Avram Bar-Cohen

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.

Least-material optimization of vertical pin-fin, plate-fin, and triangular-fin heat sinks in natural convective heat transfer

Abstract: A least-material optimization of pin-fin, plate-fin, and triangular-fin array geometries is performed, by extending the use of least-material single fin analysis to multiple fin arrays. The heat dissipation from vertical fin arrays in natural convection is calculated using the Nusselt number correlation by Aihara et al. (Int. J. Heat and Mass Transfer vol. 33, no. 6, pp. 1223-32, 1990) for pin-fins, by Bar-Cohen and Rohsenow (Trans IEEE CHMT vol. 6, pp. 154-8, 1983) for rectangular plate fins, and by Karagiozis et al (Air, vol. 116, pp. 105-11, 1994) for triangular plate fins. Comparisons of the thermal capability of the three different array geometries are carried out on the basis of total heat dissipation and material-specific volumetric heat dissipation. Manufacturability constraints of these heat sinks, and their effects on the final design, are briefly discussed.

Two-Phase Thermal Transport in Microgap Channels—Theory, Experimental Results, and Predictive Relations

Abstract: A comprehensive literature review and analysis of recent microchannel/microgap heat transfer data for two-phase flow of refrigerants and dielectric liquids is presented. The flow regime progression in such a microgap channel is shown to be predicted by the traditional flow regime maps. Moreover, Annular flow is shown to be the dominant regime for this thermal transport configuration and to grow in importance as the channel diameter decreases. The results of heat transfer studies of single miniature channels, as well as the analysis and inverse calculation of IR images of a heated microgap channel wall, are used to identify the existence of a characteristic M-shaped heat transfer coefficient variation with quality (or superficial velocity), with inflection points corresponding to transitions in the two-phase cooling modalities. For the high-quality, Annular flow conditions, the venerable Chen correlation is shown to yield predictive agreement for microgap channels that is comparable to that attained for macrochannels and to provide a mechanistic context for the thermal transport rates attained in microgap channels. Results obtained from infrared imaging, revealing previously undetected, large surface temperature variations in Annular flow, are also reviewed and related to the termination of the favorable thin-film evaporation mode in such channels.

Hybrid 3D-IC Cooling System Using Micro-fluidic Cooling and Thermal TSVs

Abstract: 3D-ICs bring about new challenges to chip thermal management due to their high heat densities. Micro-channel based liquid cooling and thermal through-silicon-vias (TSVs) have been adopted to alleviate the thermal issues in 3D-ICs. Thermal TSV (which have no electrical significance), enables higher interlayer thermal conductivity thereby achieving a more uniform thermal profile. While somewhat effective in reducing temperatures, they are limited by the nature of the heat sink. On the other hand, micro-channel based liquid cooling is significantly capable of addressing 3D IC cooling needs but consumes a lot of extra power for pumping coolant through channels. This paper proposes a hybrid 3D-IC cooling scheme which combines micro-channel liquid cooling and thermal TSV with one acting as heat removal agent while the other enabling beneficial heat conduction paths to the micro-channel structures. The experimental results show that, the proposed hybrid cooling scheme provides much better cooling capability than using only thermal TSVs, while consuming 55% less cooling power compared with pure micro-channel cooling.

Light-emitting diodes

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.

A review of Ga2O3 materials, processing, and devices

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.

Low loss dielectric materials for LTCC applications: a review

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...