Enhanced thermal conductivity of epoxy/alumina composite through multiscale-disperse packing

2020 ◽  
Vol 55 (1) ◽  
pp. 17-25
Author(s):  
Hongkun Li ◽  
Weidong Zheng
Keyword(s):  
Thermal Conductivity ◽  
Volume Fraction ◽  
Mean Field ◽  
High Volume ◽  
Theory Model ◽  
Spherical Particles ◽  
Particle Sizes ◽  
Interfacial Resistance ◽  
Steady State Method ◽  
Cure Shrinkage

Inspired by the size of the voids in closest packing structures, we propose to use the combination of spherical particles with different size scales to increase the loading fraction of the fillers in epoxy-based composites. In this study, high loading up to 79 vol% has been achieved with multiscale particle sizes of spherical Al2O3 particles. The highest thermal conductivity of Al2O3-filled liquid epoxy measured by steady-state method is 6.7 W m−1 K−1 at 25°C, which is approximately 23 times higher than the neat epoxy (0.28 W m−1 K−1). Three models based on Maxwell mean-field scheme (MMF), differential effective medium (DEM) and percolation theory model (PTM) were utilized to assess our measured thermal conductivity data. We found that both DEM and PTM models could give good results at high volume fraction regime. We have also observed a considerable reduction (10–15%) of thermal conductivity in our Al2O3-filled cured epoxy samples. We attribute this reduction to the increasing of thermal interfacial resistance between Al2O3 particles and cured epoxy matrix, induced by cure shrinkage during the reaction. Our experiments have demonstrated that systems with multiscale particle sizes exhibit lower viscosity and can be filled with much higher fraction of fillers. We thus expect that higher thermal conductivity (probably >12 W m−1 K−1 based on DEM) can be achieved in future via filling higher thermal conductivity spherical fillers (e.g., AlN, SiC), increasing loading fraction by multiscale-disperse packing and reducing the effect from cure shrinkage.

Numerical prediction of thermal conductivity in ZrB2-particulate-reinforced epoxy composites based on finite element models

2018 ◽  
Vol 25 (2) ◽  
pp. 337-342
Author(s):  
Yicheng Wu ◽  
Zhiqiang Yu
Keyword(s):  
Thermal Conductivity ◽  
Finite Element ◽  
Volume Fraction ◽  
High Volume ◽  
Epoxy Composites ◽  
Spherical Particles ◽  
Homogeneous Distribution ◽  
Finite Element Models ◽  
Negative Effect ◽  
Thermal Conductivities

AbstractEpoxy composites reinforced by Zirconium diboride (ZrB2) particles were investigated by finite element models (FEMs). It helped to explore the relationship between the thermal conductivity of composites and the volume fraction, size, shape, orientation, and arrangement of the ZrB2particles. The results showed that the thermal conductivity performance of composites was improved effectively when filled with ZrB2particles. Specifically, epoxy composites filled with 50 vol% spherical ZrB2particles had 12.05 times the thermal conductivity of epoxy resin. At the same volume fraction, the number of ZrB2particles in the epoxy matrix has little influence on thermal conductivity due to the dimensionless models. At a high volume fraction, rectangular ZrB2particles improved thermal conductivity more effectively than spherical particles. In the comparison of thermal conductivities among composites reinforced by rectangular fillers, the thermal conductivities of composites were clearly affected by the length-width ratios of fillers, and this effect was monotonically increasing. The vertical orientations of particles could conduct heat most effectively compared with slant and parallel orientations. The agglomerate distribution of ZrB2particles has the negative effect of thermal diffusion in a certain direction compared with homogeneous distribution.

Brownian-Motion-Based Convective-Conductive Model for the Effective Thermal Conductivity of Nanofluids

2005 ◽  
Vol 128 (6) ◽  
pp. 588-595 ◽  
Author(s):  
Ravi Prasher ◽  
Prajesh Bhattacharya ◽  
Patrick E. Phelan
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Particle Sizes ◽  
Brownian Movement ◽  
Liquid Temperature ◽  
Interfacial Resistance ◽  
Conduction Model ◽  
Order Of Magnitude ◽  
Base Liquid ◽  
Good Agreement

Here we show through an order-of-magnitude analysis that the enhancement in the effective thermal conductivity of nanofluids is due mainly to the localized convection caused by the Brownian movement of the nanoparticles. We also introduce a convective-conductive model which accurately captures the effects of particle size, choice of base liquid, thermal interfacial resistance between the particles and liquid, temperature, etc. This model is a combination of the Maxwell-Garnett (MG) conduction model and the convection caused by the Brownian movement of the nanoparticles, and reduces to the MG model for large particle sizes. The model is in good agreement with data on water, ethylene glycol, and oil-based nanofluids, and shows that the lighter the nanoparticles, the greater the convection effect in the liquid, regardless of the thermal conductivity of the nanoparticles.

Thermal Conductivity Prediction for Thermal Barrier Coatings

2010 ◽  
Author(s):  
Monica B. Silva ◽  
S. M. Guo ◽  
Patrick F. Mensah ◽  
Ravinder Diwan
Keyword(s):  
Thermal Conductivity ◽  
Thermal Barrier Coatings ◽  
Volume Fraction ◽  
Mercury Porosimetry ◽  
Laser Flash ◽  
Atmospheric Plasma ◽  
Thermal Barrier ◽  
Interfacial Resistance ◽  
Barrier Coatings ◽  
Spray Process

Thermal barrier coatings (TBCs) are used in gas turbine engines to achieve a higher working temperature and thus lead to a better efficiency. Yttria-Stabilized-Zirconia (YSZ), a material with low thermal conductivity, is commonly used as the TBC top coat to provide the thermal barrier effect. In this paper, an analytical model is proposed to estimate the effective thermal conductivity of the TBCs based on the microstructures. This model includes the micro structure details, such as grain size, pore size, volume fraction of pores, and the interfacial resistance. To validate the model, two sets of TBC samples were fabricated and tested for thermal conductivity and associated microstructures. The first set of samples were disk shaped YSZ-Al2O3 samples fabricated using a pressing machine. The YSZ-Al2O3 powder mixture was 0, 1, 2, 3, 4 and 5 wt% Al2O3/YSZ powder ratio. The second set of samples were fabricated by Atmospheric Plasma Spray process for two different microstructure configurations, standard (STD) and vertically cracked (VC), at two different thicknesses, 400 and 700 urn respectively. A laser flash system was used to measure the thermal conductivity of the coatings. Experiments were performed over the temperature range from 100°C to 800°C. The porosity of the YSZ samples was measured using a mercury porosimetry analyzer, POREMASTER 33 system. A Scanning Electron Microscope (SEM) was used to study the microstructure of the samples. It is observed that the microstructure and the porosity are directly linked with the thermal conductivity values. The relationship of the properties to the real microstructure determines the validity of the proposed model.

Influencing factors and measuring method of the heat conducting performance of UHMWPE single fiber

2017 ◽  
Vol 47 (8) ◽  
pp. 1908-1924 ◽  
Author(s):  
Dai Guoliang ◽  
Li Li ◽  
Xiao Hong ◽  
Zhai Maolin ◽  
Shi Meiwu
Keyword(s):  
Thermal Conductivity ◽  
Volume Fraction ◽  
Measuring Method ◽  
Theory Model ◽  
Single Fiber ◽  
Heat Conducting ◽  
Drawing Ratio ◽  
Equivalent Thermal Conductivity ◽  
Uhmwpe Fiber ◽  
The Difference

The fiber with higher thermal conductivity is rare and it is difficult to measure the thermal conductivity of a single fiber. In this paper, the composite samples of ultra-high molecular weight polyethylene (UHMWPE) fiber and epoxy resin were prepared in order to study the heat conducting properties of the UHMWPE fiber. The specific heat capacity and thermal conductivity of the samples were tested by the transient plane source method. Based on the serial–parallel equivalence theory model, the axial and radial thermal conductivities of the UHMWPE filament were calculated. Effects of the volume fraction of fiber, fineness and drawing ratio on thermal conductivity were explored. Also, the relationship between the structure and thermal conductive capacity was revealed. The results showed that the volume fraction of fibers should be large to obtain a relative accurate value. Moreover, the difference in fineness led to different thermal conductivity of the UHMWPE fiber, the cruder the fiber, the higher the thermal conductivity. Besides, as the drawing ratio increased, the crystallinity and orientation of the fibers also increased. Thus, the results were that the axial equivalent thermal conductivity of the filament was dramatically increased, while the radial equivalent thermal conductivity grew a little. The paper showed that UHMWPE fibers had much higher thermal conductivity than other fibers, and also provided a new method to get the thermal conductivity of UHMWPE single fiber.

Liquid Layering and the Enhanced Thermal Conductivity of Ar-Cu Nanofluids: A Molecular Dynamics Study

2016 ◽  
Author(s):  
Jithu Paul ◽  
A. K. Madhu ◽  
U. B. Jayadeep ◽  
C. B. Sobhan
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Particle Size ◽  
Molecular Dynamics Simulations ◽  
Volume Fraction ◽  
Strong Dependence ◽  
Particle Sizes ◽  
Dynamics Simulations ◽  
Enhanced Thermal Conductivity ◽  
Liquid Layering

Nanofluids — colloidal suspensions of nanoparticles in base fluids — are known to possess superior thermal properties compared to the base fluids. Various theoretical models have been suggested to explain the often anomalous enhancement of these properties. Liquid layering around the nanoparticle is one of such reasons. The effect of the particle size on the extent of liquid layering around the nanoparticle has been investigated in the present study. Classical molecular dynamics simulations have been performed in the investigation, considering the case of a copper nanoparticle suspended in liquid argon. The results show a strong dependence of thickness of the liquid layer on the particle size, below a particle diameter of 4nm. To establish the role of liquid layering in the enhancement of thermal conductivity, simulations have been performed at constant volume fraction for different particle sizes using Green Kubo formalism. The thermal conductivity results show 100% enhancement at 3.34% volume fraction for particle size of 2nm. The results establish the dominant role played by liquid layering in the enhanced thermal conductivity of nanofluids at the low particle sizes used. Contrary to the previous findings, the molecular dynamics simulations also predict a strong dependence of the liquid layer thickness on the particle size in the case of small particles.

scholarly journals Microstructural Evolution and Strengthening Mechanism of SiC/Al Composites Fabricated by a Liquid-Pressing Process and Heat Treatment

Materials ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3374 ◽  
Author(s):  
Sangmin Shin ◽  
Seungchan Cho ◽  
Donghyun Lee ◽  
Yangdo Kim ◽  
Sang-Bok Lee ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Compressive Strength ◽  
Microstructural Evolution ◽  
Load Transfer ◽  
Volume Fraction ◽  
High Volume ◽  
Strengthening Mechanism ◽  
Spherical Particles ◽  
Pressing Process ◽  
Liquid Pressing Process

Aluminum alloy (Al7075) composites reinforced with a high volume fraction of silicon carbide (SiC) were produced by a liquid-pressing process. The characterization of their microstructure showed that SiC particles corresponding to a volume fraction greater than 60% were uniformly distributed in the composite, and Mg2Si precipitates were present at the interface between the matrix and the reinforcement. A superior compressive strength (1130 MPa) was obtained by an effective load transfer to the hard ceramic particles. After solution heat treatment and artificial aging, the Mg2Si precipitates decomposed from rod-shaped large particles to smaller spherical particles, which led to an increase of the compressive strength by more than 200 MPa. The strengthening mechanism is discussed on the basis of the observed microstructural evolution.

On Thermal Interface Materials With Polydisperse Fillers: Packing Algorithm and Effective Properties

2018 ◽  
Author(s):  
Piyas Chowdhury ◽  
Kamal Sikka ◽  
Anuja De Silva ◽  
Indira Seshadri
Keyword(s):  
Thermal Conductivity ◽  
Elastic Modulus ◽  
Volume Fraction ◽  
Effective Properties ◽  
Material Design ◽  
High Volume ◽  
Thermal Interface Materials ◽  
Thermal Interface ◽  
Packing Algorithm ◽  
Interface Materials

Thermal interface materials (TIMs), which transmit heat from semiconductor chips, are indispensable in today’s microelectronic devices. Designing superior TIMs for increasingly demanding integration requirements, especially for server-level hardware with high power density chips, remains a particularly coveted yet challenging objective. This is because achieving desired degrees of thermal-mechanical attributes (e.g. high thermal conductivity, low elastic modulus, low viscosity) poses contradictory challenges. For instance, embedding thermally conductive fillers (e.g. metallic particles) into a compliant yet considerably less conductive matrix (e.g. polymer) enhances heat transmission, however at the expense of overall compliance. This leads to extensive trial-and-error based empirical approaches for optimal material design. Specifically, high volume fraction filler loading, role of filler size distribution, mixing of various filler types are some outstanding issues that need further clarification. To that end, we first forward a generic packing algorithm with ability to simulate a variety of filler types and distributions. Secondly, by modeling the physics of heat/force flux, we predict effective thermal conductivity, elastic modulus and viscosity for various packing cases.

Stability of Zinc Oxide Nanofluids Prepared with Aggregated Nanocrystalline Powders

2008 ◽  
Vol 8 (12) ◽  
pp. 6361-6366
Author(s):  
J. P. Leonard ◽  
S. J. Chung ◽  
I. Nettleship ◽  
Y. Soong ◽  
D. V. Martello ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Particle Size ◽  
Zinc Oxide ◽  
Brownian Motion ◽  
Preparation Method ◽  
Volume Fraction ◽  
High Volume ◽  
Nanocrystalline Powders ◽  
Zno Powder ◽  
20 Nm

Aqueous zinc oxide (ZnO) suspensions were prepared using a two-step preparation method in which an aggregated nanocrystalline ZnO powder was dispersed in water using a polyelectrolyte. The fluid showed anomalously high thermal conductivity when compared with the Maxwell and Hamilton-Crosser predictions. However, analysis of the particle size distribution showed that the fluid contained aggregated 20 nm crystallites of ZnO with a high volume fraction of particles larger than 100 nm. Sedimentation experiments revealed that particles settled out of the stationary fluid over times ranging from 0.1 hours to well over 10,000 hours. The size of the particles remaining in suspension agreed well with predictions made using Stoke's law, suggesting flocculation was not occurring in the fluids. Finally, a new concept of nanofluid stability is introduced based on the height of the fluid, sedimentation, Brownian motion and the kinetic energy of the particles.

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