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Author

Avram Bar-Cohen

Other affiliations: Auburn University, DARPA, Ben-Gurion University of the Negev  ...read more
Bio: Avram Bar-Cohen is an academic researcher from University of Maryland, College Park. The author has contributed to research in topics: Heat transfer & Heat sink. The author has an hindex of 50, co-authored 329 publications receiving 8329 citations. Previous affiliations of Avram Bar-Cohen include Auburn University & DARPA.


Papers
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Reference EntryDOI
20 Feb 2015

2 citations

Proceedings ArticleDOI
01 Jan 2011
TL;DR: In this article, the use of once-through seawater cooling as a replacement for freshwater recirculating systems is identified as a viable way to reduce the usage of freshwater and to increase power plant efficiency.
Abstract: Polymer heat exchangers (PHXs), using thermally-enhanced composites, constitute a “disruptive” thermal technology that can lead to significant water and energy savings in the thermoelectric energy sector. This paper reviews current trends in electricity generation, water use, and the inextricable relationship between the two trends in order to identify the possible role of PHXs in seawater cooling applications. The use of once-through seawater cooling as a replacement for freshwater recirculating systems is identified as a viable way to reduce the use of freshwater and to increase power plant efficiency. The widespread use of seawater as a coolant can be made possible by the favorable qualities of thermally-enhanced polymer composites: good corrosion resistance, higher thermal conductivities, higher strengths, low embodied energy and good manufacturability. The authors use several seawater cooling case studies to explore the potential water and energy savings made possible by the use of PHX technology. The results from three case studies suggest that heat exchangers made with thermally enhanced polymer composites require less energy input over their lifetime than corrosion resistant metals, which generally have much higher embodied energy than polymers and polymers composites. Also, the use of seawater can significantly reduce the use of freshwater as a coolant, given the inordinate amounts of water required for even a 1MW heat exchanger.Copyright © 2011 by ASME

2 citations

Proceedings ArticleDOI
01 Jan 2009
TL;DR: In this article, a minimum energy, design-for-manufacturability approach is followed in the design and commercialization of air-cooled heat sinks, and a least energy optimization methodology is combined with a least-energy optimization methodology, using the total Coefficient of Performance (COPT ), to identify practical low energy designs and existing gaps in manufacturing capability that prevent the attainment of the ideal minimum energy solutions.
Abstract: The substantial material stream, and energy consumption, associated with the cooling of desktop computers, servers, routers, and power electronic modules contribute significantly to the depletion of key resources. To reduce this severe environmental impact, while meeting the thermal management requirements of these components and systems, it is essential that a minimum energy, design-for-manufacturability approach be followed in the design and commercialization of such air-cooled heat sinks. In this paper, a design-for-manufacturability methodology (DFM) is combined with a least-energy optimization methodology, using the total Coefficient of Performance (COPT ), to identify practical low energy designs and existing gaps in manufacturing capability that prevent the attainment of the ideal minimum energy solutions. The COPT methodology relates the heat sink cooling capability to the invested fan pumping work and the thermodynamic work required to manufacture and assemble the heat sink and seeks to maximize the thermal energy that can be extracted from a specified space, while minimizing the material and energy consumed in the fabrication and operation of the specified heat sink. This combined methodology was applied to aluminum, copper, and magnesium as potential heat sink materials for a fixed input work of 20 kWh, and for three different duty cycles, namely, sporadic (1500 h), periodic (6000 h), and continuous (26208 h), respectively. The results presented herein, are derived for heat sinks on a 10 cm by 10 cm isothermal base, and 5 cm fin height, operating at an excess temperature of 25 K relative to the inlet air. The thermo-fluid analysis of the forced convection rectangular plate-fin array has been carried out using a well-validated semi-analytical model. The energy-optimal aluminum, copper and magnesium designs are compared to draw quantitative and qualitative conclusions.Copyright © 2009 by ASME

2 citations

Book ChapterDOI
01 Jan 1994
TL;DR: It is concluded that new reliability models and figures-of-merit, based on the phenomenological understanding of the failure mechanisms, are needed in order to predict the thermal dependence of the probability of failure.
Abstract: This paper begins with a discussion of the physical phenomena associated with thermally-induced/accelerated failures, including diffusion-driven and thermo-mechanical failure mechanisms. Attention is then turned to the results of ongoing Northern Telecom “field-return” surveys and to the identification of the factors controlling device field reliability for newly designed equipment, mature technologies in mild environments, and equipment operated under harsh environmental conditions. It is concluded that new reliability models and figures-of-merit, based on the phenomenological understanding of the failure mechanisms, are needed in order to predict the thermal dependence of the probability of failure.

2 citations

Proceedings ArticleDOI
28 May 2008
TL;DR: In this paper, confinement-driven boiling enhancement trends and experimental data from narrow parallel plate channels are presented and analyzed via comparison with numerical simulations of buoyancydriven boiling and two phase flow using the commercially available Fluent CFD software package.
Abstract: In this study, confinement-driven boiling enhancement trends and experimental data from narrow parallel plate channels are presented and analyzed via comparison with numerical simulations of buoyancy-driven boiling and two phase flow using the commercially-available Fluent CFD software package. An Euler-Euler multiphase approach, known as the volume of fluid (VOF) method, is employed, as bubbles sizes are on the order of the channel dimensions. Numerical results suggest that enhanced natural convection already accounts for a large portion of the unconfined pool boiling heat flux. While the increased buoyancy from large vapor fractions in narrow channels may lead to an order of magnitude increase in channel mass flux, confinement-driven convective enhancement is found to increase the unconfined boiling heat flux by less than 10%. Further, simulated convective enhancement is found to be a maximum for intermediate size channels, in direct contrast to experimental data which show maximum enhancement (500%) for the smallest channels investigated. Experimental results for different channel wall materials suggest an enhancement mechanism highly dependent on boiling surface characteristics.

2 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, a review of the history of thermal energy storage with solid-liquid phase change has been carried out and three aspects have been the focus of this review: materials, heat transfer and applications.

4,019 citations

Journal ArticleDOI
01 Jan 1977-Nature
TL;DR: Bergh and P.J.Dean as discussed by the authors proposed a light-emitting diode (LEDD) for light-aware Diodes, which was shown to have promising performance.
Abstract: Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.

1,560 citations

Journal ArticleDOI
TL;DR: The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed in this article.
Abstract: Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

1,535 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present a review of low temperature co-fired ceramic (LTCC) technologies for high frequency applications, which will be of immense help to researchers and technologists all over the world.
Abstract: Small, light weight and multifunctional electronic components are attracting much attention because of the rapid growth of the wireless communication systems and microwave products in the consumer electronic market. The component manufacturers are thus forced to search for new advanced integration, packaging and interconnection technologies. One solution is the low temperature cofired ceramic (LTCC) technology enabling fabrication of three-dimensional ceramic modules with low dielectric loss and embedded silver electrodes. During the past 15 years, a large number of new dielectric LTCCs for high frequency applications have been developed. About 1000 papers were published and ∼500 patents were filed in the area of LTCC and related technologies. However, the data of these several very useful materials are scattered. The main purpose of this review is to bring the data and science of these materials together, which will be of immense help to researchers and technologists all over the world. The comme...

968 citations