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.

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.

An Improved Predictive Model for Effective Thermal Conductivity of Polymer Composites With Non-Dilute Filler Concentrations

2019 ◽  
Author(s):  
Kabeer Raza ◽  
Syed Sohail Akhtar ◽  
Abul Fazal M. Arif ◽  
Abbas Saeed Hakeem
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Polymer Composites ◽  
Polymer Matrix Composites ◽  
Effective Medium Theory ◽  
Material Design ◽  
Filler Concentration ◽  
Volume Fractions ◽  
Proposed Model ◽  
Thermal Conductivities

Abstract Most of the predictive models for thermal conductivity of composites are derived based on the assumption that the filler concentration in the matrix is dilute. This assumption leads to inaccurate predictions when filler concentration is essentially non-dilute and hence there is a need to propose a model that could handle a non-dilute filler concentration. In this work an improved and realistic model for effective thermal conductivity of polymer matrix composites with non-dilute filler’s concentrations is derived and validated by experiments. The proposed model can handle fillers with variable size and shapes. The derivation is based on the Bruggeman’s differential effective medium theory where the high volume fractions can be obtained by incrementally adding ‘small volume fractions’ into the ‘existing composite’ at each stage. The proposed model is validated by experimentally produced different series of ceramic particles-polymer composites. Differently sized and shaped alumina (Al2O3) & aluminum nitride (AlN) particulate fillers, and high density polyethylene (HDPE) & polypropylene (PP) matrices were used as the variable ingredients. Using different combinations of filler, matrix and particle size six different series of composites were produced with variable filler concentrations up to 50% by volume. The microstructure of the produced samples was studied by field emission scanning electron microscope to relate the morphology with the predictions. The predictions of proposed model are found in close agreement with the measured thermal conductivities. To understand the detailed effects of different parameters, parametric studies are presented and discussed. It is found that aspect ratio of particulate fillers is the most sensitive parameter to enhance effective thermal conductivity. Overall, the proposed model is proven to be useful in composite material design for heat transfer applications. It is expected that the proposed model will open new doors for the researchers and polymer composite industry to develop new composite designs for achieving ultrahigh thermal conductivities.

Analysis of Heat Conduction in Dilute Nanofluids

2009 ◽  
Author(s):  
Le-Ping Zhou ◽  
Bu-Xuan Wang ◽  
Xiao-Ze Du ◽  
Yong-Ping Yang
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Steady State ◽  
Effective Thermal Conductivity ◽  
Effective Medium Theory ◽  
Constant Heat Flux ◽  
Brownian Diffusion ◽  
Uniform Temperature ◽  
Medium Theory ◽  
Basic Fluid

In this paper, we assume that a nanofluid is a mixture consisting of a continuous base fluid component and a discontinuous nanoparticle component. Then, based on the analysis of Buongiorno in 2006 for critical slip mechanisms in nanofluids, we consider the effects of Brownian diffusion and thermophoresis of nanoparticles on heat and mass flux in nanofluid. With the coupled conservation equations, we analyze the heat conduction properties of general nanofluids under three conditions: 1) stationary fluid with uniform temperature, 2) stationary fluid under constant temperature boundary, and 3) stationary fluid under constant heat flux boundary. The results show that nanofluid effective thermal conductivity depends on the thermal conductivity of nanoparticle and basic fluid, particle concentration, particle size, particle distribution, Brownian and thermal diffusion, boundary condition and time. It indicates that the nanofluid effective thermal conductivity can be well predicted for stationary fluid with uniform temperature from classical effective medium theory such as Maxwell’s approach. However, the measurements applying steady or unsteady heat conduction methods for pure materials fail to predict correctively the effective thermal conductivity of nanofluid and are influenced by boundary conditions. Preliminary conclusions include approximate correlations of effective thermal conductivity of dilute nanofluids using steady state and quasi-steady state measuring methods.

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.

Effective Thermal Conductivity of Functionally Graded Particulate Nanocomposites With Interfacial Thermal Resistance

2008 ◽  
Vol 75 (5) ◽  
Author(s):  
H. M. Yin ◽  
G. H. Paulino ◽  
W. G. Buttlar ◽  
L. Z. Sun
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Effective Thermal Conductivity ◽  
Functionally Graded ◽  
Interfacial Thermal Resistance ◽  
Conductivity Distribution ◽  
Consistent Model ◽  
The Matrix ◽  
Graded Material ◽  
Perfect Interface

By means of a fundamental solution for a single inhomogeneity embedded in a functionally graded material matrix, a self-consistent model is proposed to investigate the effective thermal conductivity distribution in a functionally graded particulate nanocomposite. The “Kapitza thermal resistance” along the interface between a particle and the matrix is simulated with a perfect interface but a lower thermal conductivity of the particle. The results indicate that the effective thermal conductivity distribution greatly depends on Kapitza thermal resistance, particle size, and degree of material gradient.

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.

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.

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