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A Numerical Study of Bubble Detachment from Solid Wall and Evaporative Growth

Title
A Numerical Study of Bubble Detachment from Solid Wall and Evaporative Growth
Authors
Muhammad Umar Afzal
Date Issued
2012
Publisher
포항공과대학교
Abstract
There are many studies available in literature which lead with enhancement of heat flux during the boiling process. Nucleate boiling is the only regime during boiling phenomena which is privileged by generation of bubbles and as a consequence of it show efficient heat transfer. Studies on nucleate boiling maintain to get attention of researchers because of its enormous potential. Poorly simulated bubbles produced somewhat misleading results to understand extremely complex simultaneous multi-transport phenomena of boiling. The effects of supplied heat to the bubble attached to the heated solid wall are investigated using numerical method. Easy access and availability towards commercial packages of "Computational Fluid Dynamics" make numerical study of bubble growth and detachment from solid heated wall quiet easier. In the present study, we used 'COMSOL Multiphysics' package with fairly realistic assumptions regarding bubble growth pattern. During the bubble growth, solutions on the shape of bubble are obtained for the governing equations which are the temperature field and the flow field. In this study we considered comparatively slower growth rate in a detailed manner. Several numerical results helped to better understand the multiphysics phenomena. First, it is found that bubble growth pattern shows week dependency on contact angle with solid wall and on the expanse of increased wall super heat larger growth rate can be achieved. Bubble diameter at moment of departure show linear decrease as the contact angle is reduced up to 20 degrees. Second, wall heat flux is found to be dominated by transient conduction mode of heat transfer. The heat fluxes are varied both temporally and spatially depending on the bubble shape and dynamics within domain of interest. Natural convection contribution is highest during the early stage of bubble growth. The highest rate in terms of energy utilization is achieved when the vapor bubble base diameter is nearly maximum. Time integrated values of heat fluxes revealed that 30% of energy is employed in vapor production, on the other hand 70% goes into superheating of liquid.
URI
http://postech.dcollection.net/jsp/common/DcLoOrgPer.jsp?sItemId=000001383460
http://oasis.postech.ac.kr/handle/2014.oak/1570
Article Type
Thesis
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