Showing papers on "Electronics cooling published in 2007"

Induction electrohydrodynamics micropump for high heat flux cooling

Abstract: Induction electrohydrodynamics (EHD) has been investigated as a possible means of pumping liquids through microchannel heat sinks for cooling microprocessors. A pump utilizing induction EHD has been microfabricated and tested. The experimental results matched the predictions from correlations to within 30%. Based on this, a micropump has been designed which is miniaturizable to a level where it can be integrated into the microchannels. The micropump utilizes a vibrating diaphragm along with induction EHD for pumping. The vibrating diaphragm does not cause any net flow by itself but causes high local bulk fluid velocities which lead to an increase in the power drawn from the electrodes and an increase in efficiency of EHD, both of which lead to a higher flow rate. The performance of the pump is predicted using an experimentally validated numerical model. The numerical model solves the three-dimensional transient fluid flow and charge transport problem due to simultaneous actuation of EHD and the vibrating diaphragm. Numerical results for micropumps integrated into trapezoidal microchannels are presented. The results indicate that the proposed micropump design has significant potential for microelectronics cooling applications: It is easy and inexpensive to fabricate, needs no added space, and can achieve the high flow rates needed.

Energy Efficiency of Low Form Factor Cooling Devices

Abstract: With increasing attention to the energy efficiency of consumer and commercial products, thermal engineering and science community is devoting greater effort and attention to the design and implementation of energy-efficient cooling solutions. This study focuses on the cooling potential and Coefficient of Performance, (COP), achievable with three distinct meso-scale cooling technologies, applicable to a wide range of electronics cooling challenges. The thermo-fluid and thermodynamic characteristics of synthetic jets, piezo-driven vibrating blades, and compact muffin fans will be addressed. We are dedicating this paper to Prof. Kakac for his contributions to heat transfer science and technology, developing young scientists, writing highly valuable heat transfer textbooks, and most importantly for his kindness and friendship.Copyright © 2007 by ASME

Design of a Porous Electroosmotic Pump, Used in Power Electronics Cooling

Abstract: The thermal cooling of the electronic components is generally implemented by a mechanical pump, which requires a minimal maintenance to ensure the reliability of the device. To solve this problem, it is proposed to replace the mechanical pump by a static one, for example an electro-osmotic (EO) pump. In this paper, we present the theory of the electro-osmosis phenomena, and a model of a porous EO pump. Then we optimize a porous EO pump made of sintered silica. It was found that the optimum operating point of the pump is determined by controlling the diameter of the effective pore size of the sintered silica and the Debye length. Using deionized (DI) water as pumping liquid, the EO pump generates 13.6 m I'm in and 2 kPa at 150 V applied voltage. The power consumed by the pump is less than 0.4 W. The EO pump works without any bubbles in the hydraulic circuit. This design can be used to cool 22.6 W of power generated by the power components with a forced convection without evaporation and 270 W with evaporation.

Vapor-Venting, Micromachined Heat Exchanger for Electronics Cooling

Abstract: The increasing complexity of modern integrated circuits and need for high-heat flux removal with low junction temperatures motivates research in a wide variety of cooling and refrigeration technologies. Two-phase liquid cooling is especially attractive due to high efficiency and low thermal resistances. While two-phase microfluidic cooling offers important benefits in required flow rate and pump size, there are substantial challenges related to flow stability and effective superheating. This work investigates the use of hydrophobic membrane to locally vent the vapor phase in microfluidic heat exchangers. Previous work has demonstrated selective venting of gas in microstructures and we extend this concept to two-phase heat exchangers. This paper details the design, fabrication and preliminary testing of the novel heat exchanger. Proof-of-concept of the device, carried out using an isothermal air-water mixture, found the air-mass venting efficiency exceeding 95%. Two-phase, thermal operation of the heat exchanger found the pressure-drop to be smaller compared to a two-phase, non-venting model. The paper also includes a discussion of design challenges such as membrane leakage and optical inaccessibility. The favorable results demonstrated in this first-generation, vapor-venting, micromachined, heat exchanger motivates further study of this and other novel microstructures aimed at mitigating the negative effects of phase-change. With continued research and optimization, we believe two-phase cooling is a viable solution for high heat flux generating electronics.Copyright © 2007 by ASME

System-Level Dynamic Thermal Modeling and Simulation for an All-Electric Ship Cooling System in VTB

Abstract: A system-level dynamic simulation of a thermo-electrical coupled model for a ship cooling system was developed in the virtual test bed (VTB) platform. This paper presents dynamic simulations for two most essential cooling schemes used in the ship thermal management. One configuration is freshwater cooling with seawater as the secondary coolant. The other configuration is chilled water cooling from the ship's air conditioning plants. Details of some major thermal components used in the simulations are identified. The results from these simulations clearly demonstrate the ability of the VTB environment to simulate the dynamic behavior of complex and coupled devices. The work presented in this paper provides the first step to use VTB as a potential system-level dynamic simulation platform for an all-electric ship thermal management.

Evaluation of cooling solutions for outdoor electronics

Abstract: The thermal management of an outdoor electronic enclosure can be quite challenging due to the additional thermal load from the sun and the requirement of having an air-sealed enclosure. It is essential to consider the effect of solar heating loads in the design process; otherwise, it can shorten the life expectancy of the electronic product or lead to catastrophic failure. The main objective of this work is to analyze and compare the effectiveness of different cooling techniques used for outdoor electronics. Various cooling techniques were compared like special coats and paints on the outer surface, radiation shield, double-walled enclosure, fans for internal air circulation and air-to-air heat exchangers. A highly simplified, typical outdoor system was selected for this study measuring approximately 300times300times400 mm (WxLxH). Solar radiation was incident on 3 sides of the enclosure. There were 8 equally spaced PCBs inside the enclosure dissipating 12.5 W each uniformly (100 watts total). A computational fluid dynamics (CFD) model of the system was built and analyzed. This was followed by building a mock-up of the system and conducting experiments to validate the CFD model. It was found that some of the simplest cooling techniques like white oil paint on the outer surface can significantly reduce the impact of solar loads. Adding internal circulation fans can also be very effective. Using air-to-air heat exchangers was found to be the most effective solution although it is more complex and costly.

Modeling of Synthetic Jet Ejectors for Electronics Cooling

Abstract: This paper presents the modeling results for prediction of thermal performance using synthetic jets ejectors. A synthetic jet is an intense, small-scale turbulent jet synthesized directly from the fluid in which it is embedded. A jet ejector consists of a primary high momentum jet inducing a secondary flow within a channel. In the work presented here, a 2D synthetic jet is used as the primary jet causing secondary flow to be induced in a channel. The flow entrainment prediction for the model is based on the solution of mass and momentum equations within the channel. A resistance network model is used to predict the thermal performance. The modeling results are compared with data from past tests of synthetic jet cooling within channels as well as a completely integrated synthetic jet heat sink module.

Experimental and Theoretical Analysis on Enhanced Flat Miniature Heat Pipes with Axial Capillary Grooves and Screen Meshes

Abstract: Combined experimental and analytical studies are realized in order to verify the flat mini heat pipe (FMHP) concept for cooling high power dissipation electronic components, and determine the potential advantages of constructing arrays of mini channels as an integrated part of a heat pipe. A mixed capillary system, which is composed of screen meshes and mini-channels, is used in order to manufacture the FMHP. In the experimental study, different FMHP prototypes are manufactured and tested. The number of screen meshes is kept the same for the different tested configurations; however different meshing sizes are used. The heat transfer improvement, obtained by comparing the heat pipe thermal resistance to the heat conduction thermal resistance of a copper plate having the same dimensions as the tested heat pipes, is demonstrated for the different prototypes. The heat transfer enhancement depends on the input heat flux rate, the screen mesh porosity, and the FMHP orientation in respect to gravity. In the analytical study, a model of MHP with mixed capillary structure is developed. The comparison between the analytical and experimental results shows a good agreement in predicting both the maximum capillary limit and the FMHP thermal resistance

Enhancing Performance of Thermoelectric Coolers Through the Application of Distributed Control

Abstract: The primary drawback of thermoelectric coolers (TECs) for electronics cooling applications is their thermodynamic inefficiency due to material limitations. The present work considers a control strategy to improve the overall coefficient of performance in an engineering system instead of addressing material shortcomings. Typical TECs are composed of several individual thermocouples that are powered in series and remove heat in parallel. If one of the numerous thermocouples is powered, all the thermocouples receive the some power whether or not they are needed. The fact that chips heat nonuniformly provides an opportunity for performance enhancement, by sensing and controlling the power to individual couples within the device. The current work presents evidence that applying distributed control to TEC operation can realize appreciable improvement in performance. Compared to monolithic cooling devices, a distributed control strategy can realize a factor of 2 increase in performance for the device studied. Additionally, this type of control can be used in conjunction with many of the existing material-based research initiatives to further compound the benefits.

Assessment of Cooling Enhancement of Synthetic Jet in Conjunction With Forced Convection

Abstract: Synthetic jets are meso or micro fluidic devices, which operate on the “zero-net-mass-flux” principle. They impart a positive net momentum flux to the external environment, and are able to produce the cooling effect of a fan sans its ducting, reliability issues, and oversized dimensions. As a result, recently their application as electronics cooling devices is gaining momentum. Traditionally, synthetic jets have been sought as a replacement to the fan in many electronic devices. However, in certain large applications, complete replacement of the fan is not feasible, because it is necessary to provide the basic level of cooling over a large area of a printed assembly board. Such applications often pose a question whether synthetic jet would be able to locally provide reasonable enhancement over the forced convection of the fan flow. In the present study, we present the cooling performance of synthetic jets complementing forced convection from a fan. Both experiments and CFD computations are performed to investigate the interaction of the jet flowfield with a cross flow from fan. The inlet velocity, jet disk amplitude, and channel height are varied in the computational simulations to evaluate the impact of these changes on the cooling properties. Overall, both studies show that a synthetic jet is able to pulse and disrupt the boundary layer caused from fan flow, and improve heat transfer up to 4× over forced convection.Copyright © 2007 by ASME

Spray Cooling with Mixtures of Dielectric Fluids

Abstract: Spray cooling is one technology with the potential to help solve the thermal management issues of future generations of electronics. To date, however, its implementation has been limited by the lack of understanding of how spray cooling systems can be engineered rather than designed by trial and error. This work presents a comprehensive set of heat transfer data for single- and four-nozzle spray arrays using 5 different pure fluids and mixtures of pairs of these 5. Importantly, it was found that the heat transfer performance of the mixtures was not impaired as is often the case in convective flow boiling. In addition, a single correlation is presented that predicts all of the data to within 9% mean average error.

Heat Pipes for High Temperature Thermal Management

Abstract: Copper water heat pipes are a well-established solution for many conventional electronics cooling applications; however they have several problems when applied to high temperature electronics. The high vapor pressure of the working fluid combined with the decreasing strength of an already soft material leads to excessive wall thickness, high mass, and an inability to make thermally useful structures such as planar heat pipes (vapor chambers) or heat pipes with flat input surfaces. Titanium/water and Monel/water heat pipes can overcome the disadvantages of copper/water heat pipes and produce a viable thermal management solution for high temperature electronics. Water remains the fluid of choice at temperature up to about 280°C due to its favorable transport properties. Life tests have shown compatibility at high temperature. At temperatures above roughly 300°C, water is no longer a suitable fluid, due to high vapor pressure and low surface tension as the critical point is approached. At higher temperatures, another working fluid/envelope combination is required, either an organic or halide working fluid. Preliminary halide life test results are presented, giving fluids that can operate at temperatures as high as 425°C. At higher temperatures, alkali metal heat pipes are suitable. Water and the higher temperature working fluids can offer solutions for cooling high-temperature electronics, or those working at or above 150°C.Copyright © 2007 by ASME

Evaluation of a Liquid Cooling Concept for High Power Processors

Abstract: A high performance liquid cooling architecture for high power processors in less than 45 mm height electronics chassis (1U rack space) was proposed and investigated experimentally. A review of several system cooling approaches from CPU to data center was also provided. The present proposed method employs conventional heat pipes to transport local CPU heat to the edge of an electronics module coupled with system liquid cold plates. As coolant from external cooling distribution unit in data center flows through the system cold plates in the rack, CPU heat load is rejected to data center cooling facility. Capable of removing the processor power as high as 450W is demonstrated from a prototype built. Experiments were conducted to characterize the prototype thermal performance between liquid inlet and heat pipe evaporator base. A 25 mm times 25 mm heat block was used to simulate CPU and provide heat source to the heat pipe evaporator base. The impacts of heat transfer rate, flow rate, and liquid inlet temperature were evaluated. The total thermal resistance of below 0.090degC/W was achieved at water flow rate of 1 l/min and heat transfer rate of 450W.

Cascaded Fins for Heat Transfer Enhancement

Abstract: Recent developments in electronics cooling imposed fin structures constructed from two materials (e.g., copper and aluminum) as a thermo-economical solution for heat transfer enhancement. Such fins facilitate savings of expensive materials and reduce operating and investment costs by increasing efficiency. This paper stresses the importance of constraints on the geometrical optimization of “cascaded” fins made from two materials. Two types of constraints are analyzed in a unitary way: fixed weight (relevant to aerospace and transportation applications) and fixed investment cost. The cascaded fin geometry springs from the thermal performance maximization under constraints (constructal principle). To illustrate the design principle and derive its fundamental features, it is sufficient to consider the most basic case of one-dimensional heat conduction through rectangular-rectangular, rectangular-triangular, and rectangular-parabolic cascaded fins. The study reveals that the ideal/theoretical limit of heat tr...

Evaluation of Cooling Solutions for Outdoor Electronics

Abstract: The thermal management of an outdoor electronic enclosure can be quite challenging due to the additional thermal load from the sun and the requirement of having an air-sealed enclosure. It is essential to consider the effect of solar heating loads in the design process; otherwise, it can shorten the life expectancy of the electronic product or lead to catastrophic failure. The main objective of this work is to analyze and compare the effectiveness of different cooling techniques used for outdoor electronics. Various cooling techniques were compared like special coats and paints on the outer surface, radiation shield, double-walled enclosure, fans for internal air circulation and air-to-air heat exchangers. A highly simplified, typical outdoor system was selected for this study measuring approximately 300times300times400 mm (WxLxH). Solar radiation was incident on 3 sides of the enclosure. There were 8 equally spaced PCBs inside the enclosure dissipating 12.5 W each uniformly (100 watts total). A computational fluid dynamics (CFD) model of the system was built and analyzed. This was followed by building a mock-up of the system and conducting experiments to validate the CFD model. It was found that some of the simplest cooling techniques like white oil paint on the outer surface can significantly reduce the impact of solar loads. Adding internal circulation fans can also be very effective. Using air-to-air heat exchangers was found to be the most effective solution although it is more complex and costly.

Single- and Multiple-Stage Cascaded Vapor Compression Refrigeration for Electronics Cooling

Abstract: À ma chérie, Céline. Merci de m'avoir soutenu. Paul Kohl for his strategic guidance and support as a member of my thesis committee. I would like to thank Dr. David Gerlach for serving as my mentor and reminding me of the joy of engineering. I would like to thank the members of the Microelectronics and Emerging Technologies Thermal Laboratory, in particular Dr. Suman, for their advice and our fruitful interactions. I would like to thank the School of Mechanical Engineering administrative staff for helping me with everything from enrollment to graduation, and the machine shop personnel for advising me on how to fabricate components for my experiment. I would like to thank my parents and grandparents for drawing from their own experiences to give me needed advice. Finally, I would like to thank the Interconnect Focus Center for funding my project. Table 2.1: Predicted chip throughput enhancement for sub-ambient operation, compared with operation at 350 K (3σ = 110 mV). 15 Table 3.1: Initial compressor requirements determined from thermodynamic model. 23 Table 3.2: Performance of Danfoss BD80F operating at 4400 RPM with R134a (T = 54.4°C; T

Optimal Placement of Eletronic Devices in Forced Convective Cooling Conditions

Abstract: Implementation of genetic algorithm for electronic devices placement optimization has been done. The study includes a few cases. In the first attempt electronic devices are placed along a bottom surface of a duct and cooled with forced convection by air stream with velocity U0. Thermal model is two-dimensional (2D). Algorithm optimizes order and spacing in the view of three thermal criteria. In the second step genetic algorithm is used to optimize position of electronic devices on a surface of a printed circuit board (PCB). Thermal model is three-dimensional (3D). Devices have some specified positions on the PCB and permutations are only performed. Algorithm optimizes electronic devices position from the view of thermal criteria and wiring length.

An Experimental Characterization of Miniature Scale Cold Plates for Electronics Cooling Applications

Abstract: Contemporary electronic systems are currently constrained by the high heat fluxes in which they generate at component level. It is evident that heat fluxes are currently approaching the limits of forced air cooling, and that liquid cooling is now under consideration. In this paper five commercially-available and one custom-made cold plates were characterised experimentally. The six cold plates utilized different geometries which included: an array of jets impinging onto a pin matrix; a fin structure; a pin fin structure; a large serpentine channel structure; a slot jet impinging onto wave shaped fins; and the custom cold plate having no significant geometry associated with it, as it was used as a bench mark. The bench mark is anticipated to be the minimum cost solution. The pressure drop, thermal resistance and hydrodynamic power consumption were determined for each solution as a function of flow rate. The results showed that there was a variety of operational power consumption costs coupled with a range of performance levels reached by the six cold plates. This emphasizes the need of a optimum cooling package for a specific application. A relationship of thermal resistance as a function of hydrodynamic power consumed was formulated, thus facilitating the selection of a cold plate for a practical application.Copyright © 2007 by ASME

Evaluation on Use of Thermoelectric Devices for Electronics Cooling

Abstract: As Thermoelectric devices are getting cheaper and more powerful in cooling, these devices are getting more popular for electronics cooling applications. However, due to the additional heat production inside the thermoelectric device, the application of a TE-cooler might not always be appropriate. In some applications, use of thermoelectric devices or coolers might cause higher temperature rises on heat generating electronics than conventional cooling solutions. To authors’ best knowledge, there exists no literature that studies whether thermoelectric cooling is better than traditional convective cooling without Thermoelectrics. This study aims to evaluate the performance and effectiveness of thermoelectric cooling for electronics. Two figures of merit are proposed, to compare performances of conventional and thermoelectric cooling techniques. An attempt is made to derive this figure of merit analytically with assumptions reflecting common electronics applications. Selective case studies will be presented based on constant heat flux and constant temperature difference.Copyright © 2007 by ASME

Convective Cooling Evaluation of Electronic Devices using Lock-in Thermography

Abstract: This paper presents the basis of dynamic thermography, with its application to thermal parameters evaluation. The method is based on windowed FFT analysis, with special attention paid for the phasegrams interpretation. A thermal modeling of the investigated object based on lumped RC network has been made to estimate the sensitivity and accuracy of the method. Heat transfer coefficient, thermal conductivity of the material, and thickness of multilayer structure are the major parameters that can be evaluated. The proposed approach can be used mainly for electronic applications.

Surface plasmon assisted laser cooling of solids

Abstract: Threshold and efficiency of laser cooling can be significantly improved due to rapid energy transfer from semiconductor to metal heat sink via excitation of surface plasmon polaritons and their subsequent decay in the metal.

Modular semi-conservative and self-scaling electronics cooling system

Abstract: A modular electronic cooling system with moving parts, composed of a base unit and individual modules inserted into this base unit in respect to the expected upper limit of the heat load is presented. This cooling system utilizes thermoelectric power generation and the heat load itself to allow for operation independent of any external power source. By the same mechanism the cooling system scales within a range beyond initial configuration, automatically reacting to and dissipating a dynamic heat load via forced convection, and doing so passively, without the need for specific programming. The said cooling system comprises of porous material or multi-layered mesh parts, thermoelectric components, a modular assembly system and independent enclosure parts for described porous material or multi-layered mesh, an electronics control system that may be passively activated, and a motor assembly. Altogether the system provides maximum efficiency in terms of form factor.

Conjugate Numerical Investigation of a Miniature Flat Plate Evaporator of Capillary Pumped Loop

Abstract: The capillary pumped loop (CPL) is a two-phase thermal control device, which has become more active and interesting in the domain of electronics cooling. A two-dimensional conjugate numerical model for the miniature flat plate capillary evaporator is presented to describe liquid and vapor flow, heat transfer and phase change in the porous wick structure, liquid flow and heat transfer in the compensation cavity and heat transfer in the vapor grooves and metallic wall. The entire evaporator is solved with SIMPLE algorithm as a conjugate problem. The shape and location of vapor-liquid interface inside the wick are calculated, and side wall effect heat transfer limit is introduced to estimate the heat transport capability of capillary evaporator. The influences of different wall materials on the performance of miniature flat plate evaporator are discussed in detail, and the results show that evaporator with combined wall is capable of dissipating high heat flux and stabilizes the electronics devices temperature at a moderate temperature level.

Electronics Cooling Fan Noise Prediction

Abstract: Using the finite volume CFD software FLUENT, one fan was studied at a given flow rate (1.5m3/min) for three different operational rotating speeds : 2,000, 2,350 and 2,700 rpm. The turbulent air flow analysis predicts the acoustic behavior of the fan. The best fan operating window, i.e. the one giving the best ratio between noise emissions and cooling performance, can then be determined. The broadband noise acoustic model is used. As the computation is steady state, a simple Multiple Reference Frame model (MRF, also known as stationary rotor approach) is used to represent the fan. This approach is able to capture the effects of the flow non-uniformity at the fan inlet together with their impact on the fan performance. Furthermore, it is not requiring a fan curve as an input to the model. When compared to the available catalog data the simulation results show promising qualitative agreement that may be used for fan design and selection purposes.

Designer heat spreading materials and composites

Abstract: A solid-state system model of “Designer” thermal conducting nano/micro materials used for more effective heat spreading in electronic packaging manufacture is described. The “Designer” materials are much lighter (sp.gr. 2.5g/cc vs. 9.2g/cc) and stronger (modulus 500–820Gpa vs 120GPa) than copper. The material has a coefficient of thermal expansion (1×10−6 vs. 17×10−6) much higher thermal conductivity (500–1200W/mK vs. 390W/mK) and greater heat spreading capabilities. In addition there is the ability to control the thermal conductivity, coefficient of thermal expansion and thermal spreading coefficient in any of the three material dimensions. A brief description characterizing the material and its manufacturing process is here-within. To illustrate the performance gain of using these materials, the base plate of Intel’s CPU Cooler CL-P0030 heat-sink is chosen as an example of a high-heat source cooling device i.e. ≫100W/cm2. Heat greater than 100Wm2 is equivalent to the concentrated focused energy of ≫1000 Suns. (electronic devices melt in seconds without proper cooling) This is a macro example of a replacement for the thermal conducting packaging material structures currently used in electronics.