Experimental Investigation of Nucleate Boiling Bubble Dynamics in Normal and Zero Gravities
Author : Thomas H. Cochran
Publisher :
Page : 26 pages
File Size : 32,19 MB
Release : 1968
Category : Bubbles
ISBN :
Author : Thomas H. Cochran
Publisher :
Page : 26 pages
File Size : 32,19 MB
Release : 1968
Category : Bubbles
ISBN :
Author : Muhammad Sajid
Publisher :
Page : 153 pages
File Size : 10,43 MB
Release : 2010
Category :
ISBN :
Nucleate boiling is an efficient means of heat transfer that has been the subject of many studies which have lead to more empirical results than knowledge on the physical mechanisms that govern the phenomena. In this work, a conservative level set method (LSM) was applied to the study of bubble dynamics during nucleate pool boiling which reduces the computational cost of reinitialization techniques traditionally used with LSM to limit phase loss. Also a force-balance approach to modelling dynamic apparent contact angle (CA) was proposed in this study based on the physics of the moving contact line (CL). It was tested against the traditional CL velocity approach and validated in comparison to available experimental data. In comparison to the CL velocity model our approach reduces the non-physical stick/slip behaviour of the CL and allows a smoother transition from the minimum receding to the maximum advancing CA, which is more akin to the physical phenomena. It was also demonstrated that the heat transfer during bubble growth is proportional to the apparent CA.
Author : Sarath Ananda Kumara Abayawardana
Publisher :
Page : 227 pages
File Size : 36,88 MB
Release : 1974
Category :
ISBN :
Author : Ritchie Deane Mikesell
Publisher :
Page : 216 pages
File Size : 23,49 MB
Release : 1958
Category : Bubbles
ISBN :
Author : Thomas H. Cochran
Publisher :
Page : 21 pages
File Size : 38,94 MB
Release : 1968
Category :
ISBN :
Author : R. A. Rockow
Publisher :
Page : 58 pages
File Size : 14,43 MB
Release : 1959
Category : Fouling
ISBN :
Author : Michele David
Publisher :
Page : 76 pages
File Size : 12,51 MB
Release : 2016
Category : Bubbles
ISBN :
Boiling heat transfer is studied for its ability to dissipate high fluxes and achieve heat transfer coefficients two orders of magnitude greater than single-phase heat transfer systems. Heater surface enhancement with increased surface area, varied geometry, wettability contrast and micro/nano-structures can further enhance boiling heat transfer performance through bubble nucleation augmentation. Bubble nucleation control, growth and departure dynamics is important in understanding boiling phenomena and enhancing nucleate boiling heat transfer performance. Bi-functional surfaces for enhanced boiling heat transfer were fabricated and studied through investigation of bubble dynamics and pool boiling experiments. For the fabrication of the surface, hydrophobic polymer dot arrays are first printed on a substrate, followed by hydrophilic ZnO nanostructure deposition via microreactor-assisted nanomaterial deposition (MAND) processing. Wettability contrast between the hydrophobic polymer dot arrays and aqueous ZnO solution allows for the fabrication of surfaces with distinct wettability regions. Bi-functional surfaces with various configurations were fabricated and their bubble dynamics were examined at elevated heat flux, revealing various nucleate boiling phenomena. In particular, aligned and patterned bubbles with a tunable departure frequency and diameter were demonstrated in a boiling experiment for the first time. A pool boiling experimental facility has been designed and built to investigate nucleate pool boiling in water at atmospheric pressure. Resulting boiling curves of enhanced surfaces showed up to 3X enhancement in heat transfer coefficients at the same surface superheat using bi-functional surfaces, compared to a bare stainless steel surface. The surfaces show promising results for energy savings in two-phase change applications.
Author : Samuel Siedel
Publisher :
Page : 0 pages
File Size : 40,13 MB
Release : 2013
Category :
ISBN :
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.
Author : Christopher E. Brennen
Publisher : Cambridge University Press
Page : 269 pages
File Size : 20,86 MB
Release : 2014
Category : Mathematics
ISBN : 1107644763
Cavitation and Bubble Dynamics deals with fundamental physical processes of bubble dynamics and cavitation for graduate students and researchers.
Author : John Cheu-Wang Hsu
Publisher :
Page : 210 pages
File Size : 34,87 MB
Release : 1971
Category :
ISBN :