Particle Aspect-Ratio Effects on the Thermal Conductivity of Micro- and Nanoparticle Suspensions

2008 ◽  
Vol 130 (8) ◽  
Author(s):  
Anna S. Cherkasova ◽  
Jerry W. Shan
Keyword(s):  
Thermal Conductivity ◽  
Silicon Carbide ◽  
Aspect Ratio ◽  
Effective Thermal Conductivity ◽  
Effective Medium Theory ◽  
Effective Medium ◽  
Particulate Composites ◽  
Interfacial Thermal Resistance ◽  
Recent Experimental Data ◽  
Medium Theory

The influence of particle anisotropy on the effective thermal conductivity of a suspension is experimentally investigated. Suspensions of micron-sized, silicon-carbide particles with varying aspect-ratio distributions were prepared and measured. It is shown that the conductivity of the silicon-carbide suspensions can be quantitatively predicted by the effective medium theory of Nan et al. (1997, “Effective Thermal Conductivity of Particulate Composites With Interfacial Thermal Resistance,” J. Appl. Phys. 81(10), pp. 6692–6699), provided the volume-weighted aspect ratio of the particles is used. Recent experimental data on multiwalled-nanotube-in-oil suspensions by Yang et al. (2006, “Thermal and Rheological Properties of Carbon Nanotube-in-Oil Dispersions,” J. Appl. Phys., 99(11), 114307) are also analyzed and shown to be in at least qualitative agreement with the effective-medium-theory prediction that the thermal conductivity of suspensions is enhanced by large aspect-ratio particles.

scholarly journals Effect of Alignment on Enhancement of Thermal Conductivity of Polyethylene–Graphene Nanocomposites and Comparison with Effective Medium Theory

Nanomaterials ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 1291
Author(s):  
Fatema Tarannum ◽  
Rajmohan Muthaiah ◽  
Roshan Sameer Annam ◽  
Tingting Gu ◽  
Jivtesh Garg
Keyword(s):  
Thermal Conductivity ◽  
Thermal Management ◽  
Laser Scanning ◽  
Effective Medium Theory ◽  
Laser Scanning Confocal Microscopy ◽  
Effective Medium ◽  
Medium Theory ◽  
K Value ◽  
Graphene Nanocomposites ◽  
Scanning Confocal Microscopy

Thermal conductivity (k) of polymers is usually limited to low values of ~0.5 Wm−1K−1 in comparison to metals (>20 Wm−1K−1). The goal of this work is to enhance thermal conductivity (k) of polyethylene–graphene nanocomposites through simultaneous alignment of polyethylene (PE) lamellae and graphene nanoplatelets (GnP). Alignment is achieved through the application of strain. Measured values are compared with predictions from effective medium theory. A twin conical screw micro compounder is used to prepare polyethylene–graphene nanoplatelet (PE-GnP) composites. Enhancement in k value is studied for two different compositions with GnP content of 9 wt% and 13 wt% and for applied strains ranging from 0% to 300%. Aligned PE-GnP composites with 13 wt% GnP displays ~1000% enhancement in k at an applied strain of 300%, relative to k of pristine unstrained polymer. Laser Scanning Confocal Microscopy (LSCM) is used to quantitatively characterize the alignment of GnP flakes in strained composites; this measured orientation is used as an input for effective medium predictions. These results have important implications for thermal management applications.

On the Effective Thermal Conductivity of Nanofluids With Fractal Aggregation

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
C. G. Subramaniam
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Effective Medium Theory ◽  
Functionally Graded ◽  
Fractal Aggregates ◽  
Medium Theory ◽  
Analytical Approximations ◽  
Proposed Model ◽  
Dispersing Medium ◽  
Dilute Limit

A generalized effective medium theory (EMT) is proposed to account for the fractal structure of the dispersed phase in a dispersing medium under the dilute limit. The thermal conductivity of nanofluids with fractal aggregates is studied using the proposed model. Fractal aggregates are considered as functionally graded spherical inclusions and its effective thermal conductivity is derived as a function of its fractal dimension. The results are studied for self-consistency and accuracy within the limitations of the analytical approximations used.

Effect of Particle Size and Aggregation on Thermal Conductivity of Metal-Polymer Nanocomposite

2016 ◽  
Author(s):  
Xiangyu Li ◽  
Wonjun Park ◽  
Yong P. Chen ◽  
Xiulin Ruan
Keyword(s):  
Thermal Conductivity ◽  
Effective Medium Theory ◽  
Low Cost ◽  
Polymer Nanocomposite ◽  
Theoretical Models ◽  
Effective Medium ◽  
Metal Nanoparticle ◽  
Local Concentration ◽  
Medium Theory ◽  
Aggregation Effect

Metal nanoparticle has been a promising option for fillers in thermal interface materials due to its low cost and ease of fabrication. However, nanoparticle aggregation effect is not well understood because of its complexity. Theoretical models, like effective medium approximation model, barely cover aggregation effect. In this work, we have fabricated nickel-epoxy nanocomposites and observed higher thermal conductivity than effective medium theory predicts. Smaller particles are also found to show higher thermal conductivity, contrary to classical models indicate. A two-level EMA model is developed to account for aggregation effect and to explain the size-dependent enhancement of thermal conductivity by introducing local concentration in aggregation structures.

Impact of Altering Aspect Ratio of the Loading Particles on a Suspension’s Thermal Conductivity

2008 ◽  
Author(s):  
A. S. Cherkasova ◽  
J. W. Shan
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Carbon Nanotubes ◽  
Silicon Carbide ◽  
Aspect Ratio ◽  
Effective Medium Theory ◽  
Detailed Comparison ◽  
Interfacial Resistance ◽  
Micro Particles ◽  
Particle Aspect Ratio

It has been recognized that heat-transfer fluids used to convey thermal energy produced by one device to another can exhibit significant increases in thermal conductivity with the addition of highly conductive particles. Suspensions of nano- and micro-particles have attracted the most recent interest because of their enhanced stability against sedimentation, reduction in potential for clogging a flow system, as well as the tantalizing possibility of unexpected enhancements in thermal conductivity that have been reported in some experiments. Among various suspensions, considerable attention has focused on those containing large-aspect-ratio particles, such as carbon nanotubes. Although recent experiments have demonstrated enormous heat-transfer enhancements in these fluids, such increases were reportedly not in agreement with existing macroscale theories [1–3]. In this research we report on an experimental study of the effects of particle aspect ratio on the effective thermal conductivity of micro- and nano-particle suspensions. The influence of particle aspect ratio on the thermal properties of suspensions was first studied in dispersions of micron-sized, silicon-carbide particles with varying aspect ratio. To carry out a detailed comparison with theoretical predictions, particle aspect ratio and size distributions were measured. It is shown that the conductivity of the silicon-carbide suspensions can be quantitatively predicted by an effective-medium theory (EMT), provided the volume-weighted aspect ratio of the particles is used. The particle-aspect-ratio effect was further studied in the suspensions of multi-walled carbon nanotubes. Experimental data on the thermal conductivity of nanotube suspensions could also be interpreted in terms of the aspect-ratio dependence predicted by EMT if the additional nanoscale effect of interfacial resistance was considered.

An Effective Unit Cell Approach to Compute the Thermal Conductivity of Composites With Cylindrical Particles

2005 ◽  
Vol 127 (6) ◽  
pp. 553-559 ◽  
Author(s):  
Deepak Ganapathy ◽  
Kulwinder Singh ◽  
Patrick E. Phelan ◽  
Ravi Prasher
Keyword(s):  
Thermal Conductivity ◽  
Effective Medium Theory ◽  
Effective Medium ◽  
Unit Cell ◽  
Spherical Particles ◽  
Medium Theory ◽  
Volume Fractions ◽  
Curvature Effects ◽  
Finite Differences Method ◽  
Cylindrical Particles

This paper introduces a novel method, combining effective medium theory and the finite differences method, to model the effective thermal conductivity of cylindrical-particle-laden composite materials. Typically the curvature effects of cylindrical or spherical particles are ignored while calculating the thermal conductivity of composites containing such particles through numerical techniques, such that the particles are modeled as cuboids or cubes. An alternative approach to mesh the particles into small volumes is just about impossible, as it leads to highly intensive computations to get accurate results. On the other hand, effective medium theory takes the effect of curvature into account, but cannot be used at high volume fractions because it does not take into account the effects of percolation. In this paper, a novel model is proposed where the cylindrical particles are still treated as squares (cuboids), but to capture the effect of curvature, an effective conductivity is assigned to the particles by using the effective medium approach. The authors call this the effective unit cell approach. Results from this model for different volume fractions, on average, have been found to lie within ±5% of experimental thermal conductivity data.

Effective Thermal Conductivity of MoSi2/SiC Composites

2005 ◽  
Vol 492-493 ◽  
pp. 551-554
Author(s):  
Guang Zhao Bai ◽  
Wan Jiang ◽  
G. Wang ◽  
Li Dong Chen ◽  
X. Shi
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Effective Medium Theory ◽  
Thermal Conductance ◽  
Inclusion Size ◽  
Laser Flash ◽  
Flash Method ◽  
Medium Theory ◽  
Interfacial Thermal Conductance ◽  
Sic Composites

Thermal conductivity of as-prepared MoSi2/SiC composites has been determined by Laser Flash method. Interfacial thermal conductance for composites with 100nm SiC and with 0.5µm has been determined by using effective medium theory. The results of interfacial thermal conductance exhibit that both the inclusion size and the clustering of the inclusions play an important role in determining composite thermal conductivity.

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