Heat transfer to a vapor bubble suspended near or attached to a solid plate.
Item
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Title
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Heat transfer to a vapor bubble suspended near or attached to a solid plate.
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Identifier
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AAI9707106
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identifier
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9707106
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Creator
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Huang, Lin.
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Contributor
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Advisers: Zeev Dagan | David Rumschitzki
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Date
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1996
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Mechanical | Applied Mechanics
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Abstract
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This thesis examines the dramatic heat transfer enhancement relative to vapor-bubble-free heat transfer associated with the nucleate boiling incipience. When the vapor-liquid interface is at equilibrium, we find that the heat transfer at small Reynolds, Peclet, Capillary and Bond numbers is conductive and quasi-static, and the bubble is spherical. We find that this mechanism alone is sufficient to account for the observed enhancements and their experimentally observed scalings, without recourse to convective models. We examine embryonic vapor bubbles in the liquid that are either attached or adjacent to a nearby heating solid plate. The solid plate and liquid layer are both of finite depth and one may freely prescribe the temperatures on their far surfaces. Both layers may either be finite or infinite in the transverse direction. The former with periodic boundary conditions mimics bubble-bubble interactions of an evenly distributed collection of identical vapor bubbles. Different physical and geometrical settings reveal the fundamental mechanism of the nucleate pool boiling heat transfer. They include different conductivity ratio of the liquid and solid; different solid and liquid layer thicknesses; different contact angles when the bubble is attached to the solid-liquid interface and the distances from the bubble to the solid-liquid interface when bubble is detached; and most importantly, different numbers of bubbles per unit area.;We use these quasi-static calculations to follow the growth of an incipient bubble from micron to millimeter size and examine how its size scales with time and how the heat transfer scales with bubble density and wall superheat. We calculate a postiori and carefully follow all of the non-dimensional groups and confirm that the Capillary and Bond numbers do/indeed/remain small throughout the bubble growth until before the gravitational forces become important. The Reynolds and Peclet numbers, based on the bubbles radius, are quite large in many cases suggesting that in the bulk liquid the heat transfer might be convective and the flow turbulent. However, a careful investigation of the heat fluxes reveals that even though there is significant fluid convection near the bubble apex, practically all of the heat transfer to the bubble takes place in a very small region, near the contact line of an attached bubble. Using a local length to characterize the scales in this region leads to Peclet (and Reynolds) numbers that are indeed small in the region where the vast majority of the heat transfer takes place, thus ensuring the accuracy of the magnitude of the calculated heat transfer enhancement affiliated to conduction.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
