Enhanced heat transfer in electronic hardware by direct, small-scale actuation is investigated experimentally in two test bed configurations. The first configuration exploits the unsteady motions induced by a vibrating reed embedded within a heated duct (in contact with hardware that needs cooling) to enhance forced convection transport heat from the duct surfaces. The flow within the duct is either exclusively driven by the reed or, for higher heat flux, is augmented by an induced core flow. The time harmonic motion of the reed results in the regular shedding of vortical structures that interact with the inner surfaces in the absence and presence of a core flow. The second configuration focuses on the effects of small scale motions induced by a synthetic jet on heat transfer within an advanced heat sink. The synthetic jets emanate directly through the base of the heat sink and induce a recirculating flow between the fins, resulting in a lower thermal resistance than what is typically achieved with traditional fans. The unsteady flow characteristics in both configurations are investigated using particle image velocimetry (PIV). Of particular interest are the effects of small-scale motions and enhanced mixing on heat transfer compared to conventional time-invariant flows at similar or higher Reynolds numbers.

This thesis seeks to examine the effective convective heat exchange of sand as a heat exchange medium. The goal of this exploratory research is to quantify the heat transfer coefficient of sand in a proposed Thermal Energy Storage (TES) system which intends to complement solar thermal power generation. Standard concentrator solar thermal power plants typically employ a heat transfer fluid (HTF) that is heated in the collector field then routed to the power generators or TES unit. A fairly clear option for a TES system would be to utilize the existing HTF as the working storage medium. However, the use of conventional HTF systems may be too expensive. These fluids are quite costly as the quantity needed for storage is high and for some fluids their associated high vapor pressures require expensive highly reinforced containment vessels. The proposed storage system seeks to use sand as the storage medium; greatly reducing the expenses involved for both medium and storage costs. Most prior TES designs using sand or other solids employed them in a fixed bed for thermal exchange. The proposed TES system will instead move the sand to drive a counter flow thermal exchange. This counter flow design allows for a much closer temperature of approach when compared to a fixed bed. As cost and performance are the primary goals to tackle of the proposed system, the evaluation of the sandâ s thermal exchange effectiveness in a flowing state is necessary. Experiments will be conducted to measure the effective heat transfer coefficient between the sand and representative solid surfaces used as the heat transfer conduits. Additional experiments that will be looked at are wear caused by the sand as a consideration for long term design viability as well as angle of repose of the sand and its effect on scoop design for improved materials handling. Key investigational aspects of these experiments involve the sand grain size as well as shape of the heat exchanger surfaces. The thesis will evaluate the resulting convective heat transfer coefficient of the sand as related to these features. The data will then be compared and verified with available literature of previously studied characteristic thermal properties of sand. The measured and confirmed data will then be used to further aid in a design model for the proposed TES system.

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Orientador: Carlos Alberto Carrasco Altemani / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-24T04:10:43Z (GMT). No. of bitstreams: 1 MarchiNeto_Ismael_D.pdf: 4845997 bytes, checksum: b5f466a0bc722eba5f754b6c4ef08357 (MD5) Previous issue date: 2014 / Resumo: O resumo poderá ser visualizado no texto completo da tese digital. / Abstract: The abstract is available with the full electronic document. / Doutorado / Termica e Fluidos / Doutor em Engenharia Mecânica

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 1977 / Vita. / Includes bibliographical references. / by Edward Paul Martin, Jr. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Materials Science and Engineering

Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Meteorology. / Bibliography: leaves 107-109. / M.S.

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Meteorology. / Vita. / Bibliography: leaves 202-206. / Ph.D.