Download or read book Investigation of Inertia Controlled Bubble Departure Mechanism in Subcooled Flow Boiling Using High Speed Photography written by Viktor R. Mizo and published by . This book was released on 1995 with total page 274 pages. Available in PDF, EPUB and Kindle. Book excerpt: "A summary of important theoretical models available for bubble growth and departure behavior in flow boiling is presented. Experimental bubble growth rate curves under sub-cooled flow boiling conditions are obtained in the Thermal Analysis Laboratory in the Mechanical Engineering Department at the Rochester Institute of Technology utilizing high-speed photography. The effects of flow rate, sub-cooling, heater surface temperature, and cavity size are investigated, and specific trends observed in the bubble growth rate behavior are discussed. The growth rates in flow boiling are compared with the ones for pool boiling, and a need for an improved model for predicting bubble growth rates in flow boiling is established. The new model based on a control volume approach for the front and rear halves of a bubble developed earlier in the Thermal Analysis Lab at RIT is extended to include the inertia forces acting on a growing bubble. The predictions from the model are compared to the experimental data and are found to agree within an average absolute error of 7.45 %. The mechanism of the actual bubble departure from the heater surface is discussed, and suggestions for future work in the area are outlined."--Abstract.

Download or read book An Investigation of Bubble Departure in Subcooled Flow Boiling written by Brian J. Stumm and published by . This book was released on 1993 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt: "A summary of the major theoretical models available for departure diameter prediction in sub-cooled flow boiling is presented. A new model is developed to predict the forces acting on a bubble at the instance of departure by introducing a control volume approach for the front and the rear halves of the bubble. The predictions from the model are compared with experimental data obtained in the Thermal Analysis Laboratory in the Mechanical Engineering Department at Rochester Institute of Technology. Two competing mechanisms are identified as being responsible for bubble departure. To obtain clear evidence of the dominate mechanism, high speed photography is recommended in future work in this area."--Abstract.

Download or read book Experimental Investigation of Subcooled Flow Boiling Using Synchronized High Speed Video Infrared Thermography and Particle Image Velocimetry written by Bren Andrew Phillips and published by . This book was released on 2014 with total page 206 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Experimental Study on the Subcooled Boiling Flow Via Optical Measurement Techniques written by Jun Soo Yoo and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A series of experimental work to investigate the subcooled boiling flow in a vertical square upward flow channel is described. As experimental methods, high-speed photography and infrared (IR) thermometry were employed simultaneously. The research scope explored includes (i) measurement issues of fundamental bubble parameters through visualization, (ii) experimental methodology to achieve both enhanced two-phase flow visualization and accurate wall temperature measurement, and (iii) measurement of diverse aspects of bubble dynamics as well as wall heat transfer by applying the verified experimental approach. Before producing the actual data, substantial effort was first made to identify the critical measurement issues of fundamental bubble parameters in a forced convective boiling system. Those issues have never been explicitly addressed in previous studies despite the possibly critical impacts on the experimental results. Thus, a series of systematic experimental investigations was performed to uncover those issues and to verify the errors created by not addressing them, based on which more suitable ways of observing and characterizing such parameters through experiments were discussed. Then, an experimental strategy to achieve high-fidelity optical measurements using both high-speed photography and IR thermometry was established. To attain the goal, the important issues such as test section design, IR thermal imaging issues, visualization strategy, wall temperature tracking method, and experimental validations were extensively addressed. Also, the feasibility of current experimental approach was demonstrated through the subcooled flow boiling experiment. Finally, by employing the experimental strategy established, an experimental investigation of the subcooled boiling flow was conducted. The experiment was performed in a vertical square upward flow channel using refrigerant NovecTM 7000, in which a single nucleation site was purposely activated for a fundamental study of subcooled flow boiling process. The various aspects of bubble behavior under different subcooled flow boiling conditions were examined using both micro- and macroscopic views of high-speed cameras while measuring the wall temperature/heat flux with IR thermometry. Additionally, based on the measurements of various bubble parameters as well as wall heat transfer, relevant relations among those parameters and the underlying mechanisms were intensively discussed. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155042

Download or read book Bubble Behavior in Subcooled Flow Boiling on Surfaces of Variable Wettability written by Emily W. Tow and published by . This book was released on 2012 with total page 63 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Experimental Investigation on Multiscale Interactions in Intermittent Flow Boiling and a New Hybrid VOF Lagrangian Modeling Approach written by Xiang Zhang and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: In flow boiling, most phase change heat transfer occurs at the smallest scales: in 1 nm -- 10 [mu]m thick liquid microlayers under nucleating bubbles and in thin thermal boundary layers around such bubbles. Nucleating bubbles evolve from microscopic cavities on heated surfaces (reaching 104 - 106 sites per cm2). Theoretical closure models have been proposed for individual bubble nucleation, growth, and departure due to hydrodynamics. However, high-fidelity integration of such microscale models and theory with full channel flow processes has proven challenging due to the large range of length and time scales. Thus, contemporary boiling engineering still relies on empirical correlations. While such models are validated by large experimental databases, they are limited to specific fluids and geometries. More rigorous descriptions are needed to predict transport with emerging configurations and fluids. The first objective of this study is to experimentally characterize the coupling between micro-scale transport and large-scale hydrodynamics in flow boiling heat transfer through high-speed photography and thermal imaging. A new hybrid volume-of-fluid (VOF)-Lagrangian multi-scale simulation approach is then proposed to directly resolve and couple these processes. Experimental data from this investigation and other publications are employed to assess this modeling approach. First, a square air-oil bubble column facility is built to track the bubble trajectories at free surface and assess the hybrid VOF-Lagrangian simulation approach. High speed videos are captured from both the front and top view to measure flow parameters including: bubble size distribution (BSD), bubble rise velocity in vertical direction, as well as bubble lifetime and propagation velocity at the free surface. A hybrid VOF-Lagrangian solver is developed to characterize the coupling between micro-scale bubble transport and macro-scale hydrodynamics in such multi-scale two-phase flows. The Lagrangian model tracks the trajectory of individual injected discrete small bubbles, accounting for effects such as buoyancy, pressure, virtual mass, drag, and turbulent dispersion. Once bubbles exceed a threshold packing density or overlap with VOF structures, they are converted to the grid-scale vapor phase. An empirical bubble-lifetime model is implemented to account for the finite coalescence times of bubbles at free surfaces. Contributions of this effort include programmable closure for bubble lifetime at the free surface (before popping/coalescence), a pinning force method for bubbles at the free surface, and Lagrangian-to-VOF transition of bubbles based on packing density. Next, a two-phase flow boiling experimental facility is developed to collect simultaneous high-speed visualization and IR temperature distribution data. The test cell channel is 420 mm long with a 10 mm square-cross section. A transparent ITO coated sapphire window serves as a heater and IR interface for measuring the internal wall temperature. The facility is charged with a low boiling point fluid (HFE7000) to reduce uncertainties from heat loss. Vertical saturated flow boiling wake-nucleation interaction experiments are performed for varying volume flow rates (0.5 -- 1.5 L min-1, laminar-to-turbulent Re) and heat fluxes (0 -- 100 kW m-2). Discrete vapor slugs are injected to explore interactions with nucleate boiling processes. By measuring film-heater power, surface temperature distributions, and pressures, local instantaneous heat transfer coefficients (HTC) are obtained. A conjugate gradient method is implemented to solve the 2-D transient inverse heat conduction problem and estimate the non-uniform heat flux distribution. For nucleate flow boiling without slug injection, visualizations show that both bubble cycle and wait time are inversely proportional to the applied heat flux. The average wall temperature displays a linear relationship with heat flux. Moreover, bubble departure diameter tends to increase with increasing the bubble nucleation temperature, and stabilizes at higher temperature. With respect to the wake-nucleation interaction experiments, it is found that small nucleate bubbles only in the core region of Taylor bubble body with a certain bubble size (1.4 to 1.6 mm) would merge into the vapor slug. IR data indicate that the wake shear effect is divided into 5 stages during the whole process. Wake heat transfer enhancement is observed due to the vortex shedding and intense mixing between in the Taylor bubble wake. In addition, the nucleate boiling is firstly suppressed in the Taylor bubble body due to the falling liquid film, then recovered after the wake region. To efficiently simulate such processes, the hybrid VOF-Lagrangian model is extended to account for heat transfer, bulk- and Lagrangian-bubble-scale phase change, and nucleation site processes. The approach tracks discrete nucleation sites on walls and simulates a contact line pinning force. Bubble growth and departure is directly predicted using grid-scale VOF velocity and temperature data rather than idealized conditions. This method is first verified with literature data for pool boiling. It is then qualitatively assessed for the Taylor flow boiling processes studied experimentally.

Download or read book The Effects of Orientation Angle Subcooling Heat Flux Mass Flux and Pressure on Bubble Growth and Detachment in Subcooled Flow Boiling written by Rosemary M. Sugrue and published by . This book was released on 2012 with total page 122 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Experimental and Analytical Investigation of the Bubble Nucleation Characteristics in Subcooled Flow written by Michael D. Cartwright and published by . This book was released on 1995 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt: "An experimental and analytical study of bubble nucleation characteristics for a polished aluminum surface under sub-cooled flow boiling of water is conducted. A high magnification (up to 1350X) microscope and an atomic force magnifier were used to visualize the aluminum surface to determine a range of cavity sizes on the heater surface as well as gain insight into the shape of the cavity. A high-speed camera was incorporated to study the actual bubble nucleation from these cavities. A review of existing theoretical models available in literature to predict bubble nucleation characteristics in flow boiling is also presented. A new bubble nucleation model is proposed which uses experimentally determined bubble geometry and results from computational fluid dynamics (CFD) modeling. Experimental data was collected through the use of the high-speed flow visualization system available in RIT's Thermal Fluid Laboratory. The data is obtained to study the effects of sub-cooling, flow rate, and wall superheat on the nucleation characteristics of different size cavities. This data is also compared with existing models as well as the one proposed in this investigation."--Abstract.

Download or read book Bubble Formation in a Horizontal Channel at Subcooled Flow Condition written by Saman ShabanNejad and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Convective Boiling and Condensation written by John G. Collier and published by Clarendon Press. This book was released on 1994-05-19 with total page 646 pages. Available in PDF, EPUB and Kindle. Book excerpt: * Third edition of a well-known and well established text both in industry and for teaching * Fully up-to-date and includes extra problems This book is an aid to heat exchanger design written primarily for design and development engineers in the chemical process, power generation, and refrigeration industries. It provides a comprehensive reference on two-phase flows, boiling, and condensation. The text covers all the latest advances like flows over tube bundles and two-phase heat transfer regarding refrigerants and petrochemicals. Another feature of this third edition is many new problems at chapter ends to enhance its use as a teaching text for graduate and post-graduate courses on two-phase flow and heat transfer. - ;This book is written for practising engineers as a comprehensive reference on two-phase flows, boiling, and condensation. It deals with methods for estimating two-phase flow pressure drops and heat transfer rates. It is a well-known reference book in its third edition and is also used as a text for advanced university courses. Both authors write from practical experience as both are professional engineers. -

Download or read book Translational Research in Cardio Oncology An Issue of Heart Failure Clinics written by Ragavendra R. Baliga and published by Elsevier Health Sciences. This book was released on 2022-06-23 with total page 217 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this issue of Heart Failure Clinics, guest editors Drs. Ragavendra R Baliga and George A. Mensah bring their considerable expertise to the topic of Translational Research in Cardio-Oncology. Top experts in the field cover key topics such as radiation-induced cardiac dysfunction; training and career development; cardiovascular imaging; CAR-T cell therapy and cardiovascular disease; and more. Contains 12 relevant, practice-oriented topics including cardio-protection of high-risk individuals; myocardial metabolism; amyloidosis; arrhythmic complications associated with cancer therapies; and more. Provides in-depth clinical reviews on translational research in cardio-oncology, offering actionable insights for clinical practice. Presents the latest information on this timely, focused topic under the leadership of experienced editors in the field. Authors synthesize and distill the latest research and practice guidelines to create clinically significant, topic-based reviews.

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

Download or read book Analysis of Heat Transfer Burnout Pressure Drop and Density Data for High pressure Water written by W. H. Jens and published by . This book was released on 1955 with total page 146 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fundamentals of Multiphase Flow written by Christopher E. Brennen and published by Cambridge University Press. This book was released on 2005-04-18 with total page 376 pages. Available in PDF, EPUB and Kindle. Book excerpt: Publisher Description

Download or read book Flow boiling and condensation in microscale channels written by Fabio Toshio Kanizawa and published by Springer Nature. This book was released on 2021-04-30 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book covers aspects of multiphase flow and heat transfer during phase change processes, focusing on boiling and condensation in microscale channels. The authors present up-to-date predictive methods for flow pattern, void fraction, pressure drop, heat transfer coefficient and critical heat flux, pointing out the range of operational conditions that each method is valid. The first four chapters are dedicated on the motivation to study multiphase flow and heat transfer during phase change process, and the three last chapters are focused on the analysis of heat transfer process during boiling and condensation. During the description of the models and predictive methods, the trends are discussed and compared with experimental findings.

Download or read book Survey of Heat Transfer to Near critical Fluids written by Robert C. Hendricks and published by . This book was released on 1970 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advances in Heat Transfer written by and published by Academic Press. This book was released on 1998-05-18 with total page 467 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advances in Heat Transfer