Showing papers on "Electronics cooling published in 2014"

Electrohydrodynamic Microfabricated Ionic Wind Pumps for Thermal Management Applications

Abstract: This work demonstrates an innovative microfabricated air-cooling technology that employs an electrohydrodynamic (EHD) corona discharge (i.e., ionic wind pump) for electronics cooling applications. A single, micro fabricated ionic wind pump element consists of two parallel collecting electrodes between which a single emitting tip is positioned. A grid structure on the collector electrodes can enhance the overall heat-transfer coefficient and facilitate an IC compatible batch process. The optimized devices studied exhibit an overall device area of 5.4 mm × 3.6 mm, an emitter-to-collector gap of ~0.5 mm, and an emitter curvature radius of ~12.5 μm. The manufacturing process developed for the device uses glass wafers, a single mask-based photolithography process, and a low-cost copper-based electroplating process. Various design configurations were explored and modeled computationally to investigate their influence on the cooling phenomenon. The single devices provide a high heat-transfer coefficient of up to ~3200 W/m 2 K and a coefficient of performance (COP) of up to ~47. The COP was obtained by dividing the heat removal enhancement, ΔQ by the power consumed by the ionic wind pump device. A maximum applied voltage of 1.9 kV, which is equivalent to approximately 38 mW of power input, is required for operation, which is significantly lower than the power required for the previously reported devices. Furthermore, the microfabricated single device exhibits a flexible and small form factor, no noise generation, high efficiency, large heat removal over a small dimension and at low power, and high reliability (no moving parts); these are characteristics required by the semiconductor industry for next generation thermal management solutions.

Nanofluids for electronics cooling

Abstract: The goal of this study is to investigate experimentally the thermal performance of an electronics cooling system which is available in the market Selected system is a water block used for liquid cooling of a central processing unit (CPU) of a computer A suitable heater (resistance wire) is fabricated for producing heat similar to CPU System is instrumented with K-type thermocouples for the temperature measurement of certain points The experiments were carried out first with water and then with water-based Alumina nanofluid Nanofluid sample was supplied from NanoAmor Inc, with particle concentration of 633 volumetric percent and diluted to 1 volumetric percent with water, by using a probe type ultrasound for 2 minutes at 70 W During the experiments 60 W power applied to the CPU and the ambient temperature was 19 degree Celcius Our results show that nanofluids, with low volume concentration (1 percent vol) of Alumina particles decreases the maximum temperature of the system, almost 27 degree Celcius, compared to water

Inverse opals for fluid delivery in electronics cooling systems

Abstract: We report the fabrication and fluid flow characterization of a class of open-cell copper foams known as copper inverse opals (CIOs). This material has finely controlled structure at the pore level, which may enable its use in microscale heat exchangers for microelectronics cooling. We fabricated CIOs by electrodepositing copper around a sacrificial template of packed polystyrene microspheres. We then removed the CIOs from their substrates and used electroetching to vary the pore structure and porosity. We characterized the geometry of the samples at various stages of fabrication with visual inspection and image analysis of scanning electron micrographs. We characterized the permeability with a through-plane flow rig and developed computational models for fluid flow in ideal face-centered cubic and hexagonally close-packed unit cells. Here we report the simulated and experimentally measured values of permeability. We also report experimental challenges that arise from the microscale dimensions of the samples.

Performance Characterization of Laminar Flow in Multiple Microjet Impingement Heat Sinks

Abstract: The present study investigates the thermal performance of a silicon-based multiple microjet impingement heat sink for the thermal management of electronics. A three-dimensional numerical analysis was performed on the steady incompressible laminar flow and the conjugate heat transfer in multiple microjet impingement heat sinks. One side of the silicon substrate receives a moderate heat flux of 100 W/cm2; the other side contains the designed jet impingement system. The jet plate consists of many jet holes, so the computational domain was simplified by using symmetric boundary conditions. The effects of the design parameters such as the jet diameter, jet pitch, and standoff (that is, the distance of the nozzle exit to the heated surface) were analyzed under laminar flow conditions. Because of the low pumping power available in the micropumping system, the analysis was carried out at a low Reynolds number. The crossflow effects of the spent flow and the inline jet sweeping were investigated to determine the ...

Effect of Inclination Angle on Pulsating Heat Pipe Performance

Abstract: Micro-electronic devices are creating ever-increasing demands on their thermal management systems due to their decreasing size and increasing power. Pulsating heat pipes (PHPs) are one possible solution for electronics cooling applications. A PHP is a passive, two-phase heat transfer system which has been shown to have the advantages of the ability to accommodate very high heat fluxes and of relatively low cost, due to its wickless construction. In this investigation, a 20-turn PHP was constructed out of 1.6-mm inner diameter copper tubing. The PHP was operated in vertical and horizontal positions with a filling ratio of 77%. PHP pressure variations, indicating PHP operation, were first observed when the power was increased to 16 W for the vertical orientation (90°). For angles orientations, in general more power was required to induce pulsation. For the 60°, 45°, and 30° orientations, the required startup power was similar to that for the vertical case. In the PHP in the horizontal orientation (0°), pulsation did not begin until a heater input of 30 W was applied, and the thermal resistance only decreased slightly upon startup. Under steady-state operation at the highest heat fluxes, the thermal resistance was lowest for the vertical orientation.Copyright © 2014 by ASME

Optimum distance between vortex generators used in modern thermal systems

Abstract: Modern thermal systems in which hydrodynamics and thermal fields are strongly related to each other involve compactness and effective heating/cooling performance. Triangular ducts, having delta-wing type vortex generators (VGs) mounted on the duct’s slant surfaces, are widely used in modern thermal systems including gas turbines and electronics cooling applications. Due to the existence of completely opposite results obtained in terms of performance of the two types of VG configurations –namely “flow up” and “flow down”-, in the open literature, in the present study, both hydrodynamics and thermal fields together with the secondary flows induced by the VGs have been analysed extensively to understand which configuration has the better thermo-hydraulic performance. The results show that one configuration has a 19% higher thermo-hydraulic performance over 32 different VG configurations -containing “flow-up” and “flow-down”- for hydraulic diameter based Reynolds number, Re=5000. The angle of inclination of each VG made with the flow direction is set to 30° and the inclined surface’s wall temperatures are set to 80°C. Based on the current results, the optimum distance between successive VGs has been determined as 0.385 of the hydraulic diameter. The present CFD results have been validated against the PIV data

Influence of micro-scale aspects and jet-to-jet interaction on free-surface liquid jet impingement for micro-jet array cooling

Abstract: Arrays of impinging jets can cool large areas with good thermal uniformity and are often used in industrial processes, such as drying and electronics cooling. However, due to cross-flow of the spent liquid and interference between adjacent jets, a significant amount of the available cooling performance is lost. Under free-surface jet impingement the area beyond the hydraulic jump is associated with significantly reduced heat transfer, and locally increased temperatures, therefore the hydrodynamics in this area must be better understood. Specifically, the interaction of jets in the vicinity of this location is expected to shed light on improving multi-jet array cooling uniformity and performance. Beyond this, it has been shown that micro-scale (sub-millimeter) jets tend to behave somewhat differently from larger jets, due to the increased significance of surface tension, pumping noise and edge-effects (such as small recirculation zones, and jet widening due to contact-angle at the nozzle exit, noise and nozzle imperfections due to manufacturing). These become much more dominant at the micro-scale. These effects cannot usually be accounted for by traditional scaling laws or numerical simulations, and are preferably investigated experimentally. Moreover, at these scales a micro-machined fixed-geometry array of jets is typically used, leaving no possibility for geometric variation, optimization and limited observation.

Basic study on flow and heat transfer performance of pulsating air flow for application to electronics cooling

Abstract: Our study tries to apply a pulsating airflow to one of a heat transfer enhancement method in electronic equipment. In recent electronic equipment, a lot of electrical components are mounted while their performance increases and a level of heat dissipation becomes higher. The components cause flow separation of the cooling air and heat transfer performance rear the components generally decreases. Therefore the mounting position of the heating components is restricted in order to avoid the separated flow region. In order to improve the heat transfer rear the components, we are now focusing on the flow pulsation. By generating the flow pulsation of the airflow, the development of the separated flow region rear the components may be inhibited and the heat transfer performance rear the components may be improved. In addition, the flow pulsation can be generated by controlling the input power of the cooling fan easily. From these backgrounds, we tried to investigate flow and heat transfer characteristics of the pulsation flow around the components. In this report, we developed the experimental system in order to evaluate flow and heat transfer performance of the pulsation flow around the electrical components experimentally. By using the experimental system, we tried to evaluate the cooling performance of the pulsation flow around cylindrical blocks, which simulates electrical components. Through the experiment, we evaluated the effectiveness of the pulsation flow as the cooling method of electronic equipment.

Nonlocal Modeling and Swarm-Based Design of Heat Sinks

Abstract: Cooling electronic chips to satisfy the ever-increasing heat transfer demands of the electronics industry is a perpetual challenge. One approach to addressing this is through improving the heat rejection ability of air-cooled heat sinks, and nonlocal thermal-fluid-solid modeling based on volume averaging theory (VAT) has allowed for significant strides in this effort. 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 provide solutions, when compared to computational fluid dynamics (CFD) approaches. The particle swarm optimization (PSO) method appears to be an attractive multiparameter heat transfer device optimization tool; however, it has received very little attention in this field compared to its older population-based optimizer cousin, the genetic algorithm (GA). The PSO method is employed here to optimize smooth and scale-roughened straight-fin heat sinks modeled with VAT by minimizing heat sink thermal resistance for a specified pumping power. A new numerical design tool incorporates the PSO method with a VAT-based heat sink solver. Optimal designs are obtained with this new tool for both types of heat sinks, the performances of the heat sink types are compared, the performance of the PSO method is discussed with reference to the GA method, and it is observed that this new method yields optimal designs much quicker than traditional approaches. This study demonstrates, for the first time, the effectiveness of combining a VAT-based nonlocal thermal-fluid-solid model with population-based optimization methods, such as PSO, to design heat sinks for electronics cooling applications. The VAT-based nonlocal modeling method provides heat sink design capabilities, in terms of solution speed and model rigor, that existing modeling methods do not match. © 2014 by ASME.

Heat Transfer XIII: Simulation and Experiments in Heat and Mass Transfer

Abstract: "Heat Transfer XIII: Simulation and Experiments in Heat and Mass Transfer" contains the proceedings of the thirteenth conference in the well established series on Simulation and Experiments in Heat Transfer and its applications. Advances in computational methods for solving and understanding heat transfer problems continue to be important because heat transfer topics and related phenomena are commonly of a complex nature and different mechanisms like heat conduction, convection, turbulence, thermal radiation and phase change as well as chemical reactions may occur simultaneously. Typically, applications are found in heat exchangers, gas turbine cooling, turbulent combustion and fires, fuel cells, batteries, micro- and mini- channels, electronics cooling, melting and solidification, chemical processing etc. Heat Transfer might be regarded as an established and mature scientific discipline, but it has played a major role in new emerging areas such as sustainable development and reduction of greenhouse gases as well as for micro- and nano- scale structures and bioengineering. Non-linear phenomena other than momentum transfer may occur due to temperature-dependent thermophysical properties. In engineering design and development, reliable and accurate computational methods are requested to replace or complement expensive and time consuming experimental trial an error work. Tremendous advancements have been achieved during recent years due to improved numerical solution methods for non-linear partial differential equations, turbulence modelling advancements and developments of computers and computing algorithms to achieve efficient and rapid simulations. Nevertheless, to further progress in computational methods requires developments in theoretical and predictive procedures - both basic and innovative - and in applied research. Accurate experimental investigations are needed to validate the numerical calculations. Topics covered include: Heat transfer in energy producing devices; Heat transfer enhancements; Heat exchangers; Natural and forced convection and radiation; Multiphase flow heat transfer; Modelling and experiments; Heat recovery; Heat and mass transfer problems; Environmental heat transfer; Experimental and measuring technologies; Thermal convert studies.

Synthetic Jet Flow and Heat Transfer for Electronics Cooling

Abstract: University of Minnesota Ph.D. dissertation. May 2014. Major: Mechanical Engineering. Advisors: Terrence W. Simon, Tianhong Cui. 1 computer file (PDF); xiv, 194 pages.

Experimental measurement and modelling of heattransfer in spiral and curved channels

Abstract: Heat transfer enhancement is desired in most thermal applications. In general, there are two methods to improve the heat transfer rate: active and passive techniques Active techniques are based on external forces such as electro-osmosis, magnetic stirring, etc. to perform the augmentation. Active techniques are effective; however, they are not always easy to implement with other components in a system. They also increase the total cost of the system manufacturing. On the other hand, passive techniques employ fluid additives or special surface geometry. Using the surface geometry approach is easier, cheaper and does not interfere with other components in the system. Surface modification or additional devices incorporated in the stream are two passive augmentation techniques. With these techniques, the existing boundary layer is disturbed and the heat transfer performance is improved. However, pressure drop is also increased. Curved geometry is one of the passive heat transfer enhancement methods that fit several heat transfer applications such as: compact heat exchangers, steam boilers, gas turbine blades, electronics cooling, refrigeration and etc. This dissertation contains eight chapters.. Chapter one is the introduction and shows the originality, novelty and importance of the work. Chapter two reviews the literatures on the heat transfer and the pressure drop correlations in curved circular tubes. In chapters three and four, two heat sinks having spiral and straight channel geometry engraved on them are examined experimentally. Heat transfer and pressure drop inside them are measured, and reduced to apply two existing correlations to predict their behaviour analytically. In chapters five, six and seven, thermal and flow behaviour inside curved geometry are studied experimentally. The calculated heat transfer coefficient and pressure drop are compared to the existing models. Comparing the predicted Nusselt number from the existing models, poor accuracy was observed in the region of 5 < Pr < 15. Finally, in chapters six and seven two new asymptotic correlations are proposed to calculate the heat transfer and the pressure drop inside mini scale curved and coiled tubes.

Electronics Cooling System and Component Design According to the Second Law

Abstract: This work focuses on a comparison of second law based component design on one hand and second law based system design on the other within the context of electronics cooling. Typical electronics cooling components such as a heat sink and a heat exchanger are modeled and designed towards minimum entropy generation on individual level and on system level. A comparison of these levels allows us to qualify and quantify the influences among components induced by a system. Simultaneously, this article endeavors to be an illustrated assessment of the usefulness of efficiency criteria on component level. It turns out that the results of this work reveal a substantial influence of system dependencies on the optimal component design. As such a note of caution is raised about second law based component design which does not take into account the system in which a component has to operate.

Experimental Characterization of an Open Loop Pulsating Heat Pipe Cooler

Abstract: Pulsating heat pipes (PHP) have emerged in the last years as suitable cooling devices for dissipating the high heat loads generated by electronic devices since they allow to extend the applicability of air cooling in area nowadays covered by water cooling. Two-phase cooling technologies based on the two phase pulsating heat pipe principle are promising solutions because, being entirely passive they can comply with long term operation without maintenance. The main advantage of a PHP compared to conventional thermosyphon technologies for electronics cooling is that a PHP is orientation independent. The authors has developed a novel, compact, and low cost PHP based on automotive technology. The present paper presents the experimental results of an air cooled open loop pulsating heat pipe with optimized manifold design to minimize fluid pressure drops in the fluid turns. The effect of several parameters including filling ratio and heat load are presented. Tests have been done with the refrigerant fluid R245fa in vertical and horizontal orientations. The measurements showed a maximum thermal resistance ranging between 40 and 48 K/kW in vertical and horizontal position respectively for a heat load of 2 kW and air temperature of 20 °C.Copyright © 2014 by ASME

Thermal Ground Plane for Chip-Level Electronics Cooling

Abstract: The three-dimensional thermal ground plane was developed in response to the needs of high-power density electronics applications in which heat must be removed as close to the chip surface as possible. The novel design for this planar cooling device was proposed with three key innovations in the evaporator, wick, and reservoir layer, which provided enhanced and reliable cooling performance without wick dryout and back flows. For the evaporator and reservoir layer, a combination of a tapered channel and a triple-spike microstructure was designed to break up the pinned meniscus at the end of the vapor and liquid channels. The overall microstructure had three spikes where the main liquid meniscus was separated by a middle spike and then continued to flow between the tapered walls of the middle and side spikes. For the wick layer, a nanowire-integrated microporous silicon membrane was developed to overcome dryout by driving the coolant out of the channels and spreading the coolant on top of the wick surface with the assistance of extended capillary action. This innovative design used nanowires to extend and enhance capillary force, especially at the end of the pores where the coolant was pinned and unable to overflow out of the pores. The chronic dryout problem in micro cooling devices could be solved by these innovative designs. To analyze the thermal-fluid system, fluid dynamic and phase-change models were used to calculate thermodynamic and fluidic properties, such as operating temperature, pressure, vapor-liquid interface radius of curvature, and rate of bubble formation. The microscale heat conduction theory derived from traditional Fourier's law with classical size effect and effective medium theory were used to calculate the thermal conductivities of nanowires and porous silicon wick in the cross-plane direction, respectively. The theoretical results of porous silicon showed good agreement with the experimental results measured by the 3u technique, demonstrating the reduction of thermal conductivity from bulk silicon. Cooling performance of the developed device was demonstrated experimentally with a micro ceramic heater, thermocouple modules, and microfabrication techniques, including photoelectrochemical etching to create porous silicon, deep reactive-ion etching to form a thin wick membrane, and hydrothermal synthesis to grow nanowires on top of the wick membrane. This study shows the feasibility of reliable, continuous, and high-performance micro cooling devices using enhanced capillary forces to address the increasing requirements of thermal management for chip-level electronics.

A Comparative Study of Subcooled Flow Boiling in Uniform, Diverging Cross-Section and Segmented Finned Microchannels

Abstract: In this work an experimental investigation has been performed to assess the heat transfer characteristics during subcooled flow boiling in diverging and segmented finned microchannels relevant to applications in electronics cooling systems. Experiments have been also performed in uniform cross-section microchannels to compare their performances with other two types of channels configurations. Arrays of microchannel consisting of 12 numbers of channels with rectangular cross-section have been fabricated on individual copper block for these three different geometrical configurations. Deionized water has been used as the working fluid in the experiment. Experiments have been performed mostly in subcooled boiling regions relevant to cooling of electronic components where bulk fluid was below the saturation temperature and the surface temperature was around the saturation temperature of the coolant. The heat transfer characteristics of all three configurations have been compared in terms of heat transfer coefficient and thermal instability during highly subcooled and developed subcooled flow boiling. Although diverging channel performs significantly better in saturated and superheated regions of boiling with high heat flux as observed in literature, in present work its performance has been found slightly better in subcooled boiling regions compared to uniform cross-section channel. Segmented finned channels have shown the best performance both in sensible heating and subcooled region and thus demonstrate high potential for electronics cooling applications.Copyright © 2014 by ASME

Optimal microscale water cooled heat sinks for targeted alleviation of hotspot in microprocessors

Abstract: Hotspots in microprocessors arise due to non-uniform utilization of the underlying integrated circuits during chip operation. Conventional liquid cooling using microchannels leads to undercooling of the hotspot areas and overcooling of the background area of the chip resulting in excessive temperature gradients across the chip. These in turn adversely affect the chip performance and reliability. This problem becomes even more acute in multi-core processors where most of the processing power is concentrated in specific regions of the chip called as cores. We present a 1-dimensional model for quick design of a microchannel heat sink for targeted, single-phase liquid cooling of hotspots in microprocessors. The method utilizes simplifying assumptions and analytical equations to arrive at the first estimate of a microchannel heat sink design that distributes the cooling capacity of the heat sink by adapting the coolant flow and microchannel size distributions to the microprocessor power map. This distributed cooling in turn minimizes the chip temperature gradient. The method is formulated to generate a heat sink design for an arbitrary chip power map and hence can be readily utilized for different chip architectures. It involves optimization of microchannel widths for various zones of the chip power map under the operational constraints of maximum pressure drop limit for the heat sink. Additionally, it ensures that the coolant flows uninterrupted through its entire travel length consisting of microchannels of varying widths. The resulting first design estimate significantly reduces the computational effort involved in any subsequent CFD analysis required to fine tune the design for more complex flow situations arising, for example, in manifold microchannel heat sinks.

CPU Cooling by Vapor Chamber with R-141b as Working Fluid

Abstract: Air cooling and the space limitations are encountered problems of the thermal cooling electronic development for electronics devices or computer. In the present study, results of the experimental investigation on the thermal cooling of vapor chamber with refrigerant R-141b as working fluid for cooling computer processing unit of the personal computer are presented. Parametric studies including different aspect ratios, fill ratios, and operating conditions of PC on the thermal cooling are considered. Average CPU temperatures obtained from the vapor chamber cooling system with R-141b are 19.55%, 18.61% lower than those from the conventional cooling system for no load and 90% operating loads, respectively. In additional, this cooling system requires 50% lower energy consumption for no load operating loads.

Contemporary Perspectives on Liquid Cold Plate Design: Design and Manufacturing Liquid Cooled Heat Sinks for Electronics Cooling

Abstract: The field of electronics cooling has routinely encountered the high heat flux removal that cannot be handled by air cooling systems. The design and application of liquid cooled cold plates is an important aspect of being able to provide cooling for these high heat flux technologies. The intent of this book is to provide the reader with the approach to designing and implementing liquid cold plates. The book will describe the methods to designing liquid cold plates. The fundamental theory behind the heat transfer and fluid mechanics occurring in the cold plates is presented. A state of art review of cold plate developments and industrial practices is included to familiarize the reader with the possible alternatives. One of the highlights of the book is the inclusion of a detailed insight into manufacturing techniques for producing conventional and custom-made liquid cold plates. Some of the common issues and complexities related to manufacturing these cold plates are also presented as case studies. Finally, a few examples of utilizing liquid cold plates are provided. The book is written by a team of three recognized leaders in the field of electronics cooling technology. Cliff Hayner compiled his lifetime industrial experience on designing and manufacturing the cold plates before his sad demise during the production of the book. He provided the manufacturing insight that is rarely discussed in cold plate design literature. Mark Steinke is an accomplished researcher working at IBM, Research Triangle Park, NC. Satish Kandlikar, a professor at Rochester Institute of Technology, has been engaged in advanced cooling system research for over thirty years. The book presents a unique combination of the three complimentary viewpoints in guiding the reader through the entire design and manufacturing process. The book is also intended to serve as a textbook for graduate level courses and special workshops for cold plate design. 138 pages, © 2014

Microchannel Radiator: an Investigation of Microchannel Technology with Applications in Automotive Radiator Heat Exchangers

Abstract: Microchannels have been used in electronics cooling and in air conditioning applications as condensers. Little study has been made in the application of microchannels in automotive heat exchangers, particularly the radiator. The presented research captures the need for the design improvement of radiator heat exchangers in heavy-duty vehicles in order to reduce aerodynamic drag and improve fuel economy. A method for analyzing an existing radiator is set forth including the needed parameters for effective comparisons of alternative designs. An investigation of microchannels was presented and it was determined that microchannels can improve the overall heat transfer of a radiator but this alone will not decrease the dimensions of the radiator. Investigations into improving the air-side heat transfer were considered and an improved fin design was found which allows a reduction in frontal area while maintaining heat transfer. The overall heat transfer of the design was improved from the original design by 7% well as 52% decrease in frontal area but at the cost of 300% increase in auxiliary power. The energy saved by a reduction in frontal area is not substantial enough to justify the increase of auxiliary power. The findings were verified through a computational fluid dynamic model to demonstrate the heat transfer and pressure drop of microchannel tubes. The results confirmed that heat transfer of microchannels does improve the thermal performance of the radiator but the pressure drop is such that the net benefit does not outweigh the operating cost. An additional CFD study of the new fin geometry and air-side heat transfer predictions was conducted. The results of the study confirmed the theoretical calculations for the fin geometry.

Optimization of Horizontal Plate Fin Heat Sink in Natural Convection for Electronics Cooling by Simulated Annealing Algorithm

Abstract: In this study, the simulated annealing (SA) algorithm was adopted to optimize the geometry of horizontal plate fin heat sink by the extreme entransy dissipation principle. The alculation of the entransy dissipation rate was presented in detail. Using the entransy dissipation rate as the objective condition, the geometry optimization of the fin heat sink was conducted. To verify the results, the heat source temperature and the entropy generation rate were also calculated in the procedure. It is found that the entrasy dissipation rate, entropy generation and heat source temperature have the similar trend. The extreme entransy dissipation principle and minimization of entropy generation play similar roles in the geometry optimization of plate fin heat sink.

Spacesuit Water Membrane Evaporator; An Enhanced 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 Generation 4 Spacesuit Water Membrane Evaporator (Gen4 SWME). The SWME offers several advantages when compared with prior crewmember cooling technologies, including the ability to reject heat at increased atmospheric pressures, reduced loop infrastructure, and higher tolerance to fouling. Like its predecessors, Gen4 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. Test results from the backup cooling system which is based on a similar design and the subject of a companion paper, suggested that further volume reductions could be achieved through fiber density optimization. Testing was performed with four fiber bundle configurations ranging from 35,850 fibers to 41,180 fibers. The optimal configuration reduced the Gen4 SWME envelope volume by 15% from that of Gen3 while dramatically increasing the performance margin of the system. A rectangular block design was chosen over the Gen3 cylindrical design, for packaging configurations within the AEMU PLSS envelope. Several important innovations were made in the redesign of the backpressure valve which is used to control evaporation. A twin-port pivot concept was selected from among three low profile valve designs for superior robustness, control and packaging. The backpressure valve motor, the thermal control valve, delta pressure sensors and temperature sensors were incorporated into the manifold endcaps, also for packaging considerations. Flight-like materials including a titanium housing were used for all components. Performance testing of the Gen4 SWME is underway.

Air-Cooled Heat Exchanger for High-Temperature Power Electronics

Abstract: This work demonstrates a direct air-cooled heat exchanger strategy for high-temperature power electronic devices with an application specific to automotive traction drive inverters. We present experimental heat dissipation and system pressure curves versus flow rate for baseline and optimized sub-module assemblies containing two ceramic resistance heaters that provide device heat fluxes. The maximum allowable junction temperature was set to 150°C, 175°C, and 200°C. Results were extrapolated to the inverter scale and combined with balance-of-inverter components to estimate inverter power density and specific power.