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dc.contributor.advisorOrtega, Alfonsoen_US
dc.contributor.authorLall, Balwant
dc.creatorLall, Balwanten_US
dc.date.accessioned2013-05-09T10:36:24Z
dc.date.available2013-05-09T10:36:24Z
dc.date.issued2001en_US
dc.identifier.urihttp://hdl.handle.net/10150/289741
dc.description.abstractExperiments were performed to characterize the conjugate heat transfer due to a square flush heat source mounted at the center of a square horizontal plate in a small horizontal enclosure. The plate area was six times larger than the heat source area. Three different plates with heat source facing upwards were considered: a 25mm balsa wood plate which provided a nearly adiabatic surface, a 1.57mm thick FR-4 plate with no copper, and a 1.57mm thick FR-4 plate with a single layer of 0.036mm thick copper cladding on source side. The back of the board was insulated for all cases. The experimental exploration included measurement of heat transfer coefficient over the heat source, plate surface temperature distribution and temperature distribution in the air volume above the plate. The heat transfer coefficients exhibited distinct behavior at high aspect ratios in which the dominant length scales were related to the source. At intermediate aspect ratios, length scales for both source and enclosure were relevant, and at small aspect ratios, a conduction limit was observed, which was dependent on board conductivity. The heat transfer coefficients at high aspect ratios exceeded by 14% the prior correlations for upward facing isolate plates, when the ratio of source area to perimeter was used as the significant length scale, and a stronger dependence than Ra1/4 was measured. Classical correlations for shallow differentially heated enclosure were not satisfactory in describing the dependence on enclosure height. With increasing board conductivity, board thermal spreading increased the effective source size so that the discretely heated board heat transfer coefficients tended towards the behavior of the classical uniformly heated board. New first-order thermal design formulae were derived for determining peak temperatures of sources on conducting substrates, and for determining the associated thermal "zone of influence" or "footprint." The board heat spreading was accounted for by using its effective "thermal footprint" radius and correlations for conjugate heat transfer based on this length scale were successful in describing the behavior of the average Nusselt number at large enclosure heights. Some qualitative flow visualization was also performed and representative results are shown.
dc.language.isoen_USen_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.subjectEngineering, Electronics and Electrical.en_US
dc.subjectEngineering, Mechanical.en_US
dc.subjectEngineering, Packaging.en_US
dc.titleConjugate natural convection from a discrete heat source on a conducting plate in a shallow enclosureen_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
thesis.degree.grantorUniversity of Arizonaen_US
thesis.degree.leveldoctoralen_US
dc.identifier.proquest3031399en_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineAerospace and Mechanical Engineeringen_US
thesis.degree.namePh.D.en_US
dc.identifier.bibrecord.b42287479en_US
refterms.dateFOA2018-09-06T10:19:33Z
html.description.abstractExperiments were performed to characterize the conjugate heat transfer due to a square flush heat source mounted at the center of a square horizontal plate in a small horizontal enclosure. The plate area was six times larger than the heat source area. Three different plates with heat source facing upwards were considered: a 25mm balsa wood plate which provided a nearly adiabatic surface, a 1.57mm thick FR-4 plate with no copper, and a 1.57mm thick FR-4 plate with a single layer of 0.036mm thick copper cladding on source side. The back of the board was insulated for all cases. The experimental exploration included measurement of heat transfer coefficient over the heat source, plate surface temperature distribution and temperature distribution in the air volume above the plate. The heat transfer coefficients exhibited distinct behavior at high aspect ratios in which the dominant length scales were related to the source. At intermediate aspect ratios, length scales for both source and enclosure were relevant, and at small aspect ratios, a conduction limit was observed, which was dependent on board conductivity. The heat transfer coefficients at high aspect ratios exceeded by 14% the prior correlations for upward facing isolate plates, when the ratio of source area to perimeter was used as the significant length scale, and a stronger dependence than Ra1/4 was measured. Classical correlations for shallow differentially heated enclosure were not satisfactory in describing the dependence on enclosure height. With increasing board conductivity, board thermal spreading increased the effective source size so that the discretely heated board heat transfer coefficients tended towards the behavior of the classical uniformly heated board. New first-order thermal design formulae were derived for determining peak temperatures of sources on conducting substrates, and for determining the associated thermal "zone of influence" or "footprint." The board heat spreading was accounted for by using its effective "thermal footprint" radius and correlations for conjugate heat transfer based on this length scale were successful in describing the behavior of the average Nusselt number at large enclosure heights. Some qualitative flow visualization was also performed and representative results are shown.


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