Showing papers on "Electronics cooling published in 2006"

On-Chip Thermal Management With Microchannel Heat Sinks and Integrated Micropumps

Abstract: Liquid-cooled microchannel heat sinks are regarded as being amongst the most effective solutions for handling high levels of heat dissipation in space-constrained electronics However, obstacles to their successful incorporation into products have included their high pumping requirements and the limits on available space which precludes the use of conventional pumps Moreover, the transport characteristics of microchannels can be different from macroscale channels because of different scaling of various forces affecting flow and heat transfer The inherent potential of microchannel heat sinks, coupled with the gaps in understanding of relevant transport phenomena and difficulties in implementation, have guided significant research efforts towards the investigation of flow and heat transfer in microchannels and the development of microscale pumping technologies and novel diagnostics In this paper, the potential and capabilities of microchannel heat sinks and micropumps are discussed Their working principle, the state of the art, and unresolved issues are reviewed Novel approaches for flow field measurement and for integrated micropumping are presented Future developments necessary for wider incorporation of microchannel heat sinks and integrated micropumps in practical cooling solutions are outlined

A miniature-scale refrigeration system for electronics cooling

Abstract: A miniature-scale refrigeration system suitable for electronics cooling applications was developed and experimentally investigated. A detailed review of the literature on refrigeration systems and system simulation models for application to electronics cooling is also provided. Experimental results obtained with the prototype system demonstrate its feasibility for use in cooling compact electronic devices. The cooling capacity of the system investigated varied from 121 to 268W, with a COP of 2.8 to 4.7, at pressure ratios of 1.9 to 3.2. The effectiveness of the condenser ranged from 52% to 77%, while a thermal resistance of 0.60 and 0.77degC-cm 2/W was achieved at the evaporator. The evaporator-heat spreader thermal resistance is defined as the ratio of the temperature difference between the chip surface and the refrigerant evaporator to the evaporator heat transfer rate. The overall system thermal resistance, defined as the ratio of the temperature difference between the chip surface and the condenser air inlet, is of 0.04 to 0.18degC-cm2/W. An overall second-law efficiency ranging from 33% and 52% was obtained, using a commercially available small-scale compressor. The measured overall isentropic efficiency was between 25% and 60%

Experimental Investigation of a Miniature-Scale Refrigeration System for Electronics Cooling

Abstract: A miniature-scale refrigeration system suitable for electronics cooling applications was developed and experimentally investigated. A detailed review of the literature on refrigeration systems and system simulation models for application to electronics cooling is also provided. Experimental results obtained with the prototype system demonstrate its feasibility for use in cooling compact electronic devices. The cooling capacity of the system investigated varied from 121 to 268W, with a COP of 2.8 to 4.7, at pressure ratios of 1.9 to 3.2. The effectiveness of the condenser ranged from 52% to 77%, while a thermal resistance of 0.60 and 0.77degC-cm 2/W was achieved at the evaporator. The evaporator-heat spreader thermal resistance is defined as the ratio of the temperature difference between the chip surface and the refrigerant evaporator to the evaporator heat transfer rate. The overall system thermal resistance, defined as the ratio of the temperature difference between the chip surface and the condenser air inlet, is of 0.04 to 0.18degC-cm2/W. An overall second-law efficiency ranging from 33% and 52% was obtained, using a commercially available small-scale compressor. The measured overall isentropic efficiency was between 25% and 60%

Small scale refrigeration system for electronics cooling within a notebook computer

Abstract: The cooling of high power components in notebook computers is uniquely challenging due to space constraints that limit the size of the thermal solution. As a result, for some applications, a method of inserting a "negative" thermal resistance into the heat flow path may be required in order to achieve higher component powers. In this paper we describe a small-scale refrigeration system for the cooling of high power components in notebook form factors. The small-scale refrigeration system includes a compressor, cold plate, condenser, and throttling device. These components are designed for a vapor-compression cycle with iso-butane as the working fluid. All of these components are designed such that the entire system can be incorporated within a notebook form factor. In order to achieve the targeted performance, the cold plate and condenser contain microchannels to efficiently transfer heat to and from the refrigerant. Prototypes of each of the components were built and tested in order to assess their individual performance. A complete form factor loop was also built and tested in order to determine overall system feasibility and performance. The test results show that the targeted performance of the system (COP > 2.25) is achievable in this form factor at the moderate temperature rise expected in this application

Micropump for electronics cooling

Abstract: A micropump including one or more microchannels for receiving a fluid and a plurality of electrodes arranged on a diaphragm and energized in a manner to provide an enhanced electrohydrodynamic flow of fluid through the one or more microchannels. The micropump may be used for pumping a working fluid for removing heat from a heat-generating electronic component or for delivery of a drug, medicine, or other treatment agent as or in a fluid to a patient.

The Electro-Adsorption Chiller: Performance Rating of a Novel Miniaturized Cooling Cycle for Electronics Cooling

Abstract: The paper describes the successful amalgamation of the thermoelectric and the adsorption cycles into a combined electro-adsorption chiller (EAC). The symbiotic union produces an efficiency or COP (coefficient of performance) more than threefold when compared with their individual cycles. The experiments conducted on the bench-scale prototype show that it can meet high cooling loads, typically 120 W with an evaporator foot print of 25 cm 2 , that is 5 W/cm 2 at the heated surface temperature of 22°C, which is well below that of the room temperature. The COPs of the EAC chiller vary from 0.7 to 0.8, which is comparable to the theoretical maximum of about 1.1 at the same operating conditions. With a copper-foam cladded evaporator, the high cooling rates have been achieved with a low temperature difference. In addition to meeting high cooling rates, the EAC is unique as (i) it has almost no moving parts and hence has silent operation, (ii) it is environmentally friendly as it uses a nonharmful adsorbent (silica gel), and (iii) water is used as the refrigerant.

Cavity-induced two-phase heat transfer in silicon microchannels

Abstract: Modern developments in microelectronics manufacturing and architecture continue to lead to reductions in feature sizes on microprocessor chips. The demand for faster and more powerful systems has approached the limits of conventional passive and active electronics cooling schemes. Future high-powered electronics require new and innovative heat removal methods. The research study presented in this paper is conducted in order to better understand two-phase heat transfer in a microchannel heat sink using FC-72 as the test fluid. The test section consists of an (1cm /spl times/ 1cm) array of nineteen parallel microchannels etched into silicon with the following dimensions: hydraulic diameter (D/sub h/ = 253 microns) with a ratio of (L/D/sub h/= 39.52). The base of each channel contains six re-entrant type cavities spaced evenly along the length. Each cavity, measuring 20 microns in mouth size, is used to promote controlled nucleation activity. The experimental results presented include the bulk fluid temperature and pressure at the inlet and outlet. To simulate the heat generated by a typical microprocessor, a uniform heat flux was applied to the base of the channel array using a series of thin film serpentine aluminum heaters. System parameters that were varied in this study include the applied heat flux and mass flow rate.

Analytical Modeling For Prediction of Hot Spot Chip Junction Temperature for Electronics Cooling Applications

Abstract: Microprocessor driven escalation of thermal management needs has resulted in significant cooling challenges at several different design levels, including the chip, package, module, board, and the rack, respectively, as well as for data centers in the case of servers. The spatial non-uniformity in the input power at the chip device or junction side, leads to the occurrence of hot spots that often represents a significant component of the total junction-to-ambient thermal resistance. In this paper, an analytical chip junction temperature prediction model is developed using a resistance network approach and techniques from recent literature. The analytical model is numerically validated for air cooling applications. Examples that represent capped (or lidded) air cooling modules as well as those using a directly attached heat sink are presented. The analytical model takes as an input, the chip power map, various dimensional parameters and thermo -physical properties for the chip, the thermal interfaces, and the spreaders, respectively, and a convective boundary condition that describes the heat sink fins, and the output is the spatial temperature distribution at the device/junction side of the chip. The analytical predictions for the total hot spot junction to ambient thermal resistance were within 5% of numerical results for a broad range of design parameters, including thermal interface material and spreader thermal conductivity, respectively, and effective convective heat transfer coefficient. The analytical temperature estimates were found to be conservative for the majority of the cases. The spatial variation at the device side analytical chip temperature also compared well with the data from the more sophisticated numerical computations. Solution times were found to be about 60 seconds or less for typical problems on a conventional PC, which greatly reduces and simplifies the estimation of thermal performance

Method and apparatus for electronics cooling

Abstract: A method and apparatus for actively cooling a device, space or circuit board are disclosed. The device may be an electrical or electronic component that includes an integrated circuit or embedded control. The apparatus employs a fluid in a closed loop, at least two heat exchangers and a fluid driver.

Numerical Simulation of Phase Change Heat Transfer in PCM-Encapsulated Heat Sinks

Abstract: An enthalpy-based computational model is developed for analyzing PCM-encapsulated heat sinks for electronics chips. Solution is obtained by developing a control volume-based finite difference code and results are validated by comparing results with an analytical solution for a limiting case problem. Results based on a parametric study indicate that the two-dimensional code developed for this study can be used in evaluating PCM, and selecting geometrical dimensions of the PCM encapsulated heat sink

Thermal performance of thermoelectric cooler (tec) integrated heat sink and optimizing structure for low acoustic noise / power consumption

Abstract: In this paper, authors are proposing the idea of applying thermoelectric cooler (TEC) to CPU cooling. The proposed cooling system is a no moving parts apparatus that can improve thermal performance by keeping same form factor. This system will accommodate an increase in the CPU thermal design power and/or lower the noise of the cooling solution. The thermal performance of this proposed device will be presented together with the optimization for low acoustic noise and low TEC power consumption. As a result, we found out that "hybrid structure", which was composed of an integrated combination of TEC integrated heat sink and heat pipe remote heat sink, could reduce acoustic fan noise and required TEC power consumption to cool the CPU. In one particular case, we succeeded to develop a compact cooling device which had a capability of CPU cooling for 130 W at acoustic fan noise less than 40 dB, with COP = 10.8

Boiling at sub-atmospheric conditions with enhanced structures

Abstract: Liquid cooling with phase change is a very attractive option for thermal management of electronics because it achieves very high heat transfer coefficients compared to single phase liquid cooling. Phase change liquid cooling can be implemented in a thermosyphon loop, where heat is transferred from the heated surface to the evaporator and rejected to the ambient from the condenser. Optimized design of the evaporator requires a fundamental understanding of boiling in the evaporator. Past studies with dielectric working fluids have shown the importance of using boiling enhancement structures in lowering incipience overshoot, increasing heat flux and reducing evaporator volume. Water possesses superior thermal properties than dielectric liquids, but there is a lack in the understanding of boiling of water from enhancement structures. Since in silicon devices, a maximum surface temperature of 85/spl deg/C is typically allowed, boiling of water at sub-atmospheric pressures for lowering the saturation temperature and thus aiding in early initiation of nucleate boiling is required. The present study aims to provide a detailed understanding of the effects of boiling enhancement structure and sub-atmospheric pressures on the boiling of water and investigate their effectiveness in electronics cooling applications. The effects of system pressures and enhancement structure geometry on the boiling heat transfer are investigated. Experiments were performed at three different pressures, 9.7, 15 and 21 kPa using a stacked enhancement structure with four different geometries (1, 2, 4 and 6 layers). The results are compared with sub-atmospheric pressure boiling from a plain surface.

Fundamentals of a floating loop concept based on R134a refrigerant cooling of high heat flux electronics

Abstract: The Oak Ridge National Laboratory (ORNL) Power Electronics and Electric Machinery Research Center (PEEMRC) has been developing technologies to address the thermal concerns associated with hybrid electric vehicles (HEVs). This work is part of the ongoing FreedomCAR and Vehicle Technologies program (FCVT), performed for the Department of Energy (DOE). Removal of the heat generated from electrical losses in traction motors and their associated power electronics is essential for the reliable operation of motors and power electronics. As part of a larger thermal management project, which includes shrinking inverter size and direct cooling of electronics, ORNL has developed U.S. Patent No. 6,772,603 B2, Methods and Apparatus for Thermal Management of Vehicle Systems and Components (Hsu, 2004), and patent pending floating loop system for cooling integrated motors and inverters using hot liquid refrigerant (Hsu, 2004). The floating-loop system provides a large coefficient of performance (COP) for hybrid-electric drive component cooling. This loop (based on R-134a) shares a vehicle's existing air-conditioning (AC) condenser, which dissipates waste heat to the ambient air. Because the temperature requirements for cooling of power electronics and electric machines are not as low as that required for passenger compartment air, this adjoining loop can operate on the high-pressure side of the existing AC system. This arrangement also allows for the floating loop to run without the need for the compressor and only needs a small pump to move the liquid refrigerant. For the design to be viable, the loop must not adversely affect the existing system. The loop would also provide a high COP, a flat temperature profile, and a low pressure drop. The floating-loop test prototype has been successfully integrated into a 9 kW automobile passenger AC system. In this configuration, the floating loop has been tested up to 2 kW of heat rejected during operation with and without the automotive AC system running. The floating-loop system has demonstrated a very respectable COP of 40-45, as compared to a typical AC system COP of about 2-4. The estimated required waste-heat load for future HEV cooling applications is 5.5 kW, and the existing system should be easily scalable to this larger load

Cooling structure for EMC shielded high frequency electronics

Abstract: Cooling of electronics is normally achieved using air passing through apertures in the enclosure; as a result the shielding effectiveness of the shielded enclosure is reduced. In this paper, the design of a new cooling structure and its evaluation in a wind tunnel is presented. The developed design presented here is a double heat sink in extruded aluminum. Into one side of the heat sink, the printed circuit boards (PCBs) are inserted and enclosed by a complementary shielding surface. The other side of the heat sink is cooled by forced ventilation. The heat transport between these parts is completely inside the same body, without any heat flow interruptions. Tests carried out on a prototype have shown that the performance of the cooling structure is satisfactory for electronic cooling. An additional electromagnetic compatibility (EMC)-test has also elucidated the satisfactory shielding effectiveness of the structure. The cooling structure is scaleable and can accommodate for both future smaller printed circuit boards (PCBs) and those of today. The entire enclosure is furthermore based on near-standard items, which allows it to be inexpensive in high volume production.

Analysis of transient thermal management characteristics of PCM with an embedded carbon fiber heat sink

Abstract: There has been a strong interest in the use of phase change materials (PCMs) for the transient thermal abatement of small size electronics and several experimental studies have examined various aspects of PCM implementation. However, the adaptation of this technology for larger systems will require a scale-up in both physical size and power density. In larger volumes, the poor thermal conductivity of the PCM itself (around 0.2 W/m/spl middot/K) becomes a considerable limitation. The thermal resistance into a large volume of PCM is significant and the design must be adapted to facilitate greater heat flow into the PCM container. This study experimentally investigates the performance of PCM with an embedded light weight carbon fiber heat sink as an effective thermal management technique for high power transient applications.

A Simple and Intuitive Graphical Approach to the Design of Thermoelectric Cooling Systems

Abstract: In various applications, thermoelectric active cooling systems can help maintain electronic devices at a desired temperature condition better than passive coolers. Thermoelectric Coolers (TEC) are especially useful when the temperature of a device needs to be precisely controlled. This study proposes a user-friendly graphical method for calculating the steady-state operational point of a TEC based active cooling system, including the heatsink role. The method is simple and intuitive and provides comprehensive information about the cooling system such as its feasibility, required heatsink, the TEC current, temperatures of the cold side and others. The method could help designers to examine and choose a thermoelectric module from catalogues to meet a specific cooling problem. To start using the method, designers need only the experimental TEC data provided by practically all manufacturers of such devices. The experimental results of this study verify the high accuracy of the proposed model and graphical approach.

Using refrigeration and heat pipe for electronics cooling applications

Abstract: A cooling system includes a heat pipe and a refrigerator. A combination at least one or more of the heat pipe and the refrigerator is used to cool an electronic component capable of generating heat. Depending on the cooling requirement, a different cooling combination may be used.

Extensive Development of the Loop Heat Pipe Technology

Abstract: The development of LHPs for space applications have shown the possibility of using them in several ground applications, such as water heating systems, electronics cooling, etc. Some issues related to the use of LHPs rely on their design and development depending on the required use. In this case, the most indicated configuration for their reliable operation will depend on the correct selection of working fluid, materials and configuration regarding the maximum heat management requirement. This paper presents what has been developed in this institute regarding the LHP technology, which includes devices for electronics cooling operating at its classical design (one evaporator and condenser), reversible, ramified and miniature LHPs. The results obtained have shown the great potential in using LHPs as passive thermal control devices. Continuous development have shown that the LHPs can promote a reliable control of the heat source temperature within the required designed limits, even when considering the issue of miniaturizing these devices.

2D numerical modeling of the thermal and hydraulic performances of a very thin sintered powder copper flat heat pipe

Abstract: As integrated circuits become faster and more densely packed with transistors, conventional methods of cooling are not able to overcome the heat problem. Recently heat pipes have proven their efficiency for many applications where high heat fluxes suppress the possibility of using conventional cooling systems. The presented work aims to find efficient passive thermal solution for double sided electronic substrate, part of multifunctional 3D electronic module (European project “Microcooling”). Integrating heat pipe into the double sided slices satisfies the heat transfer requirements and minimizes the overall dimensions of the 3D packaging. To improve the design of the device under test and to provide better understanding of the physical phenomena of the fluid flow and heat transfer in the heat pipes, simplified 2D model was created. Further, according to the real prototype and the experimental setup, the simplified model was developed in more detailed formulation. The results are presented in terms of liquid and vapor pressures within the heat pipe and maximal heat power. Experimental validation, which proves that the new model can be used to predict the heat capacity and to improve the design of flat heat pipes for specific applications, is also presented.

Liquid cooling module using FC-72 for electronics cooling

Abstract: A liquid cooling module as a cooling means for electronic devices using boiling and condensation heat transfer was designed and its performance was investigated. The liquid cooling module was comprised of a boiling plate, spacer, and condenser plate and used FC-72 as the working fluid. The size of the module was 101 mm /spl times/ 108 mm /spl times/ 18 mm and the chip size (heat source) used was 10 mm /spl times/ 10 mm. To enhance boiling performance, pin fins combined with the microporous coating technique were used on the boiling plate surface. Heat rejection from the module was achieved using two different methods; a water-cooled cold plate and an air-cooled heat sink/fan assembly. In addition to experimental testing, an empirically based performance prediction method was also developed. Using the water-cooled cold plate and a chip temperature constraint of 100 /spl deg/C, the cooling module was capable of dissipating heat fluxes of 1850 and 2100 kW/m/sup 2/ for cold plate water inlet temperatures of 35 and 20 /spl deg/C, respectively. In addition, the total thermal resistance for the 35 /spl deg/C inlet case was calculated to be 0.355 K/W. Use of the microporous coating on the boiling section improved heat transfer by about 31%. Using the air-cooled heat sink/fan assembly and the same chip temperature constraint of 100 /spl deg/C, the cooling module was capable of dissipating a heat flux of 2200 kW/m/sup 2/ and exhibited a total thermal resistance of 0.349 K/W with an ambient air temperature of 22 /spl deg/C.

Modeling of a 3-Dimensional Conjugate Heat Transfer on the Channel-Composite-Wall for Electronics Cooling

Abstract: We report the modeling of a novel approach to passive heat transfer from electronic equipment through an enclosure wall with built-in vertical channels. This passive cooling method is based on the different temperature requirements between the enclosure surface and the internal heat-generating devices. This approach takes advantage of natural convection, known as the chimney effect, resulting from higher temperatures in vertically oriented channels. In addition to channel convection, the skin surface exposed to the environment dissipates the heat passively by both natural convection and radiation. The configuration of the wall and channels, termed a Channel-Composite-Wall (CCW), creates a novel form of passive cooling that we have analyzed and modeled. The inner side of the CCW is assumed to be uniformly heated. The three-dimensional flow regime is observed by means of PIV (particle image velocimetry) experiments and numerical studies. The unique velocity profile inside each channel is observed and can be regarded as similar to the flow in the differently heated parallel plates. The channel flow is modeled by breaking the channel down into two sections plus the exposed skin wall. Based on these observations, the relationship between the internal flow field and external convective flow can be considered to be handled separately. The thermal characteristic is also studied based on the correlations. The thermal conductivity and thickness of the solid partition of channels are found to be significant contributors to performance. The analytic model of the CCW was verified by numerical calculations and experiments. The model reasonably closely expresses the characteristics of this comprehensive conjugate heat transfer. The model can thus be used for the development of passively cooled electronics enclosure.Copyright © 2006 by ASME

An Assessment of NASA Glenn's Aeroacoustic Experimental and Predictive Capabilities for Installed Cooling Fans

Abstract: Driven by the need for low production costs, electronics cooling fans have evolved differently than the bladed components of gas turbine engines which incorporate multiple technologies to enhance performance and durability while reducing noise emissions. Drawing upon NASA Glenn's experience in the measurement and prediction of gas turbine engine aeroacoustic performance, tests have been conducted to determine if these tools and techniques can be extended for application to the aerodynamics and acoustics of electronics cooling fans. An automated fan plenum installed in NASA Glenn's Acoustical Testing Laboratory was used to map the overall aerodynamic and acoustic performance of a spaceflight qualified 80 mm diameter axial cooling fan. In order to more accurately identify noise sources, diagnose performance limiting aerodynamic deficiencies, and validate noise prediction codes, additional aerodynamic measurements were recorded for two operating points: free delivery and a mild stall condition. Non-uniformities in the fan s inlet and exhaust regions captured by Particle Image Velocimetry measurements, and rotor blade wakes characterized by hot wire anemometry measurements provide some assessment of the fan aerodynamic performance. The data can be used to identify fan installation/design changes which could enlarge the stable operating region for the fan and improve its aerodynamic performance and reduce noise emissions.

Experimental flow visalization and analytic thermal modeling of multi-channel wall for electronics

Abstract: The multi-channel wall has been proposed and demonstrated in our previous work as an effective enhancement of passive way of electronics cooling. The flow characteristics of the simplest structure observed with PIV measurement was already reported in the paper. Since the three-dimensional channel flow contains complexity, such as folk and junction or edge effect, it was essential to investigate the phenomenon with the simplest structure. And it was successfully modeled numerically. In this report, more realistic multi-channel wall is investigated in the experiments, discussed with the analytic model and studied with the numerical calculations. A new apparatus has been developed for this particular characterization. A channeled wall with six channels is prepared for the experiment. This sample is developed to simulate a part of the typical electronics enclosure. A novel PIV setup for visualization is built based on the same technique which was used previously, but is designed to set the precise slice of the airflow profiles in depth of the channels. The three-dimensional velocity profiles in the channel were successfully observed with temperature profile at the same time in this apparatus. Based on the comparison between numerical results and experimental results, characteristic of the multi-channel wall is found slightly different from the Elenbaas' isothermal wall correlation, essentially because of the inter-wall thermal radiation

Performance analysis of a miniature-scale vapor compression system for electronics cooling: bread board setup

Abstract: A Miniature-Scale vapor compression Refrigeration System (MSRS) was developed and experimentally investigated for electronics cooling. The system consists of four main components: a micro-channel cold plate evaporator-heat spreader, a compressor, a micro-channel condenser, and an expansion device. Experimental results obtained with the bread board system demonstrate the feasibility of applying a miniature-scale refrigeration system in cooling compact electronic devices. Moreover, the performance of each component and of the overall system were quantified and used to improve the efficiencies of components and system. The cooling capacity of the investigated system varied from 121 to 268 W, with a COP of 2.8 to 4.7, at pressure ratios of 1.9 to 3.2. The effectiveness of the condenser ranged from 52 to 77%, while a thermal resistance between 0.60 and 0.77 oC-cm /W 2 was achieved at the evaporator. The evaporator-heat spreader thermal resistance is defined as the ratio of the temperature difference between the chip surface and the refrigerant evaporator to the evaporator heat transfer rate. The overall system thermal resistance, defined as the ratio of the temperature difference between the chip surface and the condenser air inlet, varied from 0.04 to 0.18 oC-cm /W. 2 An overall second-law efficiency ranging from 33 and 52% was obtained, using a commercially available small-scale compressor. The measured overall isentropic efficiency was between 25 and 60%.

Cooling Technique for High Flux Electronic

Abstract: Power dissipation of high flux electronics become critical,and high performance cooling techniques are required urgentlySome promising cooling techniques and their practical application were discussed,such as flat plate Heat pipe、micro channel and liquid spray cooling