Дисертації з теми "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.
Повний текст джерелаStumm, Brian J. "An investigation on bubble departure in subcooled flow boiling /." Online version of thesis, 1993. http://hdl.handle.net/1850/11186.
Повний текст джерелаProdanovic, 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.
Повний текст джерелаSamaroo, 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.
Повний текст джерелаAir 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.
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.
Повний текст джерелаThis 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.
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.
Повний текст джерелаCataloged 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.
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.
Повний текст джерелаThis 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.
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/.
Повний текст джерелаCartwright, 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.
Повний текст джерелаNajibi, 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/.
Повний текст джерелаMizo, 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.
Повний текст джерелаKim, 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.
Повний текст джерелаCataloged 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.
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.
Повний текст джерелаCataloged 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
Becht, Charles. "Onset of Flow Instability in Uniformly Heated, Narrow, Rectangular Channels." Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16187.
Повний текст джерелаPhillips, 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.
Повний текст джерелаThis 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.
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.
Повний текст джерелаSugrue, 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.
Повний текст джерелаCataloged 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.
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.
Повний текст джерелаBruder, 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.
Повний текст джерелаNop, 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.
Повний текст джерелаIn 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
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.
Повний текст джерелаGlassman, 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.
Повний текст джерелаM.S.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering
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.
Повний текст джерелаWenzel, Ulrich. "Saturated pool boiling and subcooled flow boiling of mixtures at atmospheric pressure." 1992. http://hdl.handle.net/2292/2190.
Повний текст джерелаMing-Tsai, Huang, and 黃明才. "Subcooled Flow Boiling in Serpentine Enhanced Tubes with Refrigerants." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/29870363335409583026.
Повний текст джерелаEstrada, 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.
Повний текст джерелаFranz, 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.
Повний текст джерелаChen, 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.
Повний текст джерела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.
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.
Повний текст джерела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.
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.
Повний текст джерела[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
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.
Повний текст джерелаSchneider, 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.
Повний текст джерела