Showing papers by "Avram Bar-Cohen published in 2003"

Least-energy optimization of forced convection plate-fin heat sinks

Abstract: A coefficient of performance (COP/sub T/) analysis for plate fin heat sinks in forced convection is presented and shown to provide a viable technique for combining least-material optimization with the entropy minimization methodology. The COP/sub T/ metric relates the heat sink cooling capability to the invested fan pumping work and the thermodynamic work required to manufacture and assemble the heat sink. The proposed optimization methodology maximizes the forced convection cooling that can be achieved by a heat sink occupying a specified volume, with a fixed energy investment and entropy generation rate. In addition, the study identifies the presence of an optimal resource allocation ratio, providing the most favorable distribution of existing energy resources, between heat sink manufacturing and operation, over a fixed product life cycle.

Least-energy optimization of air-cooled heat sinks for sustainable development

Abstract: The development of heat sinks for microelectronic applications, which are compatible with sustainable development, involves the achievement of a subtle balance between a superior thermal design, minimum material consumption, and minimum pumping power. This presentation explores the potential for the least-energy optimization of natural and forced convection cooled rectangular plate heat sinks. The results are evaluated in terms of a heat sink coefficient of performance, relating the cooling capability to the energy invested in the fabrication and operation of the heat sink, and compared to the entropy generation minimization methodology (EGM).

Chip Level Refrigeration of Portable Electronic Equipment Using Thermoelectric Devices

Abstract: It is well established that the power dissipation for electronic components is increasing. At the same time, high performance portable equipment with volume, weight, and power limitations are gaining widespread acceptance in the marketplace. The combination of the above conditions requires thermal solutions that are high performance and yet small, light, and power efficient. This paper explores the possibility of using thermoelectric (TE) refrigeration as an integrated solution for portable electronic equipment accounting for heat sink and interface material thermal resistances. The current study shows that TE refrigeration can indeed have a benefit over using just a heat sink. Performance maps illustrating where TE refrigeration offers an advantage over an air-cooled heat sink are created for a parametric range of CPU heat flows, heat sink thermal resistances, and TE material properties. During the course of the study, it was found that setting the TE operating current based on minimizing the CPU temperature (Tj ), as opposed to maximizing the amount of heat pumping, significantly reduces Tj . For the baseline case studied, a reduction of 20–30°C was demonstrated over a range of CPU heat dissipation. The parametric studies also illustrate that management of the heat sink thermal resistance appears to be more critical than the CPU/TE interfacial thermal resistance. However, setting the TE current based on a minimum Tj as opposed to maximum heat pumping reduces the system sensitivity to the heat sink thermal resistance.Copyright © 2003 by ASME

Thermal compact modeling of parallel plate heat sinks

Abstract: Growing complexity of electronic systems has resulted in an increased computational effort in CFD modeling of electronic systems. To reduce the computational effort, one or several heat sinks can be represented by a compact "porous block" model, with an effective thermal conductivity and pressure loss coefficient. In this study of parallel plate heat sinks in laminar forced convection, a methodology is developed to rigorously determine the thermal properties of compact heat sink models that provide a high level of accuracy. The results of an extensive set of CFD simulations for a three heat sink channel covering two distinct heat sink geometries, air velocities from 0.25 m/s to 2 m/s and various spacings between the heat sinks, were used to create and evaluate the fidelity of compact models. The results of this study establish the validity and value in using the porous block compact model representation for noncritical heat sinks in an electronic assembly. The results also reveal that a location-independent porous-block representation can yield excellent agreement in the prediction of the thermal characteristics of state-of-the-art heat sinks.

Flow and pressure field characteristics in the porous block compact modeling of parallel plate heat sinks

Abstract: Growing complexity has resulted in an increased computational effort in CFD modeling of electronic systems. To reduce the computational effort, one or several heat sinks can be represented by a compact "porous block" model, with an effective thermal conductivity and pressure loss coefficient. In this study of parallel plate heat sinks in laminar forced convection, a methodology is developed to analytically determine the fluid properties of compact heat sink models that provide acceptable levels of approximation. The results of an extensive set of CFD simulations for a three heat sink channel, covering three distinct heat sink geometries, air velocities from 0.25 m/s to 2 m/s and various spacings between the heat sinks, were used to create and evaluate the effectiveness of compact models. Use of a two term, equivalent loss coefficient-reflecting the linear and quadratic components in the pressure drop of a porous block-has led to good agreement between the detailed numerical and compact model predictions, with compact heat sink pressure drops usually slightly higher (<10%) than detailed heat sink pressure drops.

Sustainability Assessment of Aluminum Heat Sink Design

Abstract: The present effort addresses the application of sustainability criteria to the design of "heat sinks" used to cool advanced microelectronic components. The sustainability assessment is based on several criteria, including the use of natural resources, the environment, social welfare, and economic impact. The development of forced convection heat sinks, which are compatible with sustainable development, involves a subtle balance between the achieved thermal performance and the investment of material and energy in the fabrication and operation of the heat sink. It is shown that sustainability criteria can be used to select the environmentally optimal configuration among the most promising heat sink designs, including the lowest pumping power, the least mass of material, and the lowest total (fabrication and operation) energy for a specified application. Of the options considered for cooling a 100 W microprocessor with an aluminum heat sink operating at an excess temperature of 25 K, the heat sink design wit...

Thermofluid Design of Energy Efficient and Compact Heat Sinks

Abstract: A compact, energy efficient heat sink design methodology is presented for shrouded, parallel plate fins in laminar flow. The analytic model accounts for the sensible temperature rise of the air flowing between fins, convective heat transfer to the flowing stream, and conduction in the fins. To evaluate the efficiency of the air cooling system, consideration is also given to the determination of the fan pumping power. This paper focuses on the optimization of the heat sink-fan combination for energy efficiency, subject to volumetric constraints. The design optimum is found by matching the most efficient operating point of the fan with the corresponding optimum fin geometry. A series of parametric studies was completed to identify the sensitivity of the cooling solution to parametric variations. This numerically validated model has been used to visualize the parametric impact of dealing with “real world” manufacturing limitation in the development of thermal packaging solutions for notebook computers and other electronic products.© 2003 ASME

Development of a new technique for DNA single base pair mismatch analysis

Abstract: Research on the development and progression of diseases has shown that single base pair mismatches in key genes can be associated with increased risk of particular cancers. Analytical techniques for determining these mismatches currently exist, but faster, simpler, and cheaper techniques are desirable. We present a new technique based upon DNA melting curve analysis using a temperature gradient established using a silicon wafer. Along one edge of a square silicon substrate, two electrical connectors are mounted to deliver electrical current from a power supply. Since both edge connectors are on the same side of the square, the current flow in the silicon substrate is highest near the edge with the connectors, and decreases as the distance from that edge increases. This non-uniform current distribution generates resistive heating in a manner which, when combined with thermal conductivity effects, results in a nearly linear gradient of measured temperature along the axis normal to the electrode mounting edge. Finite element modeling analysis confirms the results measured with infrared thermal imaging. Using a control loop consisting of a PID controller and an RTD to monitor temperature, gradients of varying temperature ranges can be established. For example, we have routinely created gradients of 0.3/spl deg/C per millimeter for the temperature range of 50 to 70/spl deg/C, with which we have experimentally shown that single base pair mismatches in a section of a commonly studied gene (N-ras gene) can be distinguished from sections which do not contain the mismatch.

Thermo-Optical Behavior of Passively-Cooled Polymer Waveguides

Abstract: Polymer waveguides offer considerable promise as cost-effective transmission channels for optical signals. However, thermo-optic effects induced by the intrinsic absorption of light in the waveguide material can compromise their performance. The present study seeks to define the thermo-optical issues in Bragg grating polymer waveguides, including the effects and relative importance of temperature change, thermal strain, and thermally-induced stresses. Analytical and numerical solutions are obtained for the temperature, strain, and stress fields in the core of a polymer waveguide, heated by intrinsic light energy absorption, and used to evaluate the resulting Bragg wavelength shift and reflectivity variance.© 2003 ASME

Compact Modeling of Unshrouded Plate Fin Heat Sinks

Abstract: The present work considers the compact modeling of unshrouded parallel plate heat sinks in laminar forced convection. The computational domain includes three heat sinks in series, cooled by an intake fan. The two upstream heat sinks are represented as “porous blocks”, each with an effective thermal conductivity and a pressure loss coefficient, while the downstream heat sink, assumed to be the component requiring the most accurate characterization, is modeled in detail. A large parametric space covering three typical heat sink geometries, as well as a range of common inlet velocities, separation distances between the heat sinks, and bypass clearances is considered in the development and evaluation of the compact models. The current study uses a boundary layer-based methodology, accounting for both the viscous dissipation and form drag losses, to determine the pressure drop characteristics, and an effective conductivity methodology, using a flow bypass model and Nusselt number correlation, to determine the effective thermal conductivity, for the porous block representation of the heat sink. The results indicate that the introduction of compact heat sinks has little influence on the pressure drop of the critical heat sink. Good agreement in pressure drops, typically in the range of 5%, is also obtained between “detailed” heat sink models and their corresponding porous block representation. The introduction of the compact models is found to have little influence (typically less than 1°C) on the base temperature of the critical heat sinks. For the compact heat sinks, the agreement is again within a typical difference of 5% in thermal resistance. Dramatic improvements were observed in the mesh count (factor > 10X) and solution time (factor >20X) required to achieve a high-fidelity simulation of the velocity, pressure, and temperature fields.Copyright © 2003 by ASME

Thermal analysis and design of electronic systems

Abstract: 14.1 Motivation 14-1 Thermal Packaging Options 14.2 Thermal Modeling 14-4 Conduction Heat Transfer • Convective Heat Transfer • Phase Change Heat Transfer • Flow Resistance • Radiative Heat Transfer • Environmental Heat Transfer 14.3 Thermal Resistance Networks 14-20 Chip Module Thermal Resistance • Multichip Modules • Radar System Applications