Two-Phase Thermal Ground Planes: Technology Development and Parametric Results

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Avram Bar-Cohen ◽  
Kaiser Matin ◽  
Nicholas Jankowski ◽  
Darin Sharar
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Technology Development ◽  
Low Cost ◽  
Ground Plane ◽  
Heat Pipes ◽  
Two Phase ◽  
Thermal Expansion Coefficients ◽  
Chip Size ◽  
Expansion Coefficients

Defense Advanced Research Project Agency's (DARPA's) thermal ground plane (TGP) effort was aimed at combining the advantages of vapor chambers or two-dimensional (2D) heat pipes and solid conductors by building thin, high effective thermal conductivity, flat heat pipes out of materials with thermal expansion coefficients that match current electronic devices. In addition to the temperature uniformity and minimal load-driven temperature variations associated with such two phase systems, in their defined parametric space, flat heat pipes are particularly attractive for Department of Defense and commercial systems because they offer a passive, reliable, light-weight, and low-cost path for transferring heat away from high power dissipative components. However, the difference in thermal expansion coefficients between silicon or ceramic microelectronic components and metallic vapor chambers, as well as the need for a planar, chip-size attachment surface for these devices, has limited the use of commercial of the shelf flat heat pipes in this role. The primary TGP goal was to achieve extreme lateral thermal conductivity, in the range of 10 kW/mK–20 kW/mK or approximately 25–50 times higher than copper and 10 times higher than synthetic diamond, with a thickness of 1 mm or less.

Variation of the Expansion Coefficient of Nanofluids With Temperature: A Correction for Conductivity Data

2012 ◽  
Vol 3 (4) ◽  
Author(s):  
Efstathios E. Michaelides
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Conductivity Data ◽  
Volumetric Fraction ◽  
Solid Materials ◽  
Strong Function ◽  
Temperature Changes ◽  
Thermal Expansion Coefficients ◽  
High Thermal Expansion ◽  
Expansion Coefficients

The two constituent phases of the nanofluids have thermal expansion coefficients that are significantly different. Moreover, the variability of the thermal expansion coefficients of fluids with temperature is significantly higher than that of solid materials. The mismatch of the thermal expansion coefficients creates changes of the volumetric fraction of solids with temperature changes. The changes can be significant with fluids that have high thermal expansion coefficients, such as refrigerants and fluids that operate close to their critical points. Since the thermal conductivity of nanofluids is a very strong function of the volumetric fraction of the nanoparticles, these changes of the volumetric fraction may cause significant effects on the thermal conductivity of the nanofluids, which must be accounted for in any design process.

Measurements of Thermal Properties of Gaskets for the Design of Bolted Flange Joints Under Thermal Conduction Conditions

2006 ◽  
Author(s):  
Takahiro Ohmura ◽  
Kanji Hanashima ◽  
Junichi Nyumura ◽  
Toshiyuki Sawa
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Properties ◽  
Effective Thermal Conductivity ◽  
Linear Thermal Expansion ◽  
Absolute Temperature ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
Bolted Flange ◽  
The Relationship

In this study, the thermal properties of the gaskets, which were used for designing the bolted flange joints, such as effective thermal conductivity, specific heat, linear thermal expansion coefficient and so on were measured. Especially, the effective thermal conductivities were measured by using the heat flow method. The relationship between the gasket structure and the thickness was shown by using an equivalent thermal resistance, and an empirical equation of effective thermal conductivity, which was related to the bulk density and absolute temperature, was proposed by deriving the heat conduction in solid, radiation and gas. Also, in the measurement of the linear thermal expansion coefficients of the gaskets, the measured values were shown to change substantially below 150 °C, and to depend on the heating rate and the load applied on the gasket sample.

Thermophysical Properties of Gd2O3 Doped SrHfO3 Ceramic

2015 ◽  
Vol 816 ◽  
pp. 237-241 ◽  
Author(s):  
Wen Ma ◽  
Yi Ren ◽  
Xi Long Jin ◽  
Ya Hong Liang ◽  
Bao Dong Chen ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Phase Transitions ◽  
High Temperature ◽  
Solid State ◽  
Solid State Reaction Method ◽  
Reaction Method ◽  
Long Period ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients

Gd2O3 (10mol%) doped SrHfO3 (Sr (Hf0.9Gd0.1)O2.95) was synthesized by solid state reaction method. The phase stability of the synthesized Sr (Hf0.9Gd0.1)O2.95 powder at high temperature of 1450 oC for a long period and in a temperature range of RT-1400 oC was characterized by XRD and DSC, respectively. The thermal expansion coefficients (TECs) of bulk Sr (Hf0.9Gd0.1)O2.95 were recorded by a high-temperature dilatometer, indicating that the phase transitions of SrHfO3 are suppressed remarkably by doping Gd2O3. The thermal conductivity of bulk Sr (Hf0.9Gd0.1)O2.95 at 1000 oC is ~1.95 W/m·K, which is ~11% lower than that of bulk 8YSZ.

scholarly journals Polytope Sector-Based Synthesis and Analysis of Microarchitectured Materials With Tunable Thermal Conductivity and Expansion

2015 ◽  
Author(s):  
Jonathan B. Hopkins ◽  
Howon Lee ◽  
Nicholas X. Fang ◽  
Christopher M. Spadaccini
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Material Property ◽  
Analytical Methods ◽  
Positive Zero ◽  
Bulk Property ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients ◽  
Projection Microstereolithography ◽  
2D And 3D

The aim of this paper is to (1) introduce an approach, called Polytope Sector-based Synthesis, for synthesizing 2D or 3D microstructural architectures that exhibit a desired bulk-property directionality (e.g., isotropic, cubic, orthotropic, etc.), and (2) provide general analytical methods that can be used to rapidly optimize the geometric parameters of these architectures such that they achieve a desired combination of bulk thermal conductivity and thermal expansion properties. Although the methods introduced can be applied to general beam-based microstructural architectures, we demonstrate their utility in the context of an architecture that can be tuned to achieve a large range of extreme thermal expansion coefficients — positive, zero, and negative. The material-property-combination region that can be achieved by this architecture is determined within an Ashby-material-property plot of thermal expansion vs. thermal conductivity using the analytical methods introduced. Both 2D and 3D versions of the design have been fabricated using projection microstereolithography.

scholarly journals Construction of visual 3-D fabric reinforced composite thermal performance prediction system

2019 ◽  
Vol 23 (5 Part A) ◽  
pp. 2857-2865 ◽  
Author(s):  
Shaofei Wu
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Performance ◽  
Performance Prediction ◽  
Volume Fraction ◽  
Theoretical Research ◽  
Prediction System ◽  
Reinforced Composites ◽  
Thermal Expansion Coefficients ◽  
Expansion Coefficients

In view of the construction of a visualized 3-D thermal performance prediction system for fabric reinforced composites, the thermal constants analyzer was used to analyze and compare the thermal conductivity of the 3-D fabric reinforced composites by experimental methods, such as fiber volume fraction, internal braiding angle, and different yarn reduction methods and fabric structures. The factors influencing the thermal conductivity of 3-D fabric reinforced composites were studied, and the principle of thermal conductivity was analyzed. The thermal expansion coefficients of 3-D fabric reinforced composites in X- and Y-directions are one order of magnitude smaller than those in Z-directions. When aramid fabric is used as reinforcement, the composites with negative thermal expansion coefficients can be designed. The research results provide the necessary basis for the design, application and theoretical research of the 3-D fabric reinforced composites in heat conduction. Through the research of this paper, it lays a foundation for the process selection, performance design and structure optimization of this kind of material, and promotes the further application of 3-D braided composites.

Preparation and Properties Study of Cu-MoSi2 Composites

2007 ◽  
Vol 534-536 ◽  
pp. 581-584 ◽  
Author(s):  
Xiaoou Yi ◽  
Wei Hao Xiong ◽  
Jian Li
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Properties ◽  
Mechanical And Thermal Properties ◽  
Matrix Composites ◽  
Thermal Expansion Coefficients ◽  
Low Thermal Expansion ◽  
Powder Metallurgy Process ◽  
Expansion Coefficients ◽  
Metallurgy Process

The particulate dispersive strengthened Cu-MoSi2 composites were prepared by a powder metallurgy process with aim to develop novel copper based composites of reasonable strength, high thermal conductivity and low thermal expansion coefficients. Compacted samples were sintered to over 90% of theoretical density. Microstructure of the composites was investigated by SEM while mechanical properties such as tensile strength, elongation and thermal properties such as thermal conductivity and thermal expansion coefficient (CTE) of the composites were examined as a function of the MoSi2 content and the process of fabrication. A comparative analysis of the mechanical and thermal properties of various Cu-matrix composites currently in use was given and the strengthening mechanisms for the Cu-MoSi2 composites were discussed.

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