Showing papers on "Electronics cooling published in 2005"

Miniature loop heat pipes-a promising means for cooling electronics

Abstract: Loop heat pipes (LHPs) are highly efficient heat-transfer devices, which have considerable advantages over conventional heat pipes. Currently, miniature LHPs (MLHPs) with masses ranging from 10-20 g and ammonia and water as working fluids have been developed and tested. The MLHPs are capable of transferring heat loads of 100-200 W for distances up to 300 mm in the temperature range 50-100/spl deg/C at any orientation in 1-g conditions. The thermal resistance for these conditions are in the range from 0.1 to 0.2 K/W. The devices possess mechanical flexibility and are adaptable to different conditions of location and operation. Such characteristics of MLHPs open numerous prospects for use in cooling systems of electronics and computer systems.

Advances in liquid coolant technologies for electronics cooling

Abstract: There are several liquid coolants existing today. Among these, some are based on old technologies and the others are based on new advancements. All these liquids have been divided into six chemistries and a methodology has been presented to compare their overall efficiency, which was determined from heat transfer rate as well as pumping power requirements in microchannels. It was found that potassium formate (PF) solution exhibits the highest overall efficiency among the coolant chemistries evaluated. Other factors such as flammability, toxicity, corrosivity and electrical conductivity have been discussed in reference to these coolants. Based on electrical conductivity, liquid coolants have been divided into three categories: (1) liquid in which direct immersion cooling is possible; (2) liquid in which direct immersion is not possible but a leak or a spill will not damage the electronics; and (3) liquid in which neither direct immersion nor leakage is tolerable.

A novel valveless micropump with electrohydrodynamic enhancement for high heat flux cooling

Abstract: Integrated microchannel cooling systems, with micropumps integrated into microchannels, are an attractive alternative to stand-alone micropumps for liquid-cooled microchannel heat sinks. A new micropump design capable of integration into microchannels and especially suited for electronics cooling is presented. It combines induction electrohydrodynamics (EHD) with a valveless nozzle-diffuser micropump actuated using a vibrating diaphragm. A comprehensive numerical model of the micropump has been developed to study the combined effect of EHD and valveless micropumping. The numerical model has been validated using theoretical and experimental results from the literature. The flow rate achievable from the new micropump is presented and the effect of several key parameters on the micropump performance investigated.

A hybrid CFD-mathematical model for simulation of a MEMS loop heat pipe for electronics cooling applications

Abstract: A hybrid CFD-mathematical (HyCoM) model was developed to predict the performance of a micro loop heat pipe (MLHP) as a function of input heat rate. A micro loop heat pipe is a passive two-phase heat transport device, consisting of microevaporator, microcondenser, microcompensation chamber (CC) and liquid and vapor lines. A CFD model was incorporated into a loop solver code to identify heat leak to the CC. Two-phase pressure drop in the condenser was calculated by several two phase correlations and results were compared (Izenson and Crowley 1992 AIAA Paper A92-47847). Capillary tube correlations (Blevins 1984 Applied Fluid Dynamics Handbook (New York: Van Nostrand-Reinhold)) were used for pressure drop calculations in fluid lines. Effects of working fluid and change in geometry were studied. For a heat transport distance of 10 mm, the base model MLHP was 50 mm long, 16 mm wide and 1 mm thick. In the base model, widths of the grooves, liquid and vapor lines, evaporator and condenser were 55 µm, 200 µm, 750 µm, 2 mm and 4 mm, respectively.

Effective cooling of integrated circuits using liquid alloy electrowetting

Abstract: Electrical modulation of surface tension is proposed for actuation and pumping of discrete droplets of liquid metals/alloys for active heat management of ICs and removal of hot spots on any solid surface. The proposed technique is based on two observations: (i) by using liquid metals or alloys at room temperature heat transfer rate of a cooling system can be enhanced significantly; (ii) electrowetting is an efficient, low power consumption, and low voltage actuation technique for pumping liquids at micro-scales. Preliminary calculations indicate that more than two orders of magnitude increase in heat transfer rate could be achieved by using liquid metals as compared to systems using water. Liquid velocities above 10 cm/s are observed with extremely low pumping power consumption and at low actuation voltage (/spl sim/2 V). It is expected that digitized electrowetting can offer a viable cooling strategy to achieve the most important objectives of electronic cooling; i.e. minimization of the maximum substrate temperature and reduction of the substrate temperature gradient and removing substrate hot spots.

Pump Characteristic based optimization of a direct water cooling system for a 10-kW/500-kHz Vienna rectifier

Abstract: An ultra high power density 10-kW/500-kHz three-phase pulse-width modulation rectifier (Vienna Rectifier) is under development at the Power Electronic Systems Laboratory, ETH Zurich. From preliminary measurements and numerical simulations the total efficiency is assumed to be 95% at full load, resulting in power losses of up to 150 W in each multichip power module that realizes a bridge leg of the rectifier. In order to maintain the required power density of the system high direct water cooling is employed where water is in direct contact with the module base plate. Based on the measured characteristic of the water pump (pressure drop dependent on the water flow rate) the geometry of different water channel structures below the module base plate is systematically optimized based on equations which are formulated using well-established fluid dynamics theory. The design optimization is constrained by the desire to keep the geometry of the water channels in a range which allows simple and low-cost manufacturing. The aim is to find a channel structure resulting in a minimum thermal resistance of the power module for a given pump characteristic. In this paper, a very simple slot channel is investigated. The dependency of the thermal resistance on the cooling system is calculated for various heights of the slot channel, and an optimized channel height is determined using the condition of simple manufacturability. The shortcomings of the simple slot structure are discussed, and a novel metallic inlay structure is introduced and optimized that results in a reduction of the thermal resistance of the direct water cooling scheme as compared to the slot channel system. All theoretical considerations are experimentally verified. The general optimization scheme introduced in this paper can easily be adapted to other cooling problems.

Dynamically adaptable electronics cooling fan

Abstract: In an electronic system, a method for operating a cooling fan comprises rotating an impeller about a rotational axis and detecting fan failure. The impeller is spatially expanded in response to the detected fan failure whereby airflow through the failed fan is blocked.

Two-phase cooling method using R134a refrigerant to cool power electronic devices

Abstract: This paper presents a two-phase cooling method using R134a refrigerant to dissipate the heat energy (loss) generated by power electronics (PE) such as those associated with rectifiers, converters, and inverters for a specific application in hybrid-electric vehicles (HEVs). The cooling method involves submerging PE devices in an R134a bath, which limits the junction temperature of PE devices while conserving weight and volume of the heat sink without sacrificing equipment reliability. First, experimental tests that included an extended soak for more than 300 days were performed on a submerged IGBT and gate-controller card to study dielectric characteristics, deterioration effects, and heat flux capability of R134a. Results from these tests illustrate that R134a has high dielectric characteristics, no deterioration on electrical components, and a heat flux of 114 W/cm 2 for the experimental configuration. Second, experimental tests that included simultaneous operation with a mock automotive air-conditioner (A/C) system were performed on the same IGBT and gate controller card. Data extrapolation from these tests determined that a typical automotive A/C system has more than sufficient cooling capacity to cool a typical 30 kW traction inverter. Last, a discussion and simulation of active cooling of the IGBT junction layer with R134a refrigerant is given. This technique will drastically increase the forward current ratings and reliability of the PE device

The Maisotsenko Cycle for Electronics Cooling

Abstract: The Maisotsenko Cycle (M-Cycle) combines heat exchange and evaporative cooling [1–3] in an effective indirect evaporative cooling process resulting in product flow temperature approaching incoming air dew point (not wet bulb) temperature. Thermodynamically, the M-Cycle is based on air precooling before passing through the heat rejection water evaporating area, so the difference between the enthalpy of the air at its dew point temperature and the same air saturated at a higher temperature is used to provide cooling capacity to reject the heat, for example from the electronics. Today Delphi Corp and Coolerado Inc. are working on producing M-Cycle based heat- and mass exchangers for the Coolerado Coolers™ used in air conditioning. Other market applications, including electronics cooling, are being considered as well. A broad range of the cooling capacity (for example, from 10 W to 50 kW and more) could be obtained from the coolers utilizing M-Cycle. Due to superior thermodynamic process, M-Cycle based air coolers have a very high Energy Efficiency Ratio (EER). As per National Renewable Energy Laboratory (NREL), the average cooling capacity of Coolerado Coolers™ have EER more than 45; relatively to EER equal 13 for the best conventional air coolers. The M-cycle is much more efficient than any other heat rejection/recovery cycle, and the Coolerado Cooler™, as a single air cooling device has better specific characteristics (cooling capacity, air pressure drop, power consumption, etc.) than any existing coolers. Unlike traditional vapor compression, absorption, or thermoelectric refrigeration systems, where increase of air inlet temperature dramatically reduces cooling capacity, the M-Cycle based unit cooling capacity goes up with air inlet temperature rise. M-cycle based device similar to Coolerado Cooler™ can also cool any fluid to the temperature approaching the dew point temperature of incoming air without using compressor and refrigerant. That can revolutionize the electronics cooling market. The Coolerado Cooler was recognized by the prestigious R&D 100 Awards program as one of 2004’s most technologically significant products introduced to the world.Copyright © 2005 by ASME

Extending the limits of air-cooling in microelectronic equipment

Abstract: Despite the perception that the limits of air-cooling have been reached, this paper reviews approaches that could maintain the effectiveness of this technology. Key thermal management areas that need to be addressed are discussed, including heat sink design and analysis, interface thermal resistance minimization, heat spreading, fan performance, hybrid thermal management, heat sink surface fouling, and sustainability.

Silicon/water vapor chamber as heat spreaders for microelectronic packages

Abstract: A numerical study is performed to characterize the thermal and mechanical performances of silicon/water vapor chambers as heat spreaders for electronics cooling applications and to compare their performance against Cu heat spreaders. 2D flow and energy equations are solved in the vapor and liquid regions, along with conduction in the wall. An equilibrium model for heat transfer and a Brinkman-Forchheimer extended Darcy model for fluid flow are solved in the wick region. In addition to thermal modeling, FEA is also performed to study the impact of the proposed design on die stresses. The study shows that this system can match or thermally perform better than a more standard Cu spreader while also reducing the compressive stress in the Si by as much as 96%. Analysis shows that there are two main factors contributing towards the reduction of stress in the Si die, namely, the better CTE match between the Si die and the Si heat spreader and higher compliance (less stiffness) of the vapor chamber compared to standard heat spreaders. Thus Si vapor chambers provide a good design alternative to a standard Cu heat spreader without compromising on the reliability and performance of the Si.

Selectively grooved cold plate for electronics cooling

Abstract: An improved heat exchange device adaptable for cooling electronic components mounted over at least one external surface of the device, comprising a base plate (1); a cover plate (3) ; a clad sheet (2) interposed between the base plate (1) and the cover plate (3) the base plate (1) and the cover plate (3), with the clad sheet (2) being rigidly jointed to form a single integrated plate; at least one inlet port (5) and at least one outlet port (6) at one end and/or at the opposite ends of the formed plate for entry and exit of a cooling medium, characterized in that the base plate (1) is configured to have a plurality of flow-passages each comprising several machined grooves (4) having varied dimensions predetermined in registration with respective thermal footprint of the electronic components thereby optimizing the heat transfer rate, and in that a plurality of interconnections being designed between the grooves (4) constituting one of a series and parallel flow-paths .

Centrifugal fan clutch for an electronics cooling fan

Abstract: An electronics cooling fan comprises a centrifugal clutch adapted to disengage and freewheel upon fan failure.

Study of cooling rate on lead-free soldering microstructure of Sn-3.0Ag-0.5Cu solder

Abstract: Compared to traditional Sn-Pb solder, the microstructure of lead free solder Sn-3.0Ag-0.5Cu is more complex. The cooling rate significantly affects the secondary dendrite arm size and the IMC morphology, which influence the solder joint mechanical behavior. In this paper, the solder joint microstructure and morphology of three different cooling rates: air cooling, forced air cooling and water cooling were studied. The morphology of the Ag/sub 3/Sn was relatively spherical under water cooling, and had a needle-like morphology under air cooling. The IMC of the joint was a relatively planar Cu/sub 6/Sn/sub 5/ layer under water cooling while a nodular Cu/sub 6/Sn/sub 5/ layer was formed under air cooling.

Design and Development of a Low-Cost, High Temperature Silicon Carbide Micro-Channel Recuperator

Abstract: Typically, ceramic micro-channel devices are used for high temperature heat exchangers, catalytic reactors, electronics cooling, and processing of corrosive streams where the thermomechanical benefits of ceramic materials are desired. These benefits include: high temperature mechanical and corrosion properties and tailorable material properties such as thermal expansion, electrical conductivity and thermal conductivity. In addition, by utilizing Laminated Object Manufacturing (LOM) methods, inexpensive ceramic materials can be layered, featured and laminated in the green state and co-sintered to form monolithic structures amenable to mass production. In cooperation with the DOE and Pacific Northwest National Labs, silicon carbide (SiC) based micro-channel recuperator concepts are being developed and tested. The performance benefits of a high temperature, micro-channel heat exchanger are realized from the improved thermal efficiency of the high temperature cycles and the improved effectiveness of micro-channels for heat transfer. In designing these structures, the heat and mass transfer within the micro-channels are being analyzed with heat transfer models, computational fluid dynamics models and validated with experimental results. As an example, a typical micro-turbine cycle was modified and modeled to incorporate this ceramic recuperator and it was found that the overall thermal efficiency of the micro-turbine could be improved from about 27% to over 40%. Process improvements require technical advantages and cost advantages. These LOM methodologies have been based on well-proven industry standard processes where labor, throughput and capital estimates have been tested. Following these cost models and validation at the prototype scale, cost estimates were obtained. For the micro-turbine example, cost estimates indicate that the high-temperature SiC recuperator would cost about $200 per kWe. The development of these heat exchangers is multi-faceted and this paper focuses on the design optimization of a layered micro-channel heat exchanger, its performance testing, and fabrication development through LOM methodologies.Copyright © 2005 by ASME

Modeling of Heat Spreaders for Cooling Power and Mobile Electronic Devices

Abstract: The paper addresses theoretical and modeling issues of micro heat pipes with parallelepipedal shape with regard to the capillary limit and the evaporator boiling limit. In particular, the well-established Faghri model is employed to simulate the heat transfer capability of selected heat pipes developed and tested at the Laboratory of Electrotechnique of Grenoble. An improved model is suggested and it is compared with the simulation and experimental results. The improved model implements a different analytically derived form of the friction factor-Reynolds number product in the Faghri model. The simulated results with the proposed model demonstrate better coherence to the experiment showing the importance of accurate physical modeling to heat conduction behavior of the heat spreader

Thermal characteristics of graphite foam thermosyphon for electronics cooling

Abstract: Graphite foams consist of a network of interconnected graphite ligaments and are beginning to be applied to thermal management of electronics. The thermal conductivity of the bulk graphite foam is similar to aluminum, but graphite foam has one-fifth the density of aluminum. This combination of high thermal conductivity and low density results in a specific thermal conductivity about five times higher than that of aluminum, allowing heat to rapidly propagate into the foam. This heat is spread out over the very large surface area within the foam, enabling large amounts of energy to be transferred with relatively low temperature difference. For the purpose of graphite foam thermosyphon design in electronics cooling, various effects such as graphite foam geometry, sub-cooling, working fluid effect, and liquid level were investigated in this study. The best thermal performance was achieved with the large graphite foam, working fluid with the lowest boiling point, a liquid level with the exact height of the graphite foam, and at the lowest sub-cooling temperature.

New technologies of electronics cooling

Abstract: This paper discussed the electronics objects need to be cooling and cooling methods. Some new concept cooling methods and apparatus, such as micro-channel, integrated heat circuit, heat ejection, have been introduced.

Fan clutch for an electronics cooling fan

Abstract: An electronic system, an apparatus for cooling an electronic system, an electronics cooling apparatus, and associated method use a clutch to operate a cooling fan. An electronics cooling fan for usage in cooling an electronic system comprises a clutch that disengages upon failure wherein the electronics cooling fan is configured to freewheel upon disengagement of the clutch.

Hierarchically nested channels for fast squeezing interfaces with reduced thermal resistance [IC cooling applications]

Abstract: We report a simple method to improve bondline formation kinetics by means of a hierarchical set of channels patterned into one of the surfaces. These channel arrays are used to improve the gap squeezing and cooling of single and multiple flip chip electronic modules with highly viscous fluids and thermal pastes. They allow a fast formation of thin gaps or bond lines by reducing the pressure gradient in the thermal interface material as it moves in and out of the gap. Models describing the dynamics of Newtonian fluids in these "hierarchically nested channel" (HNC) interfaces combine squeeze flow and Hagen-Poiseuille theories. Rapid bond line formation is demonstrated for Newtonian fluids and selected particle-filled pastes. Modeling of particle-laden polymeric pastes includes Bingham and Hershel-Bulkley fluid properties. Bond line formation and thermal resistance is improved particularly for high viscosity-high thermal conductivity interface materials created from higher volumetric particle loadings or for thermal interface materials with smaller filler particle diameters.

Boiling of Water at Sub-Atmospheric Conditions With Enhanced Structures

Abstract: Liquid cooling with phase change is a very attractive option for thermal management of electronics because of the very high heat transfer coefficients achievable. Two-phase liquid cooling can be implemented in a thermosyphon loop, which has an evaporator, where heat is absorbed from the source during boiling of the working fluid, and a condenser, where the absorbed heat is rejected. Water is a preferred working fluid for boiling heat transfer due to its excellent thermal properties. Using water at sub-atmospheric conditions helps in initiation of boiling at low temperatures, which is necessary for electronics cooling applications, often limiting the maximum temperature to 85°C for silicon devices. Past studies have also shown that using boiling enhancement structures improve heat transfer by lowering the incipience overshoot, increasing heat flux and reducing evaporator volume. However, detailed study on the effects of enhancement structures and sub-atmospheric saturation conditions on the boiling of water in a compact thermosyphon loop is lacking in the literature. The objective of this study is to understand the boiling phenomena under the above-mentioned conditions and to investigate their effectiveness in electronics cooling applications. Experiments were carried out in a thermosyphon setup at 9.7, 15 and 21 kPa saturation pressures for two different enhancement structure geometries at varying heat loads (1–170 W). The experimental investigation showed that very high heat fluxes (≥ 80 W/cm2 ) can be achieved by boiling at sub-atmospheric pressures with enhancement structures. It is observed that with decreasing system pressure, the surface temperature also decreased for all the heat loads. The surface temperatures attained were well below the acceptable value of 85° C for all the cases.Copyright © 2005 by ASME

Electronics cooling fan with collapsible fan blade

Abstract: An electronics cooling fan comprises at least one collapsible fan blade driven by centrifugal force to extend radially as the fan spins and driven by elastic force to retract as spinning slows or stops.

Artificial Neural Network Trained, Genetic Algorithms Optimized Thermal Energy Storage Heatsinks for Electronics Cooling

Abstract: A thermal response model for designing thermal energy storage heatsink utilized for electronics cooling is developed in this paper. In this study, thermal energy storage (TES) heatsink made out of aluminum with paraffin as the phase change material (PCM) is considered. By using numerical simulation, stabilization time and maximum operating temperature to transition temperature difference is obtained for varying fin thicknesses, fin height, number of fins and PCM volume. The numerical simulation results were then compared with existing experimental work. The numerical results matched the melting temperature variation obtained by the experimental work. The validated numerical results are then used to train the artificial neural networks (ANN) to predict stabilization time and maximum operating temperature to transition temperature difference for new fin thicknesses, fin height, number of fins and PCM volume. Finally the optimization of the fin thickness, fin height, number of fins and PCM volume of the thermal energy storage heatsink is obtained by embedding the trained ANN as a fitness function into genetic algorithms (GA). The objective of optimization is to maximize stabilization time and to minimize maximum operating temperature to transition temperature difference. Finally the optimized results for the TES heatsink is used to build a new computer model for numerical analysis. The final optimized model results and the validated preliminary model results are then compared. The final results will show a significant improvement from the validated model. Further the study will show that by combining ANN and GA, a superior tool for optimization is realized.Copyright © 2005 by ASME

Numerical Investigation Based on CFD for Air Impingement Heat Transfer in Electronics Cooling

Abstract: Air impingement cooling, as a potential air-cooling technique, has been shown to be much efficient and enabled to complement conventional forced convective air-cooling in electronics To provide reliable references to the computational thermal analyses based on CFD for effective air-cooling technique integrated in microsystem electronics packaging, the numerical simulation based on CFD for air impingement heat transfer is conducted in the case of axisymmetric impinging jet by adopting various turbulence models and wall functions The results indicate that the inherent disadvantage of the overpredictions of the turbulent kinetic energy and heat transfer rate in the stagnation region for the standard and realizable k-epsiv turbulence models primarily depends on the improper modeling of the source term in the transport equation of the turbulent energy dissipation rate, rather than the isotropic eddy viscosity assumption and high pressure gradient in the vicinity of the stagnation point The RNG k-epsiv turbulence model greatly improves the prediction accuracy of the turbulent viscosity and heat transfer rate in the stagnation region and seems to be preferable not only to the standard and realizable k-epsiv turbulence models but also to advanced Reynolds stress turbulence model to some extent in respect to the prediction capability with respect to the turbulence and heat transfer characteristics for such an axisymmetric impinging jet

Optimally shaped spreader plate for electronics cooling assembly

Abstract: A spreader plate for an electronic component cooling assembly has a flat lower surface and a substantially arcuate upper surface of larger surface area than the lower surface which is generally convex and arcuate in cross section, and which decreases in thickness, as measured between the lower and upper surfaces, moving from the central area out to the periphery. This allows the heat flux lines to be more evenly spaced and regular in length, as compared to a typical plate with flat upper and lower surfaces of equal surface area.