflow of hot water in the other channel. The effects of the imposed heat flux, mass flux, system pressure and subcooling of R-134a on the saturated and subcooled boiling heat transfer are explored in detail. The experimental data for the saturated flow boiling showed that both the boiling heat transfer coefficient and pressure drop increase almost linearly with the imposed heat flux. At a higher mass flux the pressure drop is substantially higher but the boiling heat transfer coefficient only shows slight improvement. Raising the refrigerant pressure from 0.6 to 0.8 MPa, the frictional pressure drop is significantly lower but the change in the heat transfer coefficient is small. Furthermore, it is noted that at the lowest pressure tested here for P=0.5 MPa the boiling heat transfer coefficient is lowest, but the associated rise in pressure drop is highest. Based on the present data, empirical correlations for the saturated boiling heat transfer coefficient and friction factor are proposed. Next, the results in the subcooled flow boiling are presented in terms of the boiling curves and heat transfer coefficient. The results for the boiling curves show significant change in the slopes of the boiling curves during the onset of nucleate boiling (ONB) especially at low mass flux and high saturation temperature. Besides, the boiling hysteresis is significant at a low refrigerant mass flux. The subcooled boiling heat transfer coefficient is affected noticeably by the mass flux of the refrigerant. However, the inlet subcooling and saturation temperature have little effect on the boiling heat transfer coefficient. The photos from the flow visualization for the saturated and subcooled flow boiling revealed that at higher boiling heat flux the plate surface is covered with more bubbles and the bubble generation frequency is higher, and the bubbles tend to coalesce into big bubbles. But these big bubbles are prone to break up into small bubbles as they move over the corrugated plate, producing strong agitating flow motion and hence enhancing the boiling heat transfer. We also noted that the bubbles nucleated from the plate were suppressed to a larger degree for higher inlet subcooling and mass flux. At high heat flux the boiling is so intense that there is a two phase flow pattern transition from a bubbly flow to an annular flow in the channel. Finally, empirical correlations for the heat transfer coefficient and the bubble departure diameter in the subcooled flow boiling are proposed.
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Gómez-Zarzuela, Quel Consuelo. "Development and assessment of a one-dimensional CFD solver for boiling flows in bubbly regimes." Doctoral thesis, 2020. http://hdl.handle.net/10251/148368.
Full textAbstract:
[EN] The present PhD thesis aims at the development of a one-dimensional solver
capable of solving single- and two-phase flow fluid systems. The novelty of this
project lies in the use of an open source CFD platform, called OpenFOAM, as a
development framework for the new tool.
For the new solver development, the conservation equations based on Navier-
Stokes (three-dimensional system) have been analyzed and reduced to one dimension.
For the two-phase simulations, the Two Fluid Model method was used
as base. In addition, a series of empirical models have been selected as closing
equations of the system.
The final solver includes a series of requirements that reinforce their capabilities.
Among them, the use of a second mesh that represents the solid and takes into
account the heat transmitted to the fluid by conduction through a solid, stands
out. On the other hand, the possible transfer of mass between phases in twophase
fluids has been taken into account. Similarly, a subcooled boiling model
has been implemented which takes into account the possible generation of vapor
near the wall while the bulk is kept below saturation temperature.
Finally, this paper presents the verification and validation of the solver. The verification
has been carried out mainly with the system code TRACE, whose validation
has been demonstrated in numerous works and its use is very extended
in the scientific community. For the validation, we have the results of two experimental
cases that allow us to demonstrate the physical validity of the new
application developed.
The use of this platform allows for a much more direct coupling between one- and
three-dimensional domains, obtaining a better optimization of the calculation.[ES] El presente trabajo de doctorado tiene por objetivo el desarrollo de un solver unidimensional capaz de resolver sistemas de fluidos monofásicos y bifásicos. La novedad de este proyecto reside en el uso de una plataforma CFD de código abierto, llamada OpenFOAM, como marco para el desarrollo de la nueva herramienta. Para el desarrollo del nuevo solver, se han analizado las ecuaciones de conservación basadas en Navier-Stokes (tridimensionales) y se han reducido a una dimensión. Para la parte bifásica del solver, se utiliza el método Two Fluid Model. Además, se han incluido todos los modelos empíricos necesarios como ecuaciones de cierre del sistema. El solver final incluye una serie de requerimientos que refuerzan sus capacidades. Entre ellas, destacan, por un lado, el uso de una segunda malla que represente el sólido y tenga en cuenta el calor transmitido al fluido por conducción a través de un sólido. Por otro lado, se ha tenido en cuenta la posible transferencia de masa entre fases en fluidos bifásicos. Igualmente, se ha implementado un modelo de ebullición subenfriada que tiene en cuenta la posible generación de vapor cerca de la pared mientras el centro del fluido se mantiene por debajo de la temperatura de saturación. Finalmente, este trabajo presenta la verificación y validación del solver. La verificación se ha realizado principalmente con el código de sistema TRACE. Para la validación, se cuenta con los resultados de dos casos experimentales que permiten demostrar la validez física de la nueva aplicación desarrollada. La implementación del nuevo solver en esta plataforma abierta permite un futuro acoplamiento mucho más directo entre mallas unidimensionales y tridimensionales, obteniendo una mayor optimización del cálculo.
[CA] El present treball de doctorat té per objectiu el desenvolupament d'un nou solver unidimensional capaç de solucionar sistemes amb fluids monofàsics i bifàsics. La novetat d'aquest projecte resideix en l'ús d'una plataforma CFD de codi obert, anomenada OpenFOAM com a marc de desenvolupament de la nova eina. Per al desenvolupament del nou solver, s'han analitzat les equacions de conservació basades en Navier-Stokes (tridimensionals) i s'han reduït a una dimensió. Per a la part bifàsica del solver s'utilitza el mètode Two Fluid Model. A més, s'han inclòs tots els models empírics necessaris com a equacions de tancament del sistema. El solver final inclou una sèrie de requeriments que reforcen les seues capacitats. Entre elles, destaquen, d'una banda, l'ús d'una segona malla que represente el sòlid i es tinga en compte la calor transmesa al fluid per conducció a través d'un sòlid. D'altra banda, s'ha tingut en compte la possible transferència de massa entre fases en fluids bifàsics. Igualment, s'ha implementat un model d'ebullició subrefredada que té en compte la possible generació de vapor prop de la paret mentre el centre del fluid es manté per davall de la temperatura de saturació. Finalment, aquest treball presenta la verificació i validació del solver. La verificació s'ha realitzat principalment amb el codi de sistema TRACE, la validació del qual s'ha demostrat en nombrosos treballs i el seu ús està molt estés en la comunitat científica. Per a la validació, es compta amb els resultats de dos casos experimentals que permeten demostrar la validesa física de la nova aplicació desenvolupada. L'ús d'esta plataforma permiteix un futur acoblament més directe, entre elements unidimensionals i tridimensionals, obtenint una major optimització del càlcul.
Gómez-Zarzuela Quel, C. (2020). Development and assessment of a one-dimensional CFD solver for boiling flows in bubbly regimes [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/148368
TESIS
31
顏貽乙. "= Experimental study of evaporation and condensation heat transfer and pressure drop of R-134a in plate heat exchanger and small pipe and subcooled flow boiling of R-134a in an annular duct." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/19015641460799464932.
Full text
32
Schneider, Clemens. "Experimentelle Untersuchungen zum Blasensieden bei unterkühlten Strömungen: Experimentelle Untersuchungen zum Blasensieden bei unterkühlten Strömungen." Doctoral thesis, 2014. https://tud.qucosa.de/id/qucosa%3A29008.
Full textAbstract:
Die vorliegende Dissertationsschrift beinhaltet die Ergebnisse der Untersuchung von loka-len und globalen Prozessen der Wärmeübertragung beim unterkühlten Strömungssieden. Sie ist an der Schnittstelle zwischen Reaktorsicherheitsforschung und der experimentellen Thermofluiddynamik für Phasenübergänge einzuordnen.
In technischen Anwendungen zur effizienten Übertragung großer Wärmemengen spielt der Prozess des Siedens eine wichtige Rolle. Dieser Vorgang bewirkt einen starken Anstieg des Wärmetransportes von der beizten Wand an das Fluid bei vergleichsweise geringem Anstieg der Wandtemperatur. Der maximal übertragbare Wärmestrom beim Sieden wird begrenzt durch die sogenannte kritische Wärmestromdichte, deren Überschreitung zum thermomechanischen Versagen der beheizten Komponente führen kann.
Aufgrund der Komplexität dieser Prozesse ist es trotz intensiver Arbeiten in den letzten Jahrzehnten noch nicht gelungen, diese Vorgänge detailliert zu modellieren. Eine Weiter-entwicklung der Modelle zur realistischen Beschreibung des unterkühlten Strömungssie-dens erfordert neuartige Untersuchungen, welche eine genaue Klassifizierung der partiellen Wärmeübergänge des Blasensiedens ermöglichen.
Die Analyse partieller Wärmetransportgrößen beim unterkühlten Strömungssieden sowie der Einfluss variierender thermohydraulischer Randbedingungen ist Schwerpunkt dieser Arbeit. In der entwickelten Versuchsanlage erfolgt die Erfassung der Siedevorgänge bei Strömungsgeschwindigkeiten von 0,1 – 2 m/s und Eintrittstemperaturen von 60 - 98 °C.
Mit Hilfe empfindlicher Temperaturmessungen in einem elektrisch beheizten Kapillarrohr innerhalb des Strömungskanals werden die globalen Vorgänge beim Übergang von Kon-vektion zum Sieden erfasst. Durch eine modellbasierte Bestimmung der Oberflächentem-peratur lassen sich Phänomene nachweisen, welche bisher weitestgehend unbeachtet ge-blieben sind. Die transparente Versuchsstrecke ermöglicht eine Erfassung der lokalen Sie-devorgänge mit optisch und zeitlich hochauflösenden Messverfahren. Durch die Entwick-lung neuer Algorithmen der digitalen Bildverarbeitung wurde eine umfangreiche, kenngrö-ßenorientierte Auswertung der in großem Umfang entstandenen Datenmengen realisiert.
Der Einsatz transparenter und elektrisch leitfähiger Beschichtungen ermöglicht die mikro-skopische Erfassung des Blasenwachstums in weiten thermohydraulischen Parameterberei-chen. Mit erweiterten Bildverarbeitungsalgorithmen erfolgt die detaillierte und dynamische Bewertung des Blasenwachstumsverhaltens. Die statistische Auswertung der Verläufe er-möglicht die Ableitung eines Blasenwachstumsmodells für unterkühltes Strömungssieden.
In einer weiteren Versuchsanordnung werden die lokalen Wärmetransportvorgänge bei der Ablösung quasistatisch gewachsener Blasen mit Hilfe der Infrarot-Thermographie be-stimmt. Dadurch können erstmalig die aus der lokalen Abkühlung der beheizten Oberfläche durch Blasenablösung resultierenden Wärmeströme unter Vernachlässigung der Bla-senbildung experimentell quantifiziert werden. Weiterhin können die bisher theoretisch beschriebenen Driftströmungen beim Aufstieg der Blase experimentell nachgewiesen wer-den. Die ermittelten Größen und Zusammenhänge tragen zur Weiterentwicklung und zum Abbau von Unsicherheiten bei der Modellierung von Wärmetransportvorgängen beim unterkühlten Strömungssieden bei.