Showing papers on "Electronics cooling published in 2011"

Parametric numerical study of flow and heat transfer in microchannels with wavy walls

Abstract: Wavy channels were investigated in this paper as a passive scheme to improve the heat transfer performance of laminar fluid flow as applied to microchannel heat sinks. Parametric study of three-dimensional laminar fluid flow and heat transfer characteristics in microsized wavy channels was performed by varying the wavy feature amplitude, wavelength, and aspect ratio for different Reynolds numbers between 50 and 150. Two different types of wavy channels were considered and their thermal performance for a constant heat flux of 47 W/cm 2 was compared. Based on the comparison with straight channels, it was found that wavy channels can provide improved overall thermal performance. In addition, it was observed that wavy channels with a configuration in which crests and troughs face each other alternately (serpentine channels) were found to show an edge in thermal performance over the configuration where crests and troughs directly face each other. The best configuration considered in this paper was found to provide an improvement of up to 55% in the overall performance compared to microchannels with straight walls and hence are attractive candidates for cooling of future high heat flux electronics.

A 120°C ambient temperature forced air-cooled normally-off SiC JFET automotive inverter system

Abstract: The degree of integration of power electronic converters in current hybrid electric vehicles can be increased by mitigation of special requirements of these converters, especially those regarding ambient air and cooling fluid temperature levels. Today, converters have their own cooling circuit or are placed far away from hot spots caused by the internal combustion engine and its peripheral components. In this paper, it is shown, how the use of SiC power semiconductors and active control electronics cooling employing a Peltier cooler can help to build an air-cooled inverter system for 120 °C ambient temperature. First, a detailed analysis shows, how the optimum junction of this high-temperature system can be calculated. Then, the operating temperature ranges of power semiconductors, thermal interface materials, capacitors, and control electronics are investigated, leading to a comprehensive analysis of mechanical concepts for the inverter system in order to show new ways to solve electrical and thermal tradeoffs. In particular, the operation of the signal electronics and the gate driver for power semiconductors with a junction temperature of 250 °C within the specified operating temperature range is ensured by appropriate placement and cooling methods, while taking the electrical requirements for limits on the wiring inductances and symmetry requirements into account. The analysis includes an accurate thermal model of the converter and an optimized active cooling of the signal electronics using a Peltier cooler. Finally, a hardware prototype with discrete power semiconductor devices and thus with a junction temperature limit of 175 °C driving high-speed electrical machines is shown to validate the theoretical considerations in a custom-designed high-temperature test environment.

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

Abstract: A comprehensive model of a miniature-scale linear compressor for electronics cooling is presented. Linear compressors are appealing for refrigeration applications in electronics cooling. A small number of moving components translate to less theoretical frictional losses and the possibility that this technology could scale to smaller physical sizes better than conventional compressors. The model developed here incorporates all of the major components of the linear compressor including dynamics associated with the piston motion. The results of the compressor model were validated using experimental data from a prototype linear compressor. The prototype compressor has an overall displacement of approximately 3 cm 3 , an average stroke of 0.6 cm. The prototype compressor was custom built for this work and utilizes custom parts with the exception of the mechanical springs and the linear motor. The model results showed good agreement when validated against the experimental results. The piston stroke is predicted within 1.3% MAE. The volumetric and overall isentropic efficiencies are predicted within 24% and 31%, MAE respectively.

Thermal Performance of Microchannels With Wavy Walls for Electronics Cooling

Abstract: Wavy walls are investigated in this paper as a passive scheme to improve the heat transfer performance of low-Reynolds-number laminar flows in microchannel heat sinks for electronics cooling applications. 3-D laminar fluid flow and heat transfer characteristics in microchannels with wavy walls are numerically studied for a 500-μm hydraulic diameter channel by varying the wavy feature amplitude at different Reynolds numbers (10, 20, 50, and 100). In addition, flow measurements are made using a micrometer-resolution particle image velocimetry technique for understanding the fundamentals of fluid flow in the wavy-walled microchannels for the considered Reynolds numbers. Based on the comparison with straight channels, it was found that wavy channels can provide improved heat transfer performance while keeping the pressure drop within acceptable limits. Accordingly, wavy channels are to found to provide an improvement of up to 26% in the overall performance (which includes the effect of wall waviness on heat transfer, pressure drop, and surface area) compared to microchannels with straight walls for the same pumping power and hence are attractive candidates for cooling of future electronics.

A Compact Loop Heat Pipe With Flat Square Evaporator for High Power Chip Cooling

Abstract: In this paper, systematic experimental and theoretical investigations were carried out on a copper-water compact loop heat pipe with a flat square evaporator having a bottom area of 30 mm × 30 mm. Wick structure inside the evaporator was made of fine copper powder with carefully designed vapor removal channels sintered directly on the substrate. In addition, the design and fabrication of a 120 mm air-cooled condenser was given adequate consideration. From the experimental tests, it is found that such a small loop heat pipe can manage a heat load of more than 600 W, and no dry-out occurs. In the favorable vertical configuration, with an air velocity of 2.8 m/s, this compact loop heat pipe has a thermal resistance as low as 0.042°C/W, with a corresponding evaporator thermal resistance as low as 0.018°C/W . As well, the theoretical analysis agrees in principle with the experimental data.

Aircraft electronics cooling apparatus for an aircraft having a liquid cooling system

Abstract: The invention relates to an improved aircraft electronics cooling system for an aircraft having a liquid cooling system, the aircraft electronics cooling system providing a thermal coupling between an electronic device to be cooled and the liquid cooling system of the aircraft. A coolant delivered by the liquid cooling system may flow through a board of the electronic device, through a heat sink on which the electronic device is arranged and/or through a housing in which the electronic device is arranged. The coolant may be permanently in the liquid state in a cooling circuit. The coolant may vaporize at least partially while cooling the electronic device.

Downhole Electronics Cooling Using a Thermoelectric Device and Heat Exchanger Arrangement

Abstract: This paper investigates the use of thermoelectric (TE) devices for thermal management of downhole electronics. The research carried out will help in the mitigation of costs associated with thermal damage of downhole electronics used in oil drilling industry. An experimental set up was prepared where a TE device was used in conjunction with heat exchanger and a cold plate to remove heat from electronics module. A finned copper rod in contact with hot side of TE device was used to reject the heat out to the ambient. The experimental set up was housed inside a cylindrical vacuum flask, which was in turn placed inside an oven to simulate thermally harsh downhole conditions. Experiments were carried out with electronics heat dissipation of 0–8 W and ambient temperature of 140 °C. Due to the differences in the environmental conditions of the laboratory and the practical downhole scenario, the experiment could not completely capture the conditions of downhole heat rejection. A mathematical model of the experimental apparatus was prepared and validated against the experimental results. The model was used to predict performance of a TE device for thermal management of downhole electronics at an ambient temperature of 200–250 °C. It was observed that the ability of the thermal management system to keep electronics cool varied from 30 °C to a few degrees below the surrounding temperature, for chip wattage varying from 0 W to 8 W, respectively.

Flat Miniature Heat Pipes for Electronics Cooling: State of the Art, Experimental and Theoretical Analysis

Abstract: An experimental study is realized in order to verify the Mini Heat Pipe (MHP) concept for cooling high power dissipation electronic components and determines the potential advantages of constructing mini channels as an integrated part of a flat heat pipe. A Flat Mini Heat Pipe (FMHP) prototype including a capillary structure composed of parallel rectangular microchannels is manufactured and a filling apparatus is developed in order to charge the FMHP. The heat transfer improvement obtained by comparing the heat pipe thermal resistance to the heat conduction thermal resistance of a copper plate having the same dimensions as the tested FMHP is demonstrated for different heat input flux rates. Moreover, the heat transfer in the evaporator and condenser sections are analyzed, and heat transfer laws are proposed. In the theoretical part of this work, a detailed mathematical model of a FMHP with axial microchannels is developed in which the fluid flow is considered along with the heat and mass transfer processes during evaporation and condensation. The model is based on the equations for the mass, momentum and energy conservation, which are written for the evaporator, adiabatic, and condenser zones. The model, which permits to simulate several shapes of microchannels, can predict the maximum heat transfer capacity of FMHP, the optimal fluid mass, and the flow and thermal parameters along the FMHP. The comparison between experimental and model results shows the good ability of the numerical model to predict the axial temperature distribution along the FMHP.

Green Cooling of High Performance Microprocessors: Parametric Study Between Flow Boiling and Water Cooling

Abstract: Due to the increase in energy prices and spiralling consumption, there is a need to greatly reduce the cost of electricity within data centers, where it makes up 50% of the total cost of the IT infrastructure. A technological solution to this is using on-chip cooling with a single-phase or evaporating liquid to replace energy intensive air-cooling. The energy carried away by the liquid or vapour can also potentially be used in district heating, as an example. Thus, the important issue here is “what is the most energy efficient heat removal process?” As an answer, this paper presents a direct comparison of single-phase water, a 50% water ethylene glycol mixture and several two-phase refrigerants, including the new fourth generation refrigerants HFO1234yf and HFO1234ze. Two-phase cooling using HFC134a had an average junction temperature 9 to 15˚C lower than for single-phase cooling, while the required pumping power for the CPU cooling element for single-phase cooling was on the order of 20-130 times higher to achieve the same junction temperature uniformity. Hot-spot simulations also showed that two-phase refrigerant cooling was able to adjust to local hot-spots because of flow boiling's dependency on the local heat flux, with junction temperatures being 20 to 30˚C lower when compared to water and the 50% water-ethylene glycol mixture, respectively. An exergy analysis was developed considering a cooling cycle composed by a pump, a condenser and a multi-microchannel cooler. The focus was to show the exergetic efficiency of each component and of the entire cycle when the subject energy recovery is considered. Water and HFC134a were the working fluids evaluated in such analysis. The overall exergetic efficiency was higher when using HFC134a (about 2%) and the exergy destroyed, i.e. irreversibilities, showed that the cooling cycle proposed still have a huge potential to increase the thermodynamic performance.

Cooling Methods for High-Power Electronic Systems

Abstract: Cooling Methods for High-Power Electronic Systems Thermal management is a crucial step in the design of power electronic applications, especially railroad traction and automotive systems. Mass/size parameters, robustness and reliability of the power electronic system greatly depend on the cooling system type and performance. This paper presents an approximate parameter estimation of the thermal management system required as well as different commercially available cooling solutions. Advantages and drawbacks of different designs ranging from simple passive heatsinks to complex evaporative systems are discussed.

Condenser bypass for two-phase electronics cooling system

Abstract: An electronics cooling system utilizing a refrigerant fluid that evaporates to remove heat from electronics and is condensed back to liquid through heat exchange with a cold medium (air or water). The refrigerant fluid is circulated via a liquid pump between the condenser and heated evaporators. A bypass circuit is provided to divert flow around the condenser during conditions of cold ambient temperatures, which is controlled by a feedback loop using a mechanical or electronic control valve. This prevents the refrigerant fluid temperature from becoming very low and potentially inducing condensation on the outside of the refrigerant tubing from the warm and moist indoor air.

A Honeycomb Microchannel Cooling System for Microelectronics Cooling

Abstract: A honeycomb porous microchannel cooling system for electronics cooling was proposed in this article. The design, fabrication, and test system configuration of the microchannel heat sink were summarized. Preliminary experimental investigation was conducted to understand the characteristics of heat transfer and cooling performance under steady single-phase flow. In the experiments, a brass microchannel heat sink was attached to a test heater with 8 cm2 area. The experimental results show that the cooling system is able to remove 18.2 W/cm2 of heat flux under 2.4 W pumping power, while the junction wall temperature is 48.3°C at the room temperature of 26°C. Extensive experiments in various operation conditions and parameters for the present cooling system were also conducted. The experimental results show that the present cooling system is able to perform heat dissipation well.

Modeling and Validating the Transient Behavior of Flat Miniature Heat Pipes Manufactured in Multilayer Printed Circuit Board Technology

Abstract: A novel, integrated approach in thermal management of electronic products, based on two-phase cooling, is presented. A flat miniature heat pipe, integrated inside the laminated structure of a printed circuit board (PCB), has been developed, based on mainstream PCB multilayer technology. To accurately predict the thermal performance of this two-phase heat transport device and to establish the operational limitations, a numerical model based on control volume elements is discussed. The advantage of this modular approach, compared with, e.g., finite element models, is that the model can be expanded with additional components (e.g., multiple evaporators) very easily. Actual PCBs with several hot spots cooled by flat miniature heat pipes and their parameter effects can be analyzed very quickly, without the necessity of complex and time-consuming finite element analyses. Experimental verification has shown a good comparison with model predictions. Time evolution analyses show that the developed control volume model is well capable of describing the heat pipe transient behavior.

Integrated fan motor and controller housing

Abstract: An electronics cooling system comprises a tubular fan duct and an electronics housing The fan duct includes has a fan duct casing containing a fan with rotor blades and stator vanes The electronics housing is mounted directly on the tubular fan duct, such that the electronics housing and the fan duct casing together enclose an interior space A cooling airflow path extends from a high-pressure region of the tubular fan duct, through an inlet hole into the interior space, and out a bleed hole into a surrounding environment The electronics cooling system further comprises three electronics mounts within the interior space A first electronics mount is located immediately adjacent to the inlet hole, on the fan duct A second electronics mount is located immediately radially outward of the stator vanes, on the fan duct A third electronics mount is located immediately adjacent to the bleed hole, on the housing

On the use of second law based cost functions in plate fin heat sink design

Abstract: This paper discusses the use of the second law in heat sink design. A new entropy-based cost function is proposed and compared with existing heat sink cost functions. A case study of a plate fin heat sink points out that this newly developed cost function offers a heat sink which is more than twice as efficient as a heat sink designed with the traditional thermal resistance minimization objective. The effects of this new heat sink design on data center cooling systems are considered and found to be significantly improving the system efficiency and waste heat recovery.

Evaluation of Compact and Effective Air-Cooled Carbon Foam Heat Sink

Abstract: This study investigates a V-shaped corrugated carbon foam heat sink for thermal management of electronics with forced air convection. Experiments were conducted to determine the heat sink performance in terms of heat transfer coefficient and pressure drop. The test section, with overall dimensions of 51 mm L X51 mm W ×19 mm H, enabled up to 166 W of heat dissipation, and 3280 W/m 2 K and 2210 W/m 2 K heat transfer coefficients, based on log mean and air inlet temperatures, respectively, at 7.8 m/s air flow speed, and 1320 Pa pressure loss. Compared to a solid carbon foam, the V-shaped corrugated structure enhances the heat transfer, and at the same time reduces the flow resistance. Physical mechanisms underlying the observed phenomena are briefly explained. With benefits that potentially can reduce overall weight, volume, and cost of the air-cooled electronics, the present V-shaped corrugated carbon foam emerges as an alternative heat sink.

Thermal design in the Design for Six Sigma — DIDOV framework

Abstract: Fierce competition drives continuous improvement of products and product development processes in consumer electronics. The DIDOV (Define, Identify, Design, Optimize, and Verify) version of the Design for Six Sigma (Dfss) approach is widely recommended a means to improvement, especially in R&D environments. Due to the wide field of application, the Dfss — DIDOV method is formulated in very abstract terms, which makes it difficult to relate it to the engineering world. In this paper, the method is assessed in the context of the thermal design of electronics cooling in a consumer electronics product. The paper starts with a discussion of the DIDOV methodology and a comparison to thermal design flow. Next, the method is illustrated on a thermal design case.

Small Loop Heat Pipe with Plastic Wick for Electronics Cooling

Abstract: In this paper, fabrication and test results of a small loop heat pipe (LHP) for electric cooling over a distance of 1100 mm are discussed. Poly(tetrafluoroethylene) porous material with 1.2 µm pore radius was used as a wick material for a primary pump of the loop to satisfy in both high thermal performance and low cost. High-grade ethanol was selected as a working fluid inside the loop. The small LHP with an outer diameter of 12 mm and length of 77 mm of an evaporator was made of stainless steel. The vapor and liquid transport lines are 1.8 mm in inner diameter and 1100 mm in length respectively in order to demonstrate the long-distance heat transport in a small tube, against the frictional resistance in the loop. The start-up process was monitored with an infrared camera, and quick start-up and its stable operation after the start-up were visually demonstrated. The loop could operate up to 50 W heat load with the operating temperature of around 70 °C in the evaporator. The thermal resistance between the evaporator and the condenser of the loop was 0.58 K/W at 50 W.

Nonintrusive measurement of the mass flow rate inside a closed loop two-phase thermosyphon

Abstract: Two-phase cooling is a promising technology for electronics cooling. It allows using dielectric fluids in passive systems and benefit from high heat transfer coefficients. Thermosyphons are a particularly interesting technology in the field of power electronics being entirely passive and simple equipments. Their performances are strongly related to the flow rate of the fluid inside the thermosyphon. In mini-channels thermosyphons liquid entrainment occurs so that flow rate is difficult to evaluate, hence the need for a non intrusive measurement method. For this purpose a mini-channel thermosyphon was manufactured out of borosilicate glass and equipped with a semi-transparent ITO layer as a direct current heating evaporator. It was illuminated by two lasers through the glass tube and the voltage from two photodiodes placed on the opposite side was measured. With an appropriate signal processing the maximal velocity was determined together with length and frequency of the vapor bubbles, the frequency of the thermosyphon cycle for several filling ratios and for various heating powers. From these measurements the total mass flow rate, the liquid mass flow rate, the gas mass flow rate, the void fraction, the vapor quality and the flow cycle frequency were calculated and compared to a thermosyphon simulation model developed at ABB.

Waste-Heat Driven Miniature Absorption Refrigeration System Using Ionic-Liquid as a Working Fluid

Abstract: An ionic-liquid (IL) is a salt in a liquid state usually with an organic cation and inorganic anion ILs provide an alternative to the normally toxic working fluids in absorption systems, such as the ammonia/water system They also eliminate the problems of poor temperature match, crystallization and metal-compatibility problems of the water/LiBr system In the present study, an IL is explored the working fluid of a miniature absorption refrigeration system so as to utilize waste-heat within the system for low-cost, high-power electronics cooling To determine performance benchmarks for the refrigerant/IL (eg [bmim][PF6 ]) pairs, system-level simulations have been carried out An NRTL model was built and used to predict the solubility of the mixture as well as the mixture properties such as enthalpy and entropy The properties of the refrigerants were determined using REFPROP 60 Saturation temperatures at the evaporator and condenser were 25°C and 50°C, respectively Chip power was fixed at 100 W with the operating temperature set at 85°C R32 gave the highest operating efficiency with the maximum coefficient of performance (COP) of ca 055 while R134a and R152a showed comparable performance with the maximum COP of ca 04 at the desorber outlet temperature of 80°C When waste-heat is available for the system operation, R134a and R152a COPs were comparable or better than that of R32Copyright © 2011 by ASME

Analysis and characterization of thermoelectric module and heat exchanger performance in a hybrid system cooling application

Abstract: A thermoelectric chiller is a potential replacement for sub-ambient refrigeration for electronics cooling applications, where the reliance on vapor compression refrigeration results in risk of cooling failure due to the mechanical nature of the compressor and electronic expansion valve. Another benefit of a thermoelectric chiller is that controllable cooling of the electronic component can be achieved regardless of ambient conditions, and the ultimate heat sink can be either air or facility water. The goal of the work described herein is to study a thermoelectric chiller with reasonable capacity (in Watts), coefficient of performance (COP), and reliability (mean time between failures, MTBF), for electronics cooling applications. Four sets of tests are presented: a thermoelectric module tested with a heater block and a cold plate (Figure 2), and thermoelectric heat exchanger tests where the thermoelectric module hot and cold sides are arranged in segregated loops (Figure 5), a single serial loop (Figure 6), and parallel loops (Figure 7).

Modeling of Laminar Viscous Flow in a Semi-Porous Channel Under Uniform Magnetic Field

Abstract: Laminar flow in porous channels or tubes has received a great attention in recent years due to its various applications. These applications include blood filtration in artificial kidney, blood flow in capillaries and oxygenations, transpiration, cooling of turbine blades, lubrication of ceramic machine parts, food processing, electronics cooling, gaseous diffusion, the extraction of geothermal energy, and nuclear reactor cooling systems. The present work, proposes the Galerkin method to solve the two dimensional electrically conducting flow in a semiporous channel under uniform magnetic field as governed by dimensionless: Hartman number (Ha), and Reynolds number (Re). The numerical results predict the flow field characteristics over wide ranges of Ha, and Re. These results are compared with other available analytical and numerical results at different values of Ha, and Re. Detailed results are presented and discussed.Copyright © 2011 by ASME