Download or read book Numerical Simulation of the Dynamics and Heat Transfer Associated with a Single Bubble in Subcooled Pool Boiling and in the Presence of Noncondensables written by Jinfeng Wu and published by . This book was released on 2007 with total page 258 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the present study, a numerical procedure coupling level set function with moving mesh method is established. Test problems have been chosen to validate this developed method. The numerical results show that the current adaptive method can achieve the equivalent accuracy to the methods based on more uniform grids do. The results from the above-mentioned numerical procedure coupling level set function with moving mesh method for comparing cases in the presence of noncondensables with ones in the absence of noncondensables show the evidence of effects of noncondensable air imposed on heat transfer and the induced flow pattern is presented as well.
Download or read book Numerical Simulations of Bubble Dynamics and Heat Transfer in Pool Building written by Eduardo Aktinol and published by . This book was released on 2014 with total page 173 pages. Available in PDF, EPUB and Kindle. Book excerpt: Due to the complex nature of the subprocesses involved in nucleate boiling, it has not been possible to develop comprehensive models or correlations despite decades of accumulated data and analysis. Complications such as the presence of dissolved gas in the liquid further confound attempts at modeling nucleate boiling. Moreover, existing empirical correlations may not be suitable for new applications, especially with regards to varying gravity level. More recently, numerical simulations of the boiling process have proven to be capable of reliably predicting bubble dynamics and associated heat transfer by showing excellent agreement with experimental data. However, most simulations decouple the solid substrate by assuming constant wall temperature. In the present study complete numerical simulations of the boiling process are performed--including conjugate transient conduction in the solid substrate and the effects of dissolved gas in the liquid at different levels of gravity. Finite difference schemes are used to discretize the governing equations in the liquid, vapor, and solid phases. The interface between liquid and vapor phases is tracked by a level set method. An iterative procedure is used at the interface between the solid and fluid phases. Near the three-phase contact line, temperatures in the solid are observed to fluctuate significantly over short periods. The results show good agreement with the data available in the literature. The results also show that waiting and growth periods can be related directly to wall superheat. The functional relationship between waiting period and wall superheat is found to agree well with empirical correlations reported in the literature. For the case of a single bubble in subcooled nucleate boiling, the presence of dissolved gas in the liquid is found to cause noncondensables to accumulate at the top of the bubble where most condensation occurs. This results in reduced local saturation temperature and condensation rates. The numerical predictions show reasonable agreement with the results from experiments performed at microgravity. For nucleate boiling at microgravity the simulations predict a drastic change in vapor removal pattern when compared to Earth normal gravity. The predictions match well with experimental results. However, simulated heat transfer rates were significantly under-predicted.
Download or read book Fluid Mechanics and Fluid Power Volume 5 written by Krishna Mohan Singh and published by Springer Nature. This book was released on with total page 824 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Boiling written by Yasuo Koizumi and published by Elsevier. This book was released on 2017-06-22 with total page 849 pages. Available in PDF, EPUB and Kindle. Book excerpt: Boiling: Research and Advances presents the latest developments and improvements in the technologies, instrumentation, and equipment surrounding boiling. Presented by the Japan Society of Mechanical Engineers, the book takes a holistic approach, first providing principles, and then numerous practical applications that consider size scales. Through six chapters, the book covers contributed sections from knowledgeable specialists on various topics, ranging from outlining boiling phenomena and heat transfer characteristics, to the numerical simulation of liquid-gas two phase flow. It summarizes, in a single volume, the state-of-the-art in boiling heat transfer and provides a valuable resource for thermal engineers and practitioners working in the thermal sciences and thermal engineering. Explores the most recent advancements in boiling research and technology from the last twenty years Provides section content written by contributing experts in their respective research areas Shares research being conducted and advancements being made on boiling and heat transfer in Japan, one of the major research hubs in this field
Download or read book Heat Transfer Vapour Bubble Dynamics and Sound Emission in Subcooled Nucleate Pool Boiling written by Andreas Bode and published by . This book was released on 2004 with total page 181 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Bubble Dynamics and Boiling Heat Transfer written by Samuel Siedel and published by . This book was released on 2013 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since boiling heat transfer affords a very effective means to transfer heat, it is implemented in numerous technologies and industries ranging from large power generation plants to micro-electronic thermal management. Although having been a subject of research for several decades, an accurate prediction of boiling heat transfer is still challenging due to the complexity of the coupled mechanisms involved. It appears that the boiling heat transfer coefficient is intimately related to bubble dynamics (i.e. bubble nucleation, growth and detachment) as well as factors such as nucleation site density and interaction between neighbouring and successive bubbles. In order to contribute to the understanding of the boiling phenomenon, an experimental investigation of saturated pool boiling from a single or two neighbouring artificial nucleation sites on a polished copper surface has been performed. The bubble growth dynamics has been characterized for different wall superheats and a experimental growth law has been established. The interaction between successive bubbles from the same nucleation site has been studied, showing the bubble shape oscillations that can be caused by these interactions. The forces acting on a growing bubble has been reviewed, and a complete momentum balance has been made for all stages of bubble growth. The curvature along the interface has been measured, and indications concerning the mechanism of bubble detachment have been suggested. The rise of bubble after detachment has been investigated, and the maximum velocity reached before a change of direction has been estimated and compared to existing models from the literature. The interaction between bubbles growing side by side has been studied: the generation and propagation of a wave front during the coalescence of two bubbles has been highlighted. As boiling heat transfer enhancement techniques are being imagined and developed, this study also focuses on the electrohydrodynamic enhancement technique. Boiling experiments have been performed in the presence of electric fields, and their effects on heat transfer and bubble dynamics have been characterized. Although the volume of the bubbles at detachment and the relationship between the bubble frequency and the wall superheat were not affected, the bubble growth curve was modified. The bubbles were elongated in the direction of the electric field, and this elongation was estimated and compared to other studies from the literature. The rising velocity of the bubble was reduced in the presence of electric field, and the behaviour of bubbles growing side by side was modified, the electric field causing the bubbles to repeal each other. These results, obtained in a fully controlled environment, provide compelling evidence that electric fields can be implemented to alter the bubble dynamics and subsequently heat transfer rates during boiling of dielectric fluids.
Download or read book Bubble Dynamics and Heat Transfer in Pool Boiling on Wires at Different Gravity written by Jian-Fu Zhao and published by . This book was released on 2011 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: A series of experimental studies on bubble dynamical behaviors and heat transfer in pool boiling on thin wires in different gravity conditions have been performed in the past years, including experiments in long-term microgravity aboard the 22nd Chinese recoverable satellite RS-22, in short-term microgravity in the drop tower Beijing, and in normal gravity on the ground. Steady pool boiling of degassed R113 on thin platinum wires has been studied using a temperature-controlled heating method. A voltage-controlled heating method has also been used in normal gravity. A slight enhancement of nucleate boiling heat transfer is observed in microgravity, while dramatic changes of bubble behaviors are very evident. Considering the influence of the Marangoni effects, the different characteristics of bubble behaviors in microgravity have been explained. A new bubble departure model including the influence of the Marangoni effects has also been proposed, which can predict the whole observation both in microgravity and in normal gravity. The value of CHF (critical heat flux) in microgravity is lower than that in normal gravity, but it can be predicted well by the Lienhard-Dhir correlation, although the dimensionless radius, or the square root of the Bond number, in the present case is far beyond its initial application range. A further revisit on the scaling of CHF with heater radius in normal gravity, which is focused on the case of a small Bond number, has also been performed in our laboratory using different kinds of working fluids at different subcooling conditions. Interactions between the influences of the subcooling and heater radius will be important for the case of a small Bond number. In addition to the Bond number, there may exist some other parameters, which may be material-dependent, that play important roles in the CHF phenomenon with a small Bond number.
Download or read book Numerical Simulation of Bubble Growth in Subcooled Pool and Flow Boiling Under Microgravity Conditions written by Benjamin Franz and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental Investigation of Nucleate Boiling Bubble Dynamics in Normal and Zero Gravities written by Thomas H. Cochran and published by . This book was released on 1968 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Simulation of Sub cooled Flow Boiling written by Won Cheol Park and published by . This book was released on 2003 with total page 604 pages. Available in PDF, EPUB and Kindle. Book excerpt: Predictions of heat transfer and void fraction under sub-cooled flow boiling using two-fluid models need better quantitative knowledge related to the mechanisms associated with bubble growth and detachment. When such data becomes available, they can be used to develop useful simple wall functions for two-phase flow and can yield accurate Nusselt number predictions.
Download or read book Bubble Dynamics and Forced Convection Boiling Heat Transfer with Low Velocity written by Longhu Li and published by . This book was released on 1993 with total page 866 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Zero and Reduced gravity Simulation on a Magnetic colloid Pool boiling System written by S. Stephen Papell and published by . This book was released on 1966 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book ASME 68 HT 47 written by J. D. Jacobs and published by . This book was released on 1968 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Microscale Heat Transfer Measurements During Subcooled Pool Boiling of Pentane written by Payam Delgoshaei and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental Numerical Investigation of Pool Boiling on Engineered Surfaces with Integrated Thin flim Temperature Sensors written by Vijaykumar Sathyamurthi and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of this investigation is to measure and analyze surface temperature fluctuations in pool boiling. The surface temperature fluctuations were recorded on silicon surfaces with and without multi-walled carbon nanotubes (MWCNT). Novel Thin Film Thermocouples (TFT) are micro-fabricated on test substrates to measure surface temperatures. A dielectric liquid refrigerant (PF-5060) is used as test fluid. Both nucleate and lm boiling regimes are investigated for the silicon test substrates. Dynamics of nucleate boiling is investigated on the CNT coated substrates. High frequency temperature fluctuation data is analyzed for the presence of determinism using non-linear time series analysis techniques in TISEAN© software. The impact of subcooling and micro/nano-scale surface texturing using MWCNT coatings on the dynamics of pool boiling is assessed. Dynamic invariants such as correlation dimensions and Lyapunov spectrum are evaluated for the reconstructed attractor. A non-linear noise reduction scheme is employed to reduce the level of noise in the data. Previous investigations in pool boiling chaos, reported in literature were based on temperature measurements underneath the test surface consisting of single or few active nucleation sites. Previous studies have indicated the presence of low-dimensional behavior in nucleate boiling and high-dimensional behavior in CHF and film boiling. Currently, there is no study detailing the effects of multiple nucleation sites, subcooling and surface texturing on pool boiling dynamics. The investigation comprises of four parts: i) in situ micro-machining of Chromelalumel (K-type) TFT, ii) calibration of these sensors, iii) utilizing these sensors in pool boiling experiments iv) analysis of these fluctuations using techniques of nonlinear time series analysis. Ten TFT are fabricated on a rectangular silicon surface within an area of ~ 3.00 cm x 3.00 cm. The sensing junctions of the TFT measure 50 mm in width and 250 nm in depth. Surface temperature fluctuations of the order of i) 0.65-0.93° C are observed near ONB ii) 2.3-6.5° C in FDNB iii) 2.60-5.00° C at CHF and iv) 2.3-3.5° C in film boiling. Investigations show the possible presence of chaotic dynamics near CHF and in film-boiling in saturated and subcooled pool boiling. Fully-developed nucleate boiling (FDNB) is chaotic. No clear assessment of the dynamics could be made in the onset of nucleate boiling (ONB) and partial nucleate boiling (PNB) regimes due to the effects of noise. However, the frequency spectra in these regimes appear to have two independent frequencies and their integral combinations indicating a possible quasiperiodic bifurcation route to chaos. The dimensionality in FDNB, at CHF and in film-boiling is lower in saturated pool boiling as compared to values in corresponding regimes in subcooled pool boiling. Surface temperature fluctuations can damage electronic components and need to be carefully controlled. Understanding the nature of these fluctuations will aid in deciding the modeling approach for surface temperature transients on an electronic chip. Subsequently, the TFT signals can be employed in a suitable feedback control loop to prevent the occurrence of hotspots.
Download or read book Pool Boiling Studies on Nanotextured Surfaces Under Highly Subcooled Conditions written by Vijaykumar Sathyamurthi and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Subcooled pool boiling on nanotextured surfaces is explored in this study. The experiments are performed in an enclosed viewing chamber. Two silicon wafers are coated with Multiwalled Carbon Nanotubes (MWCNT), 9 microns (Type-A) and 25 microns (Type-B) in height. A third bare silicon wafer is used for control experiments. The test fluid is PF-5060, a fluoroinert with a boiling point of 56°C (Manufacturer: 3M Co.). The apparatus is of the constant heat flux type. Pool boiling experiments in nucleate and film boiling regimes are reported in this study. Experiments are carried out under low subcooling (5 °C and 10 °C) and high subcooling conditions (20°C to ~ 38°C). At approximately 38°C, a non-departing bubble configuration is obtained on a bare silicon wafer. Increase in subcooling is found to enhance the critical heat flux (CHF) and the CHF is found to shift towards higher wall superheats. Presence of MWCNT on the test surface led to an enhancement in heat flux. Potential factors responsible for boiling heat transfer enhancement on heater surfaces coated with MWCNT are identified as follows: a. Enhanced surface area or nano - fin effect b. Higher thermal conductivity of MWCNT than the substrate c. Disruption of vapor-liquid vapor interface in film boiling, and of the "microlayer" region in nucleate boiling d. Enhanced transient heat transfer caused by local quasi-periodic transient liquid-solid contacts due to presence of the "hair like" protrusion of the MWCNT e. Enhancement in the size of cold spots f. Pinning of contact line, leading to enhanced surface area underneath the bubble leading to enhanced heat transfer Presence of MWCNT is found to enhance the phase change heat transfer by approximately 400% in nucleate boiling for conditions of low subcooling. The heat transfer enhancement is found to be independent of the height of MWCNT in nucleate boiling regime in the low subcooling cases. About 75%-120% enhancement in heat transfer is observed for surfaces coated with MWCNT under conditions of high subcooling in the nucleate boiling regime. Surfaces coated with Type-B MWCNT show a 75% enhancement in heat transfer in the film boiling regime under conditions of low subcooling.
Download or read book Effects of Subcooling and Gravity Level on Boiling in the Discrete Bubble Region written by Thomas H. Cochran and published by . This book was released on 1966 with total page 48 pages. Available in PDF, EPUB and Kindle. Book excerpt:
