Topology Optimization for an Internal Heat-Conduction Cooling Scheme in a Square Domain for High Heat Flux Applications

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Jaco Dirker ◽  
Josua P. Meyer
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Topology Optimization ◽  
Internal Heat ◽  
High Heat ◽  
High Heat Flux ◽  
Internal Cooling ◽  
Conductive Heat ◽  
Conducting Materials ◽  
The Cost

Conductive heat transfer is of importance in the cooling of electronic equipment. However, in order for conductive cooling to become effective, the use of high-conducting materials and the correct distribution thereof is essential, especially when the volume which needs to be cooled has a low thermal conductivity. An emerging method of designing internal solid-state conductive systems by means of topology optimization is considered in this paper. In this two-dimensional study, the optimum distribution of high conductive material within a square-shaped heat-generating medium is investigated by making use of the “method or moving asymptotes” (MMA) optimization algorithm coupled with a numerical model. The use of such a method is considered for a number of cost (driving) functions and different control methods to improve the definiteness of the boundaries between the heat-generating and high-conduction regions. It is found that the cost function used may have a significant influence on the optimized material distribution. Also of interest in this paper are the influences of thermal conductivity and the proportion of the volume occupied by the high-conducting solid on the resulting internal cooling structure distribution and its thermal conduction performance. For a square domain with a small exposed isothermal boundary centered on one edge, a primary V-shaped structure was found to be predominantly the most effective layout to reduce the peak operating temperature and to allow for an increase in the internal heat flux levels.

Thermal Conductivity and Operating Temperature Effect on the Interline Region in a Micro/Miniature Heat Pipe

2008 ◽  
Author(s):  
Hani H. Sait ◽  
Steve M. Demsky ◽  
HongBin Ma
Keyword(s):  
Thin Film ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Operating Temperature ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Frictional Shear Stress

An analytical model describing thin film evaporation is developed that includes the effects of surface tension, frictional shear stress, wetting characteristics and disjoining pressure. The effects of thermal conductivity of working fluids and operating temperature on the evaporating thin film region are also studied. The results indicate that when the thermal conductivity of the working fluid increases, a high heat flux can be removed from the evaporating thin film region. The operating temperature affects the thin film evaporation. The higher the operating temperature, the more heat flux can be removed from the region. The information of thin film evaporation presented in the paper results in a better understanding of heat transfer mechanism occurring in micro heat pipes.

Thermal Performance of Natural Graphite Heat Spreaders With Embedded Thermal Vias

2007 ◽  
Author(s):  
Martin Smalc ◽  
Prathib Skandakumaran ◽  
Julian Norley
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Thermal Performance ◽  
Numerical Models ◽  
Accelerated Aging ◽  
High Heat ◽  
High Heat Flux ◽  
Natural Graphite ◽  
Heat Spreaders ◽  
Graphite Heat

Natural graphite heat spreaders are in use in electronic cooling applications where heat flux density is low. Natural graphite is an anisotropic material, with a high thermal conductivity in the plane of the spreader combined with a much lower thermal conductivity through its thickness. This low through-thickness thermal conductivity poses a problem when attempting to cool heat sources with relatively high heat flux densities. This problem can be overcome by embedding a thermal via in the graphite material. This via is made from an isotropic material with a thermal conductivity significantly higher than the through-thickness graphite conductivity. This paper examines the thermal performance of a natural graphite heat spreader with an embedded thermal via. The work is primarily experimental although numerical models were used to guide the experiments. The thermal performance of these spreaders is compared to that of spreaders made from conventional isotropic materials. The effect of accelerated aging tests on the performance of these graphite spreaders is reviewed. Finally, two applications are examined; first cooling an ASIC module and second, cooling an FB-DIMM memory card.

A Vapor Chamber Using Graphite Foams as Wicks for Cooling High Heat Flux Electronics

2005 ◽  
Author(s):  
Minhua Lu ◽  
Larry Mok ◽  
R. J. Bezama
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
High Heat ◽  
High Thermal Conductivity ◽  
Working Fluid ◽  
High Heat Flux ◽  
Vapor Chamber ◽  
Capillary Limit ◽  
Wick Structure ◽  
Graphite Foam

A vapor chamber using high thermal conductivity and permeability graphite foam as a wick has been designed, built and tested. With ethanol as the working fluid, the vapor chamber has been demonstrated at a heat flux of 80 W/cm2. The effects of the capillary limit, the boiling limit, and the thermal resistance in restricting the overall performance of a vapor chamber have been analyzed. Because of the high thermal conductivity of the graphite foams, the modeling results show that the performance of a vapor chamber using a graphite foam is about twice that of one using a copper wick structure. Furthermore, if water is used as the working fluid instead of ethanol, the performance of the vapor chamber will be increased further. Graphite foam vapor chambers with water as the working fluid can be made by treating the graphite foam with an oxygen plasma to improve the wetting of the graphite by the water.

Investigation of Additive Manufactured GRCop-42 Alloy Developed by Directed Energy Deposition Methods

2020 ◽  
Author(s):  
Scott Landes ◽  
Trupti Suresh ◽  
Anamika Prasad ◽  
Todd Letcher ◽  
Paul Gradl ◽  
...  
Keyword(s):  
Heat Flux ◽  
Energy Deposition ◽  
Development Program ◽  
High Heat ◽  
Material Strength ◽  
High Heat Flux ◽  
Internal Cooling ◽  
Powder Bed ◽  
Directed Energy Deposition ◽  
Directed Energy

Abstract GRCop is an alloy family constructed of copper, chromium, and niobium and was developed by NASA for high heat flux applications. GRCop-alloys were specifically formulated for the requirements in channel-cooled main combustion chambers allowing for repeat use in high heat flux environments [1]. GRCop-84 was evolved using additive manufacturing techniques under a NASA development program. To further increase thermal conductivity while maintaining material strength characteristics, the percentage of alloying elements were cut in half and GRCop-42 was developed. In recent years, NASA has successfully additively manufactured GRCop-42 with comparable material characteristics to extruded GRCop-42 using a Laser Powder Bed Fusion (L-PBF) process. Benefits of this process include fabrication of intricate internal cooling channels as well as a decrease in manufacturing time. However, there are some large disadvantages in using this process. The nature of the powder bed process imposes a strict volume constraint as well as an excessive amount of material inventory required. A Directed Energy Deposition (DED) process addresses these limitations while also speeding up the manufacturing process. With little data on how DED performs with GRCop-42, an investigation into the mechanical properties was conducted. More specifically, Blown Powder Directed Energy Deposition (BPD), was used to compare material properties to that of the L-PBF manufactured GRCop-42. The DED manufactured material was found to have less than 0.1% porosity. Tensile tests concluded that the DED manufactured GRCop-42 had lower tensile strengths at room temperature. The results point towards a process capable of producing fully dense parts capable of meeting mechanical strength requirements with some possible refinement of printing parameters.

The Fabrication, High Heat Flux Testing, and Failure Analysis of Thermal Barrier Coatings for Power Generation Gas Turbines

2017 ◽  
Author(s):  
Mary Helen McCay ◽  
Pei-feng Hsu ◽  
D. Edward Croy ◽  
David Moreno ◽  
Mengqi Zhang
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Thermal Barrier Coatings ◽  
Gas Turbines ◽  
High Heat ◽  
Compressed Air ◽  
Thermal Barrier ◽  
High Heat Flux ◽  
Test Cases ◽  
Barrier Coatings

Thermal barrier coatings (TBC) are used to protect the hot components of gas turbines engines to enhance thermal efficiency and component service life. The coating, based on yttria stabilized zirconia, is used in this study. In this paper high heat flux testing with a temperature gradient across the coating thickness of TBC coated coupons is presented. These buttons are subject to precisely-controlled laser heating on the top side and compressed air cooling on the bottom side. Analysis of the thermal conductivity change with respect to heating time and peak temperature, failure assessment, and metallurgical examination are also presented. Some important results of using this method of testing are: definition of the service time vs temperature relationship for TBC lifetime; improved durability of TBCs under severe environmental conditions; determination of effective steady-state sintering conductivity; identification of onset of coating cracking and delamination; adjustable peak temperature, automated and accelerated thermal cycling, etc. This leads to faster testing turn-around for TBC development. Two different types of heating modes can be employed: soak test and cycle test. In soak tests, coated coupons are subjected to steady laser heat flux for up to 12 hr. In cycle tests, the laser heat flux is on for one hour and then off to cool the coated coupons for three minutes. Coupon top surface temperatures from 1200 to 1528°C are maintained in various test cases. At the highest temperature test cases, delamination of TBC (cycle test) and surface crack (soak test) are observed. All key measurements (temperatures, laser power to coupon, compressed air flow rate, etc.) are recorded per second. The normalized thermal conductivity can be computed in real time or processed after the test. It is found that the normalized thermal conductivity increases in the first few hours or cycles of heating and it either reaches a near steady state value or decreases due to surface cracking or delamination in the later state of testing.

Peltier Enhanced Heat Spreading for Localized Hot Spot Thermal Management

2005 ◽  
Author(s):  
Gary L. Solbrekken
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Thermal Management ◽  
Hot Spots ◽  
Hot Spot ◽  
Thermoelectric Module ◽  
High Heat ◽  
Peltier Effect ◽  
High Heat Flux ◽  
Heat Spreading

Localized areas of high heat flux on microprocessors are currently being identified as a dominant challenge for the thermal management community. Heat flux values up to 1 kW/cm2 prevailing over a fraction of the overall CPU surface area create local hot spots that need to be cooled. However, thermal solutions designed for the maximum heat flux overcool the rest of the CPU, wasting resources and creating large on-die temperature gradients. Wasting resources obviously has a negative economic and thermodynamic impact. However, it has been argued that large on-die temperature gradients reduce chip reliability and increase the difficulty in laying out the electric circuits. The current study proposes a strategy to reduce local hot spots by enhancing heat spreading through the use of the Peltier effect. The Peltier effect is most commonly associated with the operation of thermoelectric modules. In thermoelectric modules, heat is transported across the module by electrons. Ideally, the material used for the thermoelectric module would have a very low thermal conductivity to reduce the amount of back heat conduction through the thermoelectric elements, and the electric resistivity would be very low to minimize the Joule heating. Using today’s best commercially available thermoelectric materials, the thermal conductivity, electric resistivity, and Seebeck coefficient are such that the COP for the thermoelectric module is on the order of 1. This implies that in order to cool a processor dissipating 100W, an additional 100W of electric power must be supplied to the thermoelectric module. A total of 200W must then be rejected by the heat sink and any building HVAC system. A more pragmatic approach is to use the Peltier effect to not cool the entire CPU, but rather only the high heat flux region. This is accomplished by placing the thermoelectric elements laterally on the backside of the CPU. The cooling junction is placed in the proximity of the high flux region, while the heating junction is placed in contact with the CPU in low heat flux area that can tolerate the additional heat, effectively creating an active heat spreader. The Peltier enhanced heat spreading proposed here is shown to provide a reduction in the temperature of a localized hot spot relative to passive heat spreading. The amount of reduction in temperature depends on the thickness of the material as well as the thermal conductivity, but values up to 50% are illustrated.

scholarly journals Numerical Investigation of Heat Transfer in Garment Air Gap

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Yijie Zhang ◽  
Juhong Jia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Speed ◽  
Radiative Heat ◽  
Three Dimensional ◽  
High Heat ◽  
Air Gap ◽  
The Body ◽  
High Heat Flux ◽  
Conductive Heat

AbstractThis article aimed to study the characteristics and mechanisms of 3D heat transfer through clothing involving the air gap. A three-dimensional finite volume method is used to obtain the coupled conductive, convective, and radiative heat transfer in a body-air-cloth microclimate system. The flow contours and characteristics of temperature, heat flux, and velocity have been obtained. The reason for the high flux and temperature regions was analyzed. Computational results show that the coupled effect of the air gap and the airflow between the skin and garment strongly influences the temperature and heat flux distribution. There are several high-temperature regions on the clothing and high heat flux regions on the body skin because the conductive heat flux can cross through the narrow air gap and reach the cloth surface easily. The high-speed cooling airflow brings about high forced convective heat flux, which will result in the temperature increase on the upper cloth surface. The radiative heat flux has a strong correlation with the temperature gradient between the body and clothing. But its proportion in the total heat flux is relatively small.

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