Showing papers on "Electronics cooling published in 2013"

Recent Advances in Vapor Chamber Transport Characterization for High-Heat-Flux Applications

Abstract: Owing to their high reliability, simplicity of manufacture, passive operation, and effective heat transport, flat heat pipes and vapor chambers are used extensively in the thermal management of electronic devices. The need for concurrent size, weight, and performance improvements in high-performance electronics systems, without resort to active liquid-cooling strategies, demands passive heat-spreading technologies that can dissipate extremely high heat fluxes from small hot spots. In response to these daunting application-driven trends, a number of recent investigations have focused on the design, characterization, and fabrication of ultrathin vapor chambers for proximate heat spreading away from these hot spots. The predominant transport mechanisms and operational limits have been found to be different under these conditions relative to conventional low-power heat pipes. Noteworthy advances in the fundamental understanding of evaporation and boiling from porous microstructures fed by capillary action and improvements in vapor chamber characterization, modeling, design, and fabrication techniques are reviewed. Characterization of evaporation and boiling from idealized and realistic wick structures, observation of vapor formation regimes as a function of operating conditions, assessment of fluid dryout limitations, design of novel multiscale and nanostructured wicks for enhanced transport, and incorporation of these high-heat-flux transport phenomena into device-level models are discussed. These recent developments have successfully extended the maximum operating heat flux limits of vapor chambers.

Enhanced Pool Boiling With Ethanol at Subatmospheric Pressures for Electronics Cooling

Abstract: The growing trend in miniaturization of electronics has generated a need for efficient thermal management of these devices. Boiling has the ability to dissipate a high heat flux while maintaining a small temperature difference. A vapor chamber with pool boiling offers an effective way to provide cooling and to maintain temperature uniformity. The objective of the current work is to investigate pool boiling performance of ethanol on enhanced microchannel surfaces. Ethanol is an attractive working fluid due to its better heat transfer performance and higher heat of vaporization compared to refrigerants, and lower normal boiling point compared to water. The saturation temperature of ethanol can be further reduced to temperatures suitable for electronics cooling by lowering the pressure. Experiments were performed at four different absolute pressures, 101.3 kPa, 66.7 kPa, 33.3 kPa, and 16.7 kPa using different microchannel surface configurations. Heat dissipation in excess of 900 kW/m was obtained while maintaining the wall surface below 85 C at 33 kPa. Flammability, toxicity, and temperature overshoot issues need to be addressed before practical implementation of ethanol-based cooling systems can occur. [DOI: 10.1115/1.4024595]

Advances in Electronics Cooling

Abstract: This article highlights the advantages of on-chip microchannel cooling technology, based on first- and second-law analysis and experimental tests on two types of cooling cycles, the first driven by an oil-free liquid pump and the second by an oil-free vapor compressor. The analysis showed that the drivers of the fluid were the main culprits for major losses. It was further found that when energy recovery is of importance, making use of a vapor compression cycle increases the quality of the recovered energy, hence increasing its value. This was demonstrated by analyzing the synergy that can exist between the waste heat of a data center and heat reuse by a coal-fired power plant. It was found that power-plant efficiencies can be increased by up to 6.5% by making use of a vapor compression cycle, which results not only in significant monetary savings, but also in the reduced overall carbon footprints of both the data center and the power plant.

Linear compressors for electronics cooling: energy recovery and its benefits.

Abstract: A comprehensive model of a linear compressor for electronics cooling was previously presented by Bradshaw et al. (2011) then enhanced and used for a sensitivity analysis of the leakage gap, eccentricity, and piston geometry by Bradshaw et al. (2013). The current work utilizes the previously developed model to explore the energy recovery characteristics of a linear compressor as compared to those of a reciprocating compressor. The impact of dead (clearance) volume on both a linear and reciprocating compressor is analyzed. In contrast to a reciprocating compressor the overall isentropic efficiency of the linear compressor remains relatively unaffected by an increase in dead volume up to a certain point. This behavior is attributed to the ability of the linear compressor to recapture the energy of the compressed gas during the expansion process. This characteristic behavior allows a linear compressor to be used for efficient capacity control from roughly 35–100%.

Sensitivity Analysis of a Comprehensive Model for a Miniature-Scale Linear Compressor for Electronics Cooling

Abstract: A comprehensive model of a linear compressor for electronics cooling was previously presented by Bradshaw et al. (2011). The current study expands upon this work by first developing methods for predicting the resonant frequency of a linear compressor and for controlling its piston stroke. Key parameters governing compressor performance – leakage gap, eccentricity, and piston geometry – are explored using a sensitivity analysis. It is demonstrated that for optimum performance, the leakage gap and frictional parameters should be minimized. In addition, the ratio of piston stroke to diameter should not exceed a value of one to minimize friction and leakage losses, but should be large enough to preclude the need for an oversized motor. An improved linear compressor design is proposed for an electronics cooling application, with a predicted cooling capacity of 200 W a cylindrical compressor package size of diameter 50.3 mm and length 102 mm.

Investigation of Heat Transfer in Evaporator of Microchannel Loop Heat Pipe

Abstract: Loop heat pipes (LHP) are closed loop heat transfer devices which use evaporation and condensation of a working fluid to transfer heat and use capillary forces to provide fluid circulation. One of the main applications of LHP is cooling of electronics components. Further development in this field is associated with miniaturization. Therefore in electronics cooling there are strict limits imposed upon size of elements of heat transfer devices. One of such elements is evaporator of LHP, its main element. This paper deals with LHP evaporator and aims to find ways of reducing its thickness. An open loop experimental setup was created to investigate heat transfer phenomena in evaporator. Experiments were carried out with variety of configurations. Evaporator consists of microchannel plates with groove width 100 and 300 micrometers, wick (metal and non-metal porous materials were used) and compensation chamber (CC). Heat load varied from 20 to 140 W by steps of 20 W. The area of heater was equal to 19 mm x 19 mm. Working fluid ‐ deionised water. Experiments resulted in data on temperature distribution across wick’s height, temperature of microchannel’s surface and temperature of water in compensation chamber. The results reveal potentials to perform optimization of evaporating zone to produce thinner evaporators.

Experimental Investigation of Flow Boiling Performance of Open Microchannels With Uniform and Tapered Manifolds (OMM)

Abstract: Boiling can provide orders of magnitude higher cooling performance than a traditional air cooled system especially related to electronics cooling application. It can dissipate large quantities of heat while maintaining a low surface temperature difference. Flow boiling with microchannels has shown a lot of potential due to its high surface area to volume ratio and latent heat removal. Flow instabilities and early critical heat flux have however prevented its successful implementation. A novel flow boiling design is experimentally investigated to overcome the above mentioned disadvantages while presenting a very low pressure drop. The design uses open microchannels with a tapered manifold (OMM) to provide stable and efficient operation. Distilled, degassed water at atmospheric pressure was used as the fluid medium. Effect of tapered block with varied dimension is investigated. Pressure drop data for uniform and tapered manifold for plain and microchannel chip are presented. A maximum heat flux of 281 W/cm 2

Two-Phase Flow Control of Electronics Cooling With Pseudo-CPUs in Parallel Flow Circuits: Dynamic Modeling and Experimental Evaluation

Abstract: On-chip two-phase cooling of parallel pseudo-CPUs integrated into a liquid pumped cooling cycle is modeled and experimentally verified versus a prototype test loop. The system's dynamic operation is studied since the heat dissipated by microprocessors is continuously changing during their operation and critical heat flux (CHF) conditions in the microevaporator must be avoided by flow control of the pump speed during heat load disturbances. The purpose here is to cool down multiple microprocessors in parallel and their auxiliary electronics (memories, dc/dc converters, etc.) to emulate datacenter servers with multiple CPUs. The dynamic simulation code was benchmarked using the test results obtained in an experimental facility consisting of a liquid pumped cooling cycle assembled in a test loop with two parallel microevaporators, which were evaluated under steady-state and transient conditions of balanced and unbalanced heat fluxes on the two pseudochips. The errors in the model's predictions of mean chip temperature and mixed exit vapor quality at steady state remained within +/- 10%. Transient comparisons showed that the trends and the time constants were satisfactorily respected. A case study considering four microprocessors cooled in parallel flow was then simulated for different levels of heat flux in the microprocessors (40, 30, 20, and 10 W cm(-2)), which showed the robustness of the predictive-corrective solver used. For a desired mixed vapor exit quality of 30%, at an inlet pressure and subcooling of 1600 kPa and 3 K, the resulting distribution of mass flow rate in the microevaporators was, respectively, 2.6, 2.9, 4.2, and 6.4 kg h(-1) (mass fluxes of 47, 53, 76 and 116 kg m(-2) s(-1)) and yielded approximately uniform chip temperatures (maximum variation of 2.6, 2, 1.7, and 0.7 K). The vapor quality and maximum chip temperature remained below the critical limits during both transient and steady-state regimes.

Electronics cooling using lubricant return for a shell-and-tube style evaporator

Abstract: A refrigeration system that induces lubricant-liquid refrigerant mixture flow from a flooded or falling film evaporator by means of the lubricant-liquid refrigerant mixture flow adsorbing heat from an electronic component.

Modeling and control of single and multiple evaporator vapor compression cycles for electronics cooling

Abstract: This paper presents a dynamic model and feedback control strategies for vapor compression cycles (VCC) in electronics cooling applications. A notable difference between traditional VCC and VCC for electronics cooling is that two-phase flow is required at the evaporator outlet in order to avoid burnout. Therefore, the control objective is to avoid critical heat flux during transient heating conditions. An emphasis is placed on the heated accumulator, which is a necessary component to guarantee superheated flow in the compressor suction-line. Addition of heat in the accumulator provides control actuation that may be used to avoid the critical heat flux via the effect on system pressure. In contrast to previous work, we present more detailed evaporator and accumulator models, implement the heated accumulator as a control actuator, and consider both single and multiple evaporator systems. For single evaporator VCC, we use frequency-domain techniques to design a dual-input, proportional-integral controller using accumulator heat and compressor speed. Both simulation and experiment show this design to be superior to strategies that do not actuate accumulator heat. We then use similar design strategies to develop a controller for the much more challenging two-evaporator VCC.

Investigation of a multiple-vibrating fan system for electronics cooling

Abstract: The previous study presented a novel multiple-vibrating fan cooling system actuated by both the piezoelectric (PZT) effect and magnetic force. The thermal performance of the system was demonstrated by checking the temperature drop of the thermocouples adhered to the fin surface. In this study, the convection heat transfer coefficient of an internal multiple-vibrating fan cooling system was calculated by simulation model to verify the accuracy of the theoretical model. Furthermore, the applications of multiple-vibrating fan cooling systems were demonstrated by an external multiple-vibrating fan cooling system, and a T-shape multiple-vibrating fan cooling system. The experimental result showed that the external multiple-vibrating fan cooling system consuming 0.086W, and was able to decrease the core temperature of dummy heater B dissipating 25W from 110.1°C to 80.5°C while the ambient temperature was 27.4°C. The T-shape multiple-vibrating fan cooling system consuming 0.15W, was able to decrease the core temperature of dummy heater B dissipating 25W from 86.9°C to 55.6°C while the ambient temperature was 27.4°C.

STAR CCM+ CFD Simulations of Enhanced Heat Transfer in High-Power Density Electronics Using Forced Air Heat Exchanger and Pumped Fluid Loop Cold Plate Fabricated from High Thermal Conductivity Materials

Abstract: As telecommunication and RF power electronics applications continue to push the envelope of waste heat dissipation, more and more, we see a need for active thermal control employing forced air electronic cooling fans in unison with pumped fluid loops in order to meet temperature and performance requirements. This research paper presents results of applying Computational Fluid Dynamics (CFD) commercial industry STAR-CCM+ software for heat transfer and fluid flow simulation of a novel heat exchanger/cold plate fabricated from k-core high thermal conductivity material in order to realize thermal control system hardware design for very much applications to very large power density (~1 kW/m2) electronics packaging scenarios. Trade studies involving different heat exchanger/cold plate materials, as well as vari- ous fault scenarios within a mock-up of a typical electronics system, are used to illustrate the upper bounds placed on the convective heat transfer coefficient. Agreement between our present findings and previous research in the field of electronics cooling is presented herein.

Population-based optimization for heat sink design in electronics cooling applications

Abstract: Smooth and scale-roughened plate-fin heat sinks for electronic device cooling are considered. Developments in modeling momentum and heat transport in heterogeneous and hierarchical devices with full conjugate effects included provide the ability to rapidly obtain nonlocal descriptions of the flow and temperature fields in such devices. Such modeling, based on Volume Averaging Theory (VAT), directly incorporates the device morphology into the governing field equations, allowing geometric optimization to be based on theoretically correct governing equations that are quickly solved and rigorously derived from the fundamental Navier-Stokes and solid and fluid thermal energy equations. A number of optimization methods for heat sink designers who model heat sinks with VAT can be envisioned due to VAT's singular ability to rapidly - compared to Direct Numerical Simulations (DNS) - provide detailed solutions. Design of Experiment (DOE) has been used in the past, and more recently Genetic Algorithms (GAs) and Particle Swarm Optimizers (PSOs) have appeared attractive for multi-parameter thermal-fluid device optimization. In this study, optimization employing a GA and a PSO on two types of heat sinks modeled with VAT is carried out and the capabilities of the two optimization methods are discussed. It is found that the GA and PSO methods are both effective in locating the heat sinks' optimum configurations and that the computational time they take to do so is on the order of just several minutes when using a typical laptop computer. This study demonstrates the usefulness of population-based optimization methods in optimizing transport phenomena in heterogeneous and hierarchical heat transfer devices when VAT-based mo deling is emplo yed.

Uniform Flow Control for a Multipassage Microfluidic Sensor

Abstract: Microfluidic sensors have been very effective for rapid, portable bioanalysis, such as in determining the pH of a sample. By simultaneously detecting multiple chemicals, the overall measurement performance can be greatly improved. One such method involves a series of parallel microchannels, each of which measures one individual agent. For unbiased readings, the flow rate in each channel should be approximately the same. In addition, the system needs a compact volume which reduces both the wasted channel space and the overall device cost. To achieve these conditions, a manifold was designed using a tapered power law, based on a concept derived for electronics cooling systems. This manifold features a single feed passage of varying diameter, eliminating the excess volume from multiple branch steps. The design was simulated using computational fluid dynamics (CFD), which demonstrated uniform flow performance within 2.5% standard deviation. The design was further examined with microparticle image velocimetry (PIV), and the experimental flow rates were also uniform with approximately 10% standard deviation. Hence, the tapered power law can provide a uniform flow distribution in a compact package, as is needed in both this microfluidic sensor and in electronics cooling applications.

Experimental study of a bellows‐type reciprocating‐mechanism driven heat loop

Abstract: SUMMARY The reciprocating-mechanism driven heat loop (RMDHL) is a novel two-phase heat transfer device that could find many important applications in energy systems and electronic cooling. However, the previous RMDHL is based on a solenoid driver that may have difficulty in handling a large amount of heat transfer rate over a long distance due to the driver's inability to provide a large displacement volume. To overcome this difficulty, a bellows-type RMDHL demonstration model has been designed, fabricated, and tested. The results show that the bellows-type RMDHL has successfully overcome the weakness of the solenoid driver and may be employed for applications involving large heat transfer rates and over a large surface area. Another advantage of the bellows-type RMDHL is its potential to maintain an exceedingly uniform temperature over a relatively large surface. Additionally, the power consumption of the bellows driver was less than 5 W when the power input to the cold plate was up to 600 W, resulting in the ratio of driver's power input to the heat input to the cold plate being less than 1%, which represents a tenfold improvement over the solenoid-based RMDHL. All these technical improvements over the previous RMDHL have demonstrated significant progresses towards a refined RMDHL system for energy and electronics cooling applications. Copyright © 2012 John Wiley & Sons, Ltd.

Enhanced electronics cooling for electric machines

Abstract: An electric machine including a rotor and a stator operably coupled with the rotor, electronic components, and a drive shaft disposed along a central axis of the machine. A bearing support supportively surrounds the drive shaft, and a frame end is connected to the stator and has a backface portion to which the electronic components are mounted. The backface portion defines a frame airflow space through which cooling air can flow. The backface portion is sloped relative to the central axis and defines a frame air inlet through which cooling air is received into the frame airflow space, and the frame air inlet is located between the bearing support and the backface portion.

Next-Generation Evaporative Cooling Systems for the Advanced Extravehicular Mobility Unit Portable Life Support System

Abstract: The development of the Advanced Extravehicular Mobility Unit (AEMU) Portable Life Support System (PLSS) is currently underway at NASA Johnson Space Center. The AEMU PLSS features two new evaporative cooling systems, the Reduced Volume Prototype Spacesuit Water Membrane Evaporator (RVP SWME), and the Auxiliary Cooling Loop (ACL). The RVP SWME is the third generation of hollow fiber SWME hardware, and like its predecessors, RVP SWME provides nominal crewmember and electronics cooling by flowing water through porous hollow fibers. Water vapor escapes through the hollow fiber pores, thereby cooling the liquid water that remains inside of the fibers. This cooled water is then recirculated to remove heat from the crewmember and PLSS electronics. Major design improvements, including a 36% reduction in volume, reduced weight, and more flight like back-pressure valve, facilitate the packaging of RVP SWME in the AEMU PLSS envelope. In addition to the RVP SWME, the Auxiliary Cooling Loop (ACL), was developed for contingency crewmember cooling. The ACL is a completely redundant, independent cooling system that consists of a small evaporative cooler--the Mini Membrane Evaporator (Mini-ME), independent pump, independent feed-water assembly and independent Liquid Cooling Garment (LCG). The Mini-ME utilizes the same hollow fiber technology featured in the RVP SWME, but is only 25% of the size of RVP SWME, providing only the necessary crewmember cooling in a contingency situation. The ACL provides a number of benefits when compared with the current EMU PLSS contingency cooling technology; contingency crewmember cooling can be provided for a longer period of time, more contingency situations can be accounted for, no reliance on a Secondary Oxygen Vessel (SOV) for contingency cooling--thereby allowing a SOV reduction in size and pressure, and the ACL can be recharged-allowing the AEMU PLSS to be reused, even after a contingency event. The development of these evaporative cooling systems will contribute to a more robust and comprehensive AEMU PLSS.

Reduced Volume Prototype Spacesuit Water Membrane Evaporator; A Next-Generation Evaporative Cooling System for the Advanced Extravehicular Mobility Unit Portable Life Support System

Abstract: Development of the Advanced Extravehicular Mobility Unit (AEMU) portable life support subsystem (PLSS) is currently under way at NASA Johnson Space Center. The AEMU PLSS features a new evaporative cooling system, the reduced volume prototype (RVP) spacesuit water membrane evaporator (SWME). The RVP SWME is the third generation of hollow fiber SWME hardware. Like its predecessors, RVP SWME provides nominal crew member and electronics cooling by flowing water through porous hollow fibers. Water vapor escapes through the hollow fiber pores, thereby cooling the liquid water that remains inside of the fibers. This cooled water is then recirculated to remove heat from the crew member and PLSS electronics. Major design improvements, including a 36% reduction in volume, reduced weight, and a more flight-like backpressure valve, facilitate the packaging of RVP SWME in the AEMU PLSS envelope. The development of these evaporative cooling systems will contribute to a more robust and comprehensive AEMU PLSS.

Cooling structure for thin-profile electronics, and electronic device employing same

Abstract: When it is attempted to obtain satisfactory cooling performance in a thin-profile electronics cooling structure while the structure is installed in an electronic device, the power consumption of the electronic device increases. Accordingly, this cooling structure for thin-profile electronics has: a thin-profile flat plate receptacle provided with an opening; a substrate housed in the thin-profile flat plate receptacle and having a heating element mounted thereon; an evaporator thermally connected to the heating element, and storing a cooling medium; a condenser for condensing to liquid the vapor-phase cooling medium vaporized by the evaporator, radiating heat; and a pipeline connecting the evaporator and the condenser. The condenser is at least partially disposed to the outside of the thin-profile flat plate receptacle through the opening. The condenser is provided with a condenser plate section extending in the vertical direction on an inside surface of a condenser substrate of the condenser receptacle constituting the condenser, and the condenser substrate is thermally connected to a radiator.